The Kingdom Animalia Theory & Question Answers

 Chapter #10: The Kingdom Animalia

Theory & Question Answers
Section III – Biodiversity

THE KINGDOM ANIMALIA

It includes all eukaryotic, non-chlorophyllous multicellular, ingestive heterotrophs with no cell wall.

A true animal now defined as “a eukaryotic, multicellular, ingestive heterotrophic organism which are diploid and developed from an embryo formed by the fusion of two different haploid gametes, a large egg, and a smaller sperm”. Animals range in size and complexity from a merely microscopic parazoan Trichoplax to the giant blue whale Balaenopters that reaches a length of nearly 40 meters and weight more than 160,000 kilograms.

The kingdom Animalia is divided into 33 groups called phyla. The major phyla are Porifera, Cnidaria, Platyhelminthes, Nemathelminthes, Annelida, Mollusca, Arthropoda, Echinodermata, and Chordata.

DEVELOPMENTAL PATTERN:

"The changing process in zygote which results in an embryo produced called development”. The process of development is completed into following patterns.

  1. Cleavage:
    It is the first changing process which takes place in the zygote. Due to cleavage, the unicellular zygote is changed into a multicellular structure.

  2. Morula:
    It is a solid ball-like multicellular structure which is produced after cleavage.

  3. Blastula:
    It is a rounded-shaped structure. Inside the blastula cavity is present, called the blastocoel cavity.

  4. Gastrula:
    It is a three-germinal-layer structure which is produced after blastulation.

Organogenesis:

  • The formation of organ and organ systems through three germinal layers is called organogenesis.
  • It takes place after gastrulation and results in the production of larva.

Cellular Organization:

All living organisms are composed of cells. Animals show cellular organization. Similar cells are combined and produce tissues. Similar tissues produce organs. Different organs are combined and produce organ systems. Different organ systems combine and produce the living body. According to cellular organization, living organisms are divided into two subphyla:

  • Sub Phylum Parazoa: Animals that are multicellular but lack cellular organization, called Parazoa, e.g., animals of Phylum Porifera.

  • Sub Phylum Eumetazoa: Animals that are multicellular and have cellular organization, called Eumetazoa, e.g., animals from Phylum Coelenterata to Phylum Chordata.

TRIPLOBLASTIC AND DIPLOBLASTIC:

  • Triploblastic:
    Triploblastic is a combination of two words:
    Triplo → Three
    Blastic → Cell Layer

    "Those animals whose body wall consists of three cell layers are called triploblastic.” The three cell layers are known as:

    • Ectoderm
    • Mesoderm
    • Endoderm

    Example: animals of Phylum Platyhelminthes to Phylum Chordata are known as triploblastic.

Morula: It is a solid ball-like multicellular structure that is produced after cleavage.

Blastula: It is a rounded-shaped structure. Inside the blastula cavity is present, called the blastocoel cavity.

Gastrula: It is a three germinal layer structure that is produced after blastulation.

Organogenesis:

  • The formation of organ and organ systems through three germinal layers is called organogenesis.
  • It takes place after gastrulation, and by the result of organogenesis, larva is produced.

Cellular Organization: All living organisms are composed of cells. Animals show cellular organization. The similar cells are combined and produce tissue. Similar tissues produce organs. Different organs are combined and produce organ systems. Different organ systems are combined and produce the living body. According to cellular organization, living organisms are divided into two subphyla:

  • Sub Phylum Parazoa
  • Sub Phylum Eumetazoa

Sub Phylum Parazoa: Animals that are multicellular but lack cellular organization are called Parazoa. For example, animals of Phylum Porifera.

Sub Phylum Eumetazoa: Those animals that are multicellular and have cellular organization are called Eumetazoa. For example, animals of Phylum Coelenterata to Phylum Chordata.

Triploblastic and Diploblastic:

Triploblastic: Triploblastic is a combination of two words:

  • Triplo → Three
  • Blastic → Cell Layer

"Those animals whose body wall consists of three cell layers are called triploblastic.” The three cell layers are known as:

  • Ectoderm
  • Mesoderm
  • Endoderm

E.g., animals of Phylum Platyhelminthes to Phylum Chordata are known as triploblastic.

Diploblastic: Diploblastic is also a combination of two words:

  • Diplo → Two
  • Blastic → Cell Layer

"Those animals whose body wall consists of two cell layers called diploblastic." Two cell layers are known as:

  • Ectoderm
  • Endoderm

Between these two layers, a non-cellular jelly-like layer is also present, called mesoglea.
E.g., animals of Phylum Coelenterata.

Symmetry: "Any imaginary plane or direction which passes through the body center and divides the body into two or more than two equal parts or divides the body into equal parts is called symmetry."

Asymmetry: "Any imaginary plane or direction which passes through the body center and does not divide the body into two equal parts is called asymmetry."

Types of Symmetry: There are two types of symmetry found in animals:

  • Bilateral Symmetry
  • Radial Symmetry

Bilateral Symmetry: "Any imaginary plane or direction which passes through the body center vertically and divides the body into two equal parts is called Bilateral Symmetry."
E.g., Animals of Phylum Platyhelminthes, Nematoda, Annelida, Mollusca, Arthropoda, and Chordata have bilaterally symmetrical bodies.

Radial Symmetry: "Any imaginary plane or direction which passes through the body center and divides the body into two equal parts from every direction is called radial symmetry."
E.g., Animals of Phylum Coelenterata and Echinodermata have radially symmetrical bodies.

Coelom: The cavity that is present between the body wall and internal organs of the body is called the coelom. The mesodermal layer splits open to contain a space that widens and forms the body cavity called the coelom. It is also known as the body cavity or coelomic cavity. It is filled with a fluid known as body fluid or coelomic fluid.

Types of Animals: According to the coelom, animals are divided into three types:

  • Acoelomate Animals
  • Pseudocoelomate Animals
  • Coelomate Animals

Acoelomate Animals:

"Those animals in which coelomic cavity is absent between body wall and internal organs called acoelomate animals".
E.g., Animals of phylum Porifera, Coelentrata, and Platyhelminthes.

Pseudocoelomate Animals:

"Those animals in which false coelomic cavity is present between body wall and internal organs called pseudocoelomate animals".
E.g., Animals of phylum Aschelminthes.

Coelomate Animals:

"Those animals in which true coelomic cavity is present between body wall and internal organs called coelomate animals".
E.g., Animals of phylum Chordata.

Fate of Blastopore:

During gastrulation, an opening is produced in the gastrula which is known as the blastopore. It develops into the mouth and anus during organogenesis.

Protostomes and Deuterostomes:

  • Protostomes:

    It is also a combination of two words.

    • Protos → First
    • Stoma → Mouth

    "Those animals in which blastopore develops into the first mouth are called protostome".
    E.g., Animals of Phylum Annelida, Mollusca, and Arthropoda.

  • Deuterostomes:

    It is also a combination of two words.

    • Deutero → Second
    • Stoma → Mouth

    "Those animals in which blastopore develops into the first anus then mouth is developed are called deuterostome animals".
    E.g., Animals of Phylum Echinodermata and Chordata.

Phylum Porifera:

Introduction:

  • Porifera → Porous body
  • This phylum includes perforated body animals.
  • About 5000 species are discovered in this phylum.
  • They were considered as plants until 1764.
  • It is the only phylum that belongs to the sub-kingdom Parazoa because cellular organization is absent.

Habit and Habitat:

  • The species of phylum Porifera are aquatic and they are found in both fresh and marine water.
  • About 150 species are found in fresh water.
  • They are sessile in nature because they are attached to the rocks under water.
  • The species of phylum porifera are usually found in colonial forms.

Body Symmetry:

  • The body of poriferans is asymmetrical.

Body Structure:

  • The body of poriferans is multicellular, but the cellular organization is absent.

Cytology:

Body of poriferans is composed of four types of cells:

  • Pinacocytes
  • Choanocytes
  • Porocytes
  • Amoebocytes

  • Pinacocytes:
    They are flattened cells which produce the outer epidermal layer of the body.

  • Choanocytes:
    They are oval-shaped flagellated cells which produce the inner lining of spongocoel.

  • Porocytes:
    They are porous cells which produce the ostia of the body.

  • Amoebocytes:
    They are irregular-shaped cells which help in reproduction.

![Diagrams of Ascon, Sycon, and Leucon type sponges]

Spongocoel:

The body cavity of poriferans is called spongocoel. According to the division of spongocoel, poriferans are divided into three types:

  • Ascon Type:
    Those poriferans in which the spongocoel consists of a single large cavity called ascon type.

  • Sycon Type:
    Those poriferans in which spongocoel is divided into secondary chambers called sycon type.

  • Leucon Type:
    Those poriferans in which spongocoel is divided into secondary and tertiary chambers called leucon type.

Openings or Pores:

  • The body of poriferans is perforated and they have two types of openings or pores.
  • A large opening is present at the interior surface of the body called osculum.
  • It is also known as an excurrent opening because water exits out through it.
  • A large number of small openings present on the rest of the body are called ostia.
  • They are also known as incurrent openings because water enters through them.

Spicules:

  • Spicules are spine-like structures which are produced by CaCO₃.
  • It is present in the mesenchyme of the body.
  • In freshwater species, the body is covered by protein fibers called sponging fibers.
  • Respiratory, circulatory, digestive, and excretory systems are absent in the species of phylum porifera.

Mode of Reproduction:

They have both asexual and sexual modes of reproduction.

Asexual Reproduction:

  • Poriferans perform asexual reproduction by fragmentation, budding, and gemmule formation.

Gemmule Formation:

  • Gemmule is the nutrition-laden amoebocytes which are produced during unfavorable conditions. It is surrounded by an epithelial layer. When favorable conditions return, gemmule grows and produces a new poriferan animal.

Sexual Reproduction:

  • According to sexual reproduction, the species of poriferans are hermaphrodite or monoecious.
  • They produce two types of different gametes which are fused together and converted into a free-swimming larva called amphiblastula.
  • It attaches to the rock and changes into a sedentary adult.

Economic Importance:

  • In the past, sponge fishing culture was very common because it was used for ornamental purposes.
  • Bath sponges were commonly used in bathrooms.

  • Class Calcaria:
    Skeletal is composed of needle-shaped lime crystals, e.g., Ascon, Sycon.

  • Class Hexactinellida:
    Skeleton is composed of silicious spicules with six rays, e.g., Euplectella.

  • Class Demospongia:
    Skeleton is composed of proteinaceous fibers (sponging fibers) either with or without spicules, but spicules are never six-rayed, e.g., Spongilla.
    Example: Bath Sponge, Buplectella, Demospongia.

Phylum Cnidaria: (Coelentrata)

Introduction:

  • Coelenterate → Coelentron Cavity
  • This phylum includes those animals which have a hollow cavity called coelentron cavity.
  • About 9000 species are discovered in this phylum.
  • This is the first phylum of sub-Kingdom eumetazoa in which cellular organization is present.

Habit & Habitat:

  • Cnidarians are aquatic animals; most species are found in marine water, while few species are found in freshwater.
  • They are both sessile and motile species.
  • The species of phylum cnidaria are found in both solitary and colonial forms.

Body Symmetry:

  • The body of cnidarians is radially symmetrical.

Body Structure:

Diploblastic:

  • The body of coelenterates is diploblastic because it is composed of two cell layers.
  • The outer cell layer is known as ectoderm, while the inner cell layer is known as endoderm.
  • A plate of non-cellular gelatinous mass is present between ectoderm and endoderm, called mesoglea.

Mouth:

  • Cnidarians have a single opening called the mouth.
  • It is surrounded by tentacles of oral arms.
  • The mouth helps in both the ingestion of food and the egestion of waste.

Coelentron Cavity:

  • Inside the body of cnidarians, a hollow cavity is present, called coelentron or gastrovascular cavity.
  • It helps in both extracellular and intracellular digestion.

Cnidocyte:

  • Ectoderm of cnidarians has specialized stinging cells, called cnidocytes.
  • They are present inside the pear-shaped cavity called nematocyst.
  • Cnidocytes help to paralyze or kill the prey.

Respiratory and Circulatory System:

  • Cnidarians have no respiratory and circulatory system.

Body Forms:

The solitary species of cnidarians are found in two body forms.

  • Polyp

  • Medusa

  • Polyp:
    Those coelenterates which are cylindrical in shape. The mouth is present at the ventral surface. It is surrounded by tentacles, and they have asexual reproduction, called polyp.
    E.g., Hydra.

  • Medusa:
    Those coelenterates which are umbrella-shaped. The mouth is present at the upper surface. It is surrounded by tentacles and oral arms, and they have sexual reproduction, called medusa.
    E.g., Jellyfish.

Alternation of Generation:

The process in which one generation produces a second generation, while the second generation produces the first generation, is called alternation of generation. The two body forms of phylum Cnidaria show the alternation of generation in their life cycles. During this process, medusa species perform sexual reproduction, which results in free-swimming larvae produced, called planula larvae. It attaches to the rock and is converted into a cylindrical-shaped polyp. Then, the polyp performs asexual reproduction, which results in medusa-shaped animal production.

Polymorphism:

Polymorphism is a combination of two Greek words.

  • Poly → More than one
  • Morphism → Body forms

The occurrence of a species in two or more structurally and functionally different kinds of zooids is known as polymorphism.
E.g., Physalia. The colonial species of phylum Cnidaria body forms are known as zooids.

They have three types of zooids:

  • Gastrozooids

  • Gonozooids

  • Dactylozooids

  • Gastrozooids:
    Those zooids which gather the food and help in digestion are called gastrozooids.

  • Gonozooids:
    Those zooids which help in reproduction are called gonozooids.

  • Dactylozooids:
    Those zooids which are sensory in nature and produce body defense are called dactylozooids.

Coral & Coral Reefs:

Corals are polyp species of phylum Cnidaria, which secrete a substance largely limestone or calcium carbonate. It is combined with water and carbon dioxide and converted into a hard layer or covering which is known as coral reefs. The Great Barrier Reef of Australia on the eastern coast is the best example of coral reefs. It spreads for 100 miles under the water. Coral reefs are used for ornamental and jewelry purposes. Red Marjan is also obtained from coral reefs, which are used by hakeems for the preparation of various eastern medicines.

Phylogeny:

It is thought that the species of phylum Cnidaria evolved from the species of kingdom Protista.

Classification:

The species of phylum Cnidaria are divided into three classes.

  • Class Hydrozoa:

    • This class includes those coelenterates in which non-cellular mesoglea is present.
    • They have distinct alternation of generation in which both polypoid and medusoid phases are shown, e.g., Hydra, Obelia.

  • Class Scyphozoa:

    • This class includes those cnidarians in which cellular mesoglea is present.
    • Medusoid species are predominantly forms of this class.
    • Polyp-species are produced during development, e.g., Jellyfish.

  • Class Anthozoa:

    • This class includes those cnidarians in which fibrous mesoglea is present.
    • Class Anthozoa only includes polypoid species, e.g., sea anemone.

Phylum Platyhelminthes:

Introduction:

  • Platy → Flattened body

  • Helminthes → Worms

  • This phylum includes dorso-ventrally flattened body worms.

  • About 15,000 species are discovered in this phylum.

  • It is the first phylum of kingdom Animalia in which systems are present.

  • It is thought that Platyhelminthes evolved from ribbon-shaped coelenterates.

Habit & Habitat:

  • The species of Platyhelminthes are found in both land and water.
  • On land, they are found near the shore and in water grasses.
  • Some species are found inside animals and plants as parasites.

Body Symmetry:

  • The body of Platyhelminthes is bilaterally symmetrical.

Body Structure:

  • The body of Platyhelminthes is covered by a hard layer called cuticle.

  • The body is triploblastic because it is composed of three cell layers:

    • i. Ectoderm
    • ii. Mesoderm
    • iii. Endoderm

  • The body is acoelomate because the body cavity is absent.

  • The body has a single opening called a mouth, which helps in both ingestion of food and egestion of waste products.

  • Inside the body, a branched, closed, and tabular intestine is present in which both extra and intracellular digestion take place.

  • Respiratory and circulatory systems are absent.

Mode of Excretion:

  • Platyhelminthes have specialized excretory cells called flame cells (or protonephridia).
  • Flame cells are flickering flame-like cells which are present at both lateral sides of the body.
  • Flame cells absorb water from the body and excrete it out through excretory pores.

Mode of Reproduction:

  • According to reproduction, the species of Platyhelminthes are hermaphrodite or monoecious.
  • They have both asexual and sexual modes of reproduction.
  • Asexual reproduction takes place by fission or fragmentation, while sexual reproduction takes place by gamete formation.

Life Cycle:

The parasitic species of Platyhelminthes complete their life cycle inside one or two hosts.

  • Monogenic Parasite:
    Those parasitic species which complete their life cycle inside a single host are called monogenic parasites.
    E.g., Tapeworm.

  • Digenic Parasite:
    Those parasites which complete their life cycle in two hosts are called digenic parasites.
    E.g., Liver Fluke.

Parasitic Adaptations of Platyhelminthes:

The parasitic adaptations of Platyhelminthes are as follows:

  • Their body is covered by a thick layer which protects them from the enzyme of the host.
  • Hooks and suckers are present around the mouth, which help them in attachment with the host.
  • Locomotory organs are absent, so they have a sessile mode of life.
  • In parasites, the alimentary canal is absent or reduced because they absorb directly digested food from the body of the host.
  • Neuro-sensory organs are not developed due to their passive mode of life.
  • They have a developed reproductive system and a high rate of fertility to cope with the dangers of defense mechanisms of the host body.

Classification:

The species of phylum Platyhelminthes are divided into three classes according to their mode of living.

  • Class Turbelaria:
    This class includes free-living Platyhelminthes.
    E.g., Dugesia (Planaria).

  • Class Trematoda:
    This class includes ecto- and endo-parasitic species.

    • The alimentary canal is bifurcated.
      E.g., Fasciola hepatica (liver fluke).
  • Class Cestoda:
    • This class includes exclusively endoparasites.
    • The alimentary canal is absent in the species of class Cestoda.
    • They have a flattened ribbon-shaped body.
      E.g., Taenia saginata (Tapeworm).

Phylum Nematoda: (Aschelminthes)

Introduction:

  • Aschelminthes → Rounded body worms
  • This phylum includes rounded body worms.
  • About 20,000 species are present in this phylum.
  • It is the largest phylum of kingdom Animalia, which contains abundant animals.
  • In one count, 90,000 roundworms of several different species were found with a single rotting apple.

Habit & Habitat:

  • They are mostly found in soil, and a few species are found in water.
  • Nematodes vary in size from microscopic to nine meters long.
  • Most species are parasitic and are found inside and outside the animals and plants.
  • About 50 species are human parasites.

Body Symmetry:

  • The body of nematodes is bilaterally symmetrical.

Body Structure:

  • The body of nematodes is long, cylindrical, and rounded in shape.

  • The both ends of the body are pointed.

  • The body is triploblastic because it is composed of three cell layers:

    • i. Ectoderm
    • ii. Mesoderm
    • iii. Endoderm

  • Inside the body, a false cavity is present called a pseudocoelom.

  • The body has two openings: the anterior opening called the mouth, while the posterior opening is called the anus.

Tube System:

  • The body of nematodes is developed into a tube system.
  • Inside the body, a long, straight tube-like digestive tract is present.
  • Outside the body, it is covered by a non-living tube-like cuticle.

Mode of Reproduction:

  • The species of phylum Nematoda are heteroprocitic or dioecious.
  • They are sexually dimorphic because the male is shorter than the female species.
  • They have both asexual and sexual modes of reproduction.

Diseases Caused by Nematodes:

  • The parasitic species of nematodes cause various diseases in humans.
  • The thread-like worm Wuchereria is transmitted by blood-sucking mosquitoes, causing the disease of the lymphatic system called filariasis, in which legs and arms are inflamed, and the condition is known as elephantiasis.
  • Ancylostoma, the hookworm whose larva can penetrate through the skin of humans to reach the intestine, where it matures and sucks the blood.
  • Ascaris is a common example of phylum Nematoda, which infects millions of people worldwide.

Phylum Annelida:

Introduction:

  • Annelida → Segmented worm
  • This phylum includes those worms which have a segmented body.
  • About 15,000 species are discovered in this phylum.
  • It is the first phylum of kingdom Animalia in which worms are true coelomates.

Habit & Habitat:

  • They are found in both water and on land.
  • On land, they live in moist soil and burrowing forms.
  • Many land species are buried in mud and utilize soil as food.
  • Aquatic species are found in fresh water or in the sea.
  • They are active free-swimming predators and aquatic filter feeders.
  • Some species are ectoparasites and suck blood.

Body Symmetry:

  • The body of Annelids is bilaterally symmetrical.

Body Structure:

  • They are segmented worms and have the most complex body structures of all the worms.

Segments:

  • Annelids are segmented worms, and their segmentation is said to be metameric because all segments have similar morphology, anatomy, and physiology.
  • They are distinguished by their ring-like external segments.
  • They look like a large number of rings put on and arranged one behind the other.
  • These rings or external segments coincide with the internal partitions called septa of the body cavity.

Triploblastic:

  • The body of annelids is triploblastic and has a true body cavity or coelomic cavity.

Digestive System:

  • They have a developed digestive system that initiates from the mouth and ends at the anus. The digestive system is developed according to the parasitic, saprophytic, and other modes of nutrition.

Excretory System:

  • Each segment of annelids contains a pair of excretory organs. The excretory organs of annelids are known as nephridia.

Locomotory Organ:

  • They have elations structures called setae without parapodia. Whereas in parasitic species, they have hooks and suckers.

Circulatory System:

  • The species of phylum Annelida are the first group to have a circulatory system of closed type with definite blood vessels and many pulsatile hearts. Blood is usually red with hemoglobin dissolved in it.

Mode of Respiration:

  • The respiratory system is absent in annelids. Gaseous exchange usually takes place by diffusion through the moist skin.

Mode of Reproduction:

  • The species of phylum Annelida are both hermaphrodite and heterophrodite.
  • The reproductive system is well-developed and usually found in each segment of the body.
  • They have both asexual and sexual reproduction.

Classification:

According to the number and type of locomotory organs, Annelida are divided into three classes.

  • Class Polychaeta
  • Class Oligochaeta
  • Class Hirudinea

  • Class Polychaeta:

    • Polychaetes, the most ancient annelids, are supposed to have evolved from a primitive flat worm-like ancestor in the sea.
    • Polychaetes are usually free-living active swimmers or sedentary filter-feeding forms.
    • They are mostly marine, having a pair of lateral flap-like fleshy lobes called parapodia on each segment of the body.
    • Each parapodium also has a bundle of bristles called setae.
    • Sexes are usually separate.
    • Development passes through a trochophore larval stage.
      Example: Sabella (Peacock worm), Neries (Clam worm).

  • Class Oligochaeta (Few Setae):

    • Oligochaetes evolved from polychaetes.
    • The species of oligochaeta are usually terrestrial, free-living, and burrowing forms.
    • Parapodia are absent, but few setae are present, which are arranged in a ring.
    • Sexes are present in a single animal or they are termed as hermaphrodite.
      Example: Earthworm (Pheretima).

  • Class Hirudinea (Leeches):

    • Leeches are evolved from oligochaetes.
    • This class includes those annelids in which setae and parapodia are absent.
    • They have anterior and posterior suckers for blood sucking and attachment.
    • They are usually found in fresh water.
    • All the species are hermaphrodite.
    • Some species are predators, while most species are ectoparasites of vertebrates and invertebrates.
      Example: Hirudinaria (Common Indian leech)

Economic Importance:

Farmer Friendly:

  • Many species of phylum Annelida are considered farmer-friendly because they continuously plough the soil and add nitrogenous wastes into it, thus making the soil more fertile.

Medicinal Use:

  • They are used by Chinese, Japanese, and Indians in the preparation of various fancy medicines.

Other Uses:

  • They are also used as fish bait, as food for fish, and also in laboratories for dissections and other research activities. Leeches are ectoparasites and are also used in remote areas for sucking foul blood from a patient.

Advantages of Segmentation and Coelom:

  • Segmentation increases flexibility, allowing various parts of the body to bend independently of the other parts. Increased flexibility enhances locomotory power.
  • The coelom improves swimming and burrowing activities. It also collects waste products and excretes them through the excretory organ. It provides space for the maturation of eggs and sperm.

Phylum Mollusca:

Introduction:

  • Mollusca → Soft Body
  • This phylum includes soft-bodied animals.
  • About 50,000 living and 35,000 fossil species of Mollusca are discovered.
  • It is the second-largest phylum of kingdom Animalia after Arthropoda.
  • Phylum Mollusca contains the most remarkable species in shapes and sizes.
    • Example: The smallest mollusks are not bigger than sand grains, whereas giant squids are 18 meters long (including tentacles) and weigh 1800 kg.

Habit & Habitat:

  • The species of phylum Mollusca are found in both water and land.
  • Aquatic species are found in marine and freshwater, whereas terrestrial species are found near the shore, water, shady, and wet places.

Body Symmetry:

  • The body of Mollusca is bilaterally symmetrical.

Body Structure:

  • They have a soft body; most have bodies surrounded by an external shell, and some have an internal shell.
  • All the Mollusca have triploblastic and coelomate bodies.
  • Mollusca have varied body forms, but all the species have three common characters:
    • A head-foot position primarily concerned with sensation, feeding, and locomotion.
    • A dorsal visceral mass that includes the major organ.
    • A mantle, which is a fold of delicate tissue surrounding the entire body.
  • The body has large fluid-filled cavities of the open circulatory system, which become the major component of the hydrostatic skeleton.

Radula:

  • The species of phylum Mollusca have a rasping feeding structure in their buccal cavity called the radula.

Digestive System:

  • They have a developed digestive system consisting of a straight or coiled tube called the alimentary canal. It has two openings: the anterior opening called the mouth, while the posterior opening is known as the anus. They have extracellular digestion.

Mode of Respiration:

  • They have gills and rudiments of lungs as respiratory organs.
  • Aquatic forms respire through gills, while terrestrial forms respire through rudimentary lungs.

Mode of Reproduction:

  • According to reproduction, sexes are usually separate.
  • Fertilization takes place outside the body or in water.
  • They pass through the trochophore larval stage.
  • The species of phylum Mollusca have both asexual and sexual reproduction.

Classification:

The species of phylum Mollusca are divided into six classes, but three are discussed in detail.

  • Class Monoplacophora
  • Class Amphineura
  • Class Scaphopoda
  • Class Gastropoda
  • Class Bivalvia
  • Class Cephalopoda
  • Class Gastropoda (Foot on Visceral Mass):
    • This is the largest class of phylum Mollusca, which includes whelks, snails, and slugs.
    • Most species of this class are found in marine water, while some are found in fresh water and land.

Torsion:

  • Many species of this class become secondarily asymmetrical by twisting of visceral mass at 180° by the phenomenon called torsion.
  • They have a prominent head and muscular foot developed in the visceral mass.
  • An external shell may be present or absent. If present, it is usually spirally coiled.
    Example: Pila.

Class Bivalvia (Shell with Two Halves):

  • It is the second-largest class of phylum Mollusca.
  • They are called bivalvia because their bodies are enclosed in a shell that consists of right and left halves.
  • The halves are hinged together and movable.
  • The muscular foot is suited ventrally and laterally for creeping and burrowing in soft mud or sand.
  • They are found in both fresh and marine water.
    Example: Unio, Mytilus, and Pearl oysters.

Class Cephalopoda (Foot on the Head):

  • All the species of class cephalopoda are highly developed and found in marine environments.
  • The foot is transformed into suckers bearing tentacles and arms.
  • They are found in a ring pattern around the mouth.
  • They have both external and internal shells. For example:
    • Nautilus has an external shell,
    • Sepia and Loligo have an internal shell,
    • Octopus has no shell.

Economic Importance:

  • Mollusca have great economic importance.
  • They are important in palaeontological studies and as index fossils to underlying oil deposits.
  • A variety of mollusks, called shellfish, together with crustaceans, are still an important source of food.
  • Their shells are decorative.

Pearl Formation:

  • In some bivalve mollusks called pearl oysters, concentric layers of nacre are deposited around any foreign particle that comes to lie between the mantle and the shell. This particle transforms into the most beautiful and precious jewelry item, the pearl.
  • The pearl industry is being successfully run in Japan and China by artificially introducing fragments of man-made particles to produce pearls of various shapes in pearl oysters.

Phylum Arthropoda:

Introduction:

  • Arthropoda → Jointed legs
  • This phylum includes jointed leg species.
  • About one million species are discovered in this phylum.
  • It is the largest phylum of kingdom Animalia in terms of the number of species.
  • The species of phylum Arthropoda show the greatest diversity.

Habit & Habitat:

  • They are found everywhere on the earth wherever life is possible.
  • They are found in air, water, and land.
  • Some species are found within animals and plants as parasites.

Body Symmetry:

  • The body of arthropods is bilaterally symmetrical.

Body Structure:

  • The body of arthropods is divided into three parts:
    • i. Head
    • ii. Thorax
    • iii. Abdomen
  • The body is triploblastic because it is composed of three cell layers.
  • The body of arthropods is metamerically and externally segmented.
  • Inside the body cavity, the present coelomic space in arthropods is called a haemocoel, which contains blood.
  • The body is covered by an exoskeleton composed of chitin.
  • The body has specialized compound eyes with mosaic vision.

Mode of Nutrition:

  • Arthropods have a variety of modes of nutrition.
  • They have herbivorous, carnivorous, omnivorous, saprophytic, and parasitic modes of nutrition.
  • Arthropods have a long, coiled tube-like digestive system in which extracellular digestion takes place.

Mode of Respiration:

  • They have a variety of respiratory organs.
  • They respire through spiracles, tracheae, gills, and book lungs.
  • The blood circulatory system of arthropods does not help in gaseous exchange.

Mode of Reproduction:

  • According to reproduction, arthropods are heterophrodite or dioecious.
  • They have both asexual and sexual modes of reproduction.
  • Arthropods are egg-laying animals, and their eggs pass through a process called metamorphosis.

Metamorphosis:

  • Metamorphosis is a set of changes which transforms a larva into its developed adult form.

Types of Metamorphosis:

  • There are two types of metamorphosis found in arthropods:
    • Complete metamorphosis
    • Incomplete metamorphosis

Complete Metamorphosis:

  • The metamorphosis in which the larva hatches out of the egg and is changed into a pupa, and a pupa is changed into an adult and all stages are different from each other is called complete metamorphosis.
    E.g., Mosquito, Butterfly.

Incomplete Metamorphosis:

  • The metamorphosis in which a tiny, immature but adult-like creature called nymph comes out of the egg and grows directly into an adult.
    E.g., Cockroach, Grasshopper.

Advantages of Appendages:

  • The species of phylum Arthropoda have jointed appendages.
  • They have three, four, five, and many pairs of jointed legs.
  • Legs help in walking, swimming, capturing, copulation, and sensation.
  • They usually have two pairs of wings, which help in flying.

Advantages of Exoskeleton:

  • The body of arthropods is externally surrounded by an exoskeleton composed of chitin.
  • It is a waterproof external covering.
  • The exoskeleton provides the site of attachment for muscles for contraction.
  • The exoskeleton is non-living and shows molting or ecdysis.
  • The exoskeleton provides mechanical support to the body and helps in locomotion.

Economic Importance:

  • Arthropods are of great economic importance.
  • The predominant group of arthropods is insects, which help in pollination as well as act as predators of plant pests.
  • Some insects cause diseases in humans by transmitting viruses and bacteria,
    e.g., Trypanosoma, Plasmodium, and germs of cholera.
  • Arthropods are an important source of food for many animals and carnivorous plants.
  • They are also an important source of seafood after fish and mollusks.
  • The farming of honey bees is called apiculture, in which honey is obtained.
  • The farming of silkworms is called sericulture, which is an important source of natural silk.

Classification:

The species of phylum Arthropoda are divided into five classes.

  • Class Merostomata
  • Class Arachnida
  • Class Crustacea
  • Class Myriapoda
  • Class Insecta or Hexapoda

Class Merostomata (Mouth Plates):

  • This class includes a small group of marine arthropods.
  • The mouth is surrounded by many plates in the species of class Merostomata.
  • They are also considered as living fossils.
  • The body is covered by a hard layer called the carapace.
  • At the posterior end of the body, a tail-like structure arises called the telson.
    E.g., King Crab (Limulus).

Class Arachnida (Spider-like):

  • This class includes most of the terrestrial and a few aquatic arthropods.
  • They are usually found under leaves, wood, rocks, and near the seashore.
  • This class mostly includes all the species of scorpions and spiders.
  • The body is divided into the head and trunk.
  • They respire through tracheae, general body surface, and book lungs.
  • Scorpions have long, segmented poisonous sting trunks.
  • Spiders have silk glands that secrete a protein that, on exposure to air, forms silk threads used in building nests and webs for trapping prey.
    E.g., Scorpion and Spider.

Class Crustacea (With Carapace):

  • This class includes most of the marine and a few terrestrial species.
  • The body of crustaceans is divided into the head and cephalothorax (Thorax + Abdomen).
  • They have one pair of eyes and antennae on the head.
  • They also have a pair of mandibles and two pairs of maxillae around the mouth.
  • The head and cephalothorax are covered by a single plate of exoskeleton called the carapace.
  • They have five pairs of jointed legs.
  • The appendages help in walking, swimming, feeding, and respiration.
  • They respire through gills and tracheae.
    E.g., Prawn, Crabs, Lobsters, Shrimps.

Class Myriapoda:

  • This class includes terrestrial arthropods.
  • They are found under rock leaves, woods, and inside the soil.
  • The body is divided into the head and long segmented trunk.
  • The head contains a pair of antennae and eyes.
  • The centipede species have one pair of legs in each segment of the trunk.
  • Millipedes have two pairs of legs in each segment of the trunk.
    E.g., Centipedes, Millipedes.

Class Insecta or Hexapoda (Six Legs):

  • This class includes most of the terrestrial and few aquatic species (insects).
  • It is the largest class of phylum Arthropoda because it contains more than 90% of species. Their study is called entomology.
  • The body of insects is divided into three parts:

    • i. Head

    • ii. Thorax

    • iii. Abdomen

    • Head:

      • The head is the first and un-segmented part of the body.
      • It is present at the anterior end of the body and contains one pair of sensory antennae and compound eyes.
  • At the terminal part of head an opening is present called mouth which is surrounded by mouth parts.
    • Maxillae, Mandibles, Labrum, Labium
    • Chewing and biting type as in "Cockroach".
    • Piercing and sucking type as in "Mosquito".
    • Chewing and lapping type as in "Honey Bee".
    • Sponging type as in "House Fly".
    • Siphoning types as in "Butterfly".

ii. Thorax:

  • It is the second and middle part of the body.
  • Thorax consists of three segments:
    • a. Prothorax
    • b. Mesothorax
    • c. Metothorax
  • Two pairs of wings arise from the dorsal surface of thorax.
  • Three pairs jointed legs also arise from the ventral surface of thorax.

iii. Abdomen:

  • It is the third and last part of body.
  • Abdomen consists of six to ten segments.
  • Inside the abdomen cavity is present called "Haemocoel" in which blood is found.
  • Head, thorax, abdomen and legs are covered by exoskeleton called chitin.

Classification:

  • According to the wings the species of class insect are divided in two sub-classes.

    • Sub class Pterygota:

      • Those insects which have wings belong to the sub-class pterygota.
        • e.g. Cockroach, mosquito, butterfly, housefly.

    • Sub Class Apterygota:

      • Those insects in which wings are absent belong to sub-class apterygota.
        • e.g. Bed bugs, lice, termite, fleas.

Social Insects:

  • Some insects show the social behavior because they live in the form of colony societies.
    • There colony consists of three components.
      • King and queen which only perform the reproduction.
      • Soldiers insects with strong jaws and they protect the colony from enemies.
      • Worker insects which are involved in gathering of food and nourishment of young ones.
        • E.g. Termite, ant, honey bee.

Insects As Diseases Carrier:

  • Some insects are parasites and contain germs of diseases.
    • Mosquito contains plasmodium and trypanosoma sickness is caused.
    • House fly contains the germs of cholera, dysentery and typhoid fever.
    • Fleas are ecto-parasite and rat-fleas involve in the transmission of deadly human disease called plague.

Insects As Successful Group:

  • The species of class insect have great diversity so they are considered as the successful group of animals.
  • Insects are found everywhere in the world from low land up to the tops of Himalaya and from hot spring to antarctic temperature of minus 65°C.
  • They are even found in the oil wells.

Morphological Adaptations:

  • The body of insects is covered by exoskeleton which helps in survival in every type habitat.
  • They have two pair’s wings and three pair’s legs which help them in walking and flying.
  • They have various types of mouth parts according to the available nutrition.

Physiological Adaptations:

  • They have developed digestive system and production of variety of digestive enzymes.
  • They have reproductive potential and metamorphosis which increase survival even in the extreme environment.
  • As social behavior they live in a colony which increases the adaptability of environment (Economic important same as of arthropoda).

PHYLUM ECHINODERMATA:

Introduction:

  • Echinodermata → Spiny skin
  • This phylum includes those invertebrates which have spiny skin.
  • About 6000 species are discovered in this phylum.
  • It is the first phylum of kingdom Animalia which are referred deuterostoms.

Habit & Habitat:

  • The species of phylum Echinodermata are exclusively marine.
  • They are found in the bed of marine as sand dweller.

Body Symmetry:

  • They begin their lives as free swimming, bilaterally symmetrical larva but as adults they have radially symmetrical bodies.
  • The body of Echinodermata is pentamoerous, radially symmetrical.

Body Structure:

  • The body of Echinodermates lack head, brain and segmentation.
  • Body is triplo-blastic and coelomate.
  • Body is deuterostome with organ and organ system.
  • Body is covered by hard or moveable calcareous blades with spines.

Tube Feet:

  • Tube feet are tube like structures which are found thousands in number.
  • They are projected outside vertically from body.
  • Tube feet help in walking, holding and respiration.

Water Vascular System:

  • Inside the body of echinoderms canal system is present in which water circulates.
  • It is the specialized system which helps in respiration, nutrition, excretion, reproduction and locomotion.

Model Reproduction:

  • They have both asexual and sexual mode of reproduction.
  • Asexual reproduction only takes place by regeneration which is found in their arms.
  • Sexual reproduction takes place by gametes and development is indirect passing through a bipinnaria larval stage.

Affinities:

  • Affinities mean similarities of characters suggesting relationship.
  • Echinoderms are thought to be the relative of chordates and hemichordates.
  • They have embryological similarities like their style of cleavage pattern of blastopore.
  • The tornaria larva of hemi-chordates and bipinnaria larva, larva of chinodermata has a large number of morphological biochemical and anatomical resemblance.
  • These affinities conclude that hemi-chordata is evolved from the dipleura ancestors.
    • e.g. Star fish, brittle star, sea cucumber and sea urchin.

PHYLUM CHORDATA:

Common Characteristics Of Chordates:

Introduction:
  • The chordates comprise about fifty thousand species, which are widely distributed.
  • There is a great variety of structure and adaptations to various modes of life.
  • Chordates show the maximum range of size and include animals such as fish about an inch in length to whales as long as 100 feet and as heavy as 150 tons.
Bilaterally Symmetrical:
  • That is they possess right and left, anterior and posterior dorsal and ventral sides.
Metamerically Segmented:
  • As is shown by a serial repetition of parts in a number of different systems of organs.
    • e.g. vertebrate, ribs, muscular and excretory system.
Coelomate:
  • The chordates possess a wide body cavity or coelom lined by a mesoderm.
Post Anal Tail:
  • The posterior part of the body takes the form of a segmented post - anal tail.
  • Tail is the posterior prolongation of the body.
  • It has no coelom and contains no viscera but has extensions of muscles, nerve cord, blood vessels and notochord.
  • It serves as locomotory organ in aquatic chordates.

Ventral Heart:

  • In most chordates the circulation of blood is maintained by a muscular heart.
  • In higher chordates the heart lies in a pericardial cavity which is a modified part of the coelom.

Red - Blood Corpuscles:

  • Most chordates have red blood containing red blood corpuscles, having hemoglobin as a respiratory pigment.
  • Circulatory system is of closed type.

Notochord:

  • All chordates contain notochord.
  • A notochord is an elastic solid, skeletal rod lying below the nerve cord and above the alimentary canal.
  • It is replaced by back bone in vertebrates.

Triplo-blastic:

  • All chordates are triploblastic.

Dorsal Tubular Nerve Cord:

  • There is a dorsal, hollow, fluid filled nerve cord.

Gill - Slits:

  • These are a set of openings formed in the pharyngeal region of embryos.

Sexes:

  • The sexes are always separate.

Fundamental Features of Phylum Chordates:

  • These characters are not always present throughout the life.

Notochord:

  • It gives name to this phylum. Notochord is a stiff rod of connective tissue. It is present in the mid-dorsal region. It is present in the embryos of chordates. In lower chordates it remains present throughout life e.g. amphioxus. In vertebrates notochord is, later on, replaced by back-bone.

Gill - Slits:

  • These are a set of openings in the pharynx. These function as gills in aquatic chordates throughout life. In chordates like reptiles, birds and mammals, gill-slits are replaced by lungs. In these animals these are modified to form other structures such as bone of middle ear and jaws.

Hollow Dorsal Central Nervous System:

  • Chordates possess a hollow dorsal nervous system. It is filled with a fluid. It lies above the notochord. In vertebrates it is enclosed by back-bone.

General Characters of Vertebrata:

  • Vertebrates are the largest and most advanced animals. Some of their characters are as follows:

Cranium:

  • They have an internal living skeleton (endoskeleton) that extends to the head region in the form of the skull.
  • Most of the skull encloses brain and known as cranium.
  • For this reason name craniate is also give to this sub-phylum.

Body Regions:

  • The body of a vertebrate is divided into three regions.

    • Head:
      • Head contains brain and sense organs such as ears, eyes etc. it is the anterior part of the body.
    • Trunk:
      • Trunk region contains the body cavity or coelom and all the viscera (interior organs).
    • Tail:
      • It is the post-anal prolongation of the body. Tail contains no organs but extensions of muscles, nerve cord, and blood vessels. It is flexible and muscular. Tail serves as a locomotory or prehensile (grasping) organ.

Body wall:

  • Body wall is composed of many layered epidermis and dermis.

Exoskeleton:

  • The skin is usually covered with exoskeleton (external skeleton).
  • It forms a protective covering.
  • Exoskeleton is in the form of scales (fishes), bony plates (reptiles), feathers (birds) and hair (mammal).

Limb:

  • The vertebrates typically have two pairs of limbs or fins (fishes) which are jointed appendages.

Circulatory System:

  • Closed type of circulatory system with powerful pumping organ called heart.

Gill - Slits:

  • These are present in the early development stages of higher vertebrates but are permanent in the lower vertebrates.

Sexes:

  • Sexes are always separate. Only one pair of gonads (testes or ovaries) is present.

Nervous System:

  • It is highly developed with brain, spinal cord, cranial and spinal nerve.

Classification:

  • Vertebrates are classified into five classes.
    • Class Pisces
    • Class Amphibia
    • Class Reptelia
    • Class Aves
    • Class Mammalia

Sub Phylum Agnatha (Mouth Without Jaws) Or Jawless Fishes:

Skeleton:

  • The skeleton of jawless fishes is cartilaginous.

Jaws:

  • Jaws are absent.

Appendages:

  • The appendages are also absent.

Shape:

  • The body is eel-like or cylindrical.

Mouth:

  • Mouth has sucker-like with rows of horny teeth which are very sharp.

Nostril:

  • On the dorsal surface of the head is a single median nostril.

Respiratory System:

  • The respiratory organs are typical gill pouches which open into the pharynx in the adult. Gills are naked.

Notochord:

  • There is a persistent notochord.

Eyes:

  • Paired eyes are present and may be functional or vestigial.

Fins:

  • Unpaired fins are present, paired fins are absent.

Skin:

  • Skin is slimy and without scales.

Example:

  • Petromyzon (Lamprey), Hag-fishes.

Distinguishing Features of Class Pisces (Fish):

  • Study of Fishes is called Ichthyology.
  • A fish is an aquatic gills breathing gnathostomates whose streamlined body is provided with paired fins and covered over by dermal scales.

Shape:

  • The body is streamlined spindle-shaped i.e., pointed at both ends.
  • This shape offers minimum resistance through water with little energy wasted.

Breathing:

  • The organs of breathing are gills.
  • Gills are series of folds of pouches in the pharynx.
  • Gills present throughout the life.
  • Water enters the gills through the mouth and leaves through gill-slits.

Locomotion:

  • Tail is the major organ of locomotion.
  • Paired and unpaired fins also help in locomotion.

Exoskeleton:

  • A dermal exoskeleton of scales is usually present. It may be lost secondarily.

Back - Bone:

  • The notochord is partly or completely replaced by bony or cartilaginous vertebrate.

Skull:

  • The skull is well-developed, with upper and lower jaws. The jaws normally bear teeth.

Ear:

  • External and middle ear is absent. Internal ear is present.

Air - Bladder:

  • Air bladder is present in the body of fishes.
  • It acts as hydrostatic organ, pressure regular and as accessory respiratory organ.

Example:

  • Sharks, rays, skates, sea-horse, trout etc.

Classification:

  • The fishes of class Pisces are divided into two sub-classes.
    • Cartilaginous Fishes
    • Bony Fishes

Cartilaginous Fishes:

Endoskeleton:

  • Endoskeleton is cartilaginous, for this reason known as cartilaginous fishes.

Exoskeleton:

  • Dermal denticle-like (tooth-like) placoid scales are present on the body.

Respiration:

  • Respiration is by gills. Gills are five to seven in number and open directly to the exterior. An operculum (covering on gills) is generally absent.

Nasal Organs:

  • Paired nasal organs, each with an external opening, are present.

Air - Bladder:

  • An air-bladder or swim-bladder is absent in the cartilaginous fishes.

Cloaca:

  • A cloaca is present.

Spiral Valve:

  • A spiral valve in the intestine is present.

Urea:

  • High concentration of urea is present in the blood. The urea-laden blood does not lose fluid to the surrounding sea water.

Viviparous & Oviparous:

  • Most species are viviparous and some are oviparous. Eggs with large case.

Fertilization:

  • Fertilization is internal.

Claspers:

  • Male has a copulatory organ called the clasper, connected with the inner edge of the pelvic fin. It is used to transfer the sperms to the female.

Size:

  • These reach very large size.

Examples:

  • Sharks such as dog, fish, whale - shark (largest living species about 70 feet long), Hammer-head shark, rays. Most of them are marine and predaceous.

Bony Fishes:

Skeleton:

  • These fishes have a bony skeleton.

Scales:

  • The scales are present. These are of various types.

Operculum:

  • The gills are covered by a bony lid called operculum. Thus there is a single exit of water on each side.

Swim - Bladder:

  • In most of them swim-bladder or air-bladder is present. It is used regulating buoyancy.

Habitat:

  • They are marine or fresh-water.

Example:

  • Trout, Pike, Eel, Murrel, Sea-Horse, Cod.

Lung Fishes:

  • A small group of zoogeographically important fish called lung fishes, belonging to the order dipnoi of class osteich-thyes. They respire by the help of gills as well as during drought period by lungs, which are actually modified air bladders. E.g. American, African, Australian lung fish.

Edible Fishes of Pakistan:

  • Perches (Pomfret)
  • Hilsa (Pallah)
  • Carps (Rohu)
  • Mackerels (Surmai)
  • Salmon (Trout)
  • Catfish (Khagga)

Class Amphibia:

Distinctive Characters of Amphibia:

Introduction:
  • Amphibian is the combination of two Greek words.
    • Amphi → Dual
    • Bians → Life
  • They can live in both water as well as on land.
Least Number:
  • The present-day amphibians are the least number of the terrestrial vertebrates.

Mode of Life:

  • They are least adapted for terrestrial mode of life.

Cold-Blooded:

  • They are cold-blooded or poikilothermous.
  • Their body temperature varies with that of their environment.

Respiration:

  • In the larval stage they possess fish-like characters e.g. gills.
  • When they reach adult size, they acquire characters of terrestrial vertebrates.
  • They breathe by gills in larval stage and lungs in adult stage.
  • Some retain these gills throughout life.

Limb:

  • The limbs support the body on land, limbs are five fingered or pentadactyle.

Skin:

  • Skin is moist and glandular. It helps in breathing.

Heart:

  • Heart is three chambered with two atria and one ventricle.
  • Two additional chambers sinus venosus and truncus arteriosus may be present.
  • It may be called five chambered.

Fertilization:

  • Fertilization may be external. Early development takes place in water.

Hibernation:

  • Due to cold-blooded amphibians hibernate in winter i.e., undergo winter sleep.

Aestivation:

  • Amphibians burying themselves in the mud during hot summer to avoid the extreme temperature. This period is called aestivation.

Tailed Amphibians:

  • They bear tail i.e., salamanders and newts.

Without Tail:

  • These amphibians lose tail in adult stage. E.g. Frogs, Toads.

Class Reptilia:

Distinctive Characters of Reptilia:

First Successful Land Vertebrates:
  • Reptiles are the first successful land vertebrates as they do not depend upon water for their reproduction.

Habitat:

  • Reptiles are found both in water as turtles and on land as lizards.
  • But they are predominantly terrestrial. Adaptation to aquatic life is secondarily e.g. crocodile, sea snake.

Cold-Blooded:

  • Reptiles are cold-blooded animals.

Skin:

  • The skin is dry. It is covered by horny epidermal scales.
  • These scales are differently modified.

Limbs:

  • They are tetrapods with pentadactyle limbs may be modified differently.

Breathing:

  • Reptiles breathe by lungs.

Heart:

  • The heart is imperfectly four chambered.
  • Ventricle is incompletely divided. Thus the separation of oxygenated and deoxygenated blood is not complete.

Eggs:

  • Eggs are large with much yolk.

Fertilization:

  • Fertilization is internal.

Development:

  • Development takes place inside the egg. The embryo is well protected.

Extra Embryonic Membranes:

  • The embryo is protected by two extra-embryonic membranes called the Amnion and Allantois.
  • Snakes are limbless reptiles. Poisonous snakes have poison called venom, injected by sharp and curved teeth called Fangs.

Class Aves: (Birds)

  • A bird is a feather-covered bipedal flying vertebrate possessing wings.

Distinctive Characters Of Birds (Aves):

  • In birds many adaptations occurred due to aerial mode of life.

Shape:

  • Body shape is boat-like streamlined to offer little resistance to air.

Homoeothermic Animals:

  • Birds are warm-blooded or a homoeothermic animal i.e., the body temperature remains constant and it does not change with the environment.
  • The rate of metabolism is very high.

Feather’s:

  • The body is covered with feathers.
  • Feathers help in flight and conservation of heat.

Fore - Limbs:

  • Fore-limbs are modified into wings for flight.
  • The pectoral muscles are very strong for long flights.

Hind - Limbs:

  • Hind limbs are long, straight, and strong for walking, perching or swimming with four toes.

Skeleton:

  • Skull contains single occipital condyle.
  • The bones are light and hollow (spongy) to reduce the weight (Pneumatic bones).

Heart:

  • Heart is four chambered. Oxygenated and deoxygenated blood is completely separated.

Breathing System:

  • Breathing system is very efficient due to high rate of metabolism.
  • It contains air-sacs between the internal organs.
  • This provides double passage of air through the lungs.

Beak:

  • Jaws are modified into beak and contain no teeth. It has a horny sheath.

Nervous System:

  • The nervous system and sense organs are highly developed.

Behavior:

  • Birds show highly organized behavior in nest building, protection of the young ones, courtship and migration which comes very close to the behavior of highest apes and man.

Fertilization:

  • Internal.

Well-Developed Sense Organs:

  • Birds have well-developed sense of hearing, vision and equilibrium.

Syrinx:

  • They have sound-producing sac, the Syrinx.

Classification:

  • Birds are classified into two sub-classes.
    • Running birds → Ratitae (Sternum raft like)
    • Flying birds → Carinatae (Sternum with keel)

Running Birds: Ratitae (Sternum Raft Like)

  • Some present day birds are unable to fly. They range in size from Kiwi to Ostrich. These flightless birds have the following characteristics.
    • They have reduced or vestigial wings and feathers.
    • They are big sized, flightless heavy birds.
    • Their sternum is flat without keel.
    • Their flight muscles are poorly developed.
    • Some of them run very fast, some can swim.

Flying Birds: Carinatae (Sternum With Keel)

  • Modern birds are ‘flying birds’. They show a great variety, are distributed in most parts of the world. They show all adaptation to the flight e.g. falcon etc.

Origin of Birds:

  • Birds are evolved from Reptiles. They are also called glorified reptiles. They are superior to reptiles because they contain wings and feathers. Due to the presence of feathers, they are also called feathered dinosaurs, because they have evolved from a small insect eating Lizard, called Thecodont 2000 million years ago. Archaeopteryx is considered as the earliest bird. Its fossil was found 150 million years old. It is a connecting link between birds and reptiles.

Flight Adaptations In Birds:

  • Birds are the flying vertebrates. They have certain characters which help them in flying. These characters are as follows:

    • Wings:

      • They have special organs for flying, called wings. These are the modified form of fore-limbs.

    • Feathers:

      • Their body is covered by feathers which help to maintain the body temperature and prevent the loss of body heat.

    • Sternum With Strong Muscles:

      • The body structure is modified for flying. The sternum, central part of pectoral girdle is larger and strong for the attachment of wing-muscles and better support.

Light And Hollow Bones:

  • Their bones are hollow and light for easy flight.

Blood Circulation:

  • Their heart consists of four chambers and circulatory system is very fast. It helps to maintain the blood pressure and to control the amount of oxygen.

Energy Requirement:

  • The metabolism of the body is very rapid and fast, so great amount of energy is produced which is used in flying and maintains the body temperature. It is due to rich supply of O₂ from heart and by extra ordinary respiratory system. The lungs are supplemented by number of air-sacs. They store air which is used during flight.

Maintenance Of Body Temperature:

  • They are warm-blooded animals. The muscular activity rises temperature but it is maintained by the ventilating action (exchange of warm and cold air) of air sacs.

Class Mammalia:

  • The word Mammalia is derived from a Latin word which means having mammary glands. They are evolved from reptiles called therapsids and they are considered as the most advanced vertebrates.

  • There is a great variety in size and shape. The smallest mammal is pygmy shrew having weight only about 2 gms and the largest mammal is the blue whale, which is up to 40 meters long and with weight up to 160,000 kg. It is considered as the largest living organisms on the earth. Human beings (Homosapiens - biological name) is also included in class mammalia.

Important Characters:

  • They are warm-blooded animals (Homoiotherms). They have constant body temperature which remains between 37°C - 40°C.
  • They have bony skeleton and vertebral column.
  • Their skin is covered by hairs which helps to prevent the loss of heat and regulates the body temperature.
  • The skin has sebaceous and sweat glands.
  • They possess mammary glands which produce milk in female for nourishing the young ones.
  • Their body cavity is divided into upper thorax and lower abdomen by diaphragm.
  • External ear-pinna is present.
  • Heart is completely four chambered. The oxygenated and deoxygenated bloods remain separate from each other.
  • Respiration is by lungs.
  • Excretion is by kidneys.
  • The teeth are of different types, incisors, canines, premolars and molars. So the teeth are called heterodont. They are also thecodont because they are fixed in the gums.
  • They have seven cervical vertebrae in the neck region.
  • They are viviparous i.e., produce young ones except egg-laying mammals.

Fertilization:

  • Fertilization is internal. In most of the mammals, the fertilization of egg takes place in uterus. There is a cord between mother and developing embryo, called placenta, through which food and oxygen are supplied. Mother takes care of her young ones after the birth.

Sub Class Prototheria (Mono Tremata) Egg Laying Mammals:

  • There are egg-laying mammals.
  • This sub class has in present time two genera.
    • Tachyglossus (Echidna), it is commonly called spiny anteater.
    • Ornithorhynchus commonly called the Duck-bill Platypus.
  • These animals have certain reptilian characters and some mammalian characters.
  • They form a connecting link between reptiles and mammals.

Mammalian Characters:

  • Hairs are present on the body.
  • Diaphragm is present.
  • Presence of left aortic arch.
  • The brain is relatively large with well-developed cerebral hemispheres.
  • The mammary glands are present in the female.

Reptilian Characters:

  • They lay eggs.
  • Anus and urinogenital aperture is not separate. Instead, a common cloaca is present hence called monotremata.
  • Some characters of skeleton resemble with reptiles.

Specialization:

  • Prototherians also show some specializations. E.g., There are no teeth in the adult.
  • Prototherians seem to be intermediate between the reptiles and mammals.
  • They are not considered ancestors of mammals.
  • The prototherians became isolated and continued with little change.

Examples:

  • Platypus, Spiny Ant-Eater.

Sub Class Metatheria (Marsupials) - Pouched Mammals:

  • These are called pouched mammals. Kangaroos, Tasmanian Wolf, Opossum are included in this sub class.
  • These animals are found in Australia and America.
  • The distinctive characters of this group are as follows. The female has a pouch on abdomen which contains mammary glands.
  • The young are born in helpless condition.
  • These offspring shift in the pouch.
  • Here they get food and protection.
  • These animals do not have a true placenta.
  • For this reason the offspring are not fully developed before birth.

Reptilian Characters:

  • The brain of Marsupials has some reptilian characters. The cerebral hemispheres are small and olfactory lobes are large.
  • The urino-genital aperture and anus are not separate completely especially in female.
  • These animals are generally burrowing in habit. They are herbivorous.

Sub-Class Eutheria: (Placental - Mammals)

  • This group includes mammals with placenta. For this reason they are called placental.
  • The placental insectivores are considered ancestors of these mammals. These animals developed into several divergent populations.
  • Placental mammals are widely distributed on earth. They live in various habitats e.g., water, land, air etc.
  • They have changes like increase in size, specialization and lengthening of limbs.
  • The teeth are also specialized and reduced.
  • Large brain is present.
  • In female a placenta develops to which embryo is attached. Embryo or foetus gets nourishment from mother through placenta.

Placental Mammals Of Pakistan:

  • Bat
  • Goat
  • Buffalo
  • Donkey
  • Markhor (wild goat) - National animal of Pakistan
  • Rhesus monkey
  • Snow leopard
  • Blind dolphin
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