Phylum Annelida (segmented worm)

Main Features :

(i) They have elongated and segmented body.

(ii) Body bears lateral appendages for locomotion in the form of chitinous Setae or Parapodia.

(iii) The body is bilaterally symmetrical and triploblastic.

Fig. 7.16. Animals of Phylum Annelida.

(iv) Reproduction by sexual means. Sex may be separate or hermaphrodite (both sexes in the same individual).

(v) They are the first animals with true coelom (body cavity).

Examples. Pheretima (earthworm), Hirudinaria (cattle leech) and Nereis.

Phylum Platyhelminthes (Flatworms)

Main Features :

(i) Their body is dorsoventrally flat and leaf-like or ribbon like.

(ii) Body symmetry is bilateral.

(iii) They are mostly hermaphrodite.

(iv) Body cavity is absent.

(v) There are three layers of cells from which differentiated tissues can be formed. So, animals of this phylla are triploblastic.

Examples. Dugesia (planaria) is free living, Fasciola (liver fluke) and Taenia solium (tape worm) are parasitic animals.

Phylum Cnidaria (Coelenterata)

Main Features :

(i) The body of animals of this phylum is Radially Symmetrical.

(ii) The body bears Tentacles supplied with special stinging cells called cnidoblasts.

(iii) There is a cavity in the body.

(iv) The body is made of two layers of cells.

(v) Some coelenterates live in colony (Obelia) while others live solitary (Hydra).

(vi) Animals of this phylum exist in two types known as Zooids—Polyps and Medusae. Polyps are always fixed but Medusae are free swimming.

(vii) Reproduction is usually asexual (budding) in polyp form and sexual in medusae form.

Examples. Hydra (sea anemones) Obelia, Aurelia and Jelly fish.

Phylum Arthropoda (animals with jointed feet/appandages)

This is the largest group of animals.

Main Features :

(i) They possess jointed legs/appendages.

(ii) Arthropodes have chitinous exoskeleton.

(iii) The body is segmented and may divisible into two regions—Cephalothorax (head and thorax joined) and Abdomen or into three regions—Head, Thorax and Abdomen.

(iv) Body cavity is reduced and is known as Haemocoel (cavity filled with blood).

(v) These animals are bilaterally symmetrical.

(vi) There is an open circulatory system i.e., the blood does not flow in definite blood vessels.

Examples. Apis (honey bee), Musca, Anopheles (mosquito), Palaemon (Prawn), Crabs etc.

Phylum Nematoda (Aschelminthes) (round or thread worms)

Main Features :

(i) Most of the Aschelminthes are small cylindrical or round worms.

(ii) Body cavity is not a true coelom. A pseudocoelom is present.

(iii) Body is bilaterally symetrical and triploblastic.

(iv) Sexes are separate.

Examples. Ascaris (round worm), Ancylostoma (hook worm) and Wuchereria (filarial worm) causes elephantiasis.

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