Animal Kingdom

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Organ systems of different animals show complexities. E.g.

1)

Digestive system : It is of two types-

(a) Incomplete type : It has only a single opening that acts as

mouth & anus. E.g. Cnidaria and Platyhelminthes.

(b) Complete type : It has 2 openings (mouth & anus). E.g. Higher

animals.

2) Circulatory system : It is of two types -

(a) Open type : In which tissues in cells bath into the blood. E.g.

Cockroach

(b) Closed type : In which blood circulation occurs inside the

vessels. E.g. Higher animals

2. BØDÝ SÝMMËTRÝ

It is the arrangement of similar body parts on 2 sides of main axis of the body.

Based on symmetry, animals are of 2 types: Asymmetrical and Symmetrical.

Asymmetrical: Here,

body cannot be

divided into 2 equal

halves. E.g. Poriferans,

Snails etc.

Symmetrical: Here,

body can be divided

into 2 equal halves.

It is of 2 types: Radial

symmetry & Bilateral

symmetry

Radial symmetry: Here, body can be divided into 2 equal halves

by any plane along central axis (oral-aboral axis) of the body.

E.g. some Poriferans, Ctenophores and Echinoderms (adult).

Bilateral symmetry: Here, body can be divided into right &

left halves in only one plane. E.g. Platyhelminthes to Chordata

(except adult Echinodermata).

A

B



The body of bilaterally symmetrical animal has a dorsal side (upper),

a ventral side (lower), left & right lateral sides, anterior (cephalic) side

and posterior (anal or tail) side.