Question

Ctenoplana differs from Hormiphora and Beroe in having
(a) Pear-shaped body
(b) Conical ovate body
(c) Flat bilobed body
(d) Branched axis

Answer 1

Hint: Ctenophora is a phylum of exclusively marine and diploblastic organisms that has a wide range of body forms. Also, they lack a fluid-filled body cavity.

Complete step by step answer:
Ctenoplana, Hormiphora, and Beroe all belong to Phylum Ctenophora.
While Beroe (cigar comb jellies) have a sac-like transparent body and lack tentacles, Hormiphora (sea gooseberry) has a pear-shaped body. Ctenoplana (sea walnuts) has a circular and flattened body with tentacles to catch the prey easily. Obelia is known to have a branched axis.
Characteristics of Phylum Ctenophora:
- They are exclusively marine.
- They are radially symmetrical.
- These are diploblastic with tissue level of organization.
- They have a blind sac body plan (single opening known as stomodeum) .
- The body has eight external rows of ciliated comb plates that aid in locomotion.
- The mode of digestion can be both intracellular and extracellular.
- A significant quality of bioluminescence (light emission) is characteristic of many ctenophores.
- Sexes are not separate i.e. hermaphrodite.
- Mode of reproduction is sexual only.
- Fertilization is external with indirect development.
- The larval form is the Cydippid larva.
- They are carnivorous in nature
So, the correct answer is ‘(c) Flat bilobed body’.

Note:
- Ctenoplana is a creeping animal. It lives on the surface of the sea.
- Respiration through the general body surface.
- Circulatory and excretory system is absent.
- They have Colloblast/Lasso cells. These cells secrete some sticky substance which helps in capturing the prey.