PHYLUM-CTENOPHORA
Phylum—Ctenophora (Ktene-comb; phors—bearing) or
comb jellies or sea Walnuts are exclusively marine forms.
The term ‘Ctenophora’ was coined by Georges Cuvier. It
includes about 50 species.
General Features
Some important general features of phylum—Ctenophora are
discussed below
(i) Habitat and Habit These are of exclusively marine
forms. They are found solitary, pelagic or free-
swimming.
(ii) Body Organisation They are diploblastic,
acoelomate with tissue grade of organisation. Body is
soft, delicate, transparent and gelatinous, like jelly
fishes without segmentation.
(iii) Body Symmetry They are biradially symmetrical.
The arrangement of comb plates gives the appearance
of radial symmetry, the tentacles and branching of
gastrovascular canals show bilateral symmetry.
(iv) Digestive System Digestion is both extracellular and
intracellular. Skeletal, circulatory, respiratory and
excretory systems are absent.
(v) Respiration and Excretion These processes occur
through general body surface.
(vi) Nervous System It consists of nerve cells with an
aboral sense organ called statocyst for balance.
(vii) Reproduction and Development They are
hermaphrodite or monoecious. Gonads are
endodermal. Fertilisation is generally external.
Development is indirect, e.g., Ctenophora,
Pleurobranchia.
Note
Bioluminescence (the property of a living organism to emit light) is
well-marked in ctenophores.