Write short notes about ctenophora.

Explanation

(i) Ctenophora are exclusively marine, radially symmetrical, diploblastic animals with tissue level of organisation.
(ii) Though they are diploblastic, their mesoglea is different from that of cnidaria. It contains amoebocytes and smooth muscle cells.
(iii) They have eight external rows of ciliated comb plates (comb jellies) which help in locomotion, hence commonly called comb jellies or sea walnuts.
(iv) Bioluminescence (the ability of a living organism to emit light) is well marked in ctenophores.
(v) They possess special cells called lasso cells or colloblasts which help in food capture.
(vi) Digestion is ZOOh extracellular and intracellular.
(vii) Sexes are not separate (monoecious). They reproduce only by sexual means.
(viii) Fertilization is external and development is indirect and includes a larval stage called cydippid larva. eg. Pleurobrachia and Ctenoplana.