Biology · Animal Kingdom · NEET
Ctenophora is diploblastic. This means the body is built from only two germ layers: the outer ectoderm and the inner endoderm, with a jelly-like layer (mesoglea) in between. It is NOT triploblastic. This is the same body plan as Coelenterata (Cnidaria). NEET loves to trap you here, so remember: Porifera, Coelenterata and Ctenophora are the diploblastic phyla.
Both are marine, diploblastic, radially symmetrical, and have tissue-level organisation. The BIG difference: Coelenterata has cnidoblasts (stinging cells / nematocysts) and shows polyp-medusa forms. Ctenophora has NO stinging cells; instead it has eight rows of comb plates for locomotion and shows strong bioluminescence. So the diagnostic word for Ctenophora is comb plates + bioluminescence; for Coelenterata it is cnidoblasts.
Comb plates are eight external rows of cilia (tiny hair-like structures) fused together like a comb. They beat in waves and push the animal through water, so their job is LOCOMOTION, not digestion. NEET has directly tested the wrong statement 'comb plates help in digestion' — that is FALSE. Comb plates = swimming/locomotion only.
Ctenophora is the phylum where bioluminescence is well-marked. Bioluminescence means a living organism can produce and emit its own light. In NCERT this glowing property is a signature feature of ctenophores like Ctenoplana and Pleurobrachia. If a NEET question says 'bioluminescence', the answer is almost always Ctenophora.
Ctenophora is radially symmetrical (like the wheel of a bicycle, any cut through the centre gives equal halves). It is NOT bilaterally symmetrical. Radial symmetry is also found in Coelenterata and in adult Echinoderms. So if a question asks for a radially symmetrical acoelomate phylum, Ctenophora and Coelenterata both fit.
The two NCERT examples are Pleurobrachia and Ctenoplana. In NEET match-the-column questions, Pleurobrachia is repeatedly matched with Ctenophora, and Ctenoplana is matched with bioluminescence. Memorise both names — they appear almost every year in matching questions.
Digestion in Ctenophora is BOTH extracellular and intracellular. Food is first broken down in the gut cavity (extracellular) and then finished inside cells (intracellular). This is the same dual digestion seen in Coelenterata. Note: digestion is NOT done by comb plates — comb plates only help in swimming.
Ctenophores reproduce ONLY by sexual means. Sexes are not separate (they are hermaphrodite / monoecious). Fertilisation is external (in the water) and development is indirect (there is a larval stage). This exact set of facts was tested in NEET 2023, so learn it as a package: only sexual, external fertilisation, indirect development.
Read the following statements. (a) Metagenesis is observed in Helminths. (b) Echinoderms are triploblastic and coelomate animals. (c) Round worms have organ-system level of body organization. (d) Comb plates present in ctenophores help in digestion. (e) Water vascular system is characteristic of Echinoderms. Choose the correct answer.
Select the correct statements: A. Platyhelminthes are triploblastic pseudocoelomate and bilaterally symmetrical. B. Ctenophores reproduce only sexually and fertilization is external. C. In tapeworm, fertilization is internal but sexes are not separate. D. Ctenophores are exclusively marine, diploblastic and bioluminescent. E. In sponges, fertilization is external and development is direct.
Match List I with List II. (a) Metamerism (b) Canal system (c) Comb plates (d) Cnidoblasts — with (i) Coelenterata (ii) Ctenophora (iii) Annelida (iv) Porifera.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is called comb jelly because its body carries eight rows of ciliated comb plates that look like combs. It is called sea walnut because the jelly-like rounded body resembles a walnut. Both names are used in NCERT.
Ctenophores are exclusively marine (only found in the sea). No freshwater ctenophore is in the NEET syllabus, so if an option says 'freshwater ctenophore', it is wrong.
No. Cnidoblasts (stinging cells) belong to Coelenterata/Cnidaria only. Ctenophores lack cnidoblasts. This is the main point that separates the two look-alike phyla.
Ctenophora shows tissue-level organisation, the same as Coelenterata. Cells are arranged into tissues but there are no true organs.
Ctenophora, being diploblastic with only tissue-level organisation, has no true coelom, so it is not classed as a coelomate. The coelom concept is applied to triploblastic animals, where Ctenophora simply does not have a body cavity.
