Biology · Animal Kingdom · NEET
Platyhelminthes are ACOELOMATE. This means they have NO body cavity between the gut wall and body wall. This is the single most tested fact for NEET. Do not confuse them with Aschelminthes (roundworms), which are pseudocoelomate. Platyhelminthes are the classic example of a bilaterally symmetrical AND acoelomate animal.
Flatworms are TRIPLOBLASTIC. They have all three germ layers: ectoderm, mesoderm, and endoderm. Platyhelminthes are the FIRST phylum in the NCERT sequence to be triploblastic (triploblastic animals run from Platyhelminthes up to Chordates). Porifera and Coelenterata below them are diploblastic (only two layers).
Flame cells (also called protonephridia) are the excretory structures of Platyhelminthes. Each flame cell has a tuft of cilia that beats like a flickering flame, pushing water and waste along tiny tubes and out of the body. They mainly do OSMOREGULATION (control water and salt balance) and remove waste. NCERT links flame cells to Taenia (tapeworm) and Planaria. Remember: Taenia + flame cells is a favourite NEET match-the-column pair.
Because their body is DORSO-VENTRALLY flattened — squashed from top to bottom, like a ribbon. This flat shape is not just for the name: it helps gases and nutrients diffuse easily since no cell is far from the surface. This matters for NEET because flatworms have no special respiratory or circulatory system, so the flat body does the transport job by simple diffusion.
Learn these three from NCERT: Planaria (free-living, shows regeneration), Fasciola (liver fluke), and Taenia (tapeworm). Planaria appears in match-the-column PYQs, and Taenia is repeatedly linked to flame cells. Most Platyhelminthes are ENDOPARASITES living inside other animals, including humans, using hooks and suckers to hold on.
No. Their digestive system is INCOMPLETE — it has only a single opening that works as both mouth and anus. NCERT states this directly, and NEET 2026 tested it: 'Digestive system in Platyhelminthes is incomplete' is a CORRECT statement. Their level of organisation is ORGAN level (higher than Coelenterata's tissue level, but lower than the organ-system level of Annelida onward).
Bilaterally symmetrical and acoelomate animals are exemplified by
Match the following organisms with their characteristics: A. Pila B. Bombyx C. Pleurobrachia D. Taenia | i. Flame cells ii. Comb plates iii. Radula iv. Malpighian tubules
Select the incorrect statements: A. Digestive system in Platyhelminthes is incomplete. B. Bilateral symmetry is a characteristic of adult Echinoderms. C. Pseudocoelom is possessed by Aschelminthes. D. Notochord is persistent throughout life in Chondrichthyes. E. Members of Reptilia maintain a constant body temperature.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. In the NCERT sequence, Platyhelminthes are the first phylum with all three germ layers (ectoderm, mesoderm, endoderm). Triploblastic organisation runs from Platyhelminthes up to Chordates.
Organ level of organisation. This is higher than the tissue level of Coelenterata but lower than the organ-system level seen from Annelida onward.
Mostly parasitic. Most flatworms are endoparasites (live inside a host), like Taenia and Fasciola, and have hooks and suckers. Some, like Planaria, are free-living and famous for regeneration.
No. Flatworms like tapeworm are hermaphrodite — sexes are NOT separate — and their fertilisation is internal. NEET 2023 tested this: 'In tapeworm, fertilization is internal but sexes are not separate' is a correct statement.
Both are triploblastic and bilaterally symmetrical, but Platyhelminthes are ACOELOMATE (no cavity) while Aschelminthes are PSEUDOCOELOMATE (false cavity). Also, flatworms have an incomplete gut, while roundworms have a complete gut with mouth and anus.
