Flatworm Body Structure & Organization — NEET Biology
✅ Asked in NEET 2020Bilaterally symmetrical and acoelomate animals are exemplified by NEET Year: NEET 2020
Bilaterally symmetrical and acoelomate animals are exemplified by NEET Year: NEET 2020
Answer & NCERT explanation
Correct answer: B — Platyhelminthes
Platyhelminthes (flatworms) are bilaterally symmetrical and acoelomate (no body cavity). Ctenophora has biradial symmetry, Aschelminthes are pseudocoelomate, and Annelida are coelomate. Only flatworms like Planaria and Taenia show both characteristics mentioned in the question as per NCERT Animal Kingdom chapter.
Read more NCERT concept on the PYQ
They have dorso-ventrally flattened body, hence are called flatworms. These are mostly endoparasites found in animals including human beings. Flatworms are bilaterally symmetrical, triploblastic and acoelomate animals with organ level of organisation. Hooks and suckers are present in the parasitic forms. Some of them absorb nutrients from the host directly through their body surface. Specialised cells called flame cells help in osmoregulation and excretion. Sexes are not separate. Fertilisation is internal and development is through many larval stages. Some members like Planaria possess high regeneration capacity.
NTA focuses on flatworms being bilaterally symmetrical, triploblastic, and acoelomate animals with organ-level organization. Students commonly confuse these terms—bilateral symmetry means the body can be divided into identical left and right halves, while acoelomate means they lack a true body cavity (coelom). Remember: flatworms have three germ layers (ectoderm, mesoderm, endoderm) but NO space between organs and body wall. The presence of hooks, suckers, flame cells for osmoregulation, and internal fertilization are additional distinguishing features. NTA tests this to ensure students understand the evolutionary position of platyhelminthes—they're more complex than cnidarians but lack the coelom found in higher animals. This concept appeared in 2020 NEET and remains fundamental for animal classification questions.
What does NCERT say about They have dorso-ventrally flattened?
Has this concept appeared in NEET?
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