Problem 9 - Entrance Test

Let's analyze each option: (A) Cnidarians are primarily marine, but some freshwater forms exist (e.g., Hydra). Ctenophores are exclusively marine. So, this statement is incorrect. (B) Cnidarians are characterized by the presence of stinging cells called cnidoblasts (or nematocysts) used for defense and prey capture. Ctenophores (comb jellies) lack cnidoblasts and instead possess specialized adhesive cells called colloblasts (or lasso cells) for capturing prey. This is a fundamental distinction. So, this statement is correct. (C) Cnidarians typically exhibit radial symmetry. Ctenophores exhibit biradial symmetry due to the arrangement of comb plates and tentacles, which is a subtle variation of radial symmetry, but the statement reverses their common descriptions in some contexts. More precisely, Ctenophores are biradial. So, this statement is largely incorrect as stated. (D) Both Cnidarians and Ctenophores are diploblastic (possessing ectoderm and endoderm with a mesoglea in between). Neither is triploblastic. Cnidarians have an incomplete digestive system (single opening). Ctenophores have a complete digestive system, with a mouth and two anal pores, though their digestive system can be complex. So, this statement is incorrect on multiple counts.