Question

All triploblastic animals are:

Answer 1

The answer is D (although the way it is worded is a little off)

Not all triploblasts are eucoelomate (true coelom/body cavity surrounded entirely by mesoderm). There are two main phylums which are counterexamples: Platyhelminthes (flatworms) and Nematoda (roundworms). Flatworms are acoelomate (lack a coelom) while nematodes are pseudocoelomates (they have a false coelom, surrounded with both mesoderm and endoderm).

B is incorrect because most are not radically symmetrical, a good example being Chordata (including humans)

C is incorrect because schizocoely occurs mostly in protostomes (although some deuterostomes have it too). Schizocoely is when a mass of mesoderm cells migrate to form the coelom, which doesn’t happen in all embryos.

Letter D is the answer. Although there might be some misconceptions about this, mainly Echinodermata, which are radially symmetrical as adults. However, their larvae develop with bilateral symmetry, so letter D should say “bilateral symmetry at one point in their lives.” But bilateral symmetry is present in all triploblasts, which is why letter D is the answer.


Hope that helped! If I made a mistake, please let me know and I’ll amend my response.