Question

Which is not a larva of sponge?
A) Tornaria
B) Parenchymula
C) Stereo Gastrula
D) Amphiblastula

Answer 1

Hint: It is a planktonic larva and found in the members of some hemichordata and found in some worms.

Complete Answer:
A) Tornaria is a planktonic larva that is found in some species of hemichordata such as acorn worm. Starfishes bipinnaria larva is very similar to these. Cilia is present around their body. Larva is oval shaped and is transparent. The diameter of the body is about 3 mm. An apical plate is present that is a thickened region which is provided by a tuft of cilia and a pair of eye spots. It has a complete alimentary canal. The ciliary band stretches throughout the anterior.

B) Parenchymula is a type of larva of a demosponge composed of an envelope of flagellated cells surrounding an internal mass of cells. Demospongiae is developed directly into solid stereoblastula. It is then developed into a flagellated form to form parenchymella.

C) The solid parenchymella larvae is also called stereo- gastrula larvae. It is found in many cavities and it lacks an internal cavity and bears some flagellated cells over their entire surface, except (often) at the posterior pole. These larvae have similar appearance to the cnidarian planulae.

D) Amphiblastula larva is oval in shape and it shows some small micromeres with a flagella on their one side. They have the other half of the larva which shows large macromeres.

Hence Option A: Tornaria is the correct answer.

Note: Hemichordata is a phylum of marine deuterostome animals, generally considered the sister group of the echinoderms.