Question

Which one is the common ancestral larval form of echinoderms, hemichordates and chordates?
(a) Tornaria
(b) Bipinnaria
(c) Dipleurula
(d) Trochophore

Answer 1

Hint: This larval stage is a hypothetical ancestor which is small, collated bilateral, benthic or pelagic which means it lives in the upper or lower water of the open sea. The larvae have major similarities with the tornaria and bipinnaria larva stage.

Complete step by step answer:
Dipleurula hypothesis given by Malcolm Jolly according to which the embryonic similarities are too close to be accidental which may result from retention of characteristics derived from the ancestor. Dipleurula larva is a hypothetical ancestor having primitive features incorporated into larvae of echinoderms and hemichordates. In this larva stage, pharyngeal slits arose later in each which aids in ciliary or filter- feeding. The presence of notochord, tail, nerve tube arose to serve better locomotion and the undulatory movements accompanied by muscle segmentation. Tornaria larva of hemichordates is similar in appearance to echinoderm larva with ciliated bands. Whereas bipinnaria in Echinodermata larvae has two ciliated bands, the preoral and the pastoral.
So, the correct answer is, ‘(c) Dipleurula.’

Additional information:
- The echinoderms are exclusively marine enterococcus coelomate, triploblastic animals having pentamerous symmetry derived from an ingenious bilaterality.
- They do not have definite head or brain with an endoskeleton of calcareous plates or spicules embedded within the skin with a peculiar water system of coelomic origin, pushing out of the body surface, numerous small delicate projections the podia or tube feet, with an ectodermal systema nervosum without nephridia and with gonads opening on to the inside by special ducts.

Note:
- The side of the body, which in natural condition remains towards the substratum and contains the mouth or oral opening is named oral or actinal surface. The oral surface bears the subsequent structures.
- The side of the body, which in natural condition remains towards the substratum and contains the mouth or oral opening is named oral or actinal surface. The oral surface bears the subsequent structures.