Question

The echinoderms, hemichordates and chordates had which of the following larva as a common ancestral form?
a. Tornaria
b. Trochophore
c. Dipleurula
d. Bipinnaria

Answer 1

Hint: Echinoderms are exclusively marine animals who have spinous skin, hemichordates are the sister group of echinoderms and are closely related to chordates and share a similar body plan as that of chordates. Chordates are the higher animals who have a notochord.

Complete answer:
Echinoderms are the marine animals that are recognised by symmetry in their faces or in their biology. Example starfish.They are found in the depth of an ocean. They actually can be found above the water level or under the water level with the low tide or with the high tide. They belong to super phyla Deuterostomes.
Hemichordates belong to the family (super phylum)of deuterostome animals which is really close to the echinoderms and chordates. Example-acorn worm.
Chordate belongs to the chordata and represents the family(superphylum) deuterostomes. Example mammals, birds.
All the three phylums have evolved from the same superphylum called the deuterostomia . The Dipleurula is a hypothetical larva of echinoderms which represents the ancestral form of deuterostomia. So the common ancestral larvae of echinoderm, Chordates and Hemichordates is Dipleurula.
Tornaria: It is the larva of Hemichordata. It is similar to the bipinnaria larvae of starfish in appearance.
Trochophore: It is a free swimming marine larva which contains numerous bands of cilia. This larva is the characteristic of annelids and molluscs.
Bipinnaria: It is a first stage larval form of starfish. It also contains a band of cilia.

Hence, the correct answer is option ©.

Note: The larval form Dipleurula is bilaterally symmetrical and ciliated. All the other types of larvae (of echinoderms) like Bipinnaria, larva of sea rollers and sea-star are similar in basic plan and resemblance. The ventral concave side bears a mouth with a ventrally disposed anus.