Question

Trochophore larva occurs in
(a) Annelida and Porifers
(b) Coelenterata and Annelida
(c) Mollusca and Coelenterata
(d) Annelida and Mollusca

Answer 1

In this phylum consists of commonly segmented worms and the other phylum members are soft- bodied animals that usually have an internal or external shell.

Complete step by step answer:
Trochophore larva is similar between Annelids and Mollusks. The presence of cilia on both ends and middle. They disperse their offspring. Advantage is the presence of the shell burdened adults. Terrestrial forms develop within the egg; Not free- living.
Significance of trochophore larvae:
- The trochophore larvae was dicoerved by Harschik in 1878.
- The present in the phylum of mollusks, annelia and other phyla trochophore theory of bilateral animals from radial ancestors.
- The trochophore larvae body shape, apical sense organs, statocyst, nervous system.
- They promote ctenophora which means trochophore theory of bilateral from radial ancestors.
Characteristics of trochophore larva:
- The larva is pear shaped.
- It measures about 0.5 mm in length.
- The circle of the preoral ciliary is seen.
- Prototroch or velum divides their body into two unequal parts. Upper one consists of prostomium. Lower part bearing mouth and anus.
- Preoral part is large and convex. Upper end consists of apical tufts. Prototroch is the swimming organ.
So, the correct answer is, ‘(d) Annelida and Mollusca.’

Note:
- Larval heart and kidney present which is located at the anterior end of the body immediately behind the velum.
- Statocyst and gill- rudiments present.
- Long cilia of the velum function locomotion and shows suspension feeding.
- The Alimentary canal is complete. Their anus is shifted to the anterior side.
- Foot usually bears an operculum.
- During development of veliger larva torsion occurs.
- Internal parasites mainly have a stage which may be called larval stage in which they are transferred either by active or passive migration to a new host.