Question

Acorn worm is-
A. Doliolum
B. Salpa
C. Balanoglossus
D. Rhabdopleuro

Answer 1

Acorn worms are called so due to the presence of acorn shaped heads. It is a characteristic feature of a class of hemichordata phylum. Out of these options, only balanoglossus and rhabdopleura are hemichordates while the rest 2 options are chordates.

Complete Answer:
The enteropneusta is a class of hemichordate falling under invertebrates. The organisms of this class are commonly called acorn worms due to the appearance of their head. A muscular proboscis and a collar together forms the acorn which is used for burrowing in the soft sand or mud. Out of balanoglossus and rhabdopleura, balanoglossus belongs to the enteropneusta while the rhabdo glossus belongs to pterobranchia class.

Therefore the correct answer to this question is- C. Balanoglossus.

Additional information:
- Balanoglossus is an acorn worm and a Hemichordate, which are supposed to be the evolutionary link between invertebrates and vertebrates.
- The body of hemichordates is divided into proboscis, collar and a long trunk. Balanoglossus is an ocean-dwelling organism. It is a deuterostome, and is similar to sea squirts. Branchial openings are present in them.
- A notochord is present in the upper part of the body but the nerve cord is absent. Instead of having nerve cord, they have a stomochord present inside the collar.

Note: Balanoglossus is a member of enteropneusta, they are called acorn worms due to their appearance. Rhabdopleura being a hemichordate is a wrong answer because it falls under the pterobranchia class. Doliolum and salpa cannot be correct as they are chordates, members of a whole different phylum.