Question

The anterior part of amphioxus is:
a. Oral hood
b. Rostrum
c. Mouth
d. Both a and b

Answer 1

Hint: The animal kingdom is divided into many phyla, out of which one is phylum chordata. Chordates are characterized by the presence of the notochord, a dorsal hollow nerve cord, and paired pharyngeal gill slits. They possess a post-anal tail, closed circulatory system, and organ system level of organization.

Complete answer: The phylum chordata is divided into three subphyla. These three are:
Urochordata, Cephalochordata, and Vertebrata. In Urochordata, the notochord is present only in the larval stage; for example Ascidia, Salpa, Doliolum. In Cephalochordata, the notochord is persistent throughout their life; for example, branchiostoma (amphioxus). Amphioxus are small marine animals that are found in coastal waters of warmer parts of the world. The oral hood is the elongation of the oral cavity and bears the oral cirri (these are finger-like structures that form filters to screen out too large particles that cannot be consumed). The mouth is located at the level of the oral hood. Whereas the rostrum is the anterior-most part which projects over the oral hood.
Therefore, the right answer is option b- rostrum

Note: The amphioxus spend most of their life buried in gravel or mud in the ocean bottom since they can swim. Mostly, during the night, these swim near the bottom. These burrow into sand by using rapid movements of their body. Their body has tapered ends and is covered by a cuticle which helps in easy movement.