Question

Nerve cord of Pheretima is
A. Paired, solid and ventral
B. Paired, solid and dorsal
C. Single, solid and dorsal
D. Single, hollow and dorsal

Answer 1

A genus of earthworm which is mostly found in New Guinea and parts of Southeast Asia is the Pheretima. Species of the genus Pheretima generally have a clitellum, which is a band of glandular tissues present on segments $14$ to $16$. Individuals of this species are hermaphroditic and reproduction can either be sexual or parthenogenetic. Like most of the earthworms, Pheretima are nocturnal and have an aversion to light.

Complete answer:
Option A) Paired, solid and ventral: Earthworms do have a well-developed nervous system. The nerve cord arises from the subpharyngeal ganglion. The nerve cord of Pheretima is paired, solid and ventral. The annelids have a pair of ventral nerve cords which are joined by transverse connectives. A twin ventral nerve cord connects the two ganglia via lateral nerves.
Hence option A is the correct answer.
Option B) Paired, solid and dorsal: The nerve cord of Pheretima is a pair of ventral cords. Both paired and solid given in the option is right. But they have ventral nerve cords, not dorsal.
Hence option B is not correct.
Option C) Single, solid and dorsal: Although the nerve cord of Pheretima is solid, they are not single and dorsal. Instead, they are paired and ventral.
Hence option C is not correct.
Option D) Single, hollow and dorsal: Hollow nerve cords are generally found in dorsal nerve cords, which are mainly found in vertebrate chordate subphylum. Since the nerve cord of Pheretima are paired, solid and ventral.
Hence option D is not correct.

Option A) Paired, solid and ventral is the correct answer.

Note:
The nerve cord of Pheretima has a ganglionic swelling which starts from behind the ${5^{th}}$ segment in the posterior part of each segment. This is known as the segmental ganglion. Nerve cord is surrounded by a common sheath of connective tissue known as the epineurium. There is a layer of longitudinal muscle fibers present outside the epineurium