Question

Nereis has
A. Stereoblastula
B. Discoblastula
C. Coeloblastula
D. Superficial blastula

Answer 1

Hint: Nereis is the genus that belongs to the class polychaete and they consist of setae and polypodium for the locomotion, they belong to the marine water, found in sandy areas and have an adaptation to burry.

Complete answer:
The shape of the Neries is the round shape and as we already know that it is a marine water animal and is found in sandy areas and sometimes it is also found by clinging to the grass.
Neries are very dangerous to touch, as they give long-lasting burns to the people who touch it.
They are commonly called as ragworms or calm worms and the body is long, slender, and cylindrical and dorsoventrally the surface of these worms are flat and length is 5 to 30 cm.
When coming to the embryo of the Neries it consists of blastula and no blastocoel and the blastula is solid as it consists of the densely packed cell, so it can be said as Stereoblastula.
When coming to options given to the above question, discoblastula is usually found in the higher animals where blastula is separated from the yolk sac by the blastocoel and it is mainly found in birds.
Coeloblastula: where embryos undergo bombastic spiral cleavage and the examples for this are Coelenterates and some amphibians.
Superficial blastula: It is a type of blastula where the cleavage is superficial and the blastocoel is absent and. It is an example of insects.

So from the all above explanation, Stereoblastula is the correct answer.

Note:
Stereoblastula mainly formed by spiral cleavage and characteristic feature is the absence of blastocoel and the example for this type of embryos are annelids, flatworms, molluscan, nematodes, etc.