Question

Nereis has

• A. Coeloblastula
• B. Superficial blastula
• C. Disco blastula
• D. Stereo blastula

Answer 1

The correct option is D

Stereo blastula

The correct option is D.

Explanation for the correct option:

1. Embryos of annelid worms, turbellarian flatworms, nemertean worms, and all mollusks except cephalopods created by spiral cleavage, characterized by the lack of a blastocoel; developed by annelid worms, turbellarian flatworms, nemertean worms, and all mollusks except cephalopods.
2. Stereo blastula. Nereis is a polychaeta worm genus in the Nereididae family.
3. Stereo blastulas have a solid blastula with no blastocoel and are made up of tightly packed large-sized cells.

Explanation for the incorrect options

Option A

1. A form of blastula; a stage of embryonic development.
2. Certain Coelenterate, lower Arthropoda, Echinodermata, Tunicata, Acrania, Cyclostomata, Acipenseridae, and most Amphibia have coeloblastula. Complete radial cleavage results in its formation (even or uneven).

Option B

1. 'Superficial blastula' is another name for the peri blastula.
2. It can be found in insect eggs. The blastocoels are loaded with yolk, analogous to the coeloblastula.

Option C

1. Modified blastula observed in extremely telolecithal eggs is referred to as Discoblastula.
2. The Discoblastula is seen in fish, reptiles, and birds with enormous yolk sacs in their eggs. The blastocoel develops a yolk sac and the ceiling is epiblast in this type of blastula.

Final answer: Nereis has a stereo blastula.