Question

What is the larva of cyclostomates known as?
A) Lamprey
B) Amphioxus
C) Ascidian
D) Ammocoete

Answer 1

Hint: To approach this question, the knowledge of the class Cyclostomata is necessary. This group of animals have a specific name for their larvae.Cyclostomata is a group of agnathans that comprises the living jawless fishes: the lampreys and hagfishes.

Complete answer:
1) The origin of the name Cyclostomata comes from-cyclo, round; stoma, mouth for the reason that, instead of typical vertebrate jaws, they have round jawless sucker-like mouths by which they attach themselves to the sides of fishes or to other objects. They are more committed to a life of parasitism than any other vertebrate, and when one fastens to a fish, it may rasp a hole with its file like horny teeth that are attached to its muscular “tongue,” quite through the skin of the unfortunate host whose death eventually results.
2) The lamprey is an ancient, primitive, jawless fish, with a round, sucker-mouth which it uses to attach to other fish to feed from them. Adults live in the sea and return to freshwater to spawn.
3) Amphioxus are also known as lancelet, belonging to subphylum Cephalochordata of the phylum Chordata. Amphioxus (plural Amphioxi) are small marine animals found widely in the coastal waters of the warmer parts of the world and less commonly in temperate waters.
4) The ascidians (also known as sea squirts) are sac-like marine filter feeding invertebrates, they are found all over the world with sea waters with salinities over 2.5%.
5) The cyclostomes lay numerous eggs, about 1mm in diameter and lodge in the gravel around the nest. The egg hatches into an ammocoete larva, which is a blind, worm-like animal that burrows in the slit.

Thus, the correct answer is option D (Ammocoete).

Note:The ammocoete larva is an exclusive characteristic of cyclostomates. They aren’t found in any other classes.Ammocoete larva is important in the evolution of the petromyzon fish. The ammocoete larva undergoes metamorphosis which changes its internal organs leading to their development.