Question

Ammocoete larva belongs to
A. Petromyzon
B. Myxine
C. Amphioxus
D. Balanoglossus

Answer 1

Hint: It is the larval stage of primitive lamprey.

Complete answer:
The Ammocoete larva is the larval stage of the primitive, jawless fish, called the lamprey or Petromyzon.
The young ammocoete larvae spend many years in the rivers, where they live burrowed in fine sediment, filter-feeding on detritus and microorganisms while adult lampreys spawn in rivers and then die.

Additional information
- The sea lamprey is a parasitic lamprey native to the Northern Hemisphere. It is sometimes referred to as the “vampire fish”.
- The sea lamprey has an eel-like body without paired fins.
- 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. The ammocoete larva has several properties of ancient chordates as well as these of vertebrates.
- It serves to illustrate the concept of ontogeny recapitulating phylogeny by resembling the more primitive hemichordate Amphioxus in morphology and behavior.
- Lampreys also maintain acid-base homeostasis.
- They parasitize other fishes for their diet, including sharks and rays, which have naturally high levels of urea in their blood.
- Lampreys can tolerate much higher concentrations of urea and excrete it at extremely high rates.

So, the correct answer is Petromyzon.

Note: The life cycle is sea lampreys or Petromyzon starts with the ammocoete larva. After larval life, they transform into their parasite phase and migrate into the open waters of the Great Lakes. They spend the next 12-20 months feeding on fish. It’s life cycle from egg to adult, averages about 6 years, and may last as long as 20 years.