Caudal fin Petromyzon
The caudal fin of the petromyzon is well developed and present at the tail which is continuous with the posterior dorsal fin and the caudal fin is supported by a thin cartilaginous fin-ray. The caudal fin has two lobes, the lower longer than the upper. It is continuous with the dorsal and anal fins and have a spade-like shape.
About the Animal
Petromyzon, belong to a group of fish called Agnathans, which lack a jaw and vertebrae, and their entire skeleton is cartilaginous. Commonly known for their smooth, scaleless physique and long cylindrical bodies, they are often misidentified as eels. Sea lampreys also lack swim bladders and a lateral line system. Sea lampreys are anadromous, and migration is triggered by changes in water temperature. In general, they prefer shallow coastal areas, though they are found at depths between 0.91 and 4.57 m. Young lampreys are hatched in gravel or rock beds in small, freshwater streams and rivers. Sea lampreys are native to the Atlantic Ocean. Between the months of March and October, they can be found along the coast of the United States as far north as Massachusetts and as far south as South Carolina.
Jordan, E. L, Verma, P. S, Chordate Zoology, S. Chand $ Company ltd., New Delhi.