Question

Petromyzon is included under
A. Cephalochordate
B. Agnatha
C. Tetrapoda
D. Pisces

Answer 1

The sea lamprey is also called Petromyzon marinus. It is a parasitic lamprey native to the Northern Hemisphere. It is mostly called the ‘vampire fish’. There are nearly 38 different types of known species of lampreys and nearly 5 species are extinct.

Complete step by step answer: Agnatha is a superclass of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present living species like Cyclostomes and extinct species like Conodonts and Ostracoderms species. The sister group with jaws in all vertebrates are called gnathostomes. Therefore, Petromyzon comes under Agnatha.
i. Lancelets come under Cephalochordata which are marine organisms that possess all features of chordates. They are named Cephalochordata because they contain the notochord that extends into the head. Lancelets are the closest living relatives to vertebrates.
ii. Tetrapods are four-limbed (with a few exceptions, such as snakes) animals constituting the superclass Tetrapoda. It includes present living (extant) and extinct amphibians, reptiles like dinosaurs and birds and synapsids, and mammals.
iii. Pisces are the fishes that are living in freshwater and marine waters. Although most fish are exclusively ectothermic, there are exceptions. The only known bony fishes that exhibit endothermy are in the suborder Scombroidei. This suborder includes the billfishes, tunas, and the butterfly kingfish, a basal species of mackerel and opah.
Hence, the correct species is option B.

Note:Petromyzon has a circular mouth without a jaw. So, they belong to division: Agnatha. Classification of Petromyzon ; kingdom: Animalia, Phylum: Chordata, Subphylum: vertebrate, Division: Agnatha, Class: Cyclostomata. Sea lampreys are unique when compared to other fishes as they do not have jaws and any other bony structures, and instead of a bony skeleton, their skeleton is made of cartilage.