Question

Crocodile and penguin are similar to whale and dogfish in which one of the following features?
A. Possess sold the single-stranded central nervous system
B. Lay eggs and guard them till they hatch
C. Possess bony skeleton
D. Have gill slits at some stage

Answer 1

Hint: Crocodile, penguin, whale and dogfish are chordates. These organisms possess this structure in their early embryonic stages, which later develops into a jaw and inner ear bones.

Complete step by step answer:
A. Every chordate has some common features like notochord, which is a cartilaginous rod in vertebrates which acts to support the nerve cord.
B. The crocodile, penguin and dogfish lay eggs. But Whales are marine mammals, they are more similar to humans. Humans and whales both need to breathe air, are warm-blooded and give birth without laying eggs. Different types of whales take different lengths of time to give birth.
C. The crocodile, penguin and whales have a bony skeleton. Doggish is just like all sharks. They are also elasmobranchs and they have a cartilaginous skeleton instead of a bony skeleton.
D. The crocodile, penguin, whale and dogfish, since all of them are chordates. They have gill slits at some stage, generally during early developmental stages. Gill slits are also called gill-clefts or pharyngeal-clefts. These gill slits are one of the four common features of all chordates.
Hence, the correct answer is option D.

Note: The notochord in chordates is a flexible and rod-shaped structure that is found in the embryonic stage of all chordates. Pharyngeal slits are openings into the pharynx. This region is just posterior to the mouth which extends to the outside environment. In organisms that live in aquatic environments, pharyngeal slits allow for the exit of water that enters the mouth during feeding.