Question

In which of the following jaws are absent?
a. Petromyzon
b. Hagfish
c. Hippocampus
d. Both A and B

Answer 1

Hint: Agnatha is a superclass in the subphylum Vertebrata of the phylum Chordata of kingdom Animalia. These organisms lack jaws and use suckers and other structures for feeding purposes and are mainly parasites or scavengers.

Complete step-by-step solution:
Petromyzon i.e. Sea lamprey and Hagfish are jawless among the given options. These two belong to the superclass Agnatha of the subphylum Vertebrata. The characteristic of the organisms of this superclass is the absence of jaws and this is the reason the organisms of this class are called jawless fishes. Teeth in the fixed jaws of Petromyzon have been shown below -

Additional information:
-Agnathans do not have the ability to control their body temperature and hence are ectothermic animals. Being ectothermic in nature, their rate of metabolism becomes too slow in the cold water and it reduces their need for so much food.
-A nearly homogenous gut is found in their body in which a distinct stomach is absent.
-Skin covers the body but dermal or epidermal scales are not present.
-No paired appendages, like other fishes, are found in agnathans that are presently living.
So, the correct answer is ‘Both A and B’.

Note: Petromyzon feeds on other fishes and mammals using its sucker mouth to attach itself to the side of a fish, tears away the fish's protective covering, and sucks blood and other body fluids from the host fish. Hagfishes are scavengers and mostly eat dead animals using a row of sharp teeth to break down the dead animal.