Question

Scales in Cyclostomata are
A. Cycloid type
B. Ctenoid type
C. Placoid type
D. Absent

Answer 1

Hint: Cyclostomata are morphologically similar to eels. They are parasitic, normally in their adult stage they feed on fish.

Complete Answer:
Cyclostomata is a group of agnathans which include jawless fish. These jawless fishes are lampreys and hagfish. Both classes have jawless mouths of horny epidermal frameworks that act as teeth and branchial arches that are located internally as in jawed fish instead of externally. Without true jaws, they are considered to be the only living vertebrates, so they are called Agnatha.

Now, let us find the solution from the options-
- By having a smooth outer margin, cycloid type scales are described. This type of scales is found in Clarias and Catla. This scale is not found in Cyclostomata. Therefore, the option A is incorrect.
- Ctenoid scales are scales present in higher order teleost fish, like perch and sunfish, with a comb-like edge. The tiny teeth on the posterior margin of the scale are Cteni. Therefore, the option B is incorrect.
- Placoid scales are the tiny tough scales that cover the skin. Trygon and Pritis are included in this type of scale. Therefore, the option C is incorrect.
- The skin of Cyclostomata is smooth and soft and they are free of any scales i.e., scales are absent. Therefore, the option D is correct.

Thus, the correct answer is option D Absent.

Note: The Cyclostomata are the main vertebrate stalk's which have modified and degenerated offshoot. They're called Cyclostomata because of their circular mouths. Cyclostomata are subdivided into two groups and they are Petromyzontiformes and Myxiniformes.