Question

Chondrichthyes is characterised by
A) Ventral mouth
B) Placoid scales
C) Ventral mouth and ctenoid scales
D) Both A. and B.

Answer 1

Hint:Fishes are of two types-bony fishes or osteichthyes,cartilaginous fishes or Chondrichthyes.

Complete answer:
Chondrichthyes are a group of cartilaginous fishes that include different types of sharks, skates, rays, chimaeras etc. The other class is osteichthyes, or bony fishes.
Chondrichthyes have jaws, vertebrates, paired fins, scales, a two chambered heart and a cartilaginous skeleton. These are a few of the characters of Chondrichthian fishes:-
>They have paired fins and nostrils.
>They have scales that are toothlike called dermal denticles or placoid scales.
> Placoid scales provide protection and streamlining.
>Mucous glands exist in some species, as well.
>They have paired appendages too.
>A well developed electroreceptive system is also found in Cartilaginous fishes.
>Their endoskeleton is completely made up of cartilage.
>Lungs or swim bladders are absent.
>The mouth, nostrils and gill slits of Chondrichthyes are always found on the underside or ventral side of the fish.
>The eyes and spiracles are on the upper side.
>groups of fishes are exclusively marine.
>Operculum is also absent in them
>Their nature is predatory.
>The male fishes have claspers on their pelvic fins.
>Many species also have spines and thorns on the upper surface and tail.

Hence the correct answer is option (D.) Both A. and B.

Note:Cartilaginous fishes or Chondrichthyes can be further classified into two groups, namely, Elasmobranchii and Holocephali. Examples of Chondrichthyes are sharks, bateoids, chimaera, stingray, holocephali etc.