Read the following characteristics of an animal: (i) The mouth is located ventrally. (ii) The skin is tough, containing minute placoid scales. (iii) It lacks an air bladder and must swim constantly to avoid sinking. Identify the animal that possesses all the above characteristics from the options given below:

Step-by-step solution

The correct answer is option (3). The characteristics given in the question (ventral mouth, placoid scales, and absence of an air bladder) are the defining features of the class Chondrichthyes (cartilaginous fishes). Pristis (Saw fish) belongs to this class. Option (1) is incorrect because Clarias is a bony fish (class Osteichthyes), which typically has a mostly terminal mouth, cycloid or ctenoid scales, and possesses an air bladder to regulate buoyancy. Option (2) is incorrect because Myxine (Hagfish) belongs to t