Biology · Ch 4 — Animal Kingdom
Class – Chondrichthyes
Class – Chondrichthyes
Class Chondrichthyes comprises the cartilaginous fishes — fishes whose entire internal skeleton is made of cartilage rather than bone. They belong to the super class Pisces within the jawed vertebrates (Gnathostomata).
Body form and skeleton
These are marine animals with a streamlined body suited to moving through water, supported by a cartilaginous endoskeleton. The notochord persists throughout life. The mouth is placed on the underside of the body (ventral position).
Skin, scales and teeth
The skin is tough and bears tiny placoid scales. The teeth are themselves modified placoid scales and point backwards. The jaws are extremely powerful, and these fishes are predaceous (active hunters).
Gills and buoyancy
The gill slits are separate and are not covered by an operculum (there is no gill cover). Because Chondrichthyes lack an air bladder, they cannot control their buoyancy and would sink if they stopped moving; therefore they must swim constantly to stay afloat.
Heart, temperature and reproduction
- The heart is two-chambered, made up of one auricle and one ventricle.
- They are cold-blooded (poikilothermous), unable to regulate their own body temperature.
- Sexes are separate. In males, the pelvic fins are modified into structures called claspers.
- Fertilisation is internal, and many members are viviparous (giving birth to live young). …
Drawn by us to help you understand the concept clearly, and verified to make sure it's accurate. For exams, practice from your textbook's own diagram.
These are cartilaginous fishes of class Chondrichthyes. Their skeleton is made entirely of cartilage rather than hard bone, making it light and flexible. The mouth is placed on the underside of the head, and because they lack an air bladder they must keep swimming to avoid sinking. Their skin is tough and covered with small tooth-like placoid scales. They breathe through gill slits that are not protected by an operculum. Scoliodon is the dogfish shark, Pristis is the saw fish with a long toothed snout, and Trygon is the sti …