The word Chondrichthyes is formed from the Greek word chondros meaning cartilage and ichthys meaning fish. Cartilaginous fishes belong to the class Chondrichthyes. They are marine and carnivorous animals. Their number of species is 1,207.
Characteristics of Chondrichthys
1. Their body is flat or mace-shaped. They are jawed animals.
2. Their endoskeleton is made of cartilage.
3. Their body skin is hard and tough.
4. Body covered by placoid scales.
5. There are 5-7 pairs of gill slits on both sides of the head.
6. They do not have horns.
7. The mouth and nostrils are located at the base of the digit. There are numerous rows of placoid teeth in the jaws. Siddiq Publications
8. The body does not have air sacs or sacs.
9. The digestive system consists of a J-shaped stomach, a spiral-shaped intestine, and a fatty liver.
10. Their heart is two-chambered and known as the venus heart.
11. Caudal fin heterocercal type. That is, the caudal fin is divided into two unequal parts.
12. In male fish the pelvic fins are modified to form copulatory organ clusters.
13. They are unisexual animals. Fertilization occurs. Direct exposure. They are ovaries, ovaries or uterus. Dr. Siddiq Publications
Some animals of the Chondrichthyes
Shark- Scoliodon sorrakowah
Thutree shark- Scoliodon laticaudus
Hammerhead shark- Eusphyra blochii
Saw fish – Pristis pectinata
Ratfish- Hydrologus collei
Guitar fish – Rhinobatos rhinobatos
Raja – Raja raja
Sting Ray – Plesiobatis daviesi
Electric fish – Torpedo torpedo
White skates- Rostroraja alba
.
Placoid scale
Microscopic scales present in the skin of cartilaginous fish are called placoid scales. It is a triangular plate formed from the skin. It has three sharp spines. For example – Scoliodon laticaudus. Dr. Siddiq Publications
Heterocercal
If the caudal fin segments of fish are not equal then it is called heterocercal. Chondrichthys fishes have heterocercles. For example, Scoliodon laticaudus.
Dog fish
The fish whose mouth is shaped like a dog’s mouth are called dog fish or dog fish. Their jaws have sharp teeth. Dogfish belong to the Chondrichthyes class. For example – Scoliodon laticaudus. Dr. Siddiq Publications
Sow fish
Those fishes which have a long tip like a saw at the front of their body are called saw fish or saw fish. They belong to the Chondrichthyes class. For example – Pristis pectinata.