By: Devon H.,Lynika C., & Rachel L.

These are some of the relatives of the Cartilaginous fish, called the boney fish.

Around 400 million years ago, fish evolved into two very different ‘classes’, or groups. One of them is ‘Class Chondrichthyes’, which includes sharks, rays and chimeras. This class of fish is also known as ‘cartilaginous’ fish because they have skeletons made of cartilage The other class is ‘Class Osteichthyes’, which gave rise to the modern day bony fish, also called ‘teleost’, and their primitive relatives such as the sturgeon. Although the two groups once shared a common ancestor, there are several major biological differences.

Cartilaginous fishes are a group of fishes that includes sharks, rays, skates, and chimaera. Skate: Chimaera: Elephant Shark : Sting-Ray:

Cartilaginous fishes is that they have jaws, paired fins, paired nostrils and a two- chambered heart. They also have tough skin that is covered with small tooth-like scales called denticles. Denticles are similar to teeth in many ways. Denticles:

Members of this group include the largest and most formidable marine predators alive today such as the great white shark and the tiger shark as well as large filter feeders such as the manta ray, whale shark and basking shark. Basking Shark

Boneless skeleton These fish have dorsal fins, an anal fin, a pair of ventral fins and a single caudal fin. The swim bladder and lungs are absent and the liver is filled with oil to provide buoyancy to the body while swimming. The heart consists of two chambers like other fish and amphibians. The cartilaginous fish habitat comprises mostly of creeks and rocks where they can get their prey easily. Sharks are mostly found near the seabed.

These fish have jaws which have tiny teeth, with the upper row of teeth having a layer of enamel and the lower row of teeth is made up of bone tissue, which attaches them to the skin. The teeth are modified and are replaced by new teeth, when the older ones become worn out. Sharks and stingrays have an opening, called spiracle or gill slits that is situated on both sides of the head right behind the eyes, for breathing.

The subclass Holocephali, which is a very specialized group, lacks both Leydig's and the epigonal organ. In rays, the pectoral fins have connected to the head and are very flexible.