Chris Poulin, age 11, of St. Catharines, Ontario, Canada, for his question:
ARE SHARKS CLASSED IN A GROUP OF THEIR OWN?
Yes, they are. This is logical because they have certain features that differ greatly from all other fishes. It also is logical that the name of their group is called the cartilage fishes because their skeletons are made of gristly cartilage rather than hard, fishy type bones.
The scientific name for the cartilage boned fishes is Chondrichthyes and the sharks share this animal class with the skates and rays, whose skeletons also are made of gristly cartilage. However, the sharks are separated from their distant kinfolk in the order Selachii, which is their own special group of cartilage type fishes. However the class and order names may vary somewhat.
The shark order is subdivided into 19 separate families based on family differences and resemblances. The families are subdivided into smaller genera groups and each genus is a group of one or more different species. So far about 250 different shark species have been identified and some experts suspect that there are more to be discovered.
Other. features that set them apart from the other fishes are scaleless skins and no gill covers. Actually, their thick leathery hides are embedded with tiny plates, thought to be the remnants of ancestral teeth. Sharks absorb dissolved oxygen by gulping water that streams back through their delicate gills, just as other fishes do. However, in the sharks, the used water flows out through several pairs of slits.
Sharks are descendants of ancient fishes that dominated the seas ages before the scaly fishes arrived. Most of them are hungry meat eating hunters, always famished for more food. We tend to think of them as mighty man eaters though as far as we know, only about 10% of the various species are likely to attack humans.
The largest of the breed is the great whale shark, 60 feet long. He is the largest of all fishes and happens to be a peaceable fellow who feeds on bits of plankton.
The meat eating sharks are mighty hunters indeed, agile and keenly alert. They can smell blood in the water from a quarter of a mile and hear a struggling swimmer from almost
They do not see too far in murky water, naturally, but in clear water they can see moving objects from at least 15 yards.