What is the difference between chondrichthyes' and osteichthyes' skeletons?

Answer 1

The Chondrichthyes are the cartilaginous fishes including the sharks, rays, skates and chimaeras. The Osteichthyes are the bony fish. Both of these groups became established during the Devonian Period about 400 million years ago. The Chondrichthyes differ from the Osteichthyes in many respects, including their skeletons, scales, teeth, buoyancy, swimming, gills and reproduction. Skeleton: The Chondrichthyes have a skeleton of cartilage, composed of chondrocytes suspended in a protein matrix. The Osteichthyes skeletons' are composed of cartilage and bone. Scales: Cartilaginous fish have large scales called placoid scales. These have a bone like base embedded in the skin and a backward projecting enamel covered dentine spine. The whole thing has a central pulp cavity ( rather like the structure of teeth). The epidermis and dermis form placoid scales. In bony fish the scales are formed only by the dermis. The majority of modern bony fishes have cycloid or ctendoid scales. These lack enamel and dentine and both have overlapping design where the anterior part of the scales is overlapped by the posterior portion of the scale in front. Cycloid scales are smooth, flat and round. Ctenoid scales are similar to cycloid scales except that the posterior edge also possesses a row of comb-like extensions (ctenii) which are believed to reduce drag during swimming. As a fish with cycloid or ctenoid scales grow the scales also grow. In summer when food supplies are abundant the fish grow rapidly, and so do the scales. In winter growth slows, and it is this difference that produces concentric growth rings (annuli). These rings can be used to age fishes. Teeth: In Chondrichthyes the teeth are confined to the jaws and are embedded in the gums. They have the same basic structure as the placoid scales. They occur on ligaments and are replaced as they get worn-the new teeth grown on the inner face of the jaw and gradually move up to the jaw edge, row upon row, pushing out the old worn teeth. They work as opposing saws- hence sharks wriggle their whole body when shredding prey. In Osteichthyes the teeth are not confined to jaws. In nearlly all bony fish the teeth are shed one by one and replaced by new ones growing up in the same place. Buoyancy: In Chondrichthyes the pelagic forms remain buoyant by producing large amounts of oil, called squalene, in their livers. They can undergo extensive vertical migrations because oil does not compress/expand much with changes in pressure. In Osteichthyes buoyancy is often by a swim bladder, a lunglike, gas-filled organ. Swimming: The cartilaginous fish can swim forward only. Bony fishes can swim forward and backward. Gills: Both cartilaginous and bony fish have gill slits but the bony fish also have gill covers (an operculum). Reproduction: In the Chondrichthyes the males have claspers which assist in copulation. Fertilisation is internal-almost unique among fish. They have elaborate courtship rituals, males often bite onto the female to assist during copulation and females have thicker skins to protect against such amour. There is varied development of the eggs: Some lay them on substrates- oviparous. They eggs are large with hard shells and a large amount of yolk, taking up to a year to hatch as minature adults. They are called mermaid purses. Some species retain the developing eggs in the uterus- ovo-viviparous. In these the young are nourished by yolk in a yolk sac and live in the oviduct until birth as mini adults. In a few species there is true vivparity where nourishment is supplied directly to the developing embryos by the mother. Most cartilaginous fish mature at 6-18 years old but a few such as lemon sharks do not mature until they are 24 and spiny dogfish do not mature until they are about 35 years old. They also produce relatively few young. These two factors cause them to be vulnerable to over-exploitation and many of the shark species are now endangered. In bony fish the males do not usually have a special copulatory device. Most species are oviparous and fertilisation is external. Some species are sexually mature at one year old or less. Generally, smaller species mature at a younger age and the larger species become sexually mature at a few years old.

Answer 2

The major difference is what the skeleton is composed of. Chondrichthyes fish have a cartilage skeleton with no bone while osteichthyes fish have a bony skeleton. There are also numerous other differences in structure, articulation and function.

Answer 3

it is a class of fish with jaws but a skeletal system of cartilage. Sharks, and rays fall into this class.

Answer 4

Chondrichthyes and osteichthyes are two classes of fish. Chondrichthyes have an endoskeleton made of cartilage, while osteichthyes have an endoskeleton made of bone.

Answer 5

sharks, rays.