Tuesday, May 16, 2006

DESCRIBE THE MORPHOLOGICAL DIFFERENCES THAT EXIST BETWEEN CARTTILAGENOUS AND BONY FISH.

Bony and cartillagenous are marine vertebrates. Cartillaginous fish are the earliest vertebrate to be developed. They are found worldwide, in oceans, rivers, streams, lakes and ponds. Bony fish belong to class Osteichthyes. The subclasses of bony fish are Sarcopterygill (ray-finned fishes) and Actinopterygill (lobe-finned fishes). Sarcopterygill contain fish such as coelanths and lungfishes. Actinopterygill contains fishes such as sturgeon, gars and bowfins. Cartilaginous belong to Chondricythyes. The subclasses of Chondricythyes are Elasmobranchii and Holocephali. They vary usually in structure. Bony and cartilaginous fishes vary in shapes.

The class Osteichthyes includes all bony fish. Bony fishes include snapper, groper and gurnard. . Bony fishes are the largest group of taxonomically. It has more than twenty species world. They have bony skeleton and scales. Their scales are found all over the body surface and they are slippery. The scales cease to grow when they are completely developed however they are replaced by new scales when they as they wear. The pelvic girdle consists of a single bone on each side of the body that is freely joined ventrally. The girdles are embedded in muscle. In bony fish the basal have been lost entirely and ossified radials are reduced to a few short bones nearly hidden under the fish rays. These rays are bony, branched and jointed and called lepidotrich.

Furthermore, bony fishes have one pair of gill opening, pair of nostrils as well as pair of fins. Gas exchange in bony fish occurs across the gills. They have gills that are covered by operculum (cap), they remain stationary and respire. They do not have to physically move to ventilate. Gills do not open separately. The bony fish have organs known as swim bladder, which gives the animals buoyancy, the ability to float. The mouth is generally at front at front of the body whereas the tail fin at the top and bottom are nearly the same in size. Sharks have small eyes which are at the top of the head.

Cartillaginous fishes belong to this class Chondricythyes. Cartilaginous fish comprises of chimaeras, sharks, skate, ratfish and rays. The skins are leathery, body covered by epidermal placoid scales (a bone-like tissue is present at base of placoid scales). Sharks as the example of cartilaginous have rough, sandpaper-like placoid scales. They are made up of cartilage not bones. Cartillaginous fish have five to seven uncovered gills. They have gill silt on both of the pharynx and they separate external opening and a heterocercal tail (may or not provide lift). The fin is supported by a large basal cartillage.

The pelvic girdle is not joined in the spine. They have a row of radial cartilages and many are thin, horny, unbranched, unsegmented fin rays called ceratotrich. Both upper and lower jaws are made up of cartilages. The jaws are short and mouth is protrusible. Teeth are usually hard and they are covered with denticles. Most Cartillaginous fish have rows of teeth in their mouths, so that when a tooth is lost another is already in place to roll up and forward and thereby replace the lost tooth. Mouth of cartillaginous is found under the head. The male fish have claspers arch (hyoid) which involved in jaw suspension.

Cartillaginous are mostly covered with cartillage whereas bony fish have true bones. Although Cartilaginous and bony fishes differ in shape but they have some similarities. They share common habitat. Both have gills and fins.

References

Wikipedia contributors. [Internet]. Wikipedia, the free encyclopaedia, 2006 May 09, 13:15 UTC. [Cited May 09]. Available from: http://en.wikipedia.org.wiki/cartilagenous

Wikipedia contributors. [Internet].Wikipedia, the free encyclopaedia, 2006 May 09, 15:40 UTC. [Cited May 09]. Available from: http://en.wikipedia.org.wiki/Bony
Masiya Kedibone
CSIR PTA
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