CARTILAGINOUS FISH-CHARACTERISTICS OF CHONDRICTHYES

 

 

CARTILAGE FISH CHARACTERISTICS

The Chondricthyes are popularly called the cartilaginous fishes. They are the most generalized among the living vertebrates. They include the sharks, dogfishes, rays, skates and chimaeras.

·         also read previous topic general characteristics of fish

The cartilaginous fishes possess the following characters:

1. Body Form:

Body is laterally compressed and spindle – shaped or dorsoventrally flattened and disc-like.

2. Appendages:

Both median and paired fins are present. They are supported by slender fin rays of elastin (ceratotrichia) in the distal part. Pectoral fins act as elevators. The pelvic fins bear claspers in the male. The caudal fin is heterocercal. There are generally two dorsal fins.

cartilaginous-fish-shark

3. Skin:

Skin is tough and covered with minute placoid scales and provided with numerous mucous glands.

4. Muscles:

Muscles of the trunk and tail are arranged in < – shaped myomeres.

cartilaginous-fish-sphyrna

5. Endoskeleton:

Endoskeleton is entirely cartilaginous. Calcification may occur here and there, but bone is never formed. Vertebrae are complete and separate. Notochord is persistant, but reduced.

cartilaginous-fish-torpedo

6. Coelom:

Coelom is divided into a small anterior pericardial cavity containing the heart and a spacious peritoneal cavity having other viscera. The two parts are separated by a septum transversum perforated by a pair of pericardio-peritoneal canals.

 

Cartilaginous skeleton in the adult is not regarded as primitive condition, but as the retention of the embryonic skeletal material. This view is supported by the fact that skeleton was at least partly bony in most early fishes.

7. Digestive System:

Digestive tract leads into the cloaca. Mouth is ventral. Stomach is J-shaped. Intestine has a scroll valve.

8. Respiratory system in cartilaginous fishes :

Respiratory system includes 5 – 7 pairs of gills, the gills are lamelliform. Gills slits are usually uncovered, there being no operculum or gill cover. An additional slit, the spiracle, often occurs in front of the gill slits.

9. Air Bladder:

Air bladder is absent.

10. Circulatory System:

Heart is two-chambered, there being only one auricle and one ventricle. Sinus venous and conus arteriosus with valves are present. Heart contains only venous blood. There are 5 – 7 pairs of aortic arches. Both hepatic and renal portal systems are present. Some veins are expanded as sinuses. Red blood corpuscles are oval, biconvex and nucleated. Spleen is present.

11. Nervous system in cartilaginous fishes :

Brain has large olfactory lobes and a large cerebellum. Sympathetic chain does not extend into the head. There are 10 pairs of cranial nerves.

12. Sense Organs:

Olfactory sacs are paired and ventral. They do not open into the mouth cavity by internal ears. Ear consists only of membranous labryinth that bears three semicircular ducts. Lateral line sense organs are well developed.

13. Endocrine Glands:

Besides pituitary, pancreas, gonads, a thyroid gland and adrenal tissue occur in cartilaginous fishes.

14. Excretory System in cartilaginous fishes :

Kidneys are mesonephric. A high percentage of urea is retained in the body.

sharks-Cartilaginous-Fish

15. Cartilaginous Fishes Reproductive System:

Sexes are separate. Gonads are paired. Reproductive ducts open into the cloaca. Fertilization is internal. Most forms are oviparous or ovoviviparous. Some are viviparous having, yolk sac placenta for the nourishment of the embryo.

16. Development:

Eggs are large and have much yolk. Segmentation is meroblastic. Development is direct, there being no metamorphosis.

17. Body Temperature:

Body temperature is variable (poikilo- thermous)

18. Habit and Habitat of cartilaginous fishes :

Most Chondricthyes are marine. A few inhabit tropical rivers. All are predaceous. They have heavy bodies due to lack of air bladder. Sharks include the largest fishes that ever lived. They are next to whales alone in size. The largest living shark is the tropical, oceanic, oviparous, plankton-feeder whale shark Rhinodon. It reaches about 21 metres. The man – eating great white shark Carcharodon carcharias 10.8 metres long. About 20% of the body weight is constituted by the liver oil. There are about 3,000 species of cartilaginous fishes.

Examples Of Cartilaginous Fish

:Scoliodon, Torpedo, pristis, sphyrna.

clip_image005

clip_image006

clip_image007

clip_image008

 

 

EVOLUTIONARY ADVANCEMENT OF CHONDRICTHYES

 

The cartilaginous fishes show advancement over the cyclostomes
in having

i. an exoskeleton of scales

ii. Paired fins

iii. Paired olfactory organs

iv. Movable jaws with teeth

V. visceral arches

vi. Complete vertebrae

vii. three semicircular ducts in each ear

viii. stomach

ix. paired gonads,

x. reproductive ducts and

xi. Internal fertilization.

 

No comments:

Post a Comment