General Characters of Cyclostomata and Comparison between petromyzon and myxine B.L.P.LATHA LECTURER IN ZOOLOGY SVCRGOVT DEGREE COLLEGE PALAMANER General characters Cyclostometa - Cyclos means circular, stoma-mouth. Extant group of Jawless
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General Characters of Cyclostomata and Comparison between petromyzon and myxine B.L.P.LATHA
LECTURER IN ZOOLOGY
SVCRGOVT DEGREE COLLEGE
PALAMANER<br>
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General characters Cyclostometa - Cyclos means circular, stoma-mouth.
Extant group of Jawless vertebrates. Includes Hag fishes, Lampreys.<br>
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General Characters of Cyclostomes About 50 species are recognised ,living in the marine water but lampreys migrate into fresh water for breeding.
Body is cylindrical, elongated and eel like.
Pair fins are absent(Pectoral and pelvic fins),but dorsal fin and caudal fins are present.
Skin is smooth, slimy and without scales, contains numerous unicellular mucous glands.
Mouth-circular-base of buccal funnel- acts as a sucker for attachment(lampreys),but in hag fishes, mouth-surrounded tentacles.
Presence of Single external nostril-also called monorhina.
Presence of a pair of eyes - on lateral sides of a head.
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General Characters of Cyclostomes Tongue has teeth - acts as a rasping organ.
Presence of lateral line sense organ.
Internal ear has 1 or 2 semi circular canals.
True coelom is seen.
Endoskeleton cartilagenous
Z shaped myotomes present in trunk as well as tail, buccal funnel has radial muscle, tongue has protractor and retractor muscle.
Alimentary canal is straight.
Presence of 5-16 pairs of gill pouches – open out through 1-16 pairs of gill slits.
Presence of two chambered of heart<br>
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General Characters of Cyclostomes Notochord persists throughout the life.
Neural arches of vertebrae are incompletely formed
8-10 pairs of non myelented cranial nerves.
Presence of Mesonephric and pronephyric kidneys.
Unisexual and bisexual.
Gonad without a gonoduct
External fertilization.
Indirect and direct development and see the ammocoetes larva.
Examples:-Petromyzon, Ichthyomyzon, Lampetra, Entospherus, Myxine, Paramyxine.<br>
