1. Habit and habitat: Petromyzon is found in freshwater and salt waters. They lead an ectoparasitic life on other fishes, being attached by buccal funnel and secrete an anticoagulant for sucking blood.
2. Petromyzon is commonly known as Lamprey or lamper eel.
3. Body is eel-like measuring about 1 meter and differentiated into head , trunk and tail.
4. The surface of the body is smooth and slimy and generally heavily pigmented.
5. Two dorsal fins and one caudal fin, all are supported by cartilaginous rays and are confluent.
6. Mouth is circular and surrounded by a large , ventral suctorial funnel with numerous horny teeth. Tongue is poison-like and toothed.
7. The paired eyes are relatively large and functional. Two small median eyes- the pineal and parietal eyes.
8. Nostril is single and dorsal.
9. Seven pairs of external gill-apertures and well- developed branchial-basket.
10. Jaws and paired fins are absent.
11. Sexes are separate in adults and there is only single large gonad. Female with large anal fin and male with urinogenital( copulatory) papilla.
12. Fertilization is external.
Source:
1. Practical Zoology Vertebrates by S.S.Lal. 2. A Manual of Practical Zoology Chordates by Dr. P.S. Verma.
