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INTRODUCTION, , * The larva stage formation of the primitive lampgey, known as Ammocoete Larva. It has many propeffies 0, ancient chordates and has some properties of the, vertebrates like a dorsal nerve chord, primitive form of, nervous system, gills slits , notochord and a brain with, eyes. This larva is actually Petromyzon fish., , Petromyzon is a rather unpleasant animal. Its life cycle, includes two quite different phases. The larval phase, called ammoceote is a freshwater, sedentary, filter, feeding and microphagus creature remiscent of the, lancelet or Branchiostomata. The adult fish live in the sea, and is parasitic on fishes.

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EVOLUTIONARY SIGNIFICANCE OF AMI, LARVA, , ¢ The larval period last from 3-7 years, acco eee 7, , species during which they grow to about Rianne, , , , length and become opaque., , ¢ The Ammocoete larva is of great importance as it, probably represent the most primitive and, generalised vertebrate from intermediate between, Cephalochordates and vertebrates.

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| A) DORSAL FIN G) OLFACTORY LOBE M) SUBPHARYNGEAL GLAND, |B)NERVECORD =H) MEDIAN NOSTRIL N) PHARYNGEAL GILL SLITS, |C)NOTOCHORD — |} ORAL HOOD 0) HEART, | 0) MEDULLA J) ORAL TENTACLES P) LIVER, | E) OPTIC LOBE K) VELUM Q) INTESTINE, , F)EYE L) PHARYNGEAL GILL BARS —R) CAUDAL FINS

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EVOLUTIONARY SIGNIFICANC, , AMMOCEOTE LARVA ™, , oe SB Lee Roo mL om etimiaele Cote eee LUMAR Colel eae, several respects., , , , , 1. It has a continuous single median dorsal fin., , 2. Itis a blind, toothless and non parasitic filter, feeder., , 3. Feeding and respiration are like those of, Branchiostoma., , 4. It has no suctorial buccal funnel but a semi, circular upper lip or oral hood around the, mouth, similar to that of branchiostoma., , 5. Mouth also has a transverse lower lip.