NERIS A WORM

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ZOOLOGY

• RAM LUBHAI SAHANI GOVERNMENT GIRLS COLLEGE
• PILIBHIT

SUBMITTED TO.. DR.DINESH CHANDRA SUBMITTED
BY..KALPANA GANGWAR
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DEVELOPMENT OFNEANTHES OR NEREIS A CLAMWORM
OR A SANDWORM
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SYSTEMATIC POSITION

• KINGDOM - ANEMELIA
• PHYLUM ANNELIDA
• CLASS - POLYCHAETA
• FAMILY NEREIDAE
• GENUS NEANTHES
• SPECIES - virens

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Burrowing worm
It live in burrows in sandy shores, THTS why it
called A SANDWORM.
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EXTERNAL MORPHOLOGY
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A SEXUALLY MATURE INDIVIDUAL OR HETERONEREIs
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LIFE HISTORY OF NEREIS

• Life history of nereis has 3 mechanism
• 1.. SWARMING
• 2.. FERTILIZATION
• 3.. DEVELOPMENT

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SWARMING

• Sexually mature individuals or heteronereis swim
  at the surfce of in order to shed sperm and
  ova.it is called swarming. It genrally occurs in
  night. They perform a nuptial dance, in this male
  and female swim rapidly in circle. Female produce
  a sbstnce which attrct the male and in turn it
  attracts the female by sheding sperms.

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FERTILIZATION

• FERTILIZATION is mostly external in NEREIS
• VIRENS take place in sea water.
• PLATYNEREIS MEGALOPS has an altogether
• different Mechanism...
• The male wraps tightly around female, inserts
• His anus into her mouth injects the sperm.
• Sperm pass directly into celom of female where
• Fertilization egg are shed at once from the
  posteior end of females body.

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DEVELOPMENT

• Development of nereis has 3 distinct periods
• 1.. Pre-larval period
• 2.. Larval period (trochophore)
• 3.. Post-larval period or metamorphosis

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PRELARVAL,LARVAL POST-LARVAL PERIOD IN
DEVELOPMENT OF NEREIS

• Unfertilized egg of nereis contains numerous yolk
  spherules and oil droplets. It is coverd by a
  thick radially striated membrane, called ZONA
  RADIATA, which disappear soon after fertilization
  and yolk spherules from animal pole move into
  vegetal pole. 1st clevage of zygote are equal and
  vertical result in four cell or blastomere. 3rd
  clevage is unequal and horizontal. It has 4 small
  yolk free micromeres, four large yolky macromeres
  towards the vegetal pole. 4th,5th.6th clevage are
  also horizontal. THS CLEVAGE RESULT INTO A
  STEROBLASTULA. Gastrulation take place in gut
  pouch result into a CILLIATED EMBRYO( A - F).
  After gastrulation the cilliated embryo rapidly
  develop into a larval stage called
  TROCHOPHORE.(G).. Post trochophore larva swims
  actively for few days, feeding on microorganisms.
  While swimming it undergo es metamorphosis to
  change itself into adult. Its pre-oral apical
  prtion develop into a PROSTOMIUM ND PERISTOMIUM.
  Resulting the worm settles to the bottom at the
  low tide line and strts forming its tubular
  burrow (H-L )

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TROCHOPHORE LARVA

• STRUCTURE. IT IS cilliated, unsegmented pear
  shaped, pelagic creature with oral aboral
  surface/ in a full grown typical trochophore
  larva, the sensory organ bearing a TUFT OF
  CILLIA, brain rudiments as a GANGLION. A
  charachterstic feature of trochophore is the
  presence of preoral cilliated gridle of cells,
  called PROTOTORCH. Mouth lies ventrally behind
  the prototorch. anus is near the lower apex.
  There is a post oral cilliated band lies behind
  the mouth. These cilliated bands help in feeding
  locomotion. Gut is divided into MOUTH, STOMACH
  OESPHAGOUS INTESTINE. TROCHOPHORE AT ITS EARLY
  AGE LACK A CEOLOM

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THANK YOU

• FOR LISTENING
• ME