CLASSIFICATION OF HALISTEMMA

PHYLUM :- COELENTRATA (Tissue grade, diploblastic and acoelomate. )

CLASS :-  HYDROZOA  (The hydroids and craspedote medusa )

ORDER :- SIPHONOPHORA (Polymorphic colonies without perisarc.)

SUB-ORDER :- PHYSOPHORIDA (Upper end of colony contains float or pneumatophore.)

FAMILY :- PHYSONECTAE (Pneumatophore small. It is followed by a stem bearing column of swimming bells.)

GENUS :- Halistemma

GEOGRAPHICAL DISTRIBUTION

  • Found in Mediterranean and other seas.

HABIT AND HABITAT

  • Halistemma is colonial, pelagic and highly polymorphic siphonophore with complex zooids.
HALISTEMMA

GENERAL CHARACTERSTICS OF HALISTEMMA

  • Entire animal comprises of pneumatophore, swimming bells and simple cormidia in floating axial stem. 
  • Small pneumatophore or float represents first part of the stem which secretes gas to keep colony up in water. 
  • Float is followed by several pairs of closely-set, transparent medusa-like, swimming bells or nectocalyces or nectophores.
  • Below nectocalyx, the axial stem gives at regular intervals several closely-set individuals, called as cormidia.
  • Each cormidium contains coenosarc bract or bydropbyllium gastrozooid, large dactylozooid, male gonozooids, larger female gonozooids with eggs and tentacles with batteries of nematocyst. 
  • Nematocysts are very much elongated measuring 1-12 mm. 
  • Fertilization external life-history includes Planula larva.
HALISTEMMA

IDENTIFICATION

  • The animal has several pairs of medusae like swimming bells and all above characters and hence it is Halistemma.
HALISTEMMA
HALISTEMMA
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