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
Found in Mediterranean and other seas.
HABIT AND HABITAT
- Halistemma is colonial, pelagic and highly polymorphic siphonophore with complex zooids.
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.
- The animal has several pairs of medusae like swimming bells and all above characters and hence it is Halistemma.