Polymorphism Of Siphonophora

The following are the different types of zooids in polymorphic colonies.

(A) Medusoid Forms :-

(i) Pneumatophore :-

It is medusoid form. It functions as a float. It makes the colony floating on the surface of water. It is situated at the apex of the colony. It is filled with air. It takes different shapes in different animals. it is cup- like in Helistemma, disc-shaped in Porpita & sail like in velella.

(ii) Nectocalyces :- 

These are medusoid forms. They are bell shaped. The mouth and tentacles are absent from them. The musculature is well developed. They bring about the locomotion of the colony. Hence they are swimming bells.

Example :- Helistemma

(iii) Hydrophyllium :- 

It is a medusoid form. It is leaf like. It serves to covr and protect the other zooids of the colony.

Example :- Helistemma

(iv) Gonophores :-

These are medusoid forms. They contain gonads. These are two types of gonophores, viz male gonophores & female gonophores. The male gonophores contain the testes & the female gonophores contain the ovaris.

On reaching sexual maturity, they release sperms & ova. After the release of gamets, the gonophores die.

(B) Polypoid forms :- 

(v) Gastrozooids :- 

It is a polyp. It nutritive in function. It has a mouth & a large gastrocoel. It gas a long tentacle bearing lateral branches called tentilla. Each tentilla ends in a coil of nematocysts.

Example :- Helistemma

(vi ) Dactylozooid :- 

It is protective in funtion. It looks like a gastrozooid but it has no mouth. A coiled tentacle arises from the base. The tentacle is unbranched. 

Example :- Helistemma

(vii) Gonozooids :- 

These are reproductive zooids. They are also called blastostyles. They produce Medusa by budding.

Example :- Physalia 

Basic Unit of Polymorphism :-

(1) Polyp :- 

(A) Gastrozooids :-

(a) Siphon ( Siphonophora)

(b) Siphono zooids (Renilla)

(c) Gastrozooids of  Millipora 

(B) Dactylozooids :- 

(a) Tentaculo zooids (Hydractena)

(b) Spiral zooids (Hydractena)

(c) Sarcostyle (Plumularridae)

(d) Paplons ( Porpita/ Vellela )

(e) Syston (Siphonophora)

(f) Dactylozooids of millipora

(c) Gonozooids :-

(a) Gonosiphon (Vellela/ Porpita)

(b) Gonodendron ( Siphonophora)

(c) Gonopalpon (Siphonophora)

(2) Medusa :-

(a) Nectocalyx

(b) Pneumatophores (Siphonophore)

(c) Aurophores (Siphonophore)

(d) Bracts (Siphonophore)

(e) Gonophores (Siphonophore)

Special Types of Zooids :- 

(a) Gonostyles (Porpita)

(b) Hydrorhiza (Obelia)

(c) Hydrocaulus (Obelia)