Hydrozoans

This is a rather famous species of hydroids. Clava multicornis always lives on Ascophyllum algae. Clava is a big hydroid, its polyps reach 1.5 cm in length. These hydroids have no jellies, only gonophores - bubble-like emergences on the polypes that produce sex cells.

This is the biggest White sea hydroid, Tubularia larinx. Each polyp is about 1 cm in diameter, the whole colony may reach 10 cm in length! This species also has no jellies.

These hydroids called Perigonimus yoldiaearcticae are obligate commensalists of bivalves (usually Portlandia arctica). The Perigonimus does have the jelly generation:

 

I met also another species of hydroid jellies:

Sarsia (Coryne) tubulosa. It is a small jellyfish, about 1 cm.

 

Aglantha digitale. This is a very interesting species. It reaches 2.5 cm in length and it's extremely fast. These jellies swim by big leaps. It is possible due to developed velum that increases the jet power.

These jellies belong to the order Trachymedusae, and all the specimens of that order have no polyp generation at all.

 

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