(Kvenvær - Sør-Trøndelag / 12 meters / 3.28.2002)

Phylum: Cnidaria

Class: Hydrozoa

Order: Anthoathecata

Suborder: Filifera

Family: Hydractiniidae

Scientific name: Hydractinia echinata

 

Norwegian: eremittkrepshydroide

Distribution: This tiny hydroid may occasionally be found on rocky substrate, but is more common on shells inhabited by hermit crabs or on the shell of the common whelk. It is very common along the entire Norwegian coast.

Characteristics: The snail fur forms a 3 mm horny mat with 1-2 mm spines, on the shell it resides. The polyps may grow to a height of 13 mm. There are four types of polyps:

• The club shaped hydrants have two circles of tentacles, with eight tentacles in each.
• Female and male gonozooids are shorter and have fewer tentacles. The gonozooids spawn planula (free-swimming) larvae. These detect detect moving shells and attach themselves to them.
• The dactylozooids are long threadlike individuals.

All pictures: