Hydractinia echinata

Hydractinia echinata is a colonial marine hydroid that is found growing on the shells of gastropod shells. It is also known as snail fur, a name which describes the furry appearance that the hydroids give to a shell. These hydroids are especially common on the outside of shells that are occupied by flat-clawed hermit crabs.

Description

Hydractinia echinata forms pink patches on gastropod shells occupied by a hermit crab, often near the mouth.^[2] The horny mat or hydrorhiza is about three millimetres thick. It consists of thick jagged spines that reach three millimetres in height. Amongst these there are three types of polyps. The club like feeding polyps grow up to thirteen millimetres in length, and have two rows of eight tentacles, the lower set being shorter than the upper ones. There are also male and female reproductive polyps (gonozoids) that have a few short terminal tentacles. Scattered among these are specialized defensive stinging polyps (dactylozooids) that are long, coiled threads. The gonozoids liberate crawling planula larvae that search out moving gastropod shells^[3]

Distribution

H. echinata is found in the northeastern Atlantic Ocean including the Arctic Ocean, the Baltic Sea and the North Sea south to northwest Africa.^[4] It is common round the coasts of Britain and Ireland and is found where hermit crabs (Eupagurus bernhardus) occur, on the lower shore on sandy substrates. ^[2]

References

External links

• Marine Life Encyclopedia
• MBL Marine Organisms Database page
• Aquascope: More About the Common Hermit Crab