Description: This hydroid forms a crust on hermit crab shells and occasionally under rocks. Numerous pink athecate polyps arise from this crust. Extent of the basal crust is typically 20-30mm with individual polyps 5mm in height.

Habitat: Normally found on shells inhabited by the hermit crab Pagurus bernhardus in sheltered, muddy conditions. May also occur beneath rocks in the intertidal zone or on bedrock in the surge zone on exposed coasts.

Distribution: Found all round the coasts of Great Britain and Ireland.

Similar Species: This is the only pink athecate hydroid normally found on hermit crab shells.

Key Identification Features:

• Pink polyps arising from a basal crust.
• On hermit crab shells.

Distribution Map from NBN: Hydractinia echinata at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Hydractinia echinata at iNaturalist World Species Observations database.

WoRMS: Hydractinia echinata at World Register of Marine Species. Accepted name: Hydractinia echinata (Fleming, 1828). AphiaID: 117644.

Classification: Biota; Animalia; Cnidaria; Medusozoa; Hydrozoa; Hydroidolina; Anthoathecata; Filifera; Hydractiniidae; Hydractinia