Description: This hydroid is similar to Diphasia species in having the hydrothecae arranged in opposite pairs on the main stem and side branches of the sparsely branched, pinnate colonies. The hydrothecae are tubular in shape, large and robust and are attached for approximately 1/2 of their length, the upper 1/2 being unattached with a three pointed outer margin. Colonies are typically about 60mm to a maximum of 150mm in overall height.

Habitat: This is a circalittoral species normally found in moderate to strong tidal streams attached to bedrock or stable rocks or shells.

Distribution: Probably under-recorded, recent diving records are from Rathlin Island and the Irish sea coast of Northern Ireland and scattered records from the west coast of Ireland.

Similar Species: This species could easily be mistaken for a sparsely branched form of Abietinaria abietina but is distinguished by its opposite hydrothecae. The other species to compare are the various Diphasia species.

Key Identification Features:

• Sparsely branched, pinnate colonies.
• Hydrothecae in opposite pairs, free of the stem for their outer 1/2.

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

iNaturalist: Tamarisca tamarisca at iNaturalist World Species Observations database.

WoRMS: Tamarisca tamarisca at World Register of Marine Species. Accepted name: Tamarisca tamarisca (Linnaeus, 1758). AphiaID: 117930.

Classification: Biota; Animalia; Cnidaria; Medusozoa; Hydrozoa; Hydroidolina; Leptothecata; Sertularioidea; Sertulariidae; Tamarisca