Polyplumaria flabellata G O Sars, 1874

Polyplumaria flabellata

Description: A fan-like hydroid with irregularly branching main stems and regular side-branches arising in opposite pairs from the main stem. The hydrothecae are arranged on the upper edge of the side branch. They are tubular in shape with a smooth outer margin, and are surrounded by 4 smaller, defensive polyps, one on either side, and one above and below. The gonothecae are arranged on short pedicels. They are roughly oval shaped, and have a wide aperature. The capsule tapers towards the base, and is surrounded by four small, defensive polyps, located in the basal region. Typically 70mm with side-branches 10mm in length.

Habitat: A deep water species rarely found in less than 50m and thus not often encountered by divers. Found at sites with moderate to strong tidal streams and scour from mobile gravel.

Ecology: Grows in company of Diphasia spp. especially Diphasia alata, in sites with a high diversity of hydroids.

Distribution: The east coast of Rathlin below 40m; the Maidens, Co Antrim; North Channel 45m; east side of Ushant 50m. Also reported from Shetland, western Scotland, North Sea, Plymouth, Scillies and Roscoff.

Similar Species: This is a distinctive species, unlikely to be confused with any other apart from Polyplumaria frutescens.

Key Identification Features:

• Side branches opposite, bearing short third-order branches

Distribution Map: NBN map : National Biodiversity Network mapping facility, data for UK.

WoRMS: Species record : World Register of Marine Species.

iNaturalist: Species account : iNaturalist World Species Observations database