Hymedesmia cohesibacilla Goodwin & Picton, 2009


Family : Hymedesmiidae

Form: Forms small encrustations on boulders, between 6-10cm maximum diameter. Very thin with raised white pore sieves.

Colour: External appearance is a cream to buff crust. Surface tissues may be discoloured brown by diatoms in a subsurface layer.

Internal characters

Skeleton: Basal layer of acanthostyles with ascending columns of dermal spicules, 6-8 spicules in width. 400-600μm thick. Dense layer of chelae at the surface, diatoms present in the surface layer.

Spicules: Acanthostyles - two categories present. Both categories are similar in form with the head marked by large, dense, spines and a shaft entirely spined with smaller spines. Large acanthostyles - 140-200μm by 14-16μm (head) and 8-10μm (shaft). Small acanthostyles - 70-95μm by 10-14μm (head) or 6-8μm (shaft). Dermal spicules - 145-225μm by 3-4μm, with the majority being between 185 and 210μm. Strongylote in form and often polytylote. Chelae - Very abundant palmate isochelae are present (20-22μm).

Habitat: Specimens have been collected from rockfaces in strong tidal streams and depths of 30-40m.

Distribution: Currently only known from Rathlin Island and the Maidens with one record from Scotland.

Identity: The external appearance of this species is almost identical to several other Hymedesmia species. It is distinctive in having palmate chelae.

Editors: Claire Goodwin & Bernard Picton.

 Picton, B.E., Morrow, C.C. & van Soest, R.W.B., 2011. [In] Sponges of Britain and Ireland