Plocamionida tylotata Brondsted, 1932


Family : Hymedesmiidae

Form: Thinly encrusting, pale orange sponge forming small patches on boulders and bedrock.

Surface: Some raised oscules and oscular channels visible but not in a regular pattern. The surface is similar to an encrusting Clathriid or Plocamiancora arndti.

Apertures: Slightly raised osculae with transparent edges are visible in living specimens, but are inconspicuous.

Internal characters

Skeleton: The skeleton consists of a basal reticulation of acanthostrongyles lying tangential to the substratum and ascending acanthostyles oriented with their points towards the surface of the sponge. There is a surface layer of tornotes.

Spicules: The acanthostrongyles are 90–110 by 5–6 μm and the acanthostyles measure 95–600 by 5–10 μm. The shorter spicules are entirely spined and similar in form to the acanthostrongyles. The longer ones are almost smooth with a slight roughening around the head. The shaft just above the head is wider than the head and then tapers to a point. The ectosomal spicules are 180–230 by 2–3 μm, they are strongyles with tylote ends. Most are asymmetrical with one end wider than the other. The arcuate chelae are 17.5–20 μm and have a straight shaft and small alae giving an appearance under the light microscope similar to a Clathria (Microciona) chela.

Habitat: Found in 30m of water in tide-exposed sites on boulders and vertical bedrock faces. Also found encrusting dead Lophelia branches in deeper water.

Distribution: Described from the Faeroes as Plocamionida ambigua var. tylotata by Brondsted. Alander (1942) found specimens matching Brondsted’s description in south-west Sweden and elevated it to species rank.

Identity: Distinguished from the more common Plocamionida ambigua (Bowerbank, 1866) by having chelae with a straight rather than curved shaft and the shape of the tornotes which are strongyles rather than oxea.

Voucher: BELUM:Mc3539, Maidens, Co Antrim, Ireland.

Editors: Claire Goodwin & Bernard Picton

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