Plocamionida tylotata Bröndsted (1932) forms thin pale orange crusts, similar in spiculation to Plocamionida ambigua but differing in the shape of the ectosomal spicules (tylotes in stead of oxeas).
Colour: pale orange
Shape, size surface and consistency: Thin sponge encrusting on boulder. Some raised oscules and oscular channels visible but not in a regular pattern.
Spicules: Megascleres: Acanthostrongyles 90-110 by 5-6 µm. Acanthostyles 95-600 by 5-10 µm; the shorter individuals are entirely spined and similar in form to the acanthostrongyles, the longer are almost smooth with a slight roughening around the head; shaft above head wider than head, then tapers to a point. Ectosomal spicules strongyles with tylote ends: 180-230 by 2-3 µm, most are asymmetrical with one end wider than the other. Microscleres: Arcuate chelae 17.5-20 µm, they have a straight shaft and small alae giving an appearance under the light microscope similar to a Clathria (Microciona) chela.
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.
Distribution: Faroes, Skagerrak and Northern Ireland (Damicornis Bay (55°17.459'N 006°15.233'W).
Ecology: On cliffs, pebbles and on coldwater corals, 27-400 m.
Etymology: The name refers to the shape of the ectosomal spicules.
Type specimen information: no data (presumably in the Copenhagen Museum)
Described from the Faeroes as Plocamionida ambigua f. tylotata by Brøndsted. Alander (1942) found specimens matching Brøndsted's description in south-west Sweden and elevated it to species rank. 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/tylotes rather than oxeas.
The genus Plocamionida is currently under study (morphology and genetics). At least one other species of Plocamionida occurs in the area, P. ambigua (Bowerbank), distinct by the oxeote or mucronate condition of the ectosomal spicules (versus the tylote condition in the present species). More species may be present, P. microcionides (Carter), which may or may not be a synonym of P. ambigua, and P. grandichelata Brøndsted (1933, see figure) having larger chelae up to 35 µm in length.
Source: Picton & Goodwin (2007)