Form: A thin cushion, typically 5mm to 1cm thick, spreading in patches of diameter typically ca. 6cm. It may become massive-lobose in sheltered locations.

Colour: Variable: "scarlet", orange to dirty violet-brown.

Smell: A strong smell, variously described as like iodine or 'garlic on breath'; or (?) 'like Amphilectus'.

Consistency: Somewhat crumbly, compressible and fairly resilient.

Surface: More or less smooth or somewhat tuberculate or "conulate", with transparent tissue between the tubercles.

Apertures:

• Oscules "small", scattered, "numerous" and obvious; they may be in groups. Excurrent channels are present.

Contraction:

• Slight. (There is a tendency to 'curl up' on removal from the water).

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Synonyms: Plumohalichondria plumosa (Montagu, 1818:116) Carter, 1885:355, Microciona plumosa (Montagu, 1818:116) Parfitt, 1868:15, Pronax plumosa (Montagu, 1818:116) Gray, 1867:536.

Internal characters

Skeleton: A plumose skeleton of ascending multi-spicular fibres of acanthostyles, echinated by smaller acanthostyles. There is a well developed ectosomal skeleton of tornotes arranged in vertical brushes. Spongin is scarce.

Spicules: Megascleres of the main skeleton are large acanthostyles (a), 180-(200)-240 μm, sparsely spined and echinated by smaller acanthostyles (b), 80-(110)-140 μm, which are densely and entirely spined. The ectosomal tornotes (c) have oxeote ends and are 160-(170)-185 μm in length. The microscleres are arcuate isochelae (d) of distinctive shape, small and fine, ca. 15 μm.

Identity: The smell and appearance are fairly characteristic, but there are several other species of Stylostichon whose living characters are not known, as well as the others described here. The spicule complement with only one size of chela and no sigmata is characteristic of S. plumosum.

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

iNaturalist: Stylostichon plumosum at iNaturalist World Species Observations database.

WoRMS: Stylostichon plumosum at World Register of Marine Species. Accepted name: Phorbas plumosus (Montagu, 1814). AphiaID: 133688.

Classification: Biota; Animalia; Porifera; Demospongiae; Heteroscleromorpha; Poecilosclerida; Hymedesmiidae; Stylostichon

Voucher: BELUM : Mc525. Saltee Islands, Wexford.

Editors: D. Moss, B.E. Picton.