Form: Cushions 0.5 - 1cm thick, forming patches up to 15cm across; becoming branched - erect in deeper waters. It may form upright growths around hydroid stems.

Colour: Yellow, or "dirty rose-red", or brownish orange when alive.

Smell: None. Slime. : Considerable quantities are exuded.

Consistency: "Loose, somewhat crumbly. Elastic."

Surface: A loose, porous appearance, similar to that of M. incrustans. Slightly hispid.

Apertures:

• The oscules are scattered across the animal, and have raised edges. Exhalant channels run up to the oscules; "not apparent when preserved".

Contraction:

• None.

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Internal characters

Skeleton: The main skeleton is a reticulation (sub-isodictyal) of acanthostyles in multispicular fibres, with no echinating spicules. Special ectosomal spicules (tornotes) are present. Spongin is scarce.

Spicules: The megascleres of the main skeleton are acanthostyles (a) whose spines are few but strong, and present throughout the length of the spicule 140-(145)-152 μm . The surface tornotes (b) bear three or four small spines at the ends and are 140-(150)-160 μm long, and lie in vertical brushes at the surface. The microscleres are spatuliferous anchorate chelae (c) of two sizes (12-15 μm, 20-25 μm), which are present throughout the sponge, together with small sigmata (d), ca. 17-35 μm.

Identity: Superficially it can be very similar to M. incrustans, but it does not seem to form the raised, oscule bearing ridges of the latter species (?). Examination of the tornote ends at high power is necessary to confirm identification. It is possible that more than one species is involved here.

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

iNaturalist: Myxilla rosacea at iNaturalist World Species Observations database.

WoRMS: Myxilla rosacea at World Register of Marine Species. Accepted name: Myxilla (Myxilla) rosacea (Lieberkühn, 1859). AphiaID: 169488.

Classification: Biota; Animalia; Porifera; Demospongiae; Heteroscleromorpha; Poecilosclerida; Myxillidae; Myxilla

Voucher: BELUM : Mc1010. St Kilda.

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