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(Lieberkühn, 1859)

Species Overview

Myxilla (Myxilla) rosacea (Lieberkühn, 1859) is a yellow cushion-shaped sponge, which can have considerable lateral expansion. The surface is porous and its oscules are slightly raised. It has a slimy feeling when touched. Consistency soft, somewhat elastic. It may be easily confused macroscopically with Myxilla incrustans, so microscopic examination (tornote apices !) is necessary. This is a common form all along the coasts of Europe and into the Mediterranean.

Taxonomic Description

Colour: Yellow, or dirty rose-red, or brownish orange when alive.
Shape, size, surface and consistency: (Myxilla rosacea MCS2) (Myxilla rosacea MCS3) (Myxilla rosacea MCS4) Cushions 0.5-1 cm thick, forming patches up to 15 cm across; becoming brancbed—erect in deeper waters. It may form upright growths around hydroid stems. Surface has a loose, porous appearance, similar to that of M. incrustans. Slightly hispid. The oscules are scattered across the animal, and have raised edges. Exhalant channels run up to the oscules; not apparent when preserved. Considerable quantities of slime are exuded. Consistency loose, somewhat crumbly, elastic.
Spicules: (Myxilla rosacea spics) Megascleres: The surface tornotes bear three or four small spines at the ends and lie in vertical brushes at the surface: 140-160 µm. The megascleres of the choanosomal skeleton are acanthostyles whose spines are few but strong, and present throughout the length of the spicule: 140-152 µm.
Microscleres are spatuliferous anchorate chelae of two sizes: 12-15 µm, and 20-25 µm, which are present throughout the sponge, together with small sigmata: ca. 17-35 µm.
Skeleton: (Myxilla rosacea skel) The ectosomal skeleton consists of partly perpendicular brushes of tornotes. The choanosomal skeleton is a reticulation (sub-isodictyal) of acanthostyles in multispicular fibres, with no echinating spicules. Spongin is scarce.
Ecology: At exposed sites, on rock, on shells, from the shore down to 300 m.
Distribution: Arctic; Norway; Faroes; British Isles; Atlantic coasts of France and Spain; Mediterranean.
Etymology: The name refers to the colour.
Type specimen information: No type material in BMNH; MCS voucher BELUM: Mc 1O10, St Kilda.

Remarks

Superficially it can be very similar to M. (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 tbat more than one species is involved bere.
Source: Ackers et al., 1992.

Myxilla rosacea