Mycale (Carmia) subclavata (Bowerbank, 1866) (also known as M. similaris) is an orange massive-lobate sponge. Surface transparent and punctate, with a few large oscules. The consistency is rather tough. It occurs in shallow water encrusting molluscs and other sessile organisms.
Colour: Typically orange/red, also brown, yellow, white (the latter as small patches underneath Lithothamnia). Colour is due to certain substances found in the spheruliferous cells, seen in the mesohyl in a transverse section.
Shape, size, surface and consistency: Thin sheet, cushion or massive-lobose. May extend 10 cm or more. Surface: transparent with darker pore areas. Even, slightly conulose. The ectosomal membrane is without spicules and supported, but rarely pierced, by ascending spicular brushes, causing the conulose appearance. A few large oscules at the tops of the lobes. These are scattered and fistular in cushion-shaped forms. Converging excurrent channels are visible as darker streaks. Pores 'sprinkled' across the surface give it a punctate appearance. Consistency fairly soft but tough. Slight contraction.
Spicules: (mycale_subclavata_spics_v.jpg ) The megascleres are long, straight-shafted subtylostyles with barely formed elliptical heads: 250-300 µm.
Microscleres include palmate anisochelae of three sizes: ca. 40, 20 and 12 µm, the largest grouped into rosettes of 12-20 spicules in the ectosome. Sigmas of two sizes, the largest: ca. 65 µm, are always present and numerous, whereas the smaller: ca. 37 µm, of variable thickness can be rare. Toxas: ca.200 µm, are very long and fine with a very abbreviated central flexion in proportion to the overall length, and with the ends gently recurved; these may be very rare. Trichodragmata: ca. 27µm, of characteristic 'spindle-shape', are very small and can be overlooked.
Skeleton: Plumoreticulate, of ascending multispicular fibres of subtylostyles reinforced with variable amounts of spongin. There is no specialized ectosomal skeleton. In juvenile specimens the fibres are well spaced and independent but, as the sponge matures, the fibres branch and anastomose, and the plumosely arranged network becomes apparent.
Ecology: LWS to 30 m, growing on a wide variety of molluscs, including Ostrea, Pecten and Chlamys; on Lithophyllum, Fucus, Sertularia, stones and rocks. In Strangford Lough (N. Ireland) this species occurs on clumps of Modiolus modiolus (horse mussels) in an area of moderate current (max. 1 knot).
Distribution: British Isles; France; Mediterranean. Recorded recently from
Strangford Lough, N Ireland.
Etymology: subclavatus (Latin) = referring to the shape of the megascleres
Type specimen information: The type is in the Natural History Museum, London: BMNH 1910.1.1.376 (dry), Norman Collection.
The spicule complement, especially the large toxas and characteristic trichodragmata is quite distinctive. Until more is known about the live appearance of other Poecilosclerida it is difficult to say how characteristic the external appearance is. Mycalid species most readily confused with this species are M. (A) contareni and M. (C.) macilenta, but colour, shape and size of toxas and presence/absence of trichodragmata can help in distinguishing them.
This species is usually called M. similaris (Bowerbank, 1874), but subclavata was described in 1866 and is a clear synonym of similaris.
Source: Ackers et al., 1985 (B. Picton, S.M. Stone).