Mycale rotalis (Bowerbank, 1874)


Family : Mycalidae

Form: Thin sheet to thick cushion to massive-lobose (?), with smooth, irregular lobes.

Colour: A more or less bright carmine-red," rarely rose-red", very conspicuous.

Smell: None.

Consistency: Fairly soft but quite tough. "Resilient."

Surface: Distinctive - a closely packed series of dots can be seen under close examination or slight magnification. Porous, with dark spaces under the surface membrane. "Smooth, uneven."

Apertures: Oscules are few, large, conspicuous, "scattered and varying in size". They are slightly raised above the surface, and the ends of the excurrent channels can be seen as membranes inside each oscule.

Contraction: Slight - oscules close.

Internal characters

Skeleton: Plumoreticulate. The main skeleton consists of an irregular reticulation of multispicular fibres (of subtylostyles). The ectosomal skeleton is a tangential, triangularly meshed reticulation of multispicular fibres. Spongin reinforces the skeleton fibres to a varying degree. The ectosomal membrane is easily detached.

Spicules: Megascleres are stout, straight-shafted subtylostyles (a), 240-(280)-300Ám long. Loose interstitial subtylostyles lying between the fibres are often flexuous. The microscleres are palmate anisochelae of 3 sizes (b) (ca. 30Ám, 25Ám and 15Ám). None of these form rosettes. In other Mycale spp. the largest anisochelae usually do form rosettes. Also present are sigmata (c) of two sizes, ca. 65-70Ám and 20-25Ám.

Habitat: On vertical rock faces in sheltered, and also very exposed, sites. On boulders and rocks in sheltered areas with moderate to strong tidal streams. "Also on shells (e.g. Chlamys), stones, seaweed, hydroids, and in rock crevices."

Distribution: Widely distributed and common; "British Isles; France and Mediterranean". Known recently from Co. Wexford; Lough Hyne, Co. Cork; Co. Galway; N. coast of Co. Donegal; Strangford Lough, Co. Down; Tiree, W. Scotland.

Distribution Map from NBN: Grid map (fast) : Interactive map (slower, requires login to view records) : National Biodiversity Network mapping facility, data for UK.

Identity: The characteristic surface, once seen, is very distinctive. There is potential confusion with many other red encrusting species, but most are much thinner crusts. The spicule complement will immediately confirm Mycale spp. and the particular microsclere combination present confirms Mycale rotalis. Note the lack of rosettes of anisochelae in this species.

Voucher: BELUM : Mc475. Tiree, Hebrides.

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

 Picton, B.E., Morrow, C.C. & van Soest, R.W.B., 2011. [In] Sponges of Britain and Ireland