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(Bowerbank, 1874)

Species Overview

Mycale (Aegogropila) rotalis (Bowerbank, 1874) is a red, thinly encrusting sponge, distinguished from other such sponges by a strongly dotted surface (but to make sure, spiculation needs to be studied to make a positive identification). It is a southern species, occurring on rocks and shells in areas with tidal currents.

Taxonomic Description

Colour: A more or less bright carmine-red, rarely rose-red.
Shape, size, surface and consistency: Thin sheet to thick cushion to massive-lobose, with smooth lobes (Mycale rotalis MCS2). Size up to at least 15 cm across. Surface smooth uneven. A distinctive, closely packed series of dots can be seen under close examination or slight magnification. Punctate, with dark spaces under the surface membrane. 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. Slight contraction, oscules close. Consistency fairly soft but quite tough. Resilient.
Spicules: (Mycale rotalis spics V) Megascleres are stout, straight-shafted subtylostyles: ca. 300 µm. Loose interstitial subtylostyles lying between the fibres are often flexuous.
Microscleres are palmate anisochelae of three sizes: ca 30, 25 and 15 µm. None of these form rosettes. In other Mycale spp. the largest anisochelae usually do form rosettes. Also present are sigmas of two sizes: ca.70 and 20 µm.
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.
Ecology: 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: British Isles (recorded recently from Co. Wexford; Lough Hyne, Co. Cork; Co. Galway; N. coast of Co. Donegal; Strangford Lough, Co. Down; Tiree, W. Scotland), France and Mediterranean.
Etymology: rotalis (Latin) = wheel-like, referring to the regular surface reticulation resembling the spokes of a wheel.
Type specimen information: The type is in the Natural History Museum, London.

Remarks

The characteristic surface, once seen, is very distinctive. There is potential confusion with many other red encrusting species. The spicule complement will immediately confirm Mycale spp. and the particular microsclere combination present confirms Mycale (A.) rotalis.
Source: Ackers et al., 1985 (B.E. Picton, S.M. Stone, D. Moss).

Mycale rotalis