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(Bowerbank, 1866)

Species Overview

Mycale (Carmia) macilenta (Bowerbank, 1866) is a light yellow, thinly encrusting sponge, with distinct veinal pattern and raised oscules. It is one of several common Mycale species. Study of the spicules is needed to establish its identity. It is a southern species occurring along the Atlantic coasts of Europe in shallow waters encrusting Laminaria holdfasts and shells.

Taxonomic Description

Colour: Alive, the sponge is pale yellow; specimens have also reported as"vivid red", but that needs confirmation. When preserved it is yellow or brown.
Shape, size, surface and consistency: Encrusting, sheet or cushion, up to 10 cm across. Surface smooth. Oscules are clearly visible in living sponges, on erect tubes, but are not very numerous. Pores small, scattered over the surface. Consistency soft.
Spicules: (Mycale macilenta spics V) The megascleres are generally straight-shafted, slightly fusiform, subtylostyles, with barely formed elliptical heads, between 200 and 300 µm long.
Microscleres include palmate anisochelae of three sizes. The largest are grouped into rosettes in the ectosome: ca. 33-59 µm. The middle size are solitary and scarce: ca. 17-24 µm. Those of the smallest size are very abundant and widely dispersed throughout the body: 11-15 µm. They have a distinctive lower tooth which is very short and curved in towards the shaft. The sigmas fall into two size categories: 65-115 µm and 21-28 µm. Toxas are variable in length: 60-250 µm.
Skeleton: Plumose; ascending multispicular tracts of subtylostyles (which do not divide or anastomose), ending in loose brushes at the surface, with single megascleres lying scattered in between. Spongin is minimal. There is no specialised ectosomal skeleton. The surface is supported by the widely spaced, terminal brushes of the main skeleton, with a few single megascleres (sometimes these are absent altogether) scattered in the large interstices.
Reproduction: Larvae are found at the base of the sponge between August and mid-October.
Ecology: Littoral to 27 m, encrusting mainly on Pecten and Chlamys (Mycale macilenta MCS2). Also on Laminaria and hydroids. Nematods, annelids and crustaceans burrow in the superficial regions (Frith, 1976).
Distribution: Common along the Channel coasts of the British Isles and France; Belgium; Atlantic coasts of France, Spain, and Mediterranean.
Etymology: macilentus (Latin) = thin, referring to the shape.
Type specimen information: BMNH 1910.1.1.135 (dry), Norman Collection.

Remarks

The most difficult of all the Mycale spp. to recognise, as its appearance and spiculation can be so variable. It most closely resembles M. (C.) similaris, but the presence of trichodragmata in the latter helps to distinguish the two species, although these spicules can be so fine and so few that they are easily overlooked. It is also similar to M. micracanthoxea, differing in the lighter colour and the absence of micracanthoxeas (but these are easily overlooked as they are only 5-8 µm).
Source: Ackers et al., 1985 (S.M. Stone, D. Moss)

Mycale macilenta