Styloptilon ancoratum Cabioch, 1968


Family : Hymedesmiidae

Form: Thinly encrusting, about 1-2 mm in thickness, agglutinating shell debris. Forms extensive sheets often overgrowing bryozoans. The surface is finely hispid.

Colour: Yellow, greenish yellow.

Consistency: Soft.

Surface: Translucent, granular appearance.

Apertures: Oscules transparent and inconspicuous, at centre of star-like patterns of excurrent channels.

Contraction: None apparent

Internal characters

Skeleton: The dermal membrane is charged with microscleres and carried by bouquets of tornotes, which also form short tangential bundles. The bouquets of tornotes are in turn erected on the peripheral ends of the choanosomal spicule tracts, which consist of acanthostyles. The skeletal columns are thick and form a plumoreticulate skeleton, in which the longitudinal elements dominate.

Spicules: Megascleres are acanthostyles and tornotes. The tornotes are smooth and have pointed, but unequal ends, one being slightly swollen; they may be somewhat polytylote or have an irregular outline: 140-200 x 2.5-5 μm. The acanthostyles are entirely spined and perhaps divisible in two size categories: 100-135 x 5-8 μm and 190-280 x 5-10 μm, but they do not constitute two functional categories (main and echinating). Microscleres are spatulate anchorate isochelae in two size categories: 35-48 μm and 11-15 μm; sigmas in a single variable size category: 32-50 μm.

Habitat: On rocks in fast tidal streams, shore to 85m.

Distribution: Until recently recorded only once from Roscoff, NW France. Specimens in Ulster Museum collection from Strangford Lough. Numerous specimens from Rathlin Island.

Distribution Map: NBN map : National Biodiversity Network mapping facility, data for UK.

Identity: Appearance is quite characteristic, especially in specimens which are overgrowing bryozoans. The spiculation is distinctive, with Myxilla-like chelae combined with a plumose skeleton. Etymology: The name refers to the anchorate chelae, which are unusual in combination with a plumose skeletal structure. Its characters are in between those of Phorbas (plumose columns, pointed tornotes, two sizes of acanthostyles) and Myxilla (anchorate chelae). For that reason it is assigned to its own genus in the Myxillidae (see also Desqueyroux-Faśndez and Van Soest, 1996).

Voucher: BELUM: Mc1475

Editors: Christine Morrow, Bernard Picton & Rob van Soest.

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