Axinella flustra Topsent, 1892


Family : Axinellidae

Form: Branching-erect, the branches being very flattened (about 2-4mm thick) and lamellate, all in the same plane, with well rounded ends. There is usually a pronounced basal stalk ca. 1cm long; to about 7cms in height.

Colour: Beige, greyish yellow.

Smell: None.

Consistency: Compact, with flexible branches.

Surface: Even, slightly tuberculate, and slightly hispid, with moderate friction. Faint star shaped canal patterns are visible in situ.

Apertures: Oscules inconspicuous, regularly distributed over one surface of lamella.

Contraction: None.

Internal characters

Skeleton: The axial skeleton is compressed, conforming to the outline of the branches. The core consists of numerous, irregularly disposed, slender oxea, cemented by variable quantities of spongin. At the periphery of the axial skeleton numerous stouter oxea, orientated parallel to the surface of the axis, are found. Variations on the structure of the axial skeleton occur with styles sometimes present, and the peripheral oxea are not always clearly differentiated. Large styles echinate the axial skeleton, their heads in the axis, with their points piercing the sponge surface to give the hispid appearance.

Spicules: Megascleres are styles and oxea. The styles (a) are very variable in size, 300-(685)-900 x 7-20Ám, and are usually bent abruptly in the lower one third to one quarter of their length. The oxea (b) are stout, and often strongly curved by an abrupt bend in their centres. They measure ca. 150-(180)-220 x 4-15Ám. Microscleres are trichodragmata, up to 40Ám long by 8Ám wide. They can be difficult to see.

Habitat: Found in rocky areas, often together with Axinella dissimilis (q.v.), from ca. 25-320m. More habitat information is required.

Distribution: Rare in the British Isles, only having been recorded from Ireland (at ca. 40m on the west side of the Aran Islands). Otherwise known from Brittany, northern Spain, the Azores, and Cape Verde islands.

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

Identity: The flattened branches with their even contours give the sponge a resemblance to the bryozoan Flustra foliacea, hence its specific name. Flabellate forms of Axinella dissimilis, Axinella infundibuliformis and Phakellia ventilabrum (q.v.) have thicker branches. Endectyon delaubenfelsi (q.v.) has a similar low growing, erect habit, but with a more complicated branching arrangement. Endectyon teissieri Cabioch 1968 (see under Endectyon delaubenfelsi, this guide) has a very similar growth form to Axinella flustra, but is thinner and more extensively branched.

Voucher: BELUM : Mc1315. Aran Islands, Galway.

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

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