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(Bowerbank, 1866)

Species Overview

Adreus fascicularis (Bowerbank, 1866) is an erect thinly and sparingly branched yellow sponge. Branches are smooth and compact, and through the axial skeletal condensation are quite tough and difficult to break. Faint longitudinal striations are diagnostic. It has aster microscleres like similarly branching-erect Stelligera species, but differs clearly from these in being smooth. A southern species known from the south coasts of the British Isles as the northernmost occurrence.

Taxonomic Description

Colour: Yellow/ brown / ochre / greenish / orange to brownish-yellow.
Shape, size, surface and consistency: Branching-erect, stalked. Branches are slender, circular in cross section, tapering to a point, and coalesce where they touch. The branching tends to be dichotomous, in one plane, and can produce an antler-like appearance. Several "individuals" can arise from one flat, spreading base, which may be buried in the substrate (Adreus fascicularis MCS2). Grows up to 15 cm high. Surface even, slippery, smooth. There are irregularly positioned, faint, longitudinal striations just below the surface, visible after preservation, which are characteristic. Oscules are not apparent. A light covering of silt may be found adhering to a little mucus (Adreus fascicularis MCS3), but there are no protruding spicules to trap it. Consistency firm, rigid, wiry: ruptures through to the axial skeleton when bent through 90 degrees, but does not 'snap'. No smell, no contraction.
Spicules: (Adreus fascicularis spics) Megascleres are styles: 270-440-500 x 4-5 µm; Microscleres are small oxyasters: ca. 8 µm diameter.
Skeleton: Plumose. An axial skeleton of longitudinally orientated megascleres forms a stiff core along the centre of the branches which is surrounded by fibres radiating at right angles out to the surfaee, but not piercing it. Minimal amounts of spongin are present (?).
Reproduction: Gametes produced in September (Lévi, 1956).
Ecology: Half buried in sediment overlaying horizontal bedrock; also on vertical rock faces; tolerant of silt. Found in sites with strong tidal streams and mobile shelly gravel, usually deeper than about 12 m (but in Jersey low growing specimens are common in the lower infralittoral in direct competition with foliaceous algae).
Distribution: A southern species reaching its northward extension in the British Isles; English Channel; Spain. Recently recorded from Lundy (occasional); S. Devon (rare); Channel Isles (occasional).
Etymology: fascicularis (Latin) = bundled, referring to the often grouped branches.
Type specimen information: Syntype in the Natural History Museum, London, BMNH 1910.1.38-39, 43-44, Vajon Bay, Guernsey.

Remarks

The manner of branching and the longitudinal striations are quite characteristic, enabling this rather rare species to be recognised on first sight.
Source: Ackers et al., 1992 (S.M. Stone, G. Ackers, D. Moss, B.E Picton)

Adreus fascicularis