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(Linnaeus, 1767)

Species Overview

Phakellia ventilabrum (Linnaeus, 1767) is a cup-or fanshaped species with a greyish brownish colour. Its edges are thin and often frayed. There is a characteristic pattern of ribbed veins fanning out from the stem in the direction of the rim. The oscules are small and on the inner side. It occurs in deeper water on rocks and in gravel beds. It is a common species along most European coasts.

Taxonomic Description

Colour: Grey-beige, also reported as yellow, often with a green tint.
Shape, size, surface and consistency: (Phakellia ventilabrum MCS2) (Phakellia ventilabrum MCS3) (Spongia ventilabrum) Cup-like or lamellate, attached by fairly narrow base, i.e. sub-stipitate. Edge of cup/fan sharp, frayed, not neatly rounded, except in juvenile specimens. Surface even, slightly velvety; no projecting spicules visible to naked eye. In cuplike forms, the interior of the cup is dotted with small openings which are larger than the openings on the outer surface. Both surfaces have a tendency to be marked by an ascending system of vein-like lines. In older specimens the surface can become wrinkled (i.e. rugose), especially towards the base. Exhalant openings (oscules) are confined to one surface; in cuplike forms seen as pin-hole sized openings scattered over the inner surface of the cup. Pores are not visible with the naked eye. Consistency firm, elastic, fairly tough, but becomes laxer in older specimens, when it can become easily torn.
Spicules: (Phakellia ventilabrum spics) Megascleres are long, vermiform strongyles (i.e. flexuous spicules) forming the axlal condensation: 420-525-620 x 7.5 µm, whereas the plumose fibres consist of styles which are slightly curved at the base: 220-420-500 x 7.5 µm. Styles may be supplemented by oxeas. These are mostly anisoxeas, with one end finely tapering and the other blunt or telescoped. No microscleres are present.
Skeleton: (Phakellia Vosmaer) Plumoreticulate. An axial or mesial condensation of densely packed vermiform megascleres with radially arranged ascending plumose fibres arising from the core and branching and anastomosing towards the surface. At the surface they form brusbes. Minimal amounts of spongin encase the spicules.
Ecology: Slightly sheltered locations close to deep water, down to 200 m. At St. John's Point, Donegal, NW Ireland at 30 m on rock ridges. At Skird Rocks, Galway, W Ireland, characteristic of Könnecker's Axinellid association—Axinella polypoides, Axinella infundibuliformis, Diazona violacea, Eunicella verrucosa, Alcyonium glomeratum.
Distribution: Arctic, Atlantic coasts of Europe.
Etymology: ventile (Latin) = fan.
Type specimen information: Neotype BMNH 10.1.1.2687, dry – near Lervig, Norway; MCS voucher BELUM: Mc449, St.John's Pt, Donegal.

Remarks

Similar to Axinella infundibuliformis but often larger, more brittle, with a sharp edge to the cup (rounded in Axinella). Colour is grey, Axinella is slightly brown to yellow. Axinella has trichodragmata and lacks vermiform megascleres. Other lamellate Axinellids recorded from the area include Axinella arctica Vosmaer (1885) which has no sinuous diactines, and Phakellia robusta Bowerbank (1866). The latter differs from P. ventilabrum in having sinuous oxeas in stead of strongyles and much thicker styles.
Source: Ackers et al., 1992 (B.E. Picton, S.M. Stone).

Phakellia ventilabrum