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(Montagu, 1818)

Species Overview

Phorbas plumosus (Montagu, 1818) is a massively encrusting orange with an irregular, somewhat tuberculate surface. It differs from the related and sympatric P. fictitius by the small indistinct pore-fields (against the very clear areolae in fictitius). It is a common shallow water species on most rocky coasts of Europe.

Taxonomic Description

Colour: Variable: orange to dirty violet-brown, scarlet.
Shape, size, surface and consistency: (Phorbas plumosus IV) Massive crust to thin cushion, typically 5 mm to 1 cm thick, spreading in patches of typically ca. 6 cm in diameter. It may become massive-lobose in sheltered locations. Surface more or less smooth or somewhat tuberculate (which are in fact raised small pore-fields, but do not appear so with the naked eye), with transparent tissue between the tubercles. Oscules small, scattered, numerous and obvious; they may be in groups. Excurrent channels are visible. Consistency somewhat crumbly, compressible and fairly resilient. Contraction slight (there is a tendency to 'curl up' on removal from the water). A strong smell, variously described as like iodine or 'garlic on breath'.
Spicules: (Phorbas plumosus spics) Megascleres: The ectosomal tornotes have oxeote ends: 140-185 x 6-7 µm; the spicules of the main skeleton are large acanthostyles: 180-240 x 8-9 µm, sparsely spined and echinating smaller acanthostyles: 80-140 µm, which are densely and entirely spined.
Microscleres are arcuate isochelae of distinctive shape, small and fine: ca. 15-20 µm.
Skeleton: A plumose skeleton of ascending multispicular fibres of acanthostyles, echinated by smaller acanthostyles. There is a well developed ectosomal skeleton of tornotes arranged in vertical brushes. Spongin is scarce.
Ecology: Typically found in shallow water—the kelp zone, especially in highly exposed sites, and in 'rapids' situations on upper surfaces of rocks. It may also occur in semi-sheltered situations with moderate current. Littoral to 680 m. Common.
Distribution: Faroes, Norway, British lsles, Atlantic coasts of France and Spain, Portugal.
Etymology: The name refers to the plumose skeletal arrangement.
Type specimen information: Several unregistered slides from Montagu type (Bk 944, 945 and 452). Johnston's specimen in the Natural History Museum, BMNH 1930: 7: 3: 8: 484, may be the same as Montagu's. MCS voucher BELUM Mc525, Saltee Islands, Wexford, SE Ireland.

Remarks

The smell and appearance are fairly characteristic, but there are several other species of Phorbas whose living characters are not known. The choanosomal spicule tracts without tornotes and the spicule complement with only one size of chela and no sigmas is characteristic of P. plumosus.
Source: Ackers et al., 1992 (editors B.E. Picton, S.M. Stone, (D. Moss).

Phorbas plumosus