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Picton & Goodwin, 2007

Species Overview

Phorbas punctatus Picton & Goodwin (2007) is a yellow encrusting species with areolate surface and slightly raised oscules. Microscopic examination is necessary to find the discriminating characters. It is known only from Rathlin Island, Northern Ireland.

Taxonomic Description

Colour: Yellow-pale orange.
Shape, size, surface and consistency: Encrusting species, forming patches up to 10 cm in diameter on bedrock. Oscules surrounded by 5-8 radiating oscular channels, these channels may be grouped in pairs. Ostia seem to be grouped in patches which gives the surface a spotted appearance
Spicules: Megascleres: Primary acanthostyles 250-430 µm (mean 366 µm) long and 10-15 µm thick, they taper fairly abruptly at the end to a sharp point; spined only in bottom third to half of their shaft with small spines; the head is not tylote but may be marked by heavier spination than the rest of the shaft, may be straight or slightly curved. Echinating acanthostyles 80-160 µm (mean 120 µm) and 6-10 µm thick, entirely spined with larger spines than the primary acanthostyles; there is no development of the head; the spicules taper to a sharp point and may be straight or slightly curved. Tornotes 165-180 by 2-4 µm (mean 170 µm), ends tend towards being mucronate; one, occasionally both, ends usually slightly swollen.
Microscleres: Chelae arcuatae: two size-classes present, the larger 30-40 µm and the smaller between 12 and 15 µm.
Skeleton: Choanosome has a basal layer of acanthostyles and columns of large and small acanthostyles. Thick ectosomal layer of tornotes and chelae, chelae very abundant.
Distribution: Known only from the type locality, Rathlin Island, Northern Ireland.
Ecology: On vertical cliffs at 28-33 m.
Etymology: From the latin punctat meaning marked with pricks or punctures, named for the spotted appearance of the surface.
Type material: Holotype: [Mc2445]. Sample in IMS, section and spicule preparation, Farganlack Point (55°18.685'N 006°15.480'W; water depth: 28-33 m), 17 June 2005.

Remarks

The closest described species is Phorbas lieberkuehni (Burton, 1930), however, this is described as a bright red brown crust; although it has two classes of acanthostyles of a similar appearance the larger class range only from 250-360 µm in length; the tornotes are larger and have a larger size range (180-270 µm); and although the chelae occur in two size categories they are much smaller (10-15 µm and 18-22 µm espectively). There is no information on the form of the skeleton of this species. Most other species of Phorbas lack two size-classes of chelae, in those where there are two sizes present either sigmas are present (e.g. Phorbas roemeri (Hentschel, 1929) or the spicules are much larger (e.g. Phorbas perarmatus Bowerbank, 1866).
Source: Picton & Goodwin, 2007.

Phorbas punctatus