Hymedesmia (Stylopus) primitiva LUNDBECK 1910

HYMEDESMIA (STYLOPUS) PRIMITIVA LUNDBECK, 1910 (FIG. 11A, B)

Specimens: Specimens in IMS, sections and spicule preparations from tissue samples (Rathlin Island Sponge Biodiversity Project; specimen 1, White Cliffs, 55°17.543 ′ N, 06°14.517 ′ W; water depth, 26.4–29.4 m; Mc 2611). Collected by J. Jones and C. Goodwin, 7 July 2005. Specimen 2: White Cliffs (55°17.538 ′ N, 06°14.542 ′ W; water depth, 37–40 m; Mc 2981). Collected by B. Picton and C. Goodwin, 7 September 2005. Specimen 3: Damicornis Bay (55°17.429 ′ N, 06°15.098 ′ W; water depth, 30.5–33.5 m; Mc 3107). Collected by J. Jones and L. Scally, 16 August 2005. Specimen 4: north-east of Doon Point (55°16.454 ′ N, 06°10.296 ′ W; water depth, 35.7–38.7 m; Mc 3132). Collected by J. Jones and B. Picton, 25 August 2005. Specimen 5: Loch Garry (55°15.956 ′ N, 06°10.411 ′ W; water depth, 31–34 m; Mc 3161). Collected by C. Goodwin and A.M. Mahon, 26 August 2005. Specimen 6: Loch Garry (55°15.956 ′ N, 06°10.411 ′ W; water depth, 32–35 m; Mc 3162). Collected by J. Jones and B. Picton, 26 August 2005.

Comparative material examined: Hymedemsia primitiva spicule preparation of specimens from Ingolf expedition stations 6 and 89. ZMUC.

External morphology: The sponge is a thin cream crust with large pore sieves; in two of the sponges the area around the pore sieves was yellow from algae in the surface tissues. The sponge formed patches with maximum diameters in the range 4–15 cm.

Skeleton: Basal layer of acanthostyles, in which the smaller acanthostyles are more abundant. There are ascending columns of ectosomal spicules that are 5–8 spicules thick. The sponge is 400–500-Mm thick. Several of the specimens had diatoms present in their surface layer.

Spicules:

1. Acanthostyles: 100–315 Mm by 10–16 Mm on the head, or by 6–10 Mm on the shaft; entirely spined with small, short, recurved spines. The head is slightly tylote, and bears slightly larger spines that often have rounded tips. In the longer spicules the spines may be very sparse towards the tip, and part of the shaft may be smooth.

2. Ectosomal spicules: 200–250 Mm by 2–4 Mm. With tylotes that are usually faintly polytylote.

3. Microscleres: absent.

Remarks: The spiculation broadly agrees with that of Lundbeck’s (1910) specimens. However, the strongyles of his specimens have a slightly broader size range (196–280 Mm), and the acanthostyles are also somewhat thicker than the Rathlin specimens, with base widths varying from 14 to 27 Mm. However, Lundbeck states that there is much variation of acanthostyles between individuals in terms of robustness and spination.

This species was originally described from deep water (108–840 m) around Iceland and the Faroe Islands. It has subsequently been reported from the Caribbean (De Laubenfels, 1936) and from Wembury Bay in Devon (Burton, 1957), although it would seem unlikely that the former record is of the same species.