Hymedesmia, 1864

Goodwin, Claire E. & Picton, Bernard E., 2009, Demosponges of the genus Hymedesmia (Poecilosclerida: Hymedesmidae) from Rathlin Island, Northern Ireland, with a description of six new species, Zoological Journal of the Linnean Society 156 (4), pp. 896-912 : 898-899

HYMEDESMIA (HYMEDESMIA) COHESIBACILLA SP. NOV.

( FIG. 2A, B )

Type material: Holotype: specimen in IMS, section and spicule preparation from tissue sample ( Rathlin Island sponge biodiversity project; Damicornis Bay, 55°17.433 ′ N, 06°15.137 ′ W; water depth, 29.6–32.6 m; Mc 2626). Collected by J. Jones and C. Goodwin, 6 July 2005.

Paratypes: Specimen 1, specimen in IMS, section and spicule preparation from tissue sample (Rathlin sponge biodiversity project; Damicornis Bay, 55°17.463 ′ N, 06°15.235 ′ W); water depth, 32–35 m; Mc 3189). Collected by J. Jones and L. Scally, 17 August 2005 . Specimen 2, specimen in IMS, section and spicule preparation from tissue sample (Rathlin sponge biodiversity project; Damicornis Bay, 55°17.460 ′ N, 06°15.238 ′ W; water depth, 27–32 m; Mc 3036). Collected by J. Jones and L. Scally, 10 June 2005 .

Etymology: Named from the Latin cohereo, meaning connected, and the Latin for stick or shaft, bacillum, because of the fusion of the alae to the shaft in the chelae.

External morphology: Patches formed small encrustations on boulders, and were 6–10 cm in maximum diameter. The external appearance is a cream to buff crust, with raised white pore sieves. One of the specimens had a large number of diatoms in its surface tissues, and small numbers of diatoms were present in the other specimens.

Skeleton: Basal layer of acanthostyles with ascending columns of ectosomal spicules, of 6–8 spicules in width. Dense layer of chelae at the surface; chelae also present in small numbers throughout the tissue. Both specimens also had diatoms present in the surface layer, and were 400–600-Mm thick.

Spicules: Acanthostyles – two size categories present. Both categories are similar in form, with the head marked by large, dense spines, and a shaft entirely spined with smaller spines.

1. Large acanthostyles: 140–220 Mm (180 Mm) by 14–16 Mm (head), or by 8–10 Mm (shaft).

2. Small acanthostyles: 70–95 Mm (78 Mm) by 10–14 Mm (head), or by 6–8 Mm (shaft).

3. Ectosomal spicules: 150–240 Mm (202 Mm) by 3–4 Mm, with the majority being between 185 and 210 Mm in length; strongylote in form, and often polytylote.

4. Chelae: very abundant chelae are present [17.5– 20 Mm, (18 Mm)]. These are rather palmate in form, the lateral alae coalesce with the shaft over their entire length, and the shaft is only slightly curved, appearing straight under the light microscope. However, the end of the median ala is not widened. There are also occasional normal arcuate chelae of the same size range.

Remarks: Comparatively few species of Hymedesmia have chelae in which the lateral alae are fused onto the shaft. Of those that do, Hymedesmia palmatichela Topsent, 1928 has similar acanthostyles in terms of size and form, and also has polytylote ectosomal spicules, although these are larger (215–280 Mm), and its chelae are of a much larger size (45–46 Mm). Hymedesmia cordichela Alander, 1942 has spicules of the same size, but the chelae have distinctive ‘cordate leaves’, and the ectosomal spicules are not polytylote. In Hymedesmia palmatichelifera Van Soest, 1984 , the primary acanthostyles are larger (293–361 Mm), the ectosomal spicules are tornotes rather than strongyles, and the large acanthostyles are smooth at their tips. Hymedesmia jamaicensis Van Soest, 1984 possesses ‘whispy’ tornotes rather than strongylote ectosomal spicules.

Figures

Figure 2. A, Hymedesmia (Hymedesmia) cohesibacilla sp. nov. A, acanthostyle; B, ends and middle of ectosomal spicule; C, chelae. Scale bars: 10 Mm. B, Hymedesmia (Hymedesmia) cohesibacilla sp. nov., surface.