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 : 902-904

publication ID	https://doi.org/ 10.1111/j.1096-3642.2008.00498.x
DOI	https://doi.org/10.5281/zenodo.5114889
persistent identifier	https://treatment.plazi.org/id/AF2487CE-1463-FFF0-FCB4-ECFB31DFFD27
treatment provided by	Carolina
scientific name	Hymedesmia
status	sp. nov.

Treatment

HYMEDESMIA (HYMEDESMIA) RATHLINIA View in CoL SP. NOV.

( FIG. 5A–C View Figure 5 )

Type material: Holotype: specimen in IMS, section and spicule preparation from tissue sample ( Rathlin Island sponge biodiversity project; Damicornis Bay, 55°17.459 ′ N, 06°15.233 ′ W; water depth, 32–35 m; Mc 2792). Collected by C. Goodwin and D. Goodwin, 15 August 2005. GoogleMaps

Paratypes: 11 further specimens (specimen in IMS, section and spicule preparation from tissue sample), all from the Rathlin sponge biodiversity project (Mc2399, 2472, 2644, 2692, 2722, 2743, 2810, 2859, 3115, 3147, and 3150).

Comparative material examined: Hymedesmia versicolor Topsent, 1893 .

DT-86: thick section derived from the holotype. Monaco, 1928, no 42. MNHN .

DT-87: thick section derived from paratype. Station 299, 1908, no. xI 172.19. MNHN .

DT-198: specimen in alcohol. Banyuls. MNHN.

Etymology: Named for Rathlin Island, the type locality.

External morphology: A distinctive sponge, which may be recognised in situ. Forms small patches of 3–5 cm in diameter, often with several patches adjacent to one another; each patch bears one or two oscules. The oscules are combined with inhalent pore sieves at the tip of inflated papillae, which project from the sediment that the sponge is frequently covered in. The colour of the sponge is bright yellow, sometimes with darker yellow or orange lines radiating from the papillae. It turns a dark brown/black in alcohol.

Skeleton: Basal layer of acanthostyles, in which the small acanthostyles are very abundant. The larger acanthostyles tend to be surrounded by the columns of ectosomal spicules. It has ascending columns of ectosomal spicules that are variable in thickness: between 5 and 12 spicules in width. Chelae are present in the surface layer, but are not very abundant. The sponge is ~900-Mm thick.

Spicules:

1. Large acanthostyles: 175–390 Mm (282 Mm) by 10–14 Mm. Spined for between half and two-thirds of their length, with small straight spines. The head is not tylote.

2. Small acanthostyles: 65–125 Mm (103 Mm) by 10–12 Mm. Spined for their whole length, again the head is not tylote. The spines are very large, and are usually straight (although some are very slightly curved).

3. Ectosomal spicules: tylotes 220–335 Mm (280 Mm) by 4–6 Mm, most with both ends tylote, but in some, only one end is swollen.

4. Chelae: arcuate chelae 22.5–27.5 Mm (25 Mm) along shaft, with fairly short alae.

Remarks: The spicules are similar in size to H. versicolor . Hymedesmia versicolor has strongly curved large acanthostyles that have a slightly tylote head, and a largely smooth tip, and are 340–450 Mm by 8–11 Mm (at the head), small acanthostyles that are 115–180 Mm by 7–10 Mm (at the head), ectosomal spicules that are 250–325 Mm by 2–5 Mm, and chelae that are 25–30-Mm long. However, we have examined sections from the type of this species, and a paratype and the skeletal structure precludes its inclusion in the genus Hymedesmia . It has a reticulate choanosomal skeleton formed of bundles of large acanthostyles, which are echinated with smaller ones. There is also a dense layer of strongyles at the surface ( Fig. 6 View Figure 6 ). These characters would indicate inclusion in Lissodendoryx (Ectyodoryx) Lundbeck 1909 . The skeleton is not described in the original description ( Topsent, 1893), or the redescription ( Topsent, 1936). However, Topsent originally placed the species in the genus Myxilla . Further examination of the numerous paratypes is necessary to fully resolve the taxonomy of this species. Topsent (1893, 1936) notes that the colour and the presence of microscleres in this species is variable, and it is possible that it encompasses more than one species, some of which may be Hymedesmia .

Other authors have ascribed specimens to H. versicolor , including Sara (1961), Cabioch (1968), and Boury-Esnault (1971), and there may be a Hymedesmia with similar spiculation that remains undescribed. Unfortunately, none of these authors describe the skeleton of their specimens in detail. Hymedesmia rathlinia sp. nov. differs in spiculation to H. versicolor , in that the spines in the latter are very small, giving the acanthostyles a roughened appearance, whereas the spines in H. rathlinia sp. nov. are pronounced, particularly on the small acanthostyles. Both categories of acanthostyles of H. versicolor are larger than those found in H. rathlinia sp. nov. The ectosomal tylotes of H. versicolor are asymmetrical, with one end tylote and the other tapering to a rounded point, whereas both ends in H. rathlinia sp. nov. are normally symmetrical, with both ends being tylote.

Since the Rathlin survey H. rathlinia sp. nov. has also been found to be present on the Maidens, a group of rocks on the east coast of Northern Ireland.