Hymedesmia stellifera Goodwin & Picton 2009

Hymedesmia stellifera Goodwin & Picton, 2009 Fig. 16 Hymedesmia stellifera Goodwin & Picton, 2009: 905–906, fig. 8a–b. Material examined SWEDEN • 1 spec.; Yttre Vattenholmen; 58.8754° N, 11.1056° E; 27 m depth; 16 Nov. 2019; Mats Larsson leg.[MM-191116-1]; SCUBA; LAR-191116-PB160445, 47–48;GenBank no.: OM415624 (28S D3-D5); voucher: GNM Porifera 1122. Description The specimen is an orange-yellow crust growing on a nearly vertical rock (Fig. 16A). The colour in ethanol is beige with some dark spots. Pores are visible and oscula are very conspicuous, surrounded by excurrent channels and possessing small translucent rims (Fig. 16B). The oscula are regularly distributed giving the surface a star-like pattern (Fig. 16A). Pore sieves are absent. Skeleton The skeleton is composed of two size classes of acanthostyles erected with their heads in the basal layer and ectosomal styles raised in columns (Fig. 16C–D). Megascleres are acanthostyles of two size classes: a) The large acanthostyles (Fig. 14D) are sparsely spined at their base and smooth in the shaft, measuring 277.7– 352.3– 459.8 ± 52.58 ×6.8– 9.4– 13.0 ± 1.97 µm (N =14), and b) small acanthostyles are fully spined (Fig. 16D), with a small head, measuring 39.3– 95.1 –124.6 ± 16.34× 3.4– 7.6 –12.8 ± 2.5 µm (N=38), c) ectosomal styles, with a poorly developed tyloted head, measuring 206– 282.2 –322.5 ±24.27 ×1.6– 5.6 –9.6 ± 1.7 µm (N =36). The acanthostyles present forms that are constituted by two acanthostyles fused by the heads; however, this form is rare for the larger acanthostyles. The microscleres are: chelae (Fig. 16E), rare, measuring 12.8– 17.0 –21.5 ±2.82 µm (N =15), and sigmas (Fig. 16F) measuring 10.9– 16.5 –21.2± 2.51 µm (N =32). Ecology and distribution This species was first described between Northern Ireland and western Scotland from 25 to 32 m depth. However, there has been a recent report from southern Norway (community iNaturalist 2020; GBIF.org 2023), and given that this species has been only recently described, it is natural that its real bathymetric and geographical distribution could be much larger than what is currently known. Our specimen represents a new report for Sweden. Remarks The specimen examined has an external morphology conforming to the original description (Goodwin & Picton 2009). Furthermore, the shape of the megascleres are overall concordant with the original description, with the exception of the small acanthostyles which present fused forms, and are slightly larger (39.3– 95.1 –124.6 ×3.4– 7.6 –12.8) than what has been previously reported (65– 79 –95 ×8–10) (Goodwin & Picton 2009). However, the size range of the microscleres seems to be different than what was originally reported: here, both chelae and sigmas had the same size range while there was an obvious size class difference between sigmas and chelae in the type material (sigmas: 10–12 µm and, chelae: 15–18 µm) (Goodwin & Picton 2009). These differences might be associated with different environments, populations or simply the number of spicules measured. Since only one specimen was collected it is difficult to generalize these observations. This species was originally described within the genus Hymedesmia. However, the 28S D3-D5 sequence of our specimen does not group with sequences of Hymedesmia species (Fig. 3) but with Monanchora arbuscula (Duchassaing & Michelotti, 1864) belonging to the Crambeidae Lévi, 1969 (see Supp. file. 2 for more information in this sequence). This grouping is very well supported (bt ≥95%) and there is a sequence similarity of 97.22%. H. stellifera furthermore presents acanthostyles similar to what is reported for Hymedesmia zetlandica (Bowerbank, 1864), which is the type species of the genus, thus suggesting that the genus Hymedesmia could also belong to the Crambeidae. Alander (1937) described Hymoxenia inflata Alander, 1937 (now Hymesdesmia inflata), which also possesses acanthostyles similar to the H. zetlandica thus likely belonging to the same group. For now, it can be concluded that the genus Hymedesmia is polyphyletic but we cannot revise the classification based on our limitated sampling, with no sequences from the type species.