Hymedesmia sp. 3

Fig. 20

Material examined

SWEDEN • 1 spec.; Lunneviken; 59.0546° N, 11.169° E; 30 m depth; 16 Sep. 2018; Mats Larsson leg. [MM-180916-1]; SCUBA; LAR-180918-7197–7198; GenBank no.: OM436233 (coxI); voucher: GNM Porifera 998 .

Description

The specimen has a thin encrusting morphology. The colour alive was saffron yellow and slightly translucent, i.e., the substrate colour and structure can be seen through (Fig. 20A). The colour in ethanol is dark brown. The surface does not have obvious oscula and the canals of the aquiferous system are partially visible and slightly raised from the surface (Fig. 20B). The pores are visible, scattered regularly and not in pore-sieves.

Skeleton

Due to the size and consistency of the fragment, we could not do a section. The skeleton is composed of one single size class of acanthostyles (Fig. 20C) measuring 66.1– 122.9 –171.8 ±27.44 ×2.5– 7.0 – 12.4 ±2.59 µm (N=31), and anisotylotes (Fig. 20D), measuring 126.4– 196.8– 251.4 ±29.74 ×0.4– 1.4– 3.0± 0.54 µm (N=39).

Remarks

The placement of this specimen within the genus Hymedesmia was primarily based on the presence of tylotes (Fig.20C) and the coxI sequence. This specimen appears as sister species to specimens identified as H. primitiva (Fig. 2). There are 31 accepted species of Hymedesmia (Stylopus), a subgenus characterised by the lack of chelae. However, there are only 15 species for the NEA and Mediterranean, none of which is described to only have small acanthostyles or the very small anisotylotes, as observed in this specimen. Among the species reported for the South Atlantic, Pacific or Indian oceans, only two seem to resemble what we observe in our specimen: Hymedemia parvispicula (Burton & Rao, 1932) from the Mergui Archipelago (Andaman Sea, Indian Ocean), and b) Hymedesmia alcoladoi van Soest, 2017 from the Guyana Shelf. Our specimen seems to resemble H. parvispicula more closely, with the smooth surface, without visible pores or oscula, and the presence of small acanthostyles and anisotylotes. However, the holotype of H. parvispicula is yellow in ‘spirit’ contrasting with the dark brown colour of our specimen. Furthermore, the spicules of H. parvispicula are considerably smaller (acanthostyles: 130–105×4 µm and anisotylotes 21×3 µm) (Burton & Rao 1932) than what we measure in our specimen. As for the species H. alcoladoi, the skeleton is composed of acanthostyles and ectosomal spicules with sizes similar to what we observe in our specimen, 213–62 ×17–6.5 µm and, 151–222×2–4 µm, respectively (van Soest 2017). However, the ectosomal spicules for H. alcoladoi are tornotes with mucronate ends whereas our specimen presents tylotes. Additionally, H. alcoladoi presents two size classes of acanthostyles while we could only observe one in our specimen. Therefore, we are hesitant to assign this specimen to either H. alcoladoi or H. parvispicula, two species furthermore described from geographically remote areas and in habitats different from the shallow west coast waters of Sweden. However, we refrain from describing this specimen as a new species and prefer to wait for additional specimens and/or Hymedesmia sequences.