Hymedesmia jecusculum Bowerbank 1866

Hymedesmia jecusculum Bowerbank, 1866 Fig. 15 Hymeniacidon jecusculum Bowerbank 1866: 198–200. Hymedesmia jecusculum – Ackers 2007: 100. Material examined (4 specimens) SWEDEN • 1 spec.; Lunneviken; 59.0546° N, 11.1690° E; 30 m depth; 18 Sep. 2018; Mats Larsson leg. [MM-180916-1]; SCUBA; LAR-180918-7215, 7217; GenBank no.: OM436251 (coxI); voucher: GNM Porifera 1071 • 1 spec.; same collection data as for preceding; LAR-180918-7254, 7256; voucher: GNM Porifera 1072; 23 Sep. 2018; Mats Larsson leg. [MM-180923-1]; SCUBA; LAR-180923- 7367–7368, 7372; voucher: GNM Porifera 1073 • 1 spec.; Bergylteskär; 58.8290° N, 11.0831° E; 30 m depth; 9 Dec. 2018; Mats Larsson leg. [MM-181209-1]; SCUBA; LAR-181209-8217, 8219, 8222; GenBank no.: OM436265 (coxI); voucher: GNM Porifera 1074 • 1 spec.; Yttre Vattenholmen; 58.8754° N, 11.1056° E; 30 m depth; 16 Nov. 2019; Mats Larsson leg. [MM-191116-1]; SCUBA; LAR-191116-PB160453–55; voucher: GNM Porifera 1075. Description The specimens have a thin incrusting morphology, with a micro-velvety to smooth surface. Oscula are not visible, and pores are concentrated in elevated pore sieves (Fig. 15A). The natural colour ranges from dark orange and red to pale reddish-white, turning beige in ethanol. Skeleton Megascleres are acanthostyles curved near the base and symmetrical tornotes. The acanthostyles present two size classes: spined at the base up to 2/3 of the shaft measuring 360 ×7.5 µm (N =4), and fully spined with 120× 5 µm (N= 3) in size. The tornotes are symmetrical, measuring 277.0– 314.6 – 350.4± 22.38 ×3.1– 4.6– 6.0± 0.92 µm (N=8). Microscleres, are arcuate 20 µm long isochelae (Fig. 15B–C). Remarks The species Hymedesmia jecusculum is a new report for Sweden. However, there is significant morphological similarity between H. jecusculum and Phorbas fictitius (Bowerbank, 1866). The latter has been previously reported for Sweden by Alander (1942), under the name Hymedesmia fictitia. However, we believe this identification to be correct given that Alander’s description is closely resembling what has previously been reported for P. fictitius. Furthermore, Alander (1942) reported for the Norwegian parts of Skagerrak a single specimen of Hymedesmia proteidea (Schmidt, 1868) (spelled as Hymedesmia proteida), which is now synonymised with P. fictitius. We argue that this indicates that Alander considered H. proteidea and H. fictitia to be different species, which could indicate that the specimen identified as H. proteidea could be H. jecusculum. However, Alander’s description of H. proteidea is insufficient to test this hypothesis. There are some consistent morphological differences between specimens of H. jescusculum and P. fictitius: type of tornotes, the arrangement of spines on acanthostyles, and slight differences in external morphology features. While H. jecusculum possesses symmetrical tornotes and primary acanthostyles with spines almost entirely on the shaft, P. fictitius possesses anisotornotes and primary acanthostyles with spines only at the base. Regarding the external morphology, P. fictitius specimens are usually thick encrusting or cushions and a surface densely covered with areolae (depressions of pore sieves). This contrasts with the thin encrusting sheet-like morphology and the elevated pore sieves typical for H. jecusculum. In spite of these morphological differences, the coxI sequences of the specimens identified as P. fictitius and H. jecusculum are identical or 1 bp difference (Fig. 3), thus it is possible that these two names refer to different growth stages of the same species. A similar remark was made for Phorbas dives (Topsent 1891). Specimens could present skeletal architecture ranging from hymedesmoid architecture, i.e., single subtylostyles erected from the basal plate, to the typical Phorbas architecture, i.e., plumose tracts of subtylostyles (Soest 2002; Topsent 1891). This leads us to question the validity and circumscriptions of the genera Hymedesmia Bowerbank, 1864 and Phorbas Duchassaing & Michelotti, 1864. However, both the assessment of the validity of these two genera, and whether P. fictitius and H. jecusculum are different species or synonyms are beyond the scope of this study.