Echinoderes sp.

Grzelak, Katarzyna & Sørensen, Martin V., 2022, Echinoderes (Kinorhyncha: Cyclorhagida) from the Hikurangi Margin, New Zealand, European Journal of Taxonomy 844, pp. 1-108 : 83-85

Echinoderes sp. aff. E. balerioni

Fig. 33 ; Tables 22–23

Material examined

NEW ZEALAND • 1 ♂; Seamount 310, stn TAN1004/69; 41.3353° S, 176.1882° E; 670 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; NHMD-921971 . Mounted for LM in Fluoromount G on HS slide .

Distribution

Seamount 310, 670 m depth. See Fig. 1 for geographic location of station and Table 1 for station and specimen information.

Brief description and remarks

Echinoderes with middorsal spines on segments 4, 6, and 8 and spines in lateroventral positions on segments 6 to 9. Tubes present in subdorsal, sublateral, and ventrolateral positions on segment 2, lateroventral positions on segment 5, and lateral accessory positions on segment 8. Tergal extensions conspicuously long and spiniform.

Adult with head, neck and eleven trunk segments. Overview of measurements and dimensions in Table 22. Only a single specimen was available for LM examination, and thus some cuticular structures such as sensory spots or glandular cell outlets might not have been identified. Therefore, lack of information about structures reported in Table 23 should not necessarily be understood as a confirmation of their absence.

Segments 1 and 2 composed of complete cuticular rings. Segment 1 with sensory spots in subdorsal positions, and with glandular cell outlets type 1 in middorsal and ventrolateral positions ( Fig. 33B– C ). Posterior segment margin of this and following nine segments with well-developed pectinate fringe tips. Segment 2 with three pairs of tubes in subdorsal, sublateral and ventrolateral positions ( Fig. 33B–D ). Sensory spots observed in ventromedial positions and glandular cell outlets type 1 in middorsal position only. Cuticular hairs on this and following segments abundant, distributed evenly around segment. Segments 3 to 11 consists of one tergal and two sternal plates. Segment 3 with sensory spots in subdorsal positions, and glandular cell outlets type 1 in middorsal and ventromedial positions. Segment 4 with relatively short (23 µm) middorsal spine ( Fig. 33B ), and glandular cell outlets type 1 located paradorsally and ventromedially; no sensory spots observed. Pectinate fringe with longer fringe tips than on preceding segments. Segment 5 with lateroventral tubes ( Fig. 33C ); sensory spots present in subdorsal, midlateral and ventromedial positions, and glandular cell outlets type 1 located middorsally and ventromedially ( Fig. 33B–D ). Segment 6 with spines in middorsal and lateroventral positions ( Fig. 33F–G ), paradorsal, midlateral and ventromedial sensory spots, and glandular cell outlets type 1 located paradorsally and ventromedially ( Fig. 33G ). Segment 7 with spines in lateroventral positions, subdorsal and midlateral sensory spots, and glandular cell outlets type 1 present in middorsal and ventromedial positions ( Fig. 33F–G ). Segment 8 with spines in middorsal and lateroventral positions, and tubes in lateral accessory positions ( Fig. 33F–G ); sensory spots observed only in paradorsal positions; glandular cell outlets type 1 present in paradorsal and ventromedial positions. Segment 9 with spines in lateroventral positions ( Fig. 33G ); sensory spots located in paradorsal, subdorsal and ventrolateral positions, and glandular cell outlets type 1 present in paradorsal and ventromedial positions ( Fig. 33G ); small sieve plate located in lateral accessory positions ( Fig. 33G ). Segment 10 with glandular cell outlets type 1 located in paraventral positions and with two located middorsally ( Fig. 33G ); no sensory spots observed. Segment 11 with pair of relatively long lateral terminal spines ( Fig. 33A,H ). Three pairs of long penile spines present ( Fig. 33E, H ). Tergal extensions conspicuously long and spiniform ( Fig. 33H ). No cuticular hairs nor any other cuticular structures visible on this segment.

Echinoderes balerioni is a species described from 880 m depth at the Yermak Plateau, north of Svalbard ( Grzelak & Sørensen 2019). There is no other species with acicular spines in middorsal position on segments 4, 6, and 8, three pairs of tubes on segment 2 and conspicuously long tergal extensions. The latter constitutes almost 18.3% of the total trunk length and this is the most prominent feature of E. balerioni . The lengths of the tergal extensions in this species are comparable only with those of E. cernunnos , E. yamasakii and E. galadrielae sp. nov. – the species with the longest extensions ( Sørensen et al. 2012, 2018). However, all three species are easily distinguished from E. balerioni by their five middorsal spines on segments 4 to 8 and the presence of glandular cell outlets type 2.

The individual examined for the present study closely follows the morphology of E. balerioni , in particular in the appearance of tergal extensions (see Table 22). Most morphometric data, general trunk appearance and other cuticular structures, such as arrangements of spines and tubes (however, see below), also followed those reported for the Arctic specimen (compare Table 23 in present contribution with Grzelak & Sørensen 2019: table 3). Nevertheless, we cannot identify the examined specimen as E. balerioni with certainty because of certain morphological differences. Considering the geographical distance between northern Svalbard and New Zealand and the fact that in both cases only a single specimen was available for LM investigation, we cannot be sure whether the observed discrepancies are the result of inter-population variations or indicate the presence of two, closely related species.

Due to the fact that no specimen was available for SEM investigation, Grzelak & Sørensen (2019) did not provide details about sensory spots on segments 2 to 11, and a comparison of their patterns between the specimens from the Arctic and New Zealand is therefore not possible. The major difference between the specimen from New Zealand and E. balerioni from the Arctic is the presence of tubes on segment 2 in the subdorsal rather than the laterodorsal positions. Both specimens also slightly differ in terms of morphometric details. The specimen from New Zealand is smaller (TL: 227 µm vs 300 µm) and has a longer middorsal spine on segment 8 (MDS8: 50 µm vs 35 µm) than E. balerioni from the type locality. Nevertheless, differences in trunk length do not result in differences in TE/TL or LTS/TL ratios ( Table 22), which confirms the close similarity between specimens. Interestingly, the variation in the arrangement of the tubes on segment 2 might have resulted from inter-population variations. Recently, specimens from the Bering Sea, Alaska, clearly similar to E. balerioni , have been investigated by the first author of the present study, and all of them possess tubes on segment 2, in subdorsal, laterodorsal, sublateral and ventrolateral positions (Grzelak, unpubl. obs.). A variation regarding the presence or absence of tubes has previously been observed for several species, e.g., E. arlis , E. daenerysae , E. eximus , E. rhaegali and E. dalzottoi sp. nov., and it occurred within the same population, randomly and independently of developmental stage or sex ( Grzelak & Sørensen 2018, 2019; present study). However, uncovering this variation would require a certain number of specimens, which is why the very low number of individuals of E. balerioni from the Arctic and the single one examined in the present study hamper proper comparison, and leave us uncertain about the specimen’s identity. Nevertheless, our results, as well as the observations made by Grzelak for Alaskan specimens, stress the necessity of further investigations of this interesting species, both in terms of intra- or interspecific variation and its geographical distribution.

Figures

Fig. 33. Light micrographs showing overview and details of Echinoderes sp. aff. E. balerioni, ♂ (NHMD-921971). A. Ventral overview. B. Segments 1 to 5, dorsal view. C. Segments 1 to 5, ventral view. D. Segments 2 to 5, dorsal view. E. Segments 10 to 11, dorsal view. F. Segments 6 to 10, dorsal view. G. Segments 6 to 10, ventral view. H. Segments 10 to 11, ventral view. Abbreviations: see Material and methods.

Fig. 1. Map showing the sampling stations. Colour codes indicate slopes (red), canyons (green), and seamounts (yellow). Inset shows New Zealand with a frame marking the sampling area.