Echinoderes aff. beringiensis, Adrianov & Maiorova, 2022

Sørensen, Martin V., Macheriotou, Lara, Braeckman, Ulrike, Smith, Craig R. & Ingels, Jeroen, 2025, Antarctic Kinorhyncha: Seven new species from the Antarctic Peninsula, European Journal of Taxonomy 1000 (1), pp. 1-102 : 80-89

Echinoderes aff. beringiensis / romanoi / xalkutaat

Figs 27–28 , Tables 21–22

Material examined

ANTARCTICA – Antarctic Peninsula • 1 ♀ (mounted for LM in Fluoromount G on HS slide); CRS 1793; 64°39.53′ S, 62°55.03′ W; 701 m b.s.l.; 11 Apr. 2016; FjordEco 2; soft sediment; NHMD 1790694 • 1 ♂ (mounted for SEM); CRS 1793; 64°39.53′ S, 62°55.03′ W; 701 m b.s.l.; 11 Apr. 2016; FjordEco 2; soft sediment; MVS • 1 ♂, 3 ♀♀ (mounted for LM in Fluoromount G on HS slide.); CRS 1809; 64°39.59′ S, 62°55.09′ W; 694 m b.s.l.; 15 Apr. 2016; FjordEco 2; soft sediment; NHMD 1790695 to 1790698 • 2 ♂♂, 3 ♀♀ (mounted for SEM); CRS 1809; 64°39.59′ S, 62°55.09′ W; 694 m b.s.l.; 15 Apr. 2016; FjordEco 2; soft sediment; MVS • 2 ♀♀ (mounted for SEM); CRS 1832; 64°39.30′ S, 62°55.98′ W; 631 m b.s.l.; 21 Apr. 2016; FjordEco 2; soft sediment; MVS .

Concise description

GENERAL. An overview ( Fig. 27A ) of measurements and dimensions is given in Table 21. Distributions of cuticular structures, i.e., sensory spots, glandular cell outlets, spines and tubes, are summarized in Table 22.

SEGMENT 1. Consists of a complete cuticular ring. Sensory spots are present in subdorsal, laterodorsal, and ventromedial positions; sensory spots are minute, and consist of relatively few, very short micropapillae arranged around two pores. Glandular cell outlets type 1 are present in middorsal and lateroventral positions. Cuticular hairs are arranged in four to five rows: anterior rows are present only on dorsal side, between midlateral positions, whereas the posteriormost row extends around the entire segment; an additional short row is present between the ventromedial sensory spots. The posterior segment margin is straight and terminates in a pectinate fringe with broad and well-developed fringe tips; fringe tips on ventral side are slightly longer than those on the lateral and dorsal sides ( Figs 27B–C , 28A–C ).

SEGMENT 2. Consists of a complete cuticular ring, without any indication of a midventral fissure.Glandular cell outlets type 2 are present in subdorsal, laterodorsal, sublateral, and ventrolateral positions. Sensory spots are present in middorsal, laterodorsal, midlateral, and ventromedial positions; the micropapillary areas around the sensory spots on this, and all following segments, are small and rounded, and point in a posterior direction; one or two long and rigid hairs (extremely extended micropapillae?) project from the micropapillary area. Glandular cell outlets type 1 are present in middorsal and ventromedial positions. Fairly long bracteate cuticular hairs are arranged in four to five transverse rows around the segment. The posterior segment margin is straight, terminating in uniform, well-developed fringe tips ( Figs 27B–C , 28A–C ).

SEGMENT 3. As following seven segments, consisting of one tergal and two sternal plates. Sensory spots are present in subdorsal (not present in all specimens) and sublateral positions, and glandular cell outlets type 1 in middorsal and ventromedial positions. Cuticular hairs present in four to five rows on the tergal and lateral halves of the sternal plates, except in hair-less midlateral areas; paraventral areas completely devoid of hairs or hair-like extensions. Posterior segment margin straight and pectinate fringe as on preceding segment ( Figs 27B–C , 28D–F ).

SEGMENT 4. With spine in middorsal position. Sensory spots are not present. Glandular cell outlets type 1 are present in paradorsal and ventromedial positions. Cuticular hairs as on preceding segment, but now arranged in five to six rows. Posterior segment margin and pectinate fringe as on preceding segment ( Figs 27B–C , 28D–F ).

SEGMENT 5. With spine in middorsal position and tubes in lateroventral positions. Glandular cell outlets type 2 are present in midlateral positions. Sensory spots present in subdorsal and ventromedial positions, and glandular cell outlets type 1 in paradorsal and ventromedial positions. Cuticular hairs, posterior segment margin, and pectinate fringe as on preceding segment ( Figs 27B–D , 28F–I ).

SEGMENT 6. With spines in middorsal and lateroventral positions. Sensory spots present in paradorsal, subdorsal, midlateral, and ventromedial positions; ventromedial sensory spots situated closer to midventral articulation than those on preceding segment. Glandular cell outlets type 1 present in paradorsal and ventromedial positions. Cuticular hairs, posterior segment margin, and pectinate fringe as on preceding segment ( Figs 27B–F , 28G–I ).

SEGMENT 7. With spines in middorsal and lateroventral positions. Sensory spots present in paradorsal, midlateral, and ventromedial positions; ventromedial sensory spots situated more laterally than those on preceding segment and aligned with those on segment 5. Glandular cell outlets type 1 present in paradorsal and ventromedial positions. Cuticular hairs as on preceding segment, except for middorsal to paradorsal positions which are also devoid of hairs. Posterior segment margin and pectinate fringe as on preceding segment ( Figs 27D–F , 28I–L ).

SEGMENT 8. With spines in middorsal and lateroventral positions. Glandular cell outlets type 2 are present in sublateral positions. Sensory spots present in paradorsal positions only, and glandular cell outlets type 1 in paradorsal and ventromedial positions. Cuticular hairs as on preceding segment, but the midlateral hairless areas have moved to more laterodorsal positions. Posterior segment margin and pectinate fringe as on preceding segment ( Figs 27D–F , 28L–N ). SEGMENT 9. With spines in lateroventral positions. Sensory spots present in paradorsal, subdorsal, midlateral, and ventrolateral positions.Glandular cell outlets type 1present in paradorsal and ventromedial positions. Small rounded sieve plates located in sublateral positions. Cuticular hairs, posterior segment margin, and pectinate fringe as on preceding segment ( Figs 27E–F, H , 28O–Q ).

SEGMENT 10. With glandular cell outlets type 2 in laterodorsal positions near posterior segment margin. Sensory spots present in subdorsal and ventrolateral positions. Glandular cell outlets type 1 present as two longitudinally arranged outlets in middorsal position, and in ventromedial positions. Cuticular hair covering reduced to a small patch between subdorsal sensory spots, and otherwise only hairs in laterodorsal to ventromedial areas. The posterior segment margin of the tergal plate is straight, with minute fringe tips. Sternal plate margins oblique, with longer fringe tips in ventromedial and paraventral areas ( Figs 27G–J , 28R–U ).

SEGMENT 11. With lateral terminal spines and a middorsal protuberance emerging from the intersegmental zone between segments 10 and 11. The segment consists of two tergal and two sternal plates, but visualisation of the middorsal fissure between the tergal plates is obscured by the overlaying protuberance. Females with lateral terminal accessory spines; males with thin, tubular dorsal and ventral penile spines; medial pair of penile spines cone-shaped and well-developed. Males in addition with thin tube, attaching between dorsal and medial penile spines; the tube diameter is> 50% of the dorsal penile spine diameter and>20% of the penile spine length. Sensory spots present in paradorsal positions only. The segment is devoid of cuticular hairs, but has scattered hair-like extensions along the inferior margins of the tergal plates. Tergal extensions are triangular, with pointed tips. Sternal extensions short, broadly triangular, and not extending beyond tergal extensions ( Figs 27G–J , 28R–U ).

Distribution

Antarctic Peninsula: Gerlache Strait, 631 to 701 m b.s.l. See Fig. 1 for geographic overview of stations and Table 1 for station and specimen information.

Diagnostic remarks

Identification of these specimens turned out to be difficult, since they show a very close resemblance with no less than three congeners, i.e., E. beringiensis , E. romanoi , and E. xalkutaat . This high level of similarity not only hampers identification of the Antarctic specimens, but also indicates that the three species in question potentially could be synonymous. In the following, comparison of the Antarctic specimens with each of the three species will be carried out in separate sections. In addition, a comparison with E. angustus , E. aff. angustus (addressed above) and E. aff. beringiensis / galadrielae sensu Grzelak & Sørensen (2022) will be included, since these species also share so many similarities that it could indicate the existence of a new species group. Observed differences between the species are summarised in Table 23.

Comparison with E. beringiensis

The distribution of spines and sensory spots on segments 1 to 9 is nearly identical in E. beringiensis and the Antarctic Echinoderes aff. beringiensis / romanoi / xalkutaat ( Adrianov & Maiorova 2022; Table 22 in present contribution). The only detectable difference regards the tubes on segment 5, which are displaced to a lateral accessory position in E. beringiensis (see Adrianov & Maiorova 2022: figs 5a, 6a). The two species also share the same segment compositions, including the midtergal division of segment 11. Morphometric ranges for trunk and spine lengths are also overlapping in nearly all cases, except regarding the lateral terminal spines, which are longer in the Antarctic species, 177–205 µm vs 123–168 µm ( Table 21). The potential main differences between the two species might be found in their distribution of glandular cell outlets type 2. They have outlets in identical positions on segments 2 and 8. However, adult female specimens of E. beringiensis appear to have two pairs of outlets on segment 8, in midlateral and sublateral positions, as opposed to only a single pair in sublateral positions in the Antarctic specimens. Having a double set of large glandular cell outlets 2 type on segment 8 is truly a unique trait among species of Echinoderes , but the diagnostic value of the character gets challenged by the fact that it has only been observed in five (?) adult females (and documented in one), whereas males and younger females only have the much more common sublateral pair ( Adrianov & Maiorova 2022). It would be desirable to obtain a better understanding of this trait and, eventually through observation of a larger sample size, decide whether this is truly a consistent character or if the double outlet pairs are abnormalities.

Another potential difference might be found in the laterodorsal positions of the posterior segment margin of segment 10, where E. beringiensis is reported to have sensory spots ( Adrianov & Maiorova 2022), unlike the Antarctic specimens which have glandular cell outlets type 2 in these positions. However, these structures are quite well documented in the description of E. beringiensis , and fig. 8e in Adrianov & Maiorova (2022) clearly shows that the structures are glandular cell outlets type 2 rather than sensory spots.

Otherwise, there are no conspicuous differences between E. beringiensis and the Antarctic Echinoderes aff. beringiensis / romanoi / xalkutaat , and potential differences narrow down to the lengths of their lateral terminal spines, and the somehow questionable double pair of glandular cell outlets type 2 on segment 8.

Comparison with Echinoderes aff. beringiensis / galadrielae sensu Grzelak & Sørensen (2022)

Following their description of E. galadrielae from New Zealand, Grzelak & Sørensen (2022) reported the co-occurring species Echinoderes aff. beringiensis / galadrielae , which appeared to “represent an intermediate between E. galadrielae sp. nov. and E. beringiensis ” ( Grzelak & Sørensen 2022: 82) . The distribution of cuticular structures generally followed the pattern of E. galadrielae , whereas the tergal extensions were similar with those in E. beringiensis and thus differing considerably from the long and slender extensions in E. galadrielae .

Comparison with Echinoderes aff. beringiensis / romanoi / xalkutaat reveals that the Antarctic specimens are nearly identical with Echinoderes aff. beringiensis / galadrielae . The spine/tube pattern of the two species differs only in the position of tubes on segment 5 (lateral accessory vs lateroventral), and even the spine length ranges overlap. The only conspicuous morphometric difference between the two species regards the considerable difference in trunk length, i.e., 271–313 µm in the Antarctic species vs 210–235 µm in the New Zealand species. There are, however, more considerable differences in the sensory spot distribution, as the New Zealand species apparently lacks ventromedial sensory spots on segments 1, 5, and 7, and subdorsal sensory spots on segment 6, which are all present in the Antarctic species. The absence of subdorsal structures on segment 6 could potentially be due to intraspecific variation, and the missing ones on segments 5 and 7 might have been hidden under dirt, but the absence of ventromedial sensory spots on segment 1 is a distinct difference that could speak against conspecificity.

Echinoderes aff. beringiensis / galadrielae is reported to have males with short laterodorsal tubes on segment 10, whereas the females have ‘similar slit-like, fringed openings’ ( Grzelak & Sørensen 2022). However, a re-examination of the specimens clearly shows that these structures are glandular cell outlets type 2, which corresponds to the morphology in the Antarctic specimens.

Segment 11 is similar in composition, i.e., consisting of two tergal and two sternal plates, but it differs by the lack of a middorsal protuberance in the New Zealand species. An additional apparent difference between the two species regards the cuticular hair covering, which generally is much denser on the Antarctic specimens.

Comparison with E. romanoi

The comparison of the Antarctic species with E. romanoi from the Gulf of Mexico prompted some re-examinations of E. romanoi type specimens as well as non-types mounted for SEM. Unfortunately, the latter were in a rather sad condition, but new and significant information was nevertheless obtained. Most importantly, it could be documented that E. romanoi has laterodorsal glandular cell outlets on segment 10, and that the tergal plate of segment 11 has a middorsal fissure ( Fig. 29B, D ). Furthermore, some minor details in the original description could be corrected, i.e., 1) that the reported sublateral glandular cell outlets type 1 on segment 1 are muscular attachment sites, 2) that a middorsal sensory spot and glandular cell outlet type 1 are present on segment 2, 3) that segment 3 has a single middorsal glandular cell outlet type 1, rather than a pair of paradorsal outlets, and 4) that laterodorsal sensory spots on segment 10 are missing, whereas ventrolateral ones are present. Likewise, type specimens were remeasured ( Table 21), and a couple of potential pre-adults that were part of the original morphometric data provided by Landers & Sørensen (2016) were excluded.

With this new information established, the spine, sensory spot, and glandular cell outlet patterns for the Antarctic species and E. romanoi are the same, and differences come down to morphometrics and the absence of a middorsal protuberance on segment 11 in E. romanoi . Morphometrically, E. romanoi differ from the Antarctic species by being smaller. The trunk is shorter, 196–247 µm vs 271–313 µm, and all middorsal and laterodorsal spines are generally about 20% shorter in E. romanoi (see Table 21). Only the length ranges of the lateral terminal spines are overlapping in the two species.

Comparison with E. xalkutaat

Echinoderes xalkutaat is known from the Gulf of California, and the description was based on three specimens mounted for LM ( Cepeda et al. 2019b). The condition of the type material could have been better, and with the lack of information from SEM, some characters in E. xalkutaat remain to be confirmed. However, it is clear that the distribution patterns of spines, tubes, and glandular cell outlets types 1 and 2 are identical with the patterns in the Antarctic species. Morphometrically, ranges of trunk and spine lengths are also overlapping for the two species ( Table 21).

Potential differences might be found in the sensory spot distribution and characters related to the terminal segment. As for the latter, E. xalkutaat is described as having a terminal segment with a complete tergal plate and no middorsal protuberance. However, due to the condition of the type specimens, this information needs to be validated. It is correct that there is no evidence for the presence of a protuberance, but the dorsal view of segment 11 shown in fig. 16i by Cepeda et al. (2019a) actually has indications of a middorsal fissure on the segment, suggesting that the tergal plate could be split into two. Regarding sensory spots, the main difference appears to be expressed in the dorsal series, which are more laterodorsal in E. xalkutaat , as opposed to subdorsal in the Antarctic specimens, but again, confirmation from SEM would be desirable.

Comparison with Arctic E. angustus and Antarctic E. angustus and E. aff. angustus

The Arctic species E. angustus and the Antarctic E. angustus and E. aff. angustus clearly differ from Echinoderes aff. beringiensis / romanoi / xalkutaat and the other species discussed above by having subdorsal glandular cell outlets on segment 4. They have, however, been included in the comparison because of the striking similarities regarding all other cuticular structures. Morphometrically, E. angustus and the Antarctic, potentially conspecific population are in the upper range or larger than Echinoderes aff. beringiensis / romanoi / xalkutaat , both regarding trunk and lateral terminal spine lengths, but the ranges of other spines are overlapping. When it comes to cuticular hairs, spines, tubes, and glandular cell outlets (except type 2 outlets on segment 4), the species are basically identical, which stresses the close phylogenetic relationship between the species.

In conclusion, E. angustus and the Antarctic E. angustus and E. aff. angustus are easily distinguished from the other species in question based on their presence of subdorsal glandular cell outlets type 2 on segment 4. When it comes to the remaining species, the differential characters are much more subtle, and clear species barriers are questionable. Echinoderes beringiensis might be distinguished by its double set of glandular cell outlets type 2 on segment 8 in females, but since this character does not appear consistently – not even amongst females – its taxonomic significance needs to be validated. Echinoderes aff. beringiensis / galadrielae from New Zealand is perhaps the potential species that stands out the most, by its consistent lack of ventromedial sensory spots on segment 1. At the same time, it is also smaller than the other species, and the range of its trunk length only overlaps with that of E. romanoi . The latter species does not really stand out in any conspicuous way. One potential differential character could be the absence of a middorsal protuberance on segment 11, but since we have very limited understanding of the variability and taxonomic significance of this character, we would be hesitant about basing the species diagnosis exclusively on this trait. Echinoderes xalkutaat might be recognised by its slightly different sensory spot pattern, but since the species description is based on LM observations of very few specimens in relatively poor condition, the general morphology of this species needs to be validated. Thus, to sum up, it is not possible to assign the Antarctic Echinoderes aff. beringiensis / romanoi / xalkutaat to any known species. Instead, the three candidate species could potentially be synonymous, and morphological re-examinations, or ideally molecular barcoding, are required to solve the taxonomic nature of these species.

Figures

Fig. 27. Light micrographs showing overviews and details of Echinoderes aff. beringiensis/romanoi/ xalkutaat. A–F, I–J. Female (NHMD 1790694). G–H. Male (NHMD 1790696). A. Ventral overview. B. Segments 1 to 6, dorsal view. C. Segments 1 to 6, ventral view. D. Segments 5 to 8, focused mid- to sublaterally. E. Segments 6 to 9, dorsal view. F. Segments 6 to 9, ventral view. G. Segments 10 to 11, dorsal view. H. Segments 9 to 11, focused slightly deeper than G, showing male sexual dimorphism. I. Segments 10 to 11, focused at tergal extensions. J. Segments 10 to 11, ventral view, showing female sexual dimorphism. Scale bars: A = 100 µm; B–F, H = 20 µm; G, I–J = 15 µm.

Fig. 28. Scanning electron micrographs showing overviews and details of Echinoderes aff. beringiensis/ romanoi/xalkutaat. A. Segments 1 to 2, dorsal view. B. Segments 1 to 2, left lateral view. C. Segments 1 to 2, ventral view. D. Segments 3 to 4, dorsal view. E. Segments 3 to 4, left lateral view. F. Segments 3 to 5, ventral view. G. Segments 5 to 6, dorsal view. H. Segments 5 to 6, left lateral view. I. Segments 5 to 7, ventral view. J. Segment 7, dorsal view. K. Segment 7, left lateral view. L. Segments 7 to 8, ventral view. M. Segment 8, dorsal view. N. Segment 8, left lateral view. O. Segment 9, ventral view. P. Segment 9, dorsal view. Q. Segment 9, left lateral view. R. Segments 10 (posterior part) to 11, ventral view, showing female sexual dimorphism. S. Segments 10 to 11, dorsal view, showing male sexual dimorphism. T. Segments 10 to 11, left lateral view, showing male sexual dimorphism. U. Segments 10 (posterior part) to 11, dorsal view, showing female sexual dimorphism. All scale bars = 15 µm.

Fig. 1. Map showing the sampling stations. A. Overview of Antarctica, with the Antarctic Peninsula framed. Previous records of Polacanthoderes martinezi Sørensen, 2008 (green dots) and P. shiraseae Yamasaki et al., 2022 (red dots) are marked. B. Antarctic Peninsula with sampling area framed. C. Sampling area with station numbers and stations indicated as yellow dots. Study sites in Andvord Bay refer to OBA – Outer Basin A; MBA – Middle Basin A; IBB – Inner Basin B. Only stations yielding adult kinorhynch specimens are included.

Fig. 29. Light micrographs (A–C) and scanning electron micrographs (D) showing segments 10 to 11, dorsal view, in selected Echinoderes spp. A. Female, holotype of E. pennaki Higgins, 1960 (USNM 29746). B. Male, holotype of E. romanoi Landers & Sørensen, 2016 (NHMD 100307). C. Female, paratype of E. obtuspinosus Sørensen et al., 2012 (NHMD 99894). D. Female, non-type of E. romanoi. Scale bars: A, C = 20 µm; B = 10 µm; D = 5 µm.