Echinoderes nataliae, Sørensen & Macheriotou & Braeckman & Smith & Ingels, 2025

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 : 43-51

Echinoderes nataliae sp. nov urn:lsid:zoobank.org:act:B64378E9-7DF2-481E-BAE4-9B76D26E4819

Figs 13–15 , Tables 11–12

Diagnosis

Echinoderes with acicular spines in middorsal position on segments 4, 6, and 8, and in lateroventral positions on segments 6 to 9. Tubes present in subdorsal (almost paradorsal), laterodorsal, sublateral, and ventrolateral positions on segment 2, in lateroventral positions on segment 5, in sublateral positions on segment 8, and in laterodorsal positions on segment 10; tubes on segment 10 show sexual dimorphism and are larger in males. Laterodorsal glandular cell outlet type 2 with short, broad, projecting rectangular flap present on segment 9. Dorsal glandular cell outlets type 1 are present in middorsal positions on segments 1 to 3, 5, 7, and 10, and in paradorsal positions on segments 4, 6, 8, and 9. Sieve plates on segment 9 in lateral accessory positions, very close to base of lateroventral spine. Segment 1 completely devoid of cuticular hairs, except for those flanking the sensory spots. Males with single setal extension from secondary fringe of sternal plates on segment 10. Female papillae not present.

Etymology

The first author dedicates this species to his wife, Natalia Pouchkina-Stantcheva.

Material examined

Holotype ANTARCTICA • ♂ (mounted for LM in Fluoromount G on HS slide); Antarctic Peninsula, CRS 1778 ; 64°47.01′ S, 62°43.90′ W; 567 m b.s.l.; 8 Apr. 2016; FjordEco2; soft sediment; NHMD 1786668 .

Paratypes

ANTARCTICA – Antarctic Peninsula • 1 ♂ (mounted as holotype); CRS 1706 ; 64°50.47′ S, 62°35.12′ W; 499 m b.s.l.; 1 Dec. 2015; FjordEco1; soft sediment; NHMD 1786672 • 1 ♂ (mounted as holotype); CRS 1716; 64°52.36′ S, 62°25.49′ W; 551 m b.s.l.; 6 Dec. 2015; FjordEco2; soft sediment; NHMD 1786673 • 1 ♀ (mounted as holotype); CRS 1773; 64°52.35′ S, 62°25.88′ W; 553 m b.s.l.; 6 Apr. 2016; FjordEco2; soft sediment; NHMD 1786674 • 3 ♂♂, 2 ♀♀ (mounted as holotype); same data as for holotype; NHMD 1784769 to 1784771 , USNM 1740037 to 1740038 • 2 ♂♂, 1 ♀, 1 juv. (mounted as holotype); CRS 1790; 64°51.49′ S, 62°34.01′ W; 532 m b.s.l.; 10 Apr. 2016; FjordEco2; soft sediment; NHMD 1786675 to 1786676 , USNM 1740039 • 1 ♂ (mounted as holotype); CRS 1792 ; 64°51.40′ S, 62°34.01′ W; 525 m b.s.l.; 11 Apr. 2016; FjordEco2; soft sediment; NHMD 1786679 • 1 ♂ (mounted as holotype); CRS 1799; 64°51.51′ S, 62°33.83′ W; 541 m b.s.l.; 13 Apr. 2016; FjordEco2; soft sediment; NHMD 1786680 .

Additional material

ANTARCTICA – Antarctic Peninsula • 1 ♀ (mounted for SEM); CRS 1698; 64°51.60′ S, 62°33.80′ W; 541 m b.s.l.; 28 Nov. 2015; FjordEco1; soft sediment; MVS • 2 ♂♂, 1 ♀ (mounted for SEM); CRS 1702; 64°51.15′ S, 62°34.44′ W; 502 m b.s.l.; 30 Nov. 2015; FjordEco1; soft sediment; MVS • 1 ♂, 2 ♀♀ (mounted for SEM); CRS 1773; 64°52.35′ S, 62°25.88′ W; 553 m b.s.l.; 6 Apr. 2016; FjordEco2; soft sediment; MVS • 4 ♂♂, 1 ♀ (mounted for SEM); CRS 1790; 64°51.49′ S, 62°34.01′ W; 532 m b.s.l.; 10 Apr. 2016; FjordEco2; soft sediment; MVS • 1 ♂, 3 ♀♀ (mounted for SEM); CRS 1792; 64°51.40′ S, 62°34.01′ W; 525 m b.s.l.; 11 Apr. 2016; FjordEco2; soft sediment; MVS • 5 ♂♂, 1 ♀ (mounted for SEM); CRS 1793; 64°39.53′ S, 62°55.03′ W; 701 m b.s.l.; 11 Apr. 2016; FjordEco2; soft sediment; MVS • 1 ♀ (mounted for SEM); CRS 1799; 64°51.51′ S, 62°33.83′ W; 541 m b.s.l.; 13 Apr. 2016; FjordEco2; soft sediment; MVS • 5 ♂♂, 1 ♀ (mounted for SEM); CRS 1809; 64°39.59′ S, 62°55.09′ W; 694 m b.s.l.; 15 Apr. 2016; FjordEco2; soft sediment; MVS .

Description

GENERAL. Adults with head, neck, and eleven trunk segments ( Figs 13A–B , 14A , 15A–B ). An overview of measurements and dimensions is given in Table 11. Distributions of cuticular structures, i.e., sensory spots, glandular cell outlets, spines, and tubes, are summarized in Table 12.

HEAD. Consists of a retractable mouth cone and an introvert ( Fig. 15C–D ). Mouth cone with nine outer oral styles composed of two units; all oral styles with uniform morphology, but differ alternatingly in length, with styles in uneven numbered sectors being ca 15% longer than those in even numbered. Bases of outer oral styles with row of six slender spikes, flanked by pair of stronger spikes. A single fringe is located more basally, at the base of the mouth cone and in between the attachment points of the outer oral styles. Inner oral styles could not be examined.

INTROVERT. The arrangement of scalids follows the pattern of P. grzelakae nov. sp., thus see Fig. 6 for scalid arrangement. The introvert has ten primary spinoscalids in Ring 01. Each primary spinoscalid consists of a basal sheath and a distal end piece with a blunt tip ( Fig. 15D ). Rings 02 and 04 have 10 spinoscalids, and Rings 03 and 05 have 20. All spinoscalids in these rings are well-developed and consist of a basal sheath with fringed distal margins and a pointed end-piece. Ring 06 has only six spinoscalids, located in sectors 1, 3, 5, 6, 7, and 9; they resemble those in preceding sectors, but the distal end-pieces are slightly shorter. Ring 07 has eight scalids with very short end-pieces, i.e., shorter than the basal sheaths, located as pairs in sectors 1, 3, and 9, and as single, laterally displaced ones in sectors 5 and 7 ( Fig. 6 ). Described sector-wise ( Fig. 6 ), sectors 1, 3, and 9 are similar, having spinoscalids arranged as two double diamonds anterior to an additional pair of Ring 07 spinoscalids. Sectors 2, 4, 8, and 10 all have spinoscalids arranged as a quincunx, located in between an anterior spinoscalid in Ring 02 and a trichoscalid plate. Sectors 5 and 7 have spinoscalids forming double diamonds, anterior to an unpaired, lateral spinoscalid; the lateral spinoscalid is unpaired because a trichoscalid plate takes up the space on the opposite side of the sector. Sector 6 has its spinoscalids arranged as double diamonds. Regular trichoscalids with trichoscalid plates are present in sectors 2, 4, 5, 7, 8, and 10 ( Figs 6 , 15D ).

NECK. With 16 placids. Midventral placid broadest, 13 µm in width and length, whereas all others are narrower, measuring 8 µm in width at their bases. The trichoscalid plates are well-developed and hat-shaped.

SEGMENT 1. Consists of a complete cuticular ring. Sensory spots are present in subdorsal, laterodorsal, and ventromedial positions; subdorsal and laterodorsal sensory spots are present on the anterior half of the segment, but not immediately at the anterior margin. They are composed of a dense tuft of micropapillae around a central pore and are flanked by three to five long, bristle-like cuticular hairs, arranged along the lower margin of the micropapillary area; ventromedial sensory spots are more posterior on the segment, with same appearance as the dorsal ones, but with only two or three cuticular hairs. Glandular cell outlets type 1 are present in middorsal and ventrolateral positions. Besides the few hairs around the sensory spots, the segment is completely devoid of cuticular hairs. The posterior segment margin is straight and terminates in a pectinate fringe with narrow and slender fringe tips ( Figs 13A–B , 14B–C , 15E–G ).

SEGMENT 2. Consists of a complete cuticular ring. Tubes are located in subdorsal, laterodorsal, sublateral, and ventrolateral positions; subdorsal tubes are located very close to the paradorsal positions. Sensory spots present in middorsal, midlateral, and ventromedial positions; the micropapillary areas around the sensory spots on this, and all following segments, are rounded. The micropapillae along the posterior margin of the areas are longer, and several conspicuously long micropapillae extend from the posterior part of the areas. Glandular cell outlets type 1 are present in middorsal and ventromedial positions. Bracteate cuticular hairs are arranged in three to four transverse rows; hairs in the two to three anteriormost rows are rather short, whereas those of the most posterior row are considerably longer, reaching the pectinate fringe at the posterior segment margin. The posterior segment margin is straight along the dorsal and lateral sides, but extends into a small midventral V-shaped flap. Pectinate fringe from middorsal to ventromedial areas with narrow and slender fringe tips as on preceding segment; however, from ventromedial to midsternal positions the fringe tips are conspicuously shorter and narrower ( Figs 13A–B , 14B–C , 15E–G ).

SEGMENT 3. As remaining segments, consisting of one tergal and two sternal plates. Sensory spots are present in subdorsal and sublateral positions, and glandular cell outlets type 1 in middorsal and ventromedial positions. The hair covering of the tergal and lateral halves of sternal plates is dense on the anterior half of the segment, except in hair-less midlateral areas; bracteate cuticular hairs are arranged in five to six rows; hairs in the two anteriormost rows are conspicuously short, only 1–2 µm; hairs in the median rows are longer, 5–6 µm, and hairs in the posteriormost row are very long, reaching the pectinate fringe. Paraventral areas without bracteate hairs, but with a rhomboid patch of fine, short hair-like extensions. Posterior segment margin straight and pectinate fringe as on preceding segment ( Figs 13A–B , 14B–C , 15H, J ).

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 in addition to the hairless midlateral areas, the middorsal area is also devoid of hairs. Posterior segment margin and pectinate fringe as on preceding segment ( Figs 13A–B , 14B–C , 15H, J ).

SEGMENT 5. With tubes in lateroventral positions. Sensory spots present in subdorsal, sublateral, and ventromedial positions, and glandular cell outlets type 1 in middorsal and ventromedial positions. Cuticular hairs, posterior segment margin, and pectinate fringe as on preceding segment ( Figs 13A–B , 14B–C , 15I–J ).

SEGMENT 6. With spines in middorsal and lateroventral positions. Sensory spots present in paradorsal, sublateral, and ventromedial positions. Glandular cell outlets type 1 present in paradorsal and ventromedial positions. Cuticular hairs, posterior segment margin, and pectinate fringe as on preceding segment ( Figs 13A–B , 14B–C , 15I ).

SEGMENT 7. With spines in lateroventral positions. Sensory spots present in paradorsal, sublateral, and ventromedial positions, and glandular cell outlets type 1 in middorsal and ventromedial positions. Cuticular hairs arranged in seven to eight rows, and still differentiated into very short, uniform hairs in the three to four anteriormost, longer hairs in the three median rows, and very long hairs in the posteriormost row. Posterior segment margin and pectinate fringe as on preceding segment ( Figs 13A–B , 14D–E ).

SEGMENT 8. With spines in middorsal and lateroventral positions, and tubes 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 13A–B , 14D–F , 15L–M ).

SEGMENT 9. With spines in lateroventral positions. Sensory spots present in paradorsal, laterodorsal, and ventrolateral positions. Very large glandular cell outlets type 2, with a broad rectangular flap projecting from the outlets, are present in laterodorsal positions. Glandular cell outlets type 1 present in paradorsal and ventromedial positions. Small rounded sieve plates located in lateral accessory positions, immediately next to the attachment point of the lateroventral spines. The cuticular hair covering is similar to that on the preceding segment, but hairless middorsal area is broader. Posterior segment margin and pectinate fringe as on preceding segment ( Figs 13A–B , 14D–E, G–H , 15K–M ).

SEGMENT 10. With sexually dimorphic laterodorsal tubes located near, but not at, the posterior segment margin; female tubes are extremely small, hardly projecting from attachment site; male tubes of more regular size, reaching beyond the segment margin. Males in addition with one to three flare-like setae extending from the secondary fringes of each sternal plate. 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 hairs with same size differentiation as on preceding segments, but only present from laterodorsal to ventromedial areas; middorsal and paradorsal areas with rhomboid patch of short, hair-like extensions. The posterior segment margin of the tergal plate is straight, with fringe tips as on preceding segments; however, the narrower ventromedial to midventral fringe tips are as long as the other fringe tips. Sternal plate margins straight, but slightly oblique ( Figs 13A–D , 14I–K , 15N–P ).

SEGMENT 11. With lateral terminal spines. Females with lateral terminal accessory spines; males with thin, tubular dorsal and ventral penile spines, and well-developed, cone-shaped medial pair of penile spines. Sensory spots present in paradorsal and ventromedial positions. Middorsal protuberance-like structure extends from intersegmentary joint. The segment is devoid of cuticular hairs, but has a dense covering of minute cuticular hair-like structures on the protuberance, in the paradorsal areas, and along the inferior margins of the tergal extensions. Tergal extensions are short and triangular, with a small denticle on the inferior margins. Sternal extensions short, broadly rounded, and not extending beyond tergal extensions ( Figs 13 A–D , 14I–K , 15N–P ).

Distribution

Antarctic Peninsula: Gerlache Strait and Andvord Bay MBA, IBB, and OBA, 499 to 701 m b.s.l. See Fig. 1 for geographic overview of stations and Table 1 for station and specimen information.

Diagnostic remarks

The new species can easily be assigned to Echinoderes , and when comparing the spine pattern combined with the presence of four pairs of tubes on segment 2, the number of similar congeners is narrowed down to two described species, E. hakaiensis Herranz et al., 2018 and E. frodoi Grzelak & Sørensen, 2022 , and the undescribed Echinoderes sp. 3 , reported from abyssal plains near the Atacama Trench by Grzelak et al. (2021). However, E. nataliae sp. nov. can be distinguished from E. hakaiensis and Echinoderes sp. 3 by the presence of large glandular cell outlets type 2 on segment 9. Glandular cell outlets type 2 are not present at all in E. hakaiensis or Echinoderes sp. 3 ( Herranz et al. 2018; Grzelak et al. 2021).

The glandular cell outlets type 2 on segment 9 in E. nataliae sp. nov. are not only large. They also have a very particular morphology, with a rectangular flap projecting from the openings. Somewhat similar structures are present in E. frodoi , even though Grzelak & Sørensen (2022) reported the structures as “laterodorsal tubes”. Echinoderes frodoi has large openings, resembling glandular cell outlets type 2, in lateral accessory positions on segment 8 and in laterodorsal positions on segment 9. On both segments, there are flattened, tubular structures projecting from the openings. The structures look like collapsed tubes and were interpreted as such by Grzelak & Sørensen (2022), but they could in fact also be flattened flaps, as seen on segment 9 in E. nataliae . Although the structures in the two species are very similar, they are not identical. For instance, the flaps in E. nataliae are rectangular, close to quadratic ( Fig. 15K ), whereas they are clearly more elongate and slender in E. frodoi – at least on segment 8. On segment 9 in E. frodoi , the tubes vary between forming short but wide collars to forming elongate but yet rather wide tubes. We believe that the two species share a special and homologous variation of type 2 glandular cell outlets.

Besides the similar glandular cell outlets, and resemblance in tube and spine patterns, E. frodoi and E. nataliae sp. nov. also differ on several points. The most substantial difference between the two species is the midlateral tubes on segment 1, present in E. frodoi only. However, these tubes are not consistently present in all specimens of E. frodoi , and even though such tubes never occurred in the 50+ examined specimens of E. nataliae , their inconsistent occurrence in E. frodoi makes them less useful as a differential character. Another difference between the two species is expressed in their morphometrics. The trunk length of E. frodoi ranges from 161 to 202 µm, unlike the 240 to 312 µm in E. nataliae , and the general trunk shape of E. frodoi appears stouter or chubbier than the more slender E. nataliae . This difference is expressed in the differing Maximum Sternal Width to Trunk Length ratios, with an average of 24.7% in E. frodoi ( Grzelak & Sørensen 2022) but only 19.7% in E. nataliae . Also all middorsal spines are longer in E. nataliae , and the ranges of the middorsal spine lengths in the two species never overlap. Small differences are also expressed in the position of tubes on segment 8, with the tubes of E. frodoi attaching in lateral accessory positions, whereas they are more dorsal in E. nataliae and sit in sublateral positions. There are also distinct differences in the cuticular hair covering of the two species. Echinoderes nataliae never has cuticular hairs on segment 1 (except those associated with the sensory spots), but has a relatively dense hair covering on the following nine segments. In contrast, most specimens of E. frodoi have plenty of hairs on segment 1, whereas the hair covering of the remaining segments is less dense compared to that of E. nataliae . Finally, E. nataliae has a pair of large and distinct ventromedial sensory spots on segment 1. Such sensory spots are lacking in E. frodoi . Thus, in conclusion, E. nataliae and E. frodoi are clearly two very similar species, and very likely also closely related, but they are also easily distinguished by several conspicuous as well as more subtle differences.

The distribution of glandular cell outlets type 1 in E. nataliae sp. nov. follows the MD Seg. 1–3, 5, 7, PD 4, 6, 8–9 pattern (see table with summary of species with this pattern described up to 2020 in Sørensen et al. 2020).

Figures

Fig. 13. Line art illustrations of Echinoderes nataliae sp. nov. A. Female, dorsal view. B. Female, ventral view. C. Male, segments 10 to 11, dorsal view. D. Male, segments 10 to 11, ventral view.

Fig. 14. Light micrographs showing overviews and details of Echinoderes nataliae sp. nov. A–E, J–K. Male, holotype (NHMD 1786668). F. Female, paratype (NHMD 1786671). G. Male, paratype (NHMD 1786669). H. Female, paratype (USNM 1740038). I. Female, paratype (NHMD 1786674). A. Ventral overview. B. Segments 1 to 6, dorsal view. C. Segments 1 to 6, ventral view. D. Segments 7 to 9, dorsal view. E. Segments 7 to 9, ventral view. F. Detail showing lateral half of segment 8, ventral view. G. Segments 9, lateral view, ventral is left. H. Segment 9, focused inside specimen. I. Segments 10 to 11, ventral view, showing female sexual dimorphism. J. Segments 10 to 11, focused on tergal extensions, showing male sexual dimorphism. K. Segments 10 to 11, ventral view, showing male sexual dimorphism. Scale bars: A = 100 µm; B–E, G–K = 20 µm; F = 10 µm.

Fig. 15. Scanning electron micrographs showing overviews and details of Echinoderes nataliae sp. nov. A. Laterodorsal overview of female. B. Ventral overview of male. C. Mouth cone, ventral view. D. Introvert focused on sectors 10 (left) and 9 (right). E. Segments 1 to 2, dorsal view. F. Segments 1 to 2, right lateral view. G. Segments 1 to 2, ventral view. H. Segments 3 to 4, laterodorsal view. I. Segments 5 to 6, right lateral view. J. Segments 3 to 5, ventral view. K. Segment 8, dorsal view, inset shows close-up of laterodorsal sensory spot and glandular cell outlet type 2 with protruding flap; scale = 3 µm. L. Segments 8 to 9, right lateral view. M. Segments 8 to 9, ventral view. N. Segments 10 to 11, dorsal view, showing male sexual dimorphism. O. Segments 10 to 11, ventral view, showing male sexual dimorphism. P. Segments 10 to 11, ventral view, showing female sexual dimorphism. Scale bars: A = 100 µm; B = 50 µm; C–D, J, L–P = 10 µm; E–I, K = 20 µm.

Fig. 6. Diagram of mouth cone (grey area), introvert, and placids in Polacanthoderes grzelakae sp. nov., showing distribution of inner oral styles (closed dots), outer oral styles, scalids, and trichoscalids. Table shows the scalid arrangement by sector (S1 to S10); single-lined boxes mark quincunxes, double-lined boxes mark “double diamonds”.

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.