Echinoderes hviidarum, Sørensen & Rohal & Thistle, 2018

Sørensen, Martin V., Rohal, Melissa & Thistle, David, 2018, Deep-sea Echinoderidae (Kinorhyncha: Cyclorhagida) from the Northwest Pacific, European Journal of Taxonomy 456, pp. 1-75 : 28-36

Echinoderes hviidarum sp. nov.

urn:lsid:zoobank.org:act:58E8CD4B-12EA-49F0-8B97-167C2F5961B9

Figs 10 –13, Tables 8–9

Diagnosis

Echinoderes with middorsal spines on segments 6 and 8, and spines in lateroventral positions on segments 6 to 9. Tubes present in lateroventral positions on segment 5, lateral accessory positions on segment 8 and laterodorsal positions on segments 9 and 10. Segment 11 with small, middorsal protuberance. Glandular cell outlets type 2 not present. Males with three pairs of penile spines; females with lateral terminal accessory spines.

Etymology

The first author (MVS) dedicates this species to Heidi Hviid and Thea Hviid, for always being there with helping hands and backup when the world kicks back.

Material examined

Holotype

UNITED STATES OF AMERICA: adult ♂, US West Coast , off northern California, 39°59′53″ N, 125°26′36″ W, St. 4, 2733 m, collected from mud, mounted in Fluoromount G on a glass slide, 21 Sep. 2008 ( NHMD -213610). See Fig. 1 for localities and Table 1 for detailed station data.

Paratypes

UNITED STATES OF AMERICA: 12 ♀♀, 9 ♂♂, same collecting data as for holotype; 11 ♀♀, 9 ♂♂, St. 5; 2 ♀♀, 1 ♂, St. 6; 1 ♀, St. 7 (NHMD-213611–213661). All paratypes are mounted in Fluoromount G on glass slides.

Additional non-type material

UNITED STATES OF AMERICA: 1 ♂, St. 4; 3 ♀♀, 5 ♂♂, St. 5; 2 ♀♀, 2 ♂♂, St. 6; 3 ♀♀, 1 ♂, St. 8. All specimens mounted for SEM and stored in the first author’s personal reference collection.

Description

Adults with head, neck and eleven trunk segments ( Figs 10 A–B, 12A–B, 13A–B). The trunk appears stout in the anterior end, and turns more slender posteriorly. Segments 1 to 4 were often strongly contracted in fixed specimens. Lateral terminal spines long and slender, from 75% to slightly longer than trunk length ( Fig 10C ). For complete overview of measurements and dimensions, see Table 8. Distribution of cuticular structures, i.e., sensory spots, glandular cell outlets, spines and tubes, is summarized in Table 9 .

The head consists of a retractable mouth cone and an introvert ( Figs 11 , 13C). Inner oral styles are present, but their exact number and arrangement could not be determined. The external mouth cone armature consists of nine outer oral styles, each with five basal fringe tips. The introvert sectors are defined by the ten primary spinoscalids in Ring 01. Each primary spinoscalid consists of a basal sheath and a distal end piece with a blunt tip. The basal sheaths have marginal extensions forming two layers of transverse fringes. End pieces are smooth. Rings 02 and 04 have 10 spinoscalids and Ring 03 has 20 ( Figs 11 , 13C). All spinoscalids in these rings consist of a basal sheath and a pointed end piece. The basal sheaths terminate in fringed margins in spinoscalids of Rings 02 and 04, whereas the sheaths of Ring 03 have a median spike only. Ring 05 has 20 spinoscalids composed as those in the preceding ring, but with shorter end pieces. A ring of short fringes extends around the introvert in between spinoscalid Rings 04 and 05. Rings 06 and 07 have only 6 spinoscalids each. These scalids are considerably shorter than preceding ones. Well-developed trichoscalids, attached to trichoscalid plates, are present in sectors 2, 4, 5, 7, 8 and 10. Described sector-wise, sectors 1 and 6 are similar, having spinoscalids arranged as two double diamonds. Sectors 2, 4, 8 and 10 all have spinoscalids arranged as a quincunx, located in between a medial anterior spinoscalid (Ring 02) and a trichoscalid plate. The remaining sectors, 3, 5, 7 and 9, are almost identical, having spinoscalids forming a set of double diamonds located anterior to a pair of Ring 07 spinoscalids. However, in sectors 5 and 7, one Ring 07 spinoscalid is missing, due to the presence of a trichoscalid plate that takes up space ( Fig. 11 ).

The neck has 16 placids, measuring 12 µm in length. The midventral placid is broadest, measuring 11 µm in width at its base, whereas all others are narrower, measuring 7 µm in width at their bases. The trichoscalid plates are well-developed and nearly triangular.

Segment 1 consists of a complete cuticular ring. Sensory spots are located on the anterior half of the segment, but not at the anterior margin, in subdorsal positions ( Figs 10A , 13D); sensory spots are small and rounded. Glandular cell outlets type 1 present in middorsal (Fig. 13D) and sublateral positions. In most specimens the segment is completely devoid of cuticular hairs; however, a few specimens had a single transverse row with well-spaced hairs. The posterior segment margin is straight on the dorsal

and ventral sides, but with sublateral concave indentations, terminating in a pectinate fringe with short, triangular saw-tooth tips.

Segment 2 consists of a complete cuticular ring. Pachycyclus of the anterior segment margin is relatively thin, middorsally interrupted. Sensory spots are located in middorsal (Fig. 13D), midlateral and ventromedial positions ( Fig. 10 A–B). Sensory spots very minute, but with rather long, thin marginal cuticular hairs; all sensory spots from this segment to segment 10 have the same appearance. Glandular cell outlets type 1 not observed. Secondary pectinate fringe present near anterior segment margin of this and the following segments, but it is usually covered by the preceding segment. The segment has very few or no hairs at all. On this and all following segments, the cuticular hairs are bracteate (when present). The posterior segment margin is nearly straight, but with a rounded midventral extension; dorsally it terminates in a pectinate fringe with saw-tooth fringe tips as on preceding segment, whereas fringe tips on the lateral and ventral sides are long and slender.

Segment 3, and remaining segments, consist of one tergal and two sternal plates ( Figs 10 A–B, 12B). Pachycyclus of the anterior segment margin of medium thickness, interrupted at the tergosternal junctions and middorsally. No conspicuous cuticular structures present. Fairly long hairs are arranged in two to Fig. 13 (opposite page). Scanning electron micrographs showing overviews and details of Echinoderes hviidarum sp. nov. A. Dorsal overview. B. Ventral overview. C. Introvert sector 6 (middorsal). D. Segments 1 to 3, dorsal view. E. Detail showing attachment of lateroventral spine and lateral accessory tube on segment 8. F. Detail showing the typical stout laterodorsal tube on segment 9. G. Detail showing laterodorsal tube on segment 10, with associated papillary structure. H. ♀, segments 10 to 11, ventral view. I. Detail showing the less common slender laterodorsal tube on segment 9. J. ♂, segments 10 to 11, dorsal view. K. ♀, segments 10 to 11, dorsal view. Abbreviations: lat = lateral accessory tube; ldss = laterodorsal sensory spot; ldt = laterodorsal tube; ltas = lateral terminal accessory spine; lts = lateral terminal spine; lvs = lateroventral spine; mdgco1 = middorsal glandular cell outlet type 1; mdp = middorsal placid; mds = middorsal spine; mdss = middorsal sensory spot; pap = papillary structure; pe = penile spines; pr = protuberance; psp = primary spinoscalid; sdss = subdorsal sensory spot; sp = spinoscalid followed by introvert ring number; te = tergal extensions; tr = trichoscalid; vlss = ventrolateral sensory spot.

Glandular cell outlets type 1 only observed in paradorsal positions. Pachycycli, pectinate fringe of posterior margin and cuticular hairs as on preceding segment.

Segment 7 with acicular spines in lateroventral positions ( Figs 10B , 12B ). Sensory spots present in subdorsal ( Fig. 12C ) and sublateral positions ( Fig. 10 A–B). Glandular cell outlets type 1 not observed. Pachycycli, pectinate fringe of posterior margin and cuticular hairs as on preceding segment.

Segment 8 with acicular spines in middorsal and lateroventral positions ( Figs 10 A–B, 12A–D, 13A). Minute tubes present in lateral accessory positions ( Figs 10B , 12D , 13E). Middorsal spine is usually long, reaching the terminal segment ( Figs 10A , 12A ). Sensory spots and glandular cell outlets type 1 present in paradorsal positions only ( Figs 10A , 12C ). Pachycycli, pectinate fringe of posterior margin and cuticular hairs as on preceding segment.

Segment 9 with acicular spines in lateroventral positions ( Figs 10B , 12B, D ). Tubes present in laterodorsal positions ( Figs 10A , 12C , 13A, F, I); in most specimens (including the holotype) the tubes are short and stout (Fig. 13F), without differentiated bases or lateral wings, but a few specimens showed longer and more slender tubes, but still without bases or wings (Fig. 13I). The dimorphism is not related to gender or locality. Sensory spots present in paradorsal ( Fig. 12C ), laterodorsal (Fig. 13F, I) and ventrolateral ( Fig. 12D ) positions, and glandular cell outlets type 1 in paradorsal positions. Small rounded sieve plates are present in sublateral positions ( Fig. 10B ). Pachycycli, pectinate fringe of posterior margin and cuticular hairs as on preceding segment.

Segment 10 with laterodorsal tubes near posterior segment margin ( Figs 10A, D , 13G, J); tubes are very minute and sometimes appear to have an even shorter, protruding papillary structure located next to them (Fig. 13G), but due to their minute size, their presence was often hard to confirm. Sensory spots present in ventrolateral positions ( Figs 10B, E , 13H). Glandular cell outlets type 1 present as two middorsal ones; other glandular cell outlets type 1 not observed. Segment almost devoid of hairs (Fig. 13H, K), except for a few short ones on the lateral sides. The posterior segment margin of the tergal plate is straight, with rather shorter fringe tips than those on the tergal plate. The margins of the sternal plates have considerably longer fringe tips and extend midventrally to a point that almost reaches the posterior margin of the terminal segment (Fig. 13H). Pachycycli as on preceding segment.

Segment 11 with lateral terminal spines ( Fig. 10 A–C). Males with three pairs of penile spines ( Figs 10 A– B, 12F, 13J); dorsal and ventral penile spines are thin, flexible tubes, whereas the median ones are thicker, conical, and stout; females with short lateral terminal accessory spines ( Figs 10 D–E, 12G, 13H). Sensory spots without long marginal hairs present in paradorsal positions. Glandular cell outlets type 1 not observed. A short middorsal protuberance extends from the intersegmentary joint ( Figs 10A, D , 12E , 13J–K). The segment is completely devoid of cuticular hairs, but densely covered with short hairlike extensions, in middorsal to laterodorsal areas. Tergal extensions are short and pointed, with an extra tooth at the inferior margin ( Figs 10 , 12F , 13J–K).

Remarks

The spine and tube distribution in the lateral series of E. hviidarum sp. nov., with tubes in lateroventral positions of segment 5 and in lateral accessory positions of segment 8, and spines in lateroventral positions of segments 6 to 9, is quite common among species of Echinoderes and is shared with 21 congeners. However, the species is very easily recognized by the presence of middorsal spines on segments 6 and 8 only. This trait is shared exclusively with E. daenerysae Grzelak & Sørensen, 2017 . Furthermore, it has laterodorsal tubes on segment 9, which is otherwise found only in E. belenae Pardos, Herranz & Sánchez, 2016 and E. daenerysae ( Pardos et al. 2016b; Grzelak & Sørensen 2018). However, E. belenae cannot in any way be confused with E. hviidarum sp. nov. The species has conspicuously short and stout lateral terminal spines, middorsal spines on segments 4, 6, and 8, and numerous tubes in various positions ( Pardos et al. 2016b). Echinoderes daenerysae shows a much closer resemblance with E. hviidarum sp. nov., in terms of spine/tube distribution as well as general appearance, and we would consider the two species to be putatively closely related. They can be distinguished, though, by the presence of laterodorsal and ventrolateral tubes (ventrolateral not present in all specimens though) on segment 2 in E. daenerysae , and by the presence of a middorsal protuberance between segments 10 and 11 in E. hviidarum sp. nov. It should be stressed that the laterodorsal tubes on segment 9 are extremely difficult to visualize with LM; hence, the easiest and safest way to identify the species is by its dorsal spine pattern, combined with the absence of tubes on segment 2.

Figures

Fig. 10. Line art illustrations of Echinoderes hviidarum sp. nov. A. ♂, dorsal view. B. ♂, ventral view. C. ♂, segments 10 to 11, with lateral terminal spines drawn in full length, dorsal view. D. ♀, segments 10 to 11, dorsal view. E. ♀, segments 10 to 11, ventral view. Abbreviations: lat = lateral accessory tube; ldt = laterodorsal tube; ltas = lateral terminal accessory spine; lts = lateral terminal spine; lvs = lateroventral spine; lvt = lateroventral tube; mdgco1 = middorsal glandular cell outlet type 1; mds = middorsal spine; mlss = midlateral sensory spot; pdgco1 = paradorsal glandular cell outlet type 1; pe = penile spines; pr = protuberance; sdss = subdorsal sensory spot; si = sieve plate; slgco1 = sublateral glandular cell outlet type 1; slss = sublateral sensory spot; vlss = ventrolateral sensory spot; vmss = ventromedial sensory spot.

Fig. 1. Map showing the eight sampling stations off the US West Coast. See Table 1 for further details.

Fig. 11. Diagram of mouth cone (grey area), introvert and placids in Echinoderes hviidarum sp. nov., showing distribution of outer oral styles, scalids and trichoscalids. Table shows the scalid arrangement by sector; single-lined boxes mark quincunxes, double-lined boxes mark “double diamonds”.

Fig. 12. Light micrographs showing overviews and details of Echinoderes hviidarum sp. nov., holotype, ♂ (A–B, E–F) (NHMD-213610), paratype, ♂ (C–D) (NHMD-213614) and paratype, ♀ (G) (NHMD- 213635). A. Dorsal overview. B. Ventral overview. C. Segments 6 to 9, dorsal view. D. Segments 8 to 11, ventral view. E. ♂, segments 10 to 11, dorsal view. F. ♂, segments 10 to 11, ventral view. G. ♀, segments 10 to 11, ventral view. Abbreviations: lat = lateral accessory tube; ldt = laterodorsal tube; ltas = lateral terminal accessory spine; lts = lateral terminal spine; lvs = lateroventral spine; lvt = lateroventral tube; mds = middorsal spine; pdss = paradorsal sensory spot; pe = penile spines; pr = protuberance; sdss = subdorsal sensory spot; te = tergal extensions; vlss = ventrolateral sensory spot.