Echinoderes hamiltonorum Sørensen & Rohal & Thistle 2018, sp. nov.

Echinoderes hamiltonorum sp. nov.

urn:lsid:zoobank.org:act: B3EE641D-72E3-4BCA-A4A9-3AD3A9BD8C05

Figs 7–9, Tables 6–7

Diagnosis

Echinoderes with middorsal spines on segments 4, 6 and 8, and spines in lateroventral positions on segments 6 to 9. Tubes present in ventrolateral positions on segment 2, in lateroventral positions on segment 5, and in laterodorsal positions on segment 10. Minute glandular cell outlets type 2 present in sublateral positions on segment 1, and in subdorsal, laterodorsal and sublateral positions on segment 2. Larger glandular cell outlets type 2 may or may not be present in sublateral positions on segment 8. Males with three pairs of penile spines; females with lateral terminal accessory spines.

Etymology

The second author (MR) dedicates this species to her mother and the Hamiltons, i.e., her mother’s side of the family, for always being there, supporting her and helping her achieve her dreams.

Material examined

Holotype

UNITED STATES OF AMERICA:adult ♀, US West Coast, central California, off Monterey, 36°47′46″ N, 123°41′54″ W, St. 5, 3679 m deep, collected from mud, 23 Sep. 2008, mounted in Fluoromount G on a glass slide (NHMD-223916). See Fig. 1 for localities and Table 1 for detailed station data.

Paratypes

UNITED STATES OF AMERICA: 2 ♂♂, same collecting data as for holotype; 2 ♀♀, St. 2; 2 ♀♀, St. 3; 1 ♀, St. 6 (NHMD-223917–223923). All paratypes are mounted in Fluoromount G on glass slides.

Additional non-type material

UNITED STATES OF AMERICA: 1 ♀, St. 3; 1 ♀, 1 ♂, St. 5; 2 ♀♀, 2 ♂♂, St. 6; 1 ♀, 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 7 A–B, 8A, 9A–B). The species is quite small, and trunk and sternal plates appear nearly parallel-sided from segments 2 to 8 (Fig. 8A). Intraspecific variation is present on segment 8 where some specimens, but not all, independent of gender and population may have a pair of sublateral glandular cell outlets type 2. Lateral terminal spines are relatively short and slender, 40% to 65% of trunk length (Figs 7 A–B, 8A). For complete overview of measurements and dimensions, see Table 6. Distribution of cuticular structures, i.e., sensory spots, glandular cell outlets, spines and tubes, is summarized in Table 7.

The head consists of a retractable mouth cone and an introvert (Fig. 9 C–D). 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 (Fig. 9C). The introvert sectors are defined by 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. The arrangement of scalids follows the same pattern as in Echinoderes hviidarum sp. nov. described below; hence, see Fig. 11 for a complete overview. All spinoscalids in these rings consist of a basal sheath and a pointed end piece (Fig. 9D). The basal sheaths terminate in fringed margins on spinoscalids of Rings 02 and 04, whereas the sheaths of Ring 03 have a median spike only. Spinoscalids of Rings 05 to 07 are composed as those in the preceding ring, but with shorter end pieces.

The neck has 16 placids, measuring 10 µm in length. The midventral placid is broadest, measuring 11 µm in width at its base, whereas all other are narrower, measuring 7 µm in width at their bases. Four dorsal and two ventral trichoscalid plates are present; the plates are well-developed and hat-shaped (Fig. 7 A–B).

Segment 1 consists of a complete cuticular ring. A pair of minute glandular cell outlets type 2 is present in sublateral positions (Figs 7B, 8C, F, 9 E–F). Sensory spots are located medially on the segment in subdorsal and laterodorsal positions (Figs 7A, 8B) (laterodorsal sensory spots are missing in one nontype specimen, Fig. 9E); sensory spots on this and following nine segments are medium-sized, with a tuft of micropapillae and long marginal cuticular hairs. Glandular cell outlets type 1 present in middorsal and ventrolateral positions (Figs 7 A–B, 9F). Cuticular hairs arranged in a single transverse row near posterior segment margin. The posterior segment margin is straight, terminating in a pectinate fringe with rather long and flexible fringe tips.

Segment 2 consists of a complete cuticular ring. Pachycyclus of the anterior segment margin is relatively thin and not interrupted. Tubes present in ventrolateral positions (Figs 7B, 8C, 9F), and very minute glandular cell outlets type 2 in subdorsal, laterodorsal and sublateral (Fig. 8F) positions (Figs 7 A–B, 8B–C, 9E–F). Sensory spots are located in middorsal, laterodorsal and ventromedial positions (Figs 7 A– B, 9E–F). Glandular cell outlet type 1 present in middorsal position only, near anterior segment margin. Secondary pectinate fringe present near anterior segment margin of this and the following segments, but it is usually covered by the preceding segment. On this and the following eight segments, the cuticular hairs are bracteate. Fairly long hairs densely cover the segment. The posterior segment margin is nearly straight, terminating in a pectinate fringe with long and flexible fringe tips.

Segment 3, and remaining segments, consisting of one tergal and two sternal plates (Figs 7B, 8A, C, E, 9B). Pachycyclus of the anterior segment margin is thin and interrupted at the tergosternal junctions and middorsally. Sensory spots present in subdorsal and midlateral positions (Figs 7A, 9E), and glandular cell outlets type 1 in middorsal and paraventral positions. Posterior segment margin straight, terminating in pectinate fringe with long and flexible fringe tips. Cuticular hairs cover tergal plate, except in middorsal position, and lateral halves of sternal plates.

Segment 4 with acicular spine in middorsal position (Figs 7A, 8B). Sensory spots not present, but glandular cell outlets type 1 present in paradorsal (Fig. 8B) and paraventral positions. Pachycycli, pectinate fringe of posterior margin and cuticular hairs as on preceding segment.

Segment 5 with a pair of minute tubes in lateroventral positions (Figs 7B, 8B, 9I). Sensory spots present in midlateral positions (Fig. 9I), and glandular cell outlets type 1 in middorsal and paraventral positions. Pachycycli, pectinate fringe of posterior margin and cuticular hairs as on preceding segment.

Segment 6 with acicular spines in middorsal and lateroventral positions (Figs 7 A–B, 8D–E, 9I). Sensory spots present in paradorsal (Fig. 8D), midlateral (Fig. 9I) and ventromedial positions, and glandular cell outlets type 1 in paradorsal (Fig. 8D) and paraventral positions. Pachycycli, pectinate fringe of posterior margin and cuticular hairs as on preceding segment.

Segment 7 with acicular spines in lateroventral positions (Figs 7B, 8 D–E). Sensory spots present in paradorsal (Fig. 8D), midlateral and ventromedial positions, and glandular cell outlets type 1 in middorsal (Fig. 8D) and paraventral positions. Pachycycli and pectinate fringe of posterior margin as on preceding segment; cuticular hair covering also as on preceding segment, but with middorsal hairless area being broader, posteriorly expanding into paradorsal and subdorsal areas as well.

Segment 8 with acicular spines in middorsal and lateroventral positions (Figs 7 A–B, 8D–E, 9G–H). Some paratypes with fairly large sublateral glandular cell outlets type 2 (Figs 7B, 8G, 9H) present, but others (including the holotype) without such outlets (compare Fig. 8E vs 8G and Fig. 9H vs 9G); the outlets were present in eight females and one male, from stations 2, 3, 6 and 8, and were missing in three females and four males, from stations 3, 5 and 6. Sensory spots present in paradorsal positions (Fig. 8D), and glandular cell outlets type 1 in paradorsal (Fig. 8D) and paraventral positions. Pachycycli, pectinate fringe of posterior margin and cuticular hairs as on preceding segment.

Segment 9 with acicular spines in lateroventral positions (Figs 7B, 8G, 9H). Sensory spots present in paradorsal, laterodorsal (Fig. 9H), and ventrolateral positions, and glandular cell outlets type 1 in paradorsal (Fig. 8D) and paraventral (Fig. 8E) positions. Small rounded sieve plates are present in lateral accessory positions (Figs 7B, 8E, G, 9H). Pachycycli and pectinate fringe of posterior margin as on preceding segment; cuticular hair covering also as on preceding segment, but with subdorsal to middorsal areas covered with short, filiform, hair-like extensions.

Segment 10 with laterodorsal tubes near posterior segment margin (Figs 7A, C, 9J, L); tubes are minute and do not show sexual dimorphism. Sensory spots present in paradorsal and ventrolateral positions (Fig. 9 J–L). Glandular cell outlets type 1 present as two middorsal ones, and one pair in paraventral positions. The posterior segment margin of the tergal plate is straight, terminating in a pectinate fringe with rather short fringe tips. The margins of the sternal plates have slightly longer fringe tips, and extend midventrally into a broad comb that almost reaches the margin of the terminal segment (Fig. 9K). Pachycycli as on preceding segment; cuticular hair covering also as on preceding segment, but with short, filiform, hair-like extensions present in paradorsal to middorsal areas only.

Segment 11 with lateral terminal spines (Figs 7 A–B, 8A, H, 9L). Males with three pairs of penile spines; dorsal and ventral penile spines are thin, flexible tubes, whereas the median ones are thicker, conical, and stout (Figs 7 C–D, 9J–L); females with thin and relatively short lateral terminal accessory spines (Figs 7 A–B, 8H, 9L). Sensory spots without marginal hairs present in paradorsal positions (Fig. 9J). Glandular cell outlets type 1 not observed. The segment is completely devoid of cuticular hairs, but densely covered with short, filiform hair-like extensions, in middorsal to laterodorsal areas, and in ventromedial to midventral areas. Tergal extensions are short, with oblique margins that end in a short lateral point; lateral tips with long, extended fringe tips that looks like setae (Figs 7, 8H, 9 J–K). Sternal plates shorter than tergal ones, and without tips or extensions.

Remarks

Echinoderes hamiltonorum sp. nov. is the first species known to show intraspecific variation in the presence or absence of glandular cell outlets type 2 on segment 8. During the initial work, specimens with and without outlets on segment 8 were actually kept separate and considered as two potentially different species. However, since all meristic data overlapped between the two morphotypes, and since all other cuticular characters, including sensory spots, appeared to occur consistently in all specimens (but note that one specimen lacked laterodorsal sensory spots on segment 1), it was finally concluded that all specimens were conspecific. This was also done in the light of recent observations on other Echinoderes where the occurrence of tubes displayed intraspecific variation (see Grzelak & Sørensen in press; Sørensen 2018). However, until now this variation has seemed to be restricted to tubes only, and this is the first report of intraspecific variation in the occurrence of glandular cell outlets type 2. It can obviously not be ruled out that the dimorphism is reflected in the molecular sequences as well, and that the two morphotypes represent two semi-cryptic, sympatric species, but for now it seems most correct to consider them as one species.

The new species has the second most common spine pattern, and shares the presence of middorsal spines on segments 4, 6 and 8 combined with lateroventral spines on segments 6 to 9 with twenty additional species of Echinoderes. However, E. hamiltonorum sp. nov. is the only species with this spine pattern that also shows glandular cell outlets type 2 in subdorsal, laterodorsal and sublateral positions of segment 2, and tubes in ventrolateral positions. The ventrolateral tubes are truly very hard to visualize in LM, but even if they are confused with glandular cell outlets type 2, there would still be no other species with this particular combination of characters.

Echinoderes hamiltonorum sp. nov. probably shows most resemblance to E. hakaiensis (see Herranz et al. 2018). Echinoderes hakaiensis is the only other species with the same spine pattern as E. hamiltonorum sp. nov. that also shows cuticular structures in subdorsal, laterodorsal, sublateral and ventrolateral positions on segment 2. Echinoderes hakaiensis has tubes though, instead of glandular cell outlets type 2, but these structures may sometimes be difficult to distinguish under LM. Echinoderes hakaiensis is also larger (the smallest E. hakaiensis has the same length as the largest E. hamiltonorum sp. nov.), and its tergal extensions appear conspicuously thicker, even though they are rather short. Echinoderes hakaiensis furthermore has lateral accessory tubes on segment 8, and even though they could be confused with the type 2 sublateral glandular cell outlets of E. hamiltonorum sp. nov., it is usually easier to see the actual tubes on segment 8, compared to tubes on other segments. Finally, E. hamiltonorum sp. nov. has its rather rare sublateral glandular cell outlets type 2 on segment 1, and E. hakaiensis has no such structure.

In fact, the presence of glandular cell outlets type 2 on segment 1 in any Echinoderes was only reported very recently. The first report was on E. unispinosus (Yamasaki et al. 2018b, but see also Fig. 25C) and an undescribed species that was addressed in the same contribution (Yamasaki et al. 2018b). Both species have glandular cell outlets type 2 in midlateral positions on segment 1. Outlets in these positions were also found during the present study in E. anniae sp. nov., and the only other known example of glandular cell outlets type 2 on segment 1 is from E. hamiltonorum sp. nov. However, unique for this species, the outlets are displaced to sublateral positions, rather than midlateral positions as found in the other species.