Echinoderes landersi, Grzelak & Sørensen, 2022

Grzelak, Katarzyna & Sørensen, Martin V., 2022, Echinoderes (Kinorhyncha: Cyclorhagida) from the Hikurangi Margin, New Zealand, European Journal of Taxonomy 844, pp. 1-108 : 18-25

Echinoderes landersi sp. nov.

urn:lsid:zoobank.org:act:3F3C572F-E5CE-4645-AA8F-9472E698B2F4

Figs 5–7 ; Tables 4–5

Diagnosis

Echinoderes with spines in middorsal position on segments 4 and 6, and in lateroventral positions on segments 6 to 9. Tubes present in subdorsal, laterodorsal, sublateral and ventrolateral positions on segment 2, lateroventral positions on segment 5, subdorsal, midlateral and lateral accessory positions on segment 8, and midlateral positions on segments 9 and 10.

Etymology

The species is named after Dr Stephen C. Landers in recognition of his contributions to kinorhynch taxonomy and ecology.

Material examined

Holotype

NEW ZEALAND • ♀; Hikurangi Slope , stn TAN1004/38; 41.5937° S, 175.8532° E; 1121 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; NIWA-159402 . Mounted for LM in Fluoromount G on HS slide.

Paratype

NEW ZEALAND • 1 ♀; Pahaua Canyon , stn TAN1004/31 ; 41.4962° S, 175.6828° E; 730 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; NHMD-916627 . Mounted as holotype .

Additional material

NEW ZEALAND • 1 ♀; Hikurangi Slope , stn TAN1004/44; 41.5258° S, 175.8003° E; 728 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; personal reference collection of MVS. Mounted for SEM • 2 ♀♀; Pahaua Canyon , stn TAN1004/27; 41.4983° S, 175.7043° E; 1013 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; personal reference collection of MVS. Mounted for SEM .

Description

GENERAL. Adults with head, neck and eleven trunk segments ( Figs 5–7 ). Overview of measurements and dimensions in Table 4. Distribution of cuticular structures, i.e., sensory spots, glandular cell outlets, spines and tubes, summarized in Table 5. No details regarding scalid arrangement and morphology could be provided, because introverts of all specimens mounted for SEM fully retracted.

NECK. With 16 placids. Midventral placid broadest, 11 µm in width and 16 µm in length, whereas all others narrower, measuring 7 µm in width at their bases ( Fig. 5 ). Trichoscalid plates well developed ( Fig. 6B ).

SEGMENT 1. Consists of complete cuticular ring. Sensory spots located on anterior half of segment, in subdorsal, laterodorsal and ventromedial positions; sensory spots on this and following segment with micropapillae surrounding central pore and long marginal hair ( Figs 5A–B , 7C ). Glandular cell outlet type 1 present in middorsal and ventrolateral positions. Cuticular hairs relatively long, distributed evenly around segment. Posterior segment margin almost straight, forming pectinate fringe with very short, sawtooth-like fringe tips along dorsal margin and with slightly longer tips along ventral margin.

SEGMENT 2. Consists of complete cuticular ring, with tubes located in subdorsal, laterodorsal, sublateral and ventrolateral positions ( Figs 5A–B , 6A–B , 7C–D ); in one specimen right subdorsal tube missing. Sensory spots present in middorsal, laterodorsal and ventromedial positions. Glandular cell outlets type 1 not observed. This structure better visible in LM than in SEM but none of LM specimens orientated in way that allowed detailed examination of segments, especially its ventral side; therefore, for this and following nine segments presence of glandular cell outlets type 1 in ventral positions can neither be confirmed nor rejected. Pachycyclus of anterior segment margin of regular thickness. Secondary pectinate fringe present near anterior segment margin of this and following segments, but usually covered by preceding segment. Cuticular hairs and pectinate fringe tips as on preceding segment.

SEGMENT 3. Present segment, and eight remaining ones, consist of one tergal and two sternal plates ( Figs 5A–B , 7D ). Segment with subdorsal and midlateral sensory spots. On this and following six segments, cuticular hairs arranged in three or four rows across tergal plate, except for hairless laterodorsal areas; paraventral areas devoid of hairs on this and following seven segments ( Fig. 5 ). Posterior segment margin straight, terminating in pectinate fringe with longer and more slender fringe tips along dorsal margin than on preceding segments, otherwise as on preceding segment.

SEGMENT 4. With spine in middorsal position. Spine relatively short (27 µm), only slightly exceeding beyond posterior segment margin ( Figs 5A , 6A, D , 7A, E ). Glandular cell outlets type 1 present in paradorsal positions. No other traits observed. Cuticular hairs and secondary pectinate fringe as on preceding segment.

SEGMENT 5. With tubes in lateroventral positions ( Figs 5B , 7D ). Sensory spots present in subdorsal, midlateral and ventromedial positions ( Figs 5A–B , 6D , 7D–E ). Glandular cell outlets type 1 present in paradorsal positions. Tips of pectinate fringe of posterior segment margin slightly longer than on preceding segment. Cuticular hairs as on preceding segment.

SEGMENT 6. With spines in middorsal and lateroventral positions ( Fig. 5A–B ). Middorsal spine, as on segment 4, relatively short (31 µm), only slightly exceeding beyond posterior segment margin ( Figs 6A, D , 7A, E ). Sensory spots present in paradorsal, subdorsal, midlateral and ventromedial positions ( Figs 5A–B , 6D , 7D–E ). Glandular cell outlets type 1 present in paradorsal positions ( Figs 5A , 6D ). Pectinate fringe of posterior segment margin and cuticular hairs as on preceding segment.

SEGMENT 7. With spines in lateroventral positions, and sensory spots in subdorsal, midlateral and ventromedial positions ( Figs 5A–B , 6C–D , 7E ). Glandular cell outlets type 1 present in paradorsal positions. Tips of pectinate fringe of posterior segment margin slightly longer than on preceding segments. Segment otherwise as segment 6.

SEGMENT 8. With spines in lateroventral positions, and tubes in subdorsal, midlateral and lateral accessory positions ( Figs 5A–B , 6C , 7G–H ). Sensory spots present in subdorsal positions only. Glandular cell outlets type 1 present in paradorsal positions. Pectinate fringe of posterior segment margin and cuticular hairs as on preceding segment.

SEGMENT 9. With spines in lateroventral positions and tubes in midlateral positions ( Figs 5A–B , 6C , 7G–H ). In one specimen additional tube on right side of segment located in subdorsal position ( Fig. 7I ). Two pairs of sensory spots located in subdorsal positions and one ventrolateral pair ( Figs 5A–B , 7H ). Glandular cell outlets type 1 present in paradorsal positions. Small, rounded sieve plates located in lateral accessory positions ( Fig. 6C ). Cuticular hair covering and pectinate fringe of posterior segment margin as on preceding segment.

SEGMENT 10. With minute midlateral tubes located near posterior segment margin ( Figs 5A , 6C , 7H ). Sensory spots present in subdorsal and ventrolateral positions ( Figs 5A–B , 7H ); in one specimen extra subdorsal sensory spot present on left side of segment ( Fig. 7H ). Glandular cell outlet type 1 present in middorsal position. Cuticular hairs less dense on dorsal side than on preceding segment. Central part of tergal plate devoid of hairs. Hairs on sternal plates shorter than on preceding segments. Posterior segment margin of tergal plate straight, without fringe tips; margins of sternal plates concave, reaching posterior margin of terminal segment, with very short fringe tips.

SEGMENT 11. With lateral terminal spines ( Figs 5A–B , 6A ). Females with lateral terminal accessory spines ( Figs 5A–B , 6A , 7H ); male conditions unknown. Sensory spots and glandular cell outlets type 1 present in subdorsal positions; in one specimen sensory spot on right side of segment missing. Segment devoid of cuticular hairs, but with very short cuticular hair-like structures covering paradorsal area and very short fringes covering margins of tergal and sternal plates. Tergal extensions triangular, with elongate and pointed tips ( Figs 5A , 7H ). Sternal extensions do not extend beyond tergal extensions ( Fig. 5B ).

Distribution

Hikurangi slope and Pahaua Canyon, 728–1121 m b.s.l. See Fig. 1 for a geographic overview of stations and Table 1 for station and specimen information.

Taxonomic remarks on Echinoderes landersi sp. nov.

Echinoderes landersi sp. nov. is easily distinguished from all other congeners by its combination of spines and tubes. The spine pattern on its dorsal side, with middorsal spines on segments 4 and 6, is already an uncommon feature within Echinoderes . This trait itself is shared only with E. astridae Sørensen, 2014 , E. bispinosus Higgins, 1982 , E. uozumii Yamasaki et al., 2020 and E. dalzottoi sp. nov. described below in the present study ( Higgins 1982; Sørensen 2014; Yamasaki et al. 2020b). This character in combination with its tubes on segment 2 makes E. landersi unique among its congeners. The abovementioned species possess either three pairs of tubes as in E. dalzottoi or only one pair as in E. astridae , E. bispinosus and E. uozumii . Therefore, having four pairs of tubes on segment 2, located in subdorsal, laterodorsal, sublateral and ventrolateral positions, is uncommon and found exclusively in E. landersi . The three latter species furthermore differ from E. landersi by being equipped with glandular cell outlets type 2; such outlets are absent in E. landersi . The regular hair covering found in E. landersi also distinguishes it from E. dalzottoi , which is characterized by having a trunk cuticle with perforation sites only but no cuticular hairs.

In addition, E. landersi sp. nov. can easily be distinguished from these species by other traits, among which the composition of segment 8 with tubes in subdorsal, midlateral and lateral accessory positions is the most important, as these are not present in any other species of Echinoderes . Numerous species have various combinations of tubes on this particular segment, but no other species has three pairs of tubes. There are several species with two pairs of tubes, in laterodorsal and lateral accessory positions as observed in, e.g., E. abbreviatus Higgins, 1983 , E. belenae Pardos et al., 2016 or E. intermedius Sørensen, 2006 , or in subdorsal and lateral accessory positions as found in E. capitatus ( Zelinka, 1928) and E. isabelae GaOrdóñez et al., 2008 ( Zelinka 1928; Higgins 1983; GaOrdóñez et al. 2008; Sørensen 2006; Pardos et al. 2016b); nevertheless, the most common tube pattern is the presence of only one pair of tubes on segment 8, typically in a sublateral or lateral accessory position. Furthermore, E. landersi possesses midlateral tubes on segment 9, which is another relatively rare trait, shared with only four species, i.e., E. andamanensis Higgins & Rao, 1979 , E. annae , E. newcaledoniensis Higgins, 1967 and E. serratulus ( Higgins 1967; Higgins & Rao 1979; Sørensen et al. 2016a; Yamasaki 2016). Nevertheless, none of these species can in any way be confused with E. landersi due to their significantly different middorsal spine patterns. Hence, besides its uncommon middorsal spine pattern with spines on segments 4 and 6 only, the new species is very easily recognized by the nature of its cuticular structures of segments 2, 8 and 9.

One noteworthy observation in E. landersi sp. nov. is the inconsistent tube pattern found in one specimen ( Fig. 7F, I ). However, in contrast to recent observations of intraspecific variation in species of Echinoderes where pairs of tubes may be present or absent, it was only one tube missing from the pair in E. landersi . Variation in tube patterns, regarding their presence or absence, has been documented, e.g., in E. daenerysae Grzelak & Sørensen, 2017 in Grzelak & Sørensen (2018) for ventrolateral tubes on segment 2, in E. eximus Higgins & Kristensen, 1988 for sublateral tubes on segment 9, in E. levanderi for subdorsal tubes on segment 2, and in E. frodoi sp. nov. (present study) for midlateral tubes on segment 1 ( Grzelak & Sørensen 2018; Sørensen 2018). Among specimens of E. landersi , however, one specimen lacks the subdorsal tube on the right side on segment 2 ( Fig. 7F ), but has a subdorsal tube on the right side of segment 9 ( Fig. 7I ). Tubes in subdorsal positions on segment 9 were not observed in other specimens. A similar inconsistency was described by Yamasaki & Dal Zotto (2019) for specimens of E. capitatus that lack a ventrolateral tube on one side on segment 2 ( Yamasaki & Dal Zotto 2019). Moreover, we observed that one specimen lacks a subdorsal sensory spot on the right side of segment 10, and that this lacking sensory spot seems to be relocated to segment 9 ( Fig. 7H ). For now, we cannot explain the reason for this observed variation, but it seems most likely that it is due to individual abnormalities, rather than intraspecific variation.

Figures

Fig. 5. Line art illustrations of Echinoderes landersi sp. nov. A. ♀, dorsal view. B. ♀, ventral view. Abbreviations: see Material and methods.

Fig. 6. Light micrographs showing overview and details of Echinoderes landersi sp. nov. A. ♀, paratype (NHMD-916627). B–D. ♀, holotype (NIWA-159402). A. Lateral overview. B. Segments 1 to 3, lateral view. C. Segments 7 to 11, lateral view. D. Segments 4 to 7, lateral view. Abbreviations: see Material and methods.

Fig. 7. Scanning electron micrographs showing overviews and details of Echinoderes landersi sp. nov. A. Dorsal overview. B. Lateral overview. C. Segments 1 to 3, lateral view. D. Segments 2 to 6, ventral view. E. Segments 4 to 7, dorsolateral view. F. Segments 1 to 3 of female with inconsistent tube pattern, dorsal view. G. Segments 8 to 10, lateral view. H. Segments 8 to 11, dorsal view, with inset showing close-up of midlateral tube on segment 10. I. Segments 8 to 9 of female with inconsistent tube pattern, dorsal 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.