Echinoderes frodoi, 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 : 45-53

Echinoderes frodoi sp. nov.

urn:lsid:zoobank.org:act:85C8FA48-24D1-4C55-9B41-179E186C7037

Figs 17–19 ; Tables 12–13

Diagnosis

Echinoderes with spines in middorsal position on segments 4, 6 and 8, and in lateroventral positions on segments 6 to 9. Tubes present in midlateral positions on segment 1 (might be missing in some specimens), subdorsal, laterodorsal, sublateral and ventrolateral positions on segment 2, lateroventral positions on segment 5, lateral accessory positions on segment 8, and laterodorsal positions on segment 9. Sexually dimorphic tubes furthermore present in laterodorsal positions on segment 10: male tubes welldeveloped; female tubes minute.

Etymology

The species name refers to Frodo Baggins, the main character in the novel “ The Fellowship of the Ring ”, the first volume of J.R.R. Tolkien’s “ The Lord of the Rings ”.

Material examined

Holotype

NEW ZEALAND • ♂; Pahaua Canyon , stn TAN1004/22; 41.5100° S, 175.7187° E; 1188 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; NIWA-159414 . Mounted for LM in Fluoromount G on HS slide.

Paratypes

NEW ZEALAND • 1 ♀, 2 ♂♂; Hikurangi Slope , stn TAN1004/4; 41.6837° S, 175.6642° E; 1046 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; ♀ NIWA-159415 , 1 ♂ NHMD-916331 , 1 ♂ NIWA- 159416 . Mounted for LM in Fluoromount G on glass slides • 1 ♀; Hikurangi Slope , stn TAN1004/38; 41.5937° S, 175.8532° E; 1121 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; NHMD- 916335 . Mounted as holotype • 1 ♀; Hikurangi Slope , stn TAN1004/76; 41.6833° S, 175.6500° E; 1282 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; NHMD-916336 . Mounted as holotype • 1 ♀; Hikurangi Slope , stn TAN1004/128; 42.0485° S, 174.7000° E; 1420 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; NHMD-916337 . Mounted for LM in Fluoromount G on glass slide • 1 ♀; same collection data as for holotype; NIWA-159417 . Mounted as holotype • 1 ♂; Hikurangi Slope , stn TAN1004/31; 41.4962° S, 175.6828° E; 730 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; NHMD-916332 . Mounted for LM in Fluoromount G on glass slide • 1 ♀; Campbell Canyon , stn TAN1004/126; 42.1422° S, 174.5492° E; 1495 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; NHMD-916333 . Mounted for LM in Fluoromount G on glass slide • 1 ♂; Seamount 766 , stn TAN1004/129; 42.1345° S, 174.5860° E; 1456 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; NHMD-916334 . Mounted as holotype .

Additional material

NEW ZEALAND • 1 ♀, 1 ♂; Hikurangi Slope , stn TAN1004/38; 41.5937° S, 175.8532° E; 1121 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; personal reference collection of MVS. Mounted for SEM • 1 ♀; Hikurangi Slope , stn TAN1004/76; 41.6833° S, 175.6500° E; 1282 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; personal reference collection of MVS. Mounted for SEM • 1 ♂; 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 • 1 ♂; Honeycomb Canyon , stn TAN1004/58; 41.4080° S, 175.8977° E; 670 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; personal reference collection of MVS. Mounted for SEM • 1 ♂; Campbell Canyon , stn TAN1004/92; 41.8922° S, 174.6347° E; 683 m b.s.l.; Apr. 2010; NIWA TAN1004 Voyage; soft sediment; personal reference collection of MVS. Mounted for SEM • 1 ♀; Campbell Canyon , stn TAN1004/126; 42.1422° S, 174.5492° E; 1495 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 17–19 ). Overview of measurements and dimensions in Table 12. Distribution of cuticular structures, i.e., sensory spots, glandular cell outlets, spines and tubes, summarized in Table 13. No details regarding scalid arrangement and morphology could be provided, because introverts of all specimens mounted for SEM fully or partially retracted.

NECK. With 16 placids. Midventral placid broadest, 9 µm in width and 16 µm in length. Remaining placids narrower, 7 µm in width and 15 µm in length, similar in size ( Fig. 19B ). The trichoscalid plates well developed.

SEGMENT 1. Consists of complete cuticular ring ( Figs 17A–B , 18A–C , 19B ). Tubes present in midlateral positions in holotype and some paratypes; however, this character missing in other specimens and thus shows variation at population level ( Figs 17A , 18C , 19A, E ); no morphological or developmental differences explain presence or absence of tubes. Sensory spots located anteriorly on segment, but not at anterior margin, in subdorsal and laterodorsal positions. Sensory spots on this and following segments rounded, with numerous micropapillae surrounding central pore and several longer hairs along posterior margin. Glandular cell outlet type 1 present in middorsal position, and in lateroventral positions ( Fig. 17A–B ). Cuticular hairs lightly scattered on dorsal and lateral sides, and in small cluster ventromedially. Posterior segment margin almost straight, forming pectinate fringe with short and pointed fringe tips.

SEGMENT 2. Consists of complete cuticular ring, with tubes located in subdorsal, laterodorsal, sublateral and ventrolateral positions ( Figs 17A–B , 18A–C , 19A–B, E ). Sensory spots present in laterodorsal and ventromedial positions. Glandular cell outlet type 1 located middorsally. Pachycyclus of anterior segment margin interrupted in middorsal position. Secondary pectinate fringe present near anterior segment margin of this and following segments, but usually covered by preceding segment. Cuticular hairs lightly scattered on ventral side and more densely in dorsal and lateral areas. Pectinate fringe of posterior margin slightly longer in ventromedial areas, otherwise as on preceding segment.

SEGMENT 3. Present segment, and eight remaining ones, consist of one tergal and two sternal plates ( Figs 17A–B , 18A, C , 19B ). Pachycyclus of anterior segment margin of regular thickness, with middorsal interruption in addition to interruptions around tergosternal and midsternal junctions, on this and following segments. Segment with sensory spots in subdorsal and midlateral positons, and glandular cell outlets type 1 located ventromedially. On this and following four segments, cuticular hairs arranged in two or three rows across tergal plate, except for hairless midlateral areas and on lateral halves of sternal plates; paraventral and ventromedial areas devoid of hairs. Pectinate fringe as on preceding segment.

SEGMENT 4. With flexible spine in middorsal position and glandular cell outlets type 1 in paradorsal and ventromedial positions ( Figs 17A , 18B , 19C ). Sensory spots not present. Cuticular hairs and posterior segment margin as on preceding segment.

SEGMENT 5. With tubes in lateroventral positions, and sensory spots present in subdorsal, midlateral and ventromedial positions ( Figs 17A–B , 18B–C , 19F ). Glandular cell outlet type 1 present in middorsal position and in ventromedial positions. Pectinate fringe of posterior segment margin slightly longer; cuticular hairs as on preceding segment.

SEGMENT 6. With spines in middorsal and lateroventral positions ( Figs 17A , 18B , 19C, F ). Sensory spots present in paradorsal and midlateral positions. Glandular cell outlets type 1 present in pairs in paradorsal and ventromedial positions. Pectinate fringe on this and following two segments as on preceding one.

SEGMENT 7. With acicular spines in lateroventral positions, and sensory spots in paradorsal, midlateral and ventromedial positions ( Figs 17A–B , 18C , 19C ). Glandular cell outlets type 1 present in paradorsal and ventromedial positions. Cuticular hairs on dorsal side less dense than on preceding segment, with hairless middorsal and paradorsal patches. Pectinate fringe as on preceding segment.

SEGMENT 8. With acicular spines in middorsal and lateroventral positions, and tubes in lateral accessory positions ( Figs 17A–B , 18B, E , 19G ). Sensory spots present in paradorsal positions only. Glandular cell outlets type 1 and other structures as on preceding segment.

SEGMENT 9. With spines in lateroventral positions, and tubes in laterodorsal positions ( Figs 17A–B , 18D–E, G , 19G–H ). Tubes rather short with truncated tips, not differentiated into thicker proximal and thinner distal part. Sensory spots present in paradorsal, subdorsal and ventrolateral positions. Glandular cell outlets type 1 present in paradorsal and ventromedial positions. Small, rounded sieve plates located in lateral accessory positions. Cuticular hairs lightly scattered on dorsal side; central part of tergal plate devoid of hairs. Pectinate fringe of posterior segment margin with tips shorter than on preceding segments.

SEGMENT 10. With well-developed laterodorsal tubes in males, and minute, very slender tubes in females, located near posterior segment margin ( Figs 17A, C , 18H , 19G–H ). Sensory spots present in subdorsal and ventrolateral positions. Glandular cell outlets type 1 present as two middorsal ones and in ventromedial positions. Cuticular hairs scarcer than on preceding segment. Central part of tergal plate devoid of hairs; hairs on sternal plates present only on lateral halves. Pectinate fringe with very short tips.

SEGMENT 11. With pair of long lateral terminal spines ( Figs 17A–B , 19D ). Males with three pairs of penile spines; dorsal and ventral spines relatively long, slender and tubular, while median ones much stouter ( Figs 17A–B , 18A, H ). Females with lateral accessory spines ( Figs 17C–D , 18F , 19D ). Sensory spots present in paradorsal positions. One middorsal glandular cell outlet type 1 present. Segment devoid of cuticular hairs in both sexes, but with short cuticular hair-like structures covering paradorsal area and short fringes covering margins of tergal and sternal plates. Tergal extensions short and pointed, with two small denticles at inner margin ( Figs 17A–D , 18F ). Sternal extensions rounded, not extending beyond tergal extensions ( Figs 17B, D , 18F ).

Distribution

Hikurangi Margin, from slope, through canyon, and seamount habitats, 670–1495 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 frodoi sp. nov.

The spine and tube distribution in the middorsal and lateroventral series of E. frodoi sp. nov., with middorsal spines on segments 4, 6 and 8, and tubes/spines in lateroventral positions on segments 5 to 9, is a common pattern observed among the species of Echinoderes and shared by 24 congeners ( Yamasaki et al. 2020a). However, when we combine these characters with the presence of four pairs of tubes on segment 2, we shorten the list to only one described species, i.e., E. hakaiensis Herranz et al., 2018 from British Columbia and an undescribed species, Echinoderes sp. 3 , from the Atacama Trench ( Herranz et al. 2018; Grzelak et al. 2021). However, E. frodoi is easily distinguished from both species by the presence of short laterodorsal tubes on segment 9, and the (occasional) presence of midlateral tubes on segment 1. All three share the presence of tubes on segment 8, the positions of several sensory spots and glandular cell outlets type 1, as well as the shape of the tergal extensions. However, E. frodoi has tubes in lateral accessory positions on segment 8, which distinguishes it from E. hakaiensis and Echinoderes sp. 3 , which have their tubes in sublateral positions, making the space between lateroventral spines and the tubes conspicuously larger. Another significant difference between E. frodoi , E. hakaiensis and Echinoderes sp. 3 is evident in morphometric details. Echinoderes frodoi is markedly smaller in trunk length than both species (TL: 185 µm vs 324 µm and 211 µm, respectively), but has proportionally longer lateral terminal spines, resulting in a markedly higher LTS/TL ratio in E. frodoi in comparison with E. hakaiensis and Echinoderes sp. 3 (LTS/TL: 79% vs 40% and 69%, respectively) ( Herranz et al. 2018; Grzelak et al. 2021).

The occurrence of cuticular structures on segment 1 is very rare in echinoderid species, and the midlateral tubes on segment 1 as in E. frodoi sp. nov. is a trait shared exclusively with E. cantabricus Pardos et al., 1998 (see Pardos et al. 1998). However, E. cantabricus cannot in any way be confused with E. frodoi . The species has only a single middorsal spine on segment 4 and can also be distinguished by the absence of lateroventral spines on segment 9 ( Pardos et al. 1998). What might make the picture a bit unclear is the fact that these tubes apparently are not consistently present in all specimens of E. frodoi . We did not find any clear explanation for this intraspecific dimorphism, since the variation in tube pattern was not related to the sexual or developmental stage, neither to intraspecific variation between populations: the presence or absence of tubes were noted for specimens from the same locality. Nevertheless, a variation in spine/ tube pattern in Echinoderidae has recently been documented for several species (e.g., E. arlis Higgins, 1966 , E. eximus , E. levanderi and E. rhaegali Grzelak & Sørensen, 2017 in Grzelak & Sørensen 2018) and it seems that such morphological variation might be more frequent among Echinoderes species than previously thought ( Grzelak & Sørensen 2018, 2019; Sørensen, 2018).

Furthermore, the presence of laterodorsal tubes on segment 9 is also a rather rare feature among echinoderids.This trait has previously been described for only four species, i.e., E. belenae , E. daenerysae , E. hviidarum , E. ultraabyssalis and in the yet undescribed Echinoderes sp. 1 from the Atacama Trench ( Pardos et al. 2016b; Grzelak & Sørensen 2018; Sørensen et al. 2018; Adrianov & Maiorova 2019; Grzelak et al. 2021). The latter four cannot in any way be confused with E. frodoi sp. nov. due to the presence of only 2 middorsal spines, on segments 6 and 8. The only other species with middorsal spines on segments 4, 6 and 8 and tubes in laterodorsal position on segment 9 is E. belenae , but this species is generally very rich in tubes, and carries no less than thirteen pairs on its eleven trunk segments. The species furthermore has conspicuously short lateral terminal spines ( Pardos et al. 2016b). Laterodorsal tubes on segment 9 were also found during the present study in E. gandalfi sp. nov., E. dalzottoi sp. nov. and E. leduci sp. nov. However, the former two species can easily be distinguished from E. frodoi by the presence of only two middorsal spines. The latter, E. leduci , similarly to E. frodoi , is characterized by having middorsal spines on segments 4, 6 and 8, but can nevertheless be distinguished from E. frodoi by the lack of subdorsal and sublateral tubes on segment 2.

Figures

Fig. 17. Line art illustrations of Echinoderes frodoi sp. nov. A. ♂, dorsal view. B. ♂, ventral view. C. ♀, segments 10–11, dorsal view. D. ♀, segments 10–11, ventral view. Abbreviations: see Material and methods.

Fig. 18. Light micrographs showing overview and details of Echinoderes frodoi sp. nov. A, C (closeup). ♂, holotype (NIWA-159414). B–D, F. ♀, paratype (NHMD-916336). E. ♀, paratype (NHMD- 916335). G–H. ♂, paratype (NIWA-159416). A. Ventral overview. B. Segments 1 to 8, dorsal view. C. Segments 1 to 8, ventral view with close-up showing midlateral tube on segment 1. D. Segments 9 to 10, dorsal view. E. Segments 8 to 10, ventral view. F. Segments 10 to 11, ventral view. G. Segments 9 to 10, lateral view. H. Segments 10 to 11, lateral view. Abbreviations: see Material and methods.

Fig. 19. Scanning electron micrographs showing overviews and details of Echinoderes frodoi sp. nov. A. Lateral overview. B. Ventral overview. C. Segments 4 to 8, laterodorsal view. D. Dorsal overview. E. Segments 1 to 4, laterodorsal view. F. Segments 2 to 6, lateral view. G. Segments 8 to 10 of male, lateral view.H. Segments 9 to 11 of female, laterodorsal 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.