Echinoderes chandrasekharai Sørensen & Chatterjee, 2020

Sørensen, Martin V., Goetz, Freya E., Herranz, María, Chang, Cheon Young, Chatterjee, Tapas, Durucan, Furkan, Neves, Ricardo C., Yildiz, N. Özlem, Norenburg, Jon & Yamasaki, Hiroshi, 2020, Description, redescription and revision of sixteen putatively closely related species of Echinoderes (Kinorhyncha: Cyclorhagida), with the proposition of a new species group - the Echinoderes dujardinii group, European Journal of Taxonomy 730, pp. 1-101 : 66-73

Echinoderes chandrasekharai Sørensen & Chatterjee sp. nov.

urn:lsid:zoobank.org:act:F8BC0D7A-18AD-455C-9A82-542A062C9BC2

Figs 22–24 ; Tables 17–18

Echinoderes cf. ehlersi – Higgins & Rao 1979: 79–83, fig. 2 (specimens USNM-55391, USNM-55392, USNM-55394, USNM-55395, USNM-55397). — Adrianov & Malakhov 1999: 18–19, fig. 5.29.

Diagnosis

Echinoderes with short middorsal spines on segments 4 to 8, and lateroventral spines on segments 6 to 9; middorsal spines never reach the pectinate fringes of the posterior margins of their segments. Tubes present in lateroventral positions on segments 2 and 5, and in laterodorsal positions on 10. Minute glandular cell outlets type 2 in laterodorsal positions on segments 8 and 9. Tergal extensions of segment 11 short, pointed and well-spaced; sternal extensions short, with ventrolateral seta-like tuft of extended fringe tips. Females with female papillae with crescentic intracuticular substructure in ventrolateral positions on segments 6 and 7 and in ventromedial positions on segment 8.

Etymology

The species is dedicated to Dr G. Chandrasekhara Rao in recognition of his contributions to Indian kinorhynch studies, and for being the first to collect the new species (see Higgins & Rao 1979).

Material examined

Holotype

INDIA • ♀; Andaman Islands , Havelock Island , East Point; 11°54′ N, 093°03′ E; <1 m b.s.l.; 5 Apr. 1974; G.C. Rao leg.; intertidal black mud with macroalgae; USNM-55391 . Specimen mounted for LM on Cobb slide in Hoyer’s medium.

Paratypes

INDIA • 3 ♀♀, 1 ♂; same collection data as for holotype; USNM-55392 , 55394 , 55395 and 55397 . Mounted as holotype .

The specimens were originally reported as Echinoderes cf. ehlersi ( Higgins & Rao 1979) .

Additional material

INDIA • 1 ♀, 1 ♂; South Andaman Islands , Wandoor; 11°40′33″ N, 092°45′07″ E; <1 m b.s.l.; Dec. 2005; T. Chatterjee leg.; intertidal sand and mud mixed with macroalgae; stored in the first author’s personal reference collection • 1 ♀; South Andaman Islands , Burmanalla; 11°33′27″ N, 092°43′46″ E; <1 m b.s.l.; Dec. 2005; T. Chatterjee leg.; intertidal sand and mud mixed with macroalgae; stored in the first author’s personal reference collection. Specimens mounted for SEM. See Table 1 for an overview .

Description

Adults with head, neck and eleven trunk segments ( Figs 22 A–B, 23A, 24A). Trunk with nearly equally broad sternal plates on segments 5 to 10 ( Fig. 23A ). Lateral terminal spines long and slender, from 45% to 69% of trunk length. Secondary pectinate fringe present near anterior segment margin of segments 2 to 10, but it is usually covered by the preceding segment. For complete overview of measurements and dimensions, see Table 17. Distribution of cuticular structures, i.e., sensory spots, glandular cell outlets, spines and tubes, is summarized in Table 18.

The head consists of a retractable mouth cone and an introvert ( Fig. 24 B–C). Inner oral styles could not be examined. The external mouth cone armature consists of nine outer oral styles ( Fig. 24B ); bases of outer oral styles each with a V-shaped row of short fringe tips and a central bristle of much longer fringe tips. An additional fringe ring is present more posterior on mouth cone. 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 ( Fig. 24C ). The sheaths have two distinctively differentiated fringes: a most basal, transverse fringe, and a slightly more distal fringe where the fringe tips attach along a longitudinal line and alternatingly projects to the left and to the right (see inset Fig. 24C ). End pieces are smooth and flexible. The arrangement of scalids in Rings 01 to 07 is very similar to the arrangement in E. dujardinii and a summary can be seen in Fig. 3 . 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 and a pointed end piece. The basal sheaths terminate into fine, fringed margins in spinoscalids of Rings 02 to 05, and those of Rings 03 to 05 have in addition a basal median spike also. A ring of short fringes extend around the introvert in between spinoscalid Rings 04 and 05. Ring 06 has only six spinoscalids, located in sectors 1, 3, 5, 6, 7, and 9; ring 06 spinoscalids resemble those in preceding sectors, but without a distinct differentiation into sheath and end piece.

Ring 07 has 7 spinoscalids, located as pairs in sectors 3 and 9, unpaired but laterally displaced in sectors 5 and 7 (trichoscalids are taking up the space in the opposite side of each sector), and unpaired but centred in sector 1 ( Fig. 23I ).

Described sector-wise, sector 1 has spinoscalids arranged as two double diamonds anterior to a single spinoscalid in Ring 7. 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. Sectors 3 and 9 have spinoscalids forming double diamonds anterior to a pair of spinoscalids in Ring 7. Sectors 5 and 7 also have spinoscalids forming double diamonds, but anterior to an unpaired, laterally spinoscalid. Sector 6 has spinoscalids arranged as two double diamonds ( Fig. 3 ).

Trichoscalids with trichoscalid plates are present in sectors 2, 4, 5, 7, 8 and 10.

The neck has 16 placids, measuring 16 µm in length. The midventral placid is broadest, measuring 13 µm in width at its base, whereas all other are narrower, measuring 8 µm in width at their bases. The trichoscalid plates in the dorsal sectors are composed of a distal part and a slightly broader proximal part, whereas the proximal parts of the ventral trichoscalid plates are much broader ( Fig. 23I ).

Segment 1 consists of a complete cuticular ring. Sensory spots are located near the anterior margin in subdorsal and laterodorsal positions, and slightly more posterior in sublateral and ventrolateral positions ( Figs 22 A–B, 24D–E); sensory spots are large, and rounded to oval, with numerous micropapillae, two pores, and often a cilium emerging from one of the pores. Glandular cell outlets type 1 present in middorsal and sublateral positions ( Figs 22 A–B, 23B–C, 24D). Cuticular hairs emerging through rounded perforation sites are covering the segment, except in a W-shaped ventral area on anterior segment half ( Fig. 24E ). The posterior segment margin is straight around the segment, terminating into a pectinate fringe with short, uniform fringe tips.

Segment 2 consists of a complete cuticular ring. Pachycyclus of the anterior segment margin is of medium thickness and not interrupted ( Fig. 23 B–C). Well-developed tubes present in lateroventral positions ( Figs 22B , 23C , 24E ). Sensory spots are located in middorsal (but slightly laterally displaced), laterodorsal (twin pair) and ventromedial positions ( Figs 22 A–B, 24D–E); sensory spots on this and all following segment oval, and same size or only slightly smaller than those on segment 1. Glandular cell outlets type 1 present in middorsal and ventromedial positions ( Figs 22 A–B, 23B–C). The segment is densely covered with bracteate hairs; hair cover slightly thinner between ventromedial sensory spots. The posterior segment margin is nearly straight; pectinate fringe from middorsal to midlateral positions with short fringe tips, as on segment 1; fringe tips from midlateral to ventromedial positions conspicuously longer, and then very short again between ventromedial positions.

Segment 3, and remaining segments, consisting of one tergal and two sternal plates. Pachycyclus of the anterior segment margin of medium thickness, and interrupted only at tergosternal junctions ( Fig. 23 A– B). Sensory spots present in subdorsal, laterodorsal and sublateral positions ( Figs 22 A–B). Glandular cell outlets type 1 present in middorsal and ventromedial positions ( Figs 22 A–B, 23B–C). Bracteate cuticular hairs are densely covering the segment from middorsal to ventromedial positions; shieldshaped paraventral areas densely covered by non-bracteate, hair-like extensions. Pectinate fringe of posterior margin hairs as on preceding segment.

Segment 4 with short acicular spine in middorsal position, not reaching the posterior margin of the segment ( Figs 22A , 23B, D ). Sensory spots present in subdorsal, midlateral and ventromedial positions ( Fig. 23 A–B); midlateral sensory spots considerably smaller than all other sensory spots on the animals, but they occur consistently in all examined specimens. Glandular cell outlets type 1 present in subdorsal and ventromedial positions ( Figs 22 A–B, 23C, 24B–D). Pectinate fringe of posterior segment margin with long fringe tips from middorsal to ventromedial positions conspicuously long, but very short between ventromedial positions. Pachycycli and cuticular hairs as on preceding segment.

Segment 5 with short acicular spine in middorsal position, not reaching the posterior margin of the segment, and well-developed tubes in lateroventral positions ( Figs 22 A–B, 23D–E, 24G). Sensory spots present in subdorsal, midlateral and ventromedial positions ( Figs 22 A–B). Glandular cell outlets type 1, pachycycli, pectinate fringe of posterior margin and cuticular hairs as on preceding segment.

Segment 6 with short acicular spines in middorsal and lateroventral positions ( Figs 22 A–B, 23D–E, 24G); middorsal spine not reaching the posterior margin of the segment, and lateroventral spine just reaching the primary pectinate fringe. Sensory spots present in paradorsal, subdorsal, midlateral and ventromedial positions ( Figs 22 A–B, 24G). Females with female papillae resembling small glandular cell outlets type 2 in ventrolateral positions; the intracuticular structures of the papillae are crescentic with a small protuberance in the curved part of the structure ( Fig. 22B ). Glandular cell outlets type 1, pachycycli, pectinate fringe of posterior margin and cuticular hairs as on preceding segment.

Segment 7 with short acicular spines in middorsal and lateroventral positions ( Figs 22 A–B, 23D–E, 24G–H); middorsal spine not reaching the posterior margin of the segment, and lateroventral spine just reaching the primary pectinate fringe. Females with female papillae resembling small glandular cell outlets type 2 ( Fig. 24H ), in ventrolateral positions ( Figs 22B , 23E , 24H ); the intracuticular structures of the papillae are crescentic with a small protuberance in the curved part of the structure ( Fig. 23E ). Sensory spots, glandular cell outlets type 1, pachycycli, pectinate fringe of posterior margin and cuticular hairs as on preceding segment.

Segment 8 with short acicular spines in middorsal and lateroventral positions ( Figs 22 A–B, 23D–F, 24G, I); middorsal spine not reaching the posterior margin of the segment, and lateroventral spine slightly overlapping the primary pectinate fringe. Minute glandular cell outlets type 2 present in laterodorsal positions ( Figs 22A , 23D, F , 24F ), but very close to the midlateral areas. Sensory spots present in paradorsal, subdorsal, midlateral (posterior to glandular cell outlets), ventrolateral positions ( Figs 22 A– B, 23D–E, 24F–G, I). Females with female papillae showing same substructure as those on segment 7, but with openings in ventromedial positions ( Figs 22B , 23E, H , 24I ). Glandular cell outlets type 1, pachycycli, pectinate fringe of posterior margin and cuticular hairs as on preceding segment.

Segment 9 with acicular spines in lateroventral positions, protruding slightly beyond primary pectinate fringe of posterior segment margin ( Figs 22B ). Sensory spots, glandular cell outlets type 1 and 2 as on preceding segment, but female papillae not present ( Figs 22 A–B, 24F). Small, rounded nephridial sieve plates present in lateral accessory positions ( Fig. 24F ). Pachycycli, pectinate fringe of posterior margin and cuticular hairs as on preceding segment.

Segment 10 with well-developed laterodorsal tubes near posterior segment margin ( Figs 22 , 23 J–K, 24J, L). Sensory spots present in subdorsal (but close to paradorsal) and ventrolateral positions ( Figs 22 , 24 J–L). Glandular cell outlets type 1 present as two longitudinally arranged middorsal ones and in ventromedial positions. The posterior segment margin of the tergal plate is straight, whereas margins of sternal plates are concave (most deeply concave in males) and extend midventrally into a point that almost reaches the posterior margin of the terminal segment ( Fig. 24 K–L); fringe tips of pectinate fringe are considerably shorter than those on preceding segments. Pachycycli and cuticular hairs as on preceding segment.

Segment 11 with lateral terminal spines ( Figs 22 , 23A , J–K, 24A, J–L). Males with three pairs of tubular penile spines ( Figs 22 C–D, 23K, 24J–K); dorsal and ventral penile spines are thin, flexible tubes, whereas the median ones are slightly thicker; females with short, thin lateral terminal accessory spines. Sensory spots present in subdorsal and ventrolateral positions ( Figs 22 , 23 J–K, 24J–K). The dorsal and most of the ventral sides are densely covered with non-bracteate hair-like extensions, except in some areas near the anterior margin of the segment. Tergal extensions are well-spaced, short and pointed ( Figs 22 , 23K , 24J, L ); sternal extensions short, with ventrolateral seta-like tuft of extended fringe tips ( Figs 22 , 24K ).

Figures

Fig. 22. Line art illustrations of Echinoderes chandrasekharai Sørensen & Chatterjee sp. nov.A. Female, dorsal view. B. Female, ventral view. C. Segments 10 to 11 in male, dorsal view. D. Segments 10 to 11 in male, ventral view.

Fig. 23. Light micrographs showing overviews and details of Echinoderes chandrasekharai Sørensen & Chatterjee sp. nov. A–E, G–J. Holotype, ♀ (USNM-55391). F. Paratype, ♀ (USNM-55394). K. Paratype, ♂ (USNM-55397). A. Ventral overview. B. Segments 1 to 4, dorsal view. C. Segments 1 to 4, ventral view. D. Segments 4 to 8, dorsal view. E. Segments 5 to 8, ventral view, showing female sexual dimorphism. F. Segments 8 to 9, dorsal view. G. Detail showing ventrolateral female papilla on segment 7. H. Detail showing ventromedial female papilla on segment 8. I. Detail showing ventral trichoscalids and trichoscalid plates. J. Segments 10 to 11, ventral view, showing female sexual dimorphism. K. Segments 10 to 11, ventral view, showing male sexual dimorphism.

Fig. 24. Scanning electron micrographs showing overviews and details of Echinoderes chandrasekharai Sørensen & Chatterjee sp. nov. A–C, H–I, K. ♀ (MVS, personal reference collection). D–G, J, L. ♂ (MVS, personal reference collection). A. Ventrolateral overview. B. Mouth cone, lateroventral view. C. Introvert sector 1 (ventral); inset shows detail of primary spinoscalid fringes, alternatingly attaching along a longitudinal line. D. Segments 1 to 2, dorsal view. E. Segments 1 to 2, ventral view. F. Segments 8 to 9, lateral view. G. Segments 6 to 8, dorsal view. H. Right sternal plate of segment 7, showing female sexual dimorphism. I. Right sternal plate of segment 8, showing female sexual dimorphism. J. Segments 10 to 11 dorsal view, showing male sexual dimorphism. K. Segments 10 to 11 ventral view, showing male sexual dimorphism. L. Segments 10 to 11 ventrolateral view, showing female sexual dimorphism.

Fig. 3. Diagram of mouth cone (grey area), introvert and placids in Echinoderes dujardinii Claparède, 1863, showing distribution of inner oral styles (full circles), outer oral styles (diamonds), primary scalids (triangles), spinoscalids (thick open circles), and trichoscalids (stars), with positions of trichoscalid plates and placids indicated. Table shows the scalid arrangement by sector; single-lined boxes mark quincunxes, double-lined boxes mark ‘double diamonds’.