Elpidia soyoae, Ogawa & Morita & Fujita, 2020

Ogawa, Akito, Morita, Takami & Fujita, Toshihiko, 2020, Elpidia soyoae, a New Species of Deep-sea Holothurian (Echinodermata) from the Japan Trench Area, Species Diversity 25, pp. 153-162 : 158-161

Elpidia soyoae sp. nov.

[New Japanese name: Soyo-kuma-namako] ( Figs 1–6 ; Tables 1, 2)

Material examined. Holotype: NSMT E-12638 ( BL 18 mm; BW 11 mm), INSD accession number LC528684 , 610 bps . Paratypes: NSMT E-12635 ( BL 25 mm; BW 13 mm), INSD accession number LC528681 , 628 bps; NSMT E-12636 ( BL 21 mm; BW 12 mm), INSD accession number LC528682 , 639 bps; NSMT E-12637 ( BL 19 mm;

BW 12 mm), INSD accession number LC528683 , 636 bps; NSMT E-12639 ( BL 12 mm; BW 8 mm), INSD accession number LC528685 , 623 bps.

Diagnosis. BL up to 25 mm. Dorsal papillae up to five pairs along the entire dorsal radii; second pairs widely separated from third ones. Purple pigmentation spots on dorsal and ventral body walls, tentacles, and tube feet. Ossicles in dorsal body wall mainly rods, Elpidia type, with two pairs of horizontal arms and one pair of vertical apophyses, rod axis up to 1336 µm long, 8.1–33 µm in diameter, length of apophyses 5.1–47% of axis length; tentacle rods with arched axis, and short arms and/or apophyses.

Description. Body semi-ellipsoidal with flat ventrum, 12–25mm long (5 individuals), 1.5–1.9 times as long as wide ( Fig. 1 ). Mouth anteroventral. Anus at posterior end of body. Dorsal papillae conical, 0.2–5.0 mm long (N=49 from 5 individuals, Table 1), four or five paired and 0–3 unpaired papillae present on two dorsal radii (four to seven papillae on each radius, Fig. 2 ). Paired large papillae 0.3–5.0 mm long (N=42 from 5 individuals), anterior two pairs widely separated from third paired ones. Unpaired minute papillae 0.2–2.7 mm long (N=7 from 3 individuals), between second and third paired papillae on holotype and one paratype (NSMT E-12639), and on the posterior dorsum of holotype and one paratype (NSMT E-12635). Ventrolateral radii without conical papillae. Tube feet cylindrical, four on each ventrolateral radius. Mid-ventral radius without tube feet. Tentacles ten, with cylindrical stems, and four conical digits on terminal discs. Papillae, tube feet, and tentacles nonretractile. Calcareous ring comprising five pieces surrounding pharynx ( Fig. 3A ), each piece with four pairs of straight arms ( Fig. 3B ): inside anterior pair (495–1131 µm long, N= 10 in holotype), inside posterior pair (266–907 µm long, N= 8 in holotype), outside anterior pair (1092– 2075 µm long, N= 7 in holotype), and outside posterior pair (968–1972 µm long, N= 9 in holotype). Tips of inside arm pairs branched or broadened in holotype ( Fig. 3C ). Gonad white unpaired tuft, comprising central genital ducts and surrounding genital vesicles. Polian vesicle single, fusiform, transparent, whitish in holotype. Body skin whitish, occasionally with purple pigmentation spots composed of small purple particles on dorsal and ventral surfaces. Discs of tube feet and tentacles light yellow, sometimes with purple pigmentation spots composed of small purple particles.

Ossicles ( Table 1). Ossicles in dorsal body wall mostly rods, Elpidia - type, and rarely wheels ( Fig. 4 ). Rod axis 193–1336 µm in length (DOL, N=104 from 5 individuals), straight, with two paired horizontal arms, and one pair of vertical apophyses. Axis 8.1–33 µm in diameter (N=192 from 5 individuals), with conical tips at both ends. The height of apophyses 17–232 µm (DAH, N=236 from 5 individuals). DAH/DOL ratio between 0.051–0.47 (N=150 from 5 individuals). Wheels rare, 30–33 µm in diameter (N=3 from 3 individuals), central connecting portion 18–21 µm in diameter (N=3 from 3 individuals), with nine spokes (N=3 from 3 individuals), three central rays (N=2 from 2 individuals), and triangular brim teeth (N=3 from 3 individuals) ( Fig. 4B ). Ossicles in ventral body wall only rods, Elpidia - type ossicles ( Fig. 5 ). Rod axis 73–557 µm in length (VOL, N=200 from 5 individuals), straight, with two paired horizontal arms, and one pair of vertical apophyses, sometimes shortened. Axis in diameter 4–24µm (N=274 from 5 individuals). The height of apophyses 10–142 µm (VAH, N=438 from 5 individuals), VAH/VOL ratio between 0.071–0.70 (N=332 from 5 individuals). Ossicles in tentacles only rods, Elpidia - type ossicles ( Fig. 6 ). Rods 77– 776 µm in length (TOL, N=223 from 5 individuals), with one arched axis, shortened arms and/or shortened apophyses sometimes completely lacking arms and apophyses. Axis in diameter 4.2–39µm (N=243 from 5 individuals). The height of apophyses 2.7–227 µm (TAH, N=380 from 5 individuals), TAH/TOL ratio between 0.0077–0.58 (N=380 from 5 individuals).

Distribution. Known only from the type locality: Japan Trench area, depth 3570–4145 m.

Etymology. The species is named after the R/V Soyomaru which collected these specimens.

Remarks. Morphological features of examined specimens were well coincident with five diagnostic characters of the genus Elpidia (see the Diagnosis section for the genus above). The dorsal rods of the examined specimens ranged from 8.1 to 33 µm in axis diameter, indicating Elpidia soyoae sp. nov. belong to the slender axis group. A morphological comparison of E. soyoae sp. nov. with six species of the slen- der axis group is provided in Table 2. Elpidia soyoae sp. nov. is distinguished from other species by the following four features: i) dorsal papillae on two dorsal radii, four or five paired papillae and unpaired papillae present along the entire dorsal radii (four to seven papillae on each radius), with wide separation between second and third paired papillae, ii) maximum length of dorsal rods exceeds 1000 µm, iii) tentacle rods with arched axis and shortened or occasionally completely reduced arms and apophyses, and iv) purple pigmentation spots composed of small purple particles on dorsal and ventral body walls. In addition, this species is easily distinguished from non-grouped species, E. echinata , which has 3 papillae on each dorsal radius ( Perrier 1896).

Molecular data comparison. In BLAST searches, the closest hits for the five obtained partial COI gene sequences were those of Elpidia glacialis ( INSD accession number HM 196413 or HM 196420 , with 90.1% and 90.8% similarity in 98% to 100% coverage) . K2P genetic distances were calculated in terms of 603 bps COI partial sequences in the five obtained sequences and 17 E. glacialis sequences in GenBank (INSD accession numbers HM196413 –196429 ): the interspecific K2P distance was 0.101 –0.120 between Elpidia soyoae sp. nov. and E. glacialis , and the intra-specific distance was 0.005 –0.017 and 0–0.019 in E. soyoae sp. nov. and E. glacialis , respectively. The results confirmed that five specimens belong to the genus Elpidia , and supported that E. soyoae sp. nov. and E. glacialis are genetically independent and distinct species.

respectively.

Figures

Fig. 1. Fresh specimen of Elpidia soyoae sp. nov. (NSMT E-12635: paratype). A, dorsal view; B, ventral view.

Fig. 2. Papillae arrangements of Elpidia soyoae sp. nov. A, left side view; B, right side view; C–F, dorsal side. A–B, holotype; C, NSMT E-12635: paratype; D, NSMT E-12636: paratype; E, NSMT E-12637: paratype; F, NSMT E-12639: paratype. Abbreviations: lp, paired papillae on dorsal left radius; lu, unpaired papillae on dorsal left radius; rp, paired papillae on dorsal right radius; ru, unpaired papillae on dorsal right radius.

Fig. 3. Calcareous ring of Elpidia soyoae sp. nov. (holotype). A, entire ring in dorsal view; B, variation of isolated pieces; C, branched inside posterior arm. Black arrowheads show five pieces surrounding pharynx. Abbreviations: ba, branched arm of inside posterior arms; iaa, inside anterior arms; ipa, inside posterior arms; oaa, outside anterior arms; opa, outside posterior arms.

Fig. 4. SEM images of ossicles from dorsal body wall of Elpidia soyoae sp. nov. (NSMT E-12635: paratype). A, rods with straight axis, well developed horizontal arms, and vertical apophyses; B, wheel from convex side and obliquely lateral side. Abbreviations: ax, axis; bt, brim teeth; ccp, central connecting portion; cr, central rays; ha, horizontal arms; sp, spokes; va, vertical apophyses.

Fig. 5. SEM images of ossicles from ventral body wall of Elpidia soyoae sp. nov. (holotype). Rods with straight axis, well developed horizontal arms, and vertical apophyses. Abbreviations: ax, axis; ha, horizontal arms; va, vertical apophyses.

Fig. 6. SEM images of rods from tentacles of Elpidia soyoae sp. nov. (NSMT E-12635: paratype). Rods with arched axis, especially shortened horizontal arms, and vertical apophyses. Abbreviations: ax, axis; ha, horizontal arms; va, vertical apophyses.