Pseudothyone labradorensis, Kremenetskaia & Alvestad & Penney & Hamel & de Moura Neves & Côté & Mercier, 2024

Kremenetskaia, Antonina, Alvestad, Tom, Penney, Heather D., Hamel, Jean-François, de Moura Neves, Bárbara, Côté, David & Mercier, Annie, 2024, A new species of holothuroid from the Labrador Sea (eastern Canada): Pseudothyone labradorensis sp. nov. (Echinodermata, Holothuroidea, Dendrochirotida, Sclerodactylidae), ZooKeys 1206, pp. 191-206 : 191-206

Pseudothyone labradorensis sp. nov.

Figs 2 , 3

Type material.

Holotype. Canada • 9.5 mm in length; Labrador Sea , 56.500, - 58.084, depth 740–969 m (between bottom and recovery); 30 Aug. 2020; Station ISECOLD - 0-1000; rock dredge; substratum primarily mud with sparse rocks; IORAS ECH 02801 , ID AMLAB- 02 . Paratype. Canada • 14 mm in length, collected at same time and locality as holotype; IORAS ECH 02802 , ID PT 1210 . Both holotype and paratype are preserved and stored in 96 % ethanol.

Diagnosis.

Body curved, cylindrical, tapered at anterior and posterior ends. Body colour in vivo pinkish. Tentacles 10, two ventral tentacles smaller. Tube feet arranged in several rows along radii, also present in interradii and on tapered posterior part of body. Body-wall ossicles slightly concave plates of irregular shape with smooth margins and perforations. Ossicles of tube feet rod-shaped; terminal plate irregular in shape; rods not numerous, smooth, with enlarged tuberculous ends. Tentacle ossicles rods with enlarged perforated ends. Segments of calcareous ring with undivided posterior projections.

Description.

Body curved towards dorsal side, wider and cylindrical in the middle, anterior end tapered towards terminal mouth, posterior end tapered to a ‘ tail’ towards terminal anus, ‘ tail’ short, more prominent in paratype and short in holotype (Fig. 2 A – D ). Body colour pinkish in living specimens (Fig. 2 A, B ), tentacles, tube feet and ‘ tail’ more brightly coloured; colour in ethanol uniformly greyish, tentacles and tube feet whitish or greyish (Fig. 2 C, D ). Body length 9.5 mm in holotype, 14 mm in paratype. Body-wall skin thin, rough, non-transparent, with dense layer of scale-like ossicles (Fig. 2 G ). Tentacles (examined in holotype, in paratype they were partly retracted) ten, two ventral tentacles remarkably smaller in size. Tube feet small (Fig. 2 F ), non-transparent in ethanol, arranged in several rows along radii and also scattered in interradii; tube feet more numerous on mid body, along ventrolateral and mid-ventral radii; on ‘ tail’ tube feet smaller and less numerous, arranged in double rows (Fig. 2 E ). Anal papillae five (Fig. 2 E ). Pieces of calcareous ring up to 1.6 mm in length, united at most their length, radial segments with undivided posterior projections, with forked grooved anterior projections; interradial segments with grooved anterior projections (Fig. 2 H, I ). Retractor muscles undivided, not flat, broader anteriorly (Fig. 2 I ). Polian vesicle single, non-divided (Fig. 2 I ). Gonad in a tuft (Fig. 2 I ), gonad tubules in paratype with oocytes of different size.

Body-wall ossicles in a single dense overlapping layer, laying their concave side out; body-wall ossicles small perforated plates, usually do not exceed 200 µm in length, slightly concave, mostly irregular in shape, smooth; perforations with smooth margins, from rounded to oblong in shape, their size and shape can vary even on a same plate (Fig. 3 A, D ). Introvert with bigger flat plates, plates often narrow and elongated (Fig. 3 B ). On tube feet supporting rod-shaped ossicles, not numerous, curved in shape, with slightly enlarged perforated ends, length 100–130 µm; terminal plate delicate, irregular in shape, ~ 70 µm in diameter (Fig. 3 E ). Tentacle ossicles curved rods, most ossicles ranged 100–480 µm in length, bigger in proximal part of tentacles; smaller rods sometimes enlarged in the middle; bigger rods often with enlarged spatulated and / or bifurcated ends (Fig. 3 C ).

Differential diagnosis.

Pseudothyone labradorensis sp. nov. can be distinguished from other species by a combination of the following characters: pinkish body colour (may disappear after preservation in ethanol); tube feet arranged in double rows on tapered posterior end; body-wall ossicles only perforated plates with smooth perforation margins; introvert ossicles perforated plates; tube foot ossicles rods and terminal plate of irregular shape.

Distribution.

Canada, Labrador Sea, depth 740– 969 m.

Etymology.

The species is named after its type locality.

Figures

Figure 2. Pseudothyone labradorensis sp. nov., external and internal morphology A, C holotype, before preservation (A) and preserved in ethanol (C) B, D paratype, before preservation (B), in ethanol (D) E tapered posterior body part in paratype F tube feet in holotype G body-wall skin with dense layer of ossicles H segments of calcareous ring in holotype I dissected anterior part in paratype. Labels: ap anal papillae, g gonad, pv Polian vesicle, rm retractor muscle.

Figure 3. Ossicles of Pseudothyone labradorensis sp. nov. A, D body-wall perforated plates B introvert perforated plates C tentacle rods E tube foot rods and terminal plate F right dorsal radial (r) and interradial (ir) segments of calcareous ring. A, B, C SEM images D, E light microscope images F drawing.