Holothuria (Holothuria) algeriensis n. sp.

Figure 3, Table 4

Synonymy.

Holothuria (Holothuria) tubulosa “B” Mezali, 2008, p. 116, fig. 23.

Material examined. Holotype. UF5187, Figuier-plage, Algeria, 36°46.750’N, 3°30.821’E, 0.5–10 m, Summer 2006. Paratype. UF5475, Figuier-plage, Algeria, 36°46.750’N, 3°30.821’E, 0.5–10 m, Summer 2006, 1 spec. LPVCMRMS2020.203; LPVCMRMS2020.204, Ouillis, Algeria, 36°7.436’N, 0°15.219’E, 5 m, June 2020, 2 specs.

Diagnosis. Length up to 185 mm, body arched, very net demarcation between the dorsal surface brown bitumen and the ventral surface light gray. Mouth ventral, tentacles about 20; anus terminal. Cuvierian tubules absent, stone canals several, Polian vesicle single. Ossicles types are buttons with a large perforations and tables in dorsal and ventral surface; terminal plates in tube feet; enlarged and elongated plates in tube feet and pedicels and rods in tentacles.

Description. Body form generally arched dorsally (Figure 3A), little flattened ventrally (Figure 3B). Length up to 185 mm, width up to 45 mm when contracted. Body wall thin (up to 4 mm) in relaxed state. Pedicels/tube feet irregularly distributed on ventral side. Conical verrucosities of dorsal surface minute or lacking. Mouth ventral, tentacles usually 20, anus terminal, anal papillae well developed (5 series of 4 each, in each radius). Live colouration of dorsal surface brown bitumen, ventral surface light gray. Longitudinal muscles about 10–14 mm in thickness. Cuvierian tubules absent. Stone canals several, 5–6 on right and 2–4 on left side of dorsal mesentery, average length <1 cm. Polian vesicle single, up to 30 mm long. Tentacular ampullae> 8 mm. Collar around mouth thin (about 0.69 mm). Calcareous ring (Table 4) large/stout with expanded radial plates, each with a broad anterior notch, slightly bifurcate anterior parts and a flat or slightly indented posterior margin.

Ossicles. Dorsal and ventral surfaces comprise the same type of ossicles; tables (Figure 3 Ca) and buttons (Figure 3 Cb). Table disc of ventral surface wheel-shaped with a variable number of spokes. The four pillars of spire appear parallel to each other and do not merge at the apical end, each ending in several pointed, thorns/teeth, generally arranged in groups of 3–4 at the end of each pillar. Buttons thick, oval, about 69.10 and 58 µm long dorsally and ventrally respectively and 35.60 and 31 µm wide dorsally and ventrally respectively. Margins of buttons irregular, wavy and rough; holes average about 7, quite large, usually oval but can become obliterated to disappear completely, thus giving the button a solid, rough appearance. Average width of the holes 7.80 and 4.90 μm dorsally and ventrally respectively. Generally, the symmetrical holes in the center of the buttons are wider than the terminal ones which are rather oval in shape. Pseudo-buttons abundant, fenestrated ellipsoids scarce.

Pedicels present perforated plates. Enlarged plates (Figure 3 Da) rectangular in shape and smooth. The central perforations are surrounded by smaller, circular ones; other plates generally oval in shape with an irregular outline; elongated plates (Figure 3 Db) simple and irregular in outline. Ventral surface also present terminal plates (Figure 3 Dc). Tentacles possess thin rods (12 µm) (Figure 3 Ea and Figure 3 Eb).