Ypsilocucumis californiae Massin & Hendrickx, 2011

(Figs. 1–3)

Ypsilocucumis californiae Massin & Hendrickx, 2011: 421, figs. 7, 8A-F, pl. 1H; Hendrickx, 2012a: 394, Annex 2 (list); Hen- drickx & Cordero-Ruiz, 2014: 10.

Material examined. Four specimens off the west coast of the Baja California Peninsula. TALUD XV St. 20 (26º30’42”N, 113º56’0”W), Aug. 1 2012, 1 specimen (TL 15.0 mm, W 9.6 mm), BS, 540–568 m (ICML-EMU- 11503); TALUD XVI-B St. 5 (28º48’00’’N, 115º24’06”W), May 24 2014, 2 specimens (TL 15.0 and 10.0 mm, W 9.9 and 9.3 mm), BS, 772–776 m (ICML-EMU-11504); TALUD XVI-B St. 7 (29º21’12”N, 115º39’08”W), May 31 2014, 1 specimen (TL 17.0 mm, W 12.3 mm), BS, 710–750 m (ICML-EMU-11505).

Additional material examined. Three specimens from the Gulf of California. Holotype, TALUD VI St. 26 (24º56’17”N, 109º06’39”W), Mar. 16 2001, (TL 15.0 mm, W 9.5 mm), BS, 1190–1270 m (ICML-EMU 8613). Paratypes, TALUD VIII St. 11 (24º54’24”N, 110º25’30”W), Apr. 17 2005, 2 specimens (TL 12.0 and 15.0 mm, W 6.8 and 8.3 mm), BS, 920 m (ICML-EMU 8614).

Description. Body semi-spherical or “U” shaped, slightly flattened in the central dorsal region (Fig. 2A); ante- rior and posterior ends like sharp retractile cones (in the preserved material no more than 6 mm long). Holothuroids covered by perforated tables and plates, organized in two layers superimposed as roof tiles (Fig. 3B). Perisoma rough to the touch by the spires of the plates pointing outwards. Ambulacral feet scattered along the radius, small and rounded.At anterior end two long and digitiform tentacles, covered by small granules, observed exposed only in one specimen (TALUD XVI-B, St. 7). In the remaining specimens the crown of tentacles, including the two largest, and the introvert were contracted inside the body.

Ossicles of the body wall in two forms: (1) wide, perforated tables (921–1466 µm across) with an eccentric spire (Fig. 2B, I, II, VI); spire of the table conical, very long (up to 755 µm high), consisting of a network of pillars (Fig. 3A, I), and (2) smaller (359–861 µm across) plates oval, semi-square or thimble-shaped, without spire (Fig. 2B, III, IV, VII, IX, X), disposed as unions of plates between several plates with spire (Fig. 2B V, VII) and at the ends of body. Dorsal and ventral ossicles similar in shape; smaller plates without spire at the ends of body. Tentacles with curved bars, perforated at the ends, and with small teeth in the margin (139–227 µm long) (Fig. 3A, II).

Color. Body and tentacles white (preserved material).

Remarks. The specimens collected off the west coast of the Baja California Peninsula present the same morphological characteristics as those observed in the holotype (collected in the Gulf of California, on the east coast of the Baja California Peninsula). These specimens feature the same characteristics in the shape of the ossicles and in the external shape of the animal as described by Massin & Hendrickx (2011). The two forms of spicules that cover the body of the animal were observed in all specimens, as superimposed layers, one of the main characteristics of Y. californiae . The size of the organisms was also similar on both sides of the peninsula. Based on the new material, the length range for Y. californiae is from 10 (present research) to 21 mm (Massin & Hendrickx 2011). However, it is necessary to clarify that the size of organisms is a very plastic characteristic, little used to compare communities of holothurians.

Distribution. Northern Mexican Pacific, off the west coast of the Baja California Peninsula from 29º21’12”N to 26º30’42”N, and in the central and southern Gulf of California, Mexico.

Ecology. Environmental conditions available for the new specimens collected off western Baja California (outside the Gulf of California) were different from those observed with the type material (Gulf of California): depth, 540–776 m vs. 377 to 1270 for the type material; epibenthic parameters values, 0.15–0.28 ml O 2 /l and 5.34–8.38°C vs. 0.20–1.40 ml O 2 /l and 3.7–10.5°C for the type material (see Massin & Hendrickx 2011). In addition, the speci- mens from off the western Baja California Peninsula were collected in salinity of 34.42–34.51 ups (no data available for the type material). The new material occurs in a variety of sediments made of 7.75–11.82% clay, 45.16–77.67% silt and 11.09–47.08% sand, with an organic carbon content of 3.18–5.20 mg /g (5.47–8.95 % of organic matter) (Table 1).

Density of organisms. Ypsilocucumis californiae was not abundant off western Baja California Peninsula, with density estimated from 2.63 orgs/ha (TALUD XV, St. 20) to 3.94 orgs/ha (TALUD XVI-B, St. 7) (Table 1), in comparison with others species of holothuroids collected in the same area by the same two cruises TALUD. Such was the case of Synallactes virgullasolida for which density values were reported as up to 170.32 orgs/ha (Luna-Cruz & Hendrickx 2018).