Zygothuria oxysclera Perrier, 1902

Gebruk, Andrey V., Solis-Marin, Francisco A., Billett, David S. M., Rogacheva, Antonina V. & Tyler, Paul A., 2012, Review of the genus Zygothuria Perrier, 1898 and the Atlantic group of species of the genus Mesothuria Ludwig, 1894 (Synallactidae: Holothuroidea) with description of the new species Mesothuria milleri sp. nov., Journal of Natural History 46, pp. 265-348 : 327-331

Zygothuria oxysclera Perrier, 1902

( Figure 19 )

Zygothuria lactea var. oxysclera – Perrier, 1902: 323–327, pl. 17, figs. 7–10 (partim).

Material examined

See Table 14.

Type material

Syntypes, MNHN 1648, Talisman, St. 21, 14 June 1883, 33 ◦ 46 ′ N, 11 ◦ 22 ′ W, 1319 m, one specimen ; MNHN 1649, Talisman, St. 31, 16 June 1883, 32 ◦ 37 ′ N, 12 ◦ 07 ′ W, 1163 m , fragments; MNHN 1940, Talisman , 27 June 1883, St. 49, 28 ◦ 37 ′ N, 15 ◦ 22 ′ W, 865 m, one specimen ; MNHN 1941, Talisman , 21 June 1883, St. 36, 31 ◦ 34 ′ N , 12 ◦ 41 ′

W, 1050–1052 m, one specimen; MNHN 1944, Talisman , 17 June 1883, St. 34, 32 ◦ 27 ′ N, 12 ◦ 15 ′ W , 1052 m, two specimens.

Type locality

Atlantic Ocean, off Morocco, 865–1319 m.

Diagnosis

Modified from Perrier (1902): body oval, ventral surface evidently flatter than dorsal; skin very thick, usually wrinkled; two layers of skin often seen. Maximum known size 370 mm (live). Mouth ventral, anus almost terminal. Tentacles small, from 15 to 20 in number, usually retracted. Ventrolateral tubefeet large, arranged in two simple rows along each side, up to 15–20 in row, placed at some distance from each other, often withdrawn. Odd ambulacrum naked. Dorsal papillae small, scattered over dorsal side, partly arranged in two rows.

Ossicles triradiate tables with single spire. Disks of irregular shape, 0.15–0.20 mm in diameter; central hole surrounded with meshwork of holes of different size ( Figure 19A,B,D ). Spire high, robust, often bearing minute spines ( Figure 19C,E ).

In young specimens (<50 mm), in addition to tables with irregularly shaped disks, tables with disks having six holes only are found, resembling those of Z. lactea . However, they are always single-spined. In addition, disks of intermediate form, with six main holes and series of small holes in outer circle, are also common in small specimens ( Perrier 1902).

Remarks

The characteristic ossicles with a single-arm spire in Z. oxysclera , first noticed by Perrier, occur also in Z. lactea together with typical three-arm spires. This resulted in Perrier’s variety Z. lactea var. oxysclera being rejected by many authors. Deichmann (1930) suggested that tables with single-arm spire tables become more common in the old specimens of Z. lactea , because the description of Perrier was based mainly on large specimens, 150–230 mm long. Apparently, she overlooked that Perrier had also examined a 50-mm long specimen which had the single-tooth spire tables only. Besides single-tooth spire tables, there are some other characteristic features distinguishing Z. oxysclera from Z. lactea . The meshwork of holes on the disks is more complicated in the former and the tables are slightly bigger in general, although the whole size range of ossicles is similar in the two species. The skin seems to be much thicker in Z. oxysclera and double-layered. However, this is especially typical for the large specimens, exceeding 150–200 mm, a size unknown for Z. lactea .

Relationships

The species is closest to Z. marginata (Sluiter, 1901) , also having triradiate single spire tables. Zygothuria marginata is the only other Zygothuria species , besides Z. lactea , to have had the details of its calcareous ring described ( Heding 1940). The calcareous ring of both species have triangular radial segments. Differences between Z. oxysclera and Z. lactea are discussed above in Remarks.

Geographical and bathymetric distribution

East Atlantic (from 865 to 1319 m), Caribbean (c. 700–850 m) ( Figure 19 ). Some old records of Z. lactea from the Caribbean, the Gulf of Mexico and east Atlantic may also correspond to Z. oxysclera .

Figures

Figure 19. Zygothuria oxysclera (Perrier, 1902). Ossicles. Johnson-Sea Link, Dive 1735. (A,B,D) discs, (C,E) spires.