Thyone vilis ( Sluiter, 1901 )

Thandar, Ahmed S., 2021, Nomenclatural changes in some sea cucumbers with the erection of a new genus and description of a Thyone? juvenile (? n. sp.) from the Gulf of California (Echinodermata: Holothuroidea: Dendrochirotida), Zootaxa 5026 (4), pp. 507-526 : 519

Thyone vilis ( Sluiter, 1901)

Figures 8 & 9

Cucumariia vilis Sluiter, 1901: 86 , pl 7, fig. 5.

Thyone villis Panning, 1949: 467 (lapsus calami).

Diagnosis (see Sluiter 1901).

Material examined. ZMUA, H1114 , Banda , herein designated as lectotype, 1 spec. ; Molo Strait, ZMUA, H1109 (not conspecific with former), 1 spec. ; USNM E48738 , North Pacific Ocean, Philippines, La Union, Luzon Island, San Fernando , Sta. 5442 (16° 30’ N, 120° 11’ E), 45 m, 10 May 1909, Albatross R /V, Philippines Expedition, det. Deichmann, E., 1 spec.

Description. Specimen (USNM E48738 ) small, barrel-shaped, about 33 mm long and 11 mm wide in midbody; calcareous ring and associated structures absent. Colour, in alcohol, uniformly greyish white. Tube feet mostly retracted, usually in ambulacra but few also scattered in interambulacra, 1.5 mm long when extended, suckers well- developed. Anal teeth present. Body wall wrinkled, soft, smooth, fairly thick. Gonad (testis) well- developed, mature, tubules unbranched. Respiratory trees well-branched, one extending to about three quarter of body length. Longitudinal muscles unpaired, cylindrical. Ossicles of the body wall comprise plates and tables. Plates small, smooth, spire-less, circular to triangular, with thin margins and three or more holes of varying size ( Figure 9A & B ). Tables also with a thin-margined disc with usually four large holes ( Figure 9C ), sometimes more with a reduced two-pillared spire, ending in two clusters of teeth or teeth absent, transverse bar lacking. Table discs 73–95 µm long, 53–71 µm wide, holes 25–33 µm wide. Tube feet ossicles ( Figure 9D ) as rods, up to 237 µm long, swollen in the middle, perforated by four large central holes and a few holes at each end. End plates with large marginal and smaller medial holes.

Distribution. West Pacific ( Indonesia and Philippines).

Remarks. Despite the absence of the calcareous ring and its associated structures the identity of this specimen is in no doubt. It does possess the characteristic thin-walled tables and plates reminiscent of those of one of the syntypes of Thyone vilis (cf. Figure 8B & 9A–C ). In support of this, the tube feet rods ( Figure 9D ), which Sluiter (1901) refers to as tables, are identical to those illustrated by him for his species ( Figure 8C ) and so is also the spire of the body wall tables. I have had the opportunity to study both Sluiter’s syntypes at the ZMUA. The two specimens, one from Banda (H1114) and the other from Molo Strait (H1109), are well preserved. However, the calcareous ring and its associated structures are only present in the Banda specimen ( Figure 8A ); the Molo Strait specimen lacks the calcareous ring. The calcareous ring and ossicles of the Banda specimen illustrated in Figure 8 are copied from Sluiter’s figure, whereas those from the current specimen are illustrated in Fig. 9 . It is apparent from Sluiter’s figure that all his illustrated ossicles came from the Banda specimen, except for a single large plate ( Figure 8G ) which presumably came from the Molo Strait specimen. The large plate of the Molo Strait specimen I examined is here illustrated in Figure 8F ). From this it is apparent that both Sluiter’s specimens are not conspecific and the Molo Strait specimen may represent another species but its lack of the calcareous ring prevents any identification. The Banda specimen is therefore here designated the lectotype. The plate illustrated by Sluiter (1901) ( Figure 8G ) and herein from the Molo Strait specimen ( Figure 8F ) are larger, overlapping and often broken. The calcareous ring ( Figure 8A ) of the Banda specimen is of the typical Thyonidae type with a tube broken into a mosaic and processes of the radial plates long, distally coiled and also subdivided. The present USNM specimen appears to be a true Thyone vilis and there is no doubt that it is the second record of this species, judging from the literature at hand. Although correctly identified by Deichmann, it is regrettable this record was not published.

Figures

FIGURE 8. Thyone vilis Sluiter, 1910. Lectotype, ZMUA, H1114. A. Calcareous ring (middorsal view); B. Table from body wall; C. Rod from tube foot.; D. Table from introvert; E. Rosette from introvert; G. Plate of?Molo Strait specimen. (A–G copied from Sluiter 1910); F. Plate from Molo Strait specimen (author’s examination). (All ossicles to same scale).

FIGURE 9. Thyone vilis Sluiter, 1910. USNM E48738 A, B & C. Regular, irregular and round tables of body wall; D.Tube feet deposits.