Stolus (partim) Selenka, 1867: 355; Panning, 1949: 462; Clark & Rowe, 1971: 204.

Type species. Thyone buccalis Stimpson, 1885.

Diagnosis (from Panning, 1949, restricted herein). Tentacles 10, ventral two nearly always reduced; calcareous ring fragmented into a mosaic pattern with the radial plates carrying long, paired, subdivided posterior processes; body wall ossicles primarily as knobbed plates/buttons, often provided with a handle on one side and a spire on the opposite side, rarely plates/buttons smooth, but never reticulate.

Remarks. Panning’s (1949) diagnosis is here modified and restricted to contain species with mostly simple, knobbed, unreticulated plates in the body wall since those species with smooth, reticulated plates are now removed and assigned to the new genus Pseudostolus n. gen., while a few others originally described in Thyone or Havelockia, but agreeing with the amended diagnosis of Stolus, are herein transferred to Stolus. The genus Thyone, now containing about 80 species, has for some time now, assumed the status of a “supergenus” (sensu Pawson & Miller 1981), serving as a receptacle for any dendrochirotid holothuroid with 8+2 tentacle arrangement, scattered tube feet, a complex subdivided (mosaic-like) calcareous ring and 2-pillared tables as body wall deposits. It is therefore in need of thorough revision. While it may be argued that such an action should await a broad phylogenetic analysis based on both morphological and molecular characters, one cannot await such an analysis indefinitely. Panning’s system was initially questioned by Cherbonnier (1952) but completely ignored by Deichmann in her 1954 and subsequent papers. However, it is currently widely utilised but with some caution and many of his originally designated congenerics finding new homes, while others still await re-assignment.

Arumugam (2009), in her broad, yet unpublished research, transferred several Thyone species to Stolus or other genera, on my advice and with the concurrence of Rowe (pers. comm), as they did not correspond with T. fusus, the type species of Thyone. Some of these changes are herein published for the first time. Hence, T. uniannulata Sluiter, 1901, T. pseudofusus Deichmann, 1930, Thyone parafusus Deichmann, 1941 [(overlooked by Panning (1949)] and T. axiologa H.L. Clark, 1938, are now re-assigned to Stolus. The assignment of T. pseudofusus, T. parafusus and T. uniannulata is discussed below. Thyone axiologa, on the other hand, has tables with a very prominent spiny handle on one side, typical of T. pseudofusus as Clark (1938) himself commented, but the disc of the table illustrated by him, appears smooth. It is here stated that T. crassidisca Pawson & Miller, 1981, whose ossicles and calcareous ring resemble those of Stolus canescens (Semper, 1867) and T. pawsoni Tommasi, 1972 may one day suffer the same fate.