Thyone Oken, 1815

Arumugam-Moonilal, Preyan & Thandar, Ahmed S., 2023, Designation of a neotype for the dendrochirotid holothuroid, Thyone fusus (Müller) (Echinodermata: Holothuroidea: Dendrochirotida: Thyonidae), Zootaxa 5369 (4), pp. 585-590 : 586-587

Genus Thyone Oken, 1815

Thyone Oken, 1815: 351 ; Jaeger, 1833: 8; Panning 1949: 467; Pawson & Miller, 1981: 394; Thandar, 1990: 211; Paulay & O’loughlin, 2012.

Anaperus Troschel, 1846: 60 (partim).

Diagnosis (after Panning 1949, Thandar 1990, McKenzie 1991, amended herein)

Small to medium-sized dendrochirotid holothuroids, reaching a length of? 200 mm, according to Mortensen (1927) but usually much shorter. Tube feet numerous, distributed throughout the body, more numerous in ambulacra, scattered in interambulacra, often more crowded ventrally; in young individuals restricted to ambulacra. Tentacles 10, ventral pair reduced. Calcareous ring tubular, radial and interradial plates sub-divided; radials with long, paired subdivided posterior processes. Body wall ossicles comprise only two-pillared tables or the like, often reduced with age or absent. Introvert variously supported: tables only, rosettes only, tables and rosettes, tables and plates (?reduced tables), plates only, or introvert deposits absent or unknown.

Remarks

Pawson & Miller (1981) commented that Oken’s work (1815–1816) was listed under the Official Index of Rejected Works by the International Commission on Zoological Nomenclature (opinion 417, 1956). They then suggested that the genus Thyone must therefore be attributed to Jaeger (1833) who was the first to validate the genus in accordance with the requirements of the International Code of Zoological Nomenclature (ICZN). This step was followed by a.o Thandar (1990) but the genus name continued to be attributed to Oken (1815). In order to resolve this nomenclatural issue, Paulay & O’Loughlin (2012), submitted an appeal to the ICZN, resulting in the validation of Oken’s (1815) publication under opinion 3598. Therefore, the genus must again be attributed to Oken.

Type species: Holothuria fusus Müller, 1776 , by subsequent designation Jaeger (1833).

Remarks

After transferring some species to other genera, Arumugam (2011) attempted to separate the remaining species on the bases of introvert ossicles, where known, a character introduced by Panning (1949). According to WoRMS (2023) Thyone now contains some 67 nominal species. Hence, the genus still remains a “supergenus”. Thandar & Rajpal (1999), at the 5 th European Echinoderm Conference in Milan, and Thandar (2001), at the 10 th International Echinoderm Conference in Dunedin reported on some differences in the gross structure of the calcareous ring. Thandar (2001), reported some evidence of geographic variations in the gross structure of the calcareous ring, based on the following three characters: a) dorsal radial plates posteriorly prolonged before bifurcating into paired processes, b) dorsal radial plates bifurcate at the posterior border of the interradial plates and c) dorsal radial plates bifurcate well before the posterior border on the interradial plates (producing posteriorly cleft or deeply incised radial plates. He reported certain geographic variations in the structure of the ring: e.g. in the Indo-West Pacific region, including southern Africa, all three types of ring exist, whereas in Madagascar, including the Mascarene Islands, and the North East Atlantic waters, including the Mediterranean and North Seas, only the former two types are prevalent, with some exceptions, while in the West Atlantic and East Pacific waters, with a couple of exceptions from the West Atlantic, only the third type predominates. However, relating these differences in the calcareous ring to the ossicles of the general body wall, introvert and tentacles proved unsuccessful.

The diagnosis of the genus is here amended, now based upon our better knowledge of the species it contains and the varied forms of its introvert ossicles. The taxonomic classification follows that of Smirnov (2012), who elevated the subfamily Thyoninae Panning, 1949 to full family status. Although this system has not yet been adopted by WoRMS² (accessed 21/09/2023), it proposes it as an alternative classification. Smirnov’s (2012) system was used by Thandar (2018) for his paper on some miscellaneous holothuroids in the South African Museum and also in his subsequent papers ( Thandar 2021; Thandar & Arumugam 2022), and more recently, in his comprehensive monograph of the southern African sea cucumbers (Thandar 2022).

When reporting on the holothuroids of the Norwegian Sea and adjacent waters, Madsen & Hansen (1994) erroneously attributed T. fusus and T. gadeana to the family Cucumariidae . Although they stated that the type material of T. fusus , is in all probability lost, they made no attempt to designate a neotype with ample material at hand. McKenzie (1991) also shied away from this prerogative in his revision of north Atlantic dendrochirotid fauna. Our attempt to trace the holotype from German museums proved unsuccessful. Thus, the establishment of the neotype is imperative since this species is the type species of Thyone and has been confused several times with many of its congeners, especially those coming from the North Atlantic, Adriatic and Mediterranean waters. This omission is here rectified from material obtained from the type locality.