A critical assessment of the dendrochirotid subfamilies, sclerodactylinae and thyoninae, with the taxonomic management of the "supergenus" thyone (echinodermata : holothuroidea)

Abstract

The key character separating the dendrochirotid families Sclerodactylidae (sensu Pawson & Fell, 1965) and the Phyllophoridae (sensu Pawson & Fell, 1965), i.e. entire or undivided radial processes to the calcareous ring in the former and sub-divided processes in the latter, is unjustified since most sclerodactylid species also have subdivided processes. It is here assumed that the basis of elevating the subfamily Sclerodactylinae Panning to family level was established on a misinterpretation or mistranslation of the original diagnosis of this subfamily or a lapsus calumni meaning “plates” instead of “processes”. Panning (1949) categorically states that the processes in the Sclerodactylinae are composed of 3–4 large pieces of calcite and only as an exception they are unbroken. Since Pawson & Fell gave no other distinction between the Sclerodactylidae and the Phyllophoridae, the former is here considered an invalid taxon and its three current subfamilies (Sclerodactylinae, Sclerothyoninae Thandar and Cladolabinae Heding & Panning) are re-assigned to the Phyllophoridae. This family now includes six subfamilies: Cladolabinae, Phyllophorinae Östergren, Sclerodactylinae, Sclerothyoninae, Semperiellinae Heding & Panning and Thyoninae Panning. The diagnosis of the Sclerodactylinae, restricted by Thandar (1989), is now modified to include also those forms whose radial and interradial plates may be slightly sub-divided but still form a short tube. Of the eleven genera placed within this subfamily subsequent to its erection, only ten of these remain. Neothyone Deichmann is a preoccupied name for which Lisacucumis is here proposed as a replacement. Thandar’s (1989) diagnosis of the Thyoninae is here accepted, however, the genus Thorsonia Heding is transferred to the Sclerodactylinae. Of the 66 nominal species which currently stand in the “supergenus” Thyone Jaeger, 10 are transferred to Havelockia Pearson within the Sclerodactylinae, while one species is regarded as a synonym of H. herdmani Pearson. In addition, six species are transferred to Stolus Selenka within the Thyoninae. Finally, three species are transferred to Sclerothyoninae, two within Sclerothyone Thandar and one within Temparena Thandar. Two species show an uncertain affinity to Thyone and are temporally removed from the genus. Furthermore, two species currently classified within Havelockia are transferred to Thyone. The now remaining 46 species are separated into seven groups based on the composition of their introvert deposits: tables only (8 spp.), rosettes only (5 spp.), tables and rosettes (21 spp.), tables and plates/?reduced tables (2 spp.), rosettes and plates/?reduced tables (3 spp.), plates only (2 spp.), or introvert deposits absent or unknown (5 spp.). Regrettably, no other character could be used in conjunction with the above to suggest at least sub-generic levels. Within the genus Havelockia, Cucumaria redimita Sluiter indicates an affinity with Pentamera Ayres. It is here transferred to this genus within the Thyoninae. Havelockia, now containing 17 species, is also revised. Keys, diagnoses and figures are provided for all nominal species now included in Thyone and Havelockia.