Tanarctus Renaud-Debyser 1959

Genus Tanarctus Renaud-Debyser, 1959

Diagnosis (following Jørgensen & Kristensen 2001): Tanarctinids without dorso-lateral epicuticle long rodshaped pillars. All four digits with simple external claws without dorsal spurs, internal claws with microscopic spurs or without spurs. The internal digits may be fused proximal and form a pretarsus. The external digits have a basal cuticular fold. The primary clava, when present, is very long and similar to the IV leg appendages, or the IV leg appendages are strongly modified with long spines, leaf-like appendages or balloon-like ampullae. The buccal clavae may consist of fused secondary and tertiary clavae and then appear H-shaped around the mouth, or they can be located rostrally as club-shaped clavae (secondary clavae?). Finally the buccal clavae may be absent or indistinct as a dome- or lens-shaped structure.

FIGURE 16. LM of Tholoarctus oleseni nov. sp. A–D. Allotypic female. A. Overview. B. Close-up of the head. C. Close-up of the buccal apparatus. D. Close-up of the fourth pair of legs. E. Overview of the holotypic male. Abbreviations: bt—buccal tube; cE—cirrus E; ec—external cirrus; ed—external digit; ic—internal cirrus; id—internal digit; oe—outer epicuticle; pb—pharyngeal bulb; pc—primary clava; pi—cuticular pillars; sc—secondary clava; se3—leg sense organ 3; ss—stylet support; st—stylet; ta—tarsus.

Type species: Tanarctus tauricus Renaud-Debyser, 1959.

Additional species: Tanarctus arborspinosus Lindgren, 1971; Tanarctus bubulubus Jørgensen & Kristensen, 2001; Tanarctus dendriticus Renaud-Mornant, 1980; Tanarctus diplocerus Fujimoto, Miyazaki & Suziki, 2013; Tanarctus gracilis Renaud-Mornant, 1980; Tanarctus helleouetae Renaud-Mornant, 1984; Tanarctus heterodactylus Renaud-Mornant, 1980; Tanarctus longisetosus Grimaldi de Zio, D'Addabbo Gallo, Morone De Lucia, Vaccarella & Grimaldi, 1982; Tanarctus minotauricus Renaud-Mornant, 1984; Tanarctus ramazzottii Renaud-Mornant, 1975; Tanarctus tauricus Renaud-Debyser, 1959; Tanarctus velatus McKirdy, Schmidt & McGinty-Bayly, 1976.

Remarks. Several new species of tanarctids with unknown phylogenetic relationships have been reported from the coarse shell gravel of the Faroe Bank (Hansen et al. 2001). These species might represent a North Atlantic radiation, and together with the common occurance of Tanarctus in subtidal samples (R.M. Kristensen pers. obs.), suggest that this genus is much more numerous than the current number of described species. If all the undescribed species residing in various tardigrade collections were examined, the number of known Tanarctus species would greatly increase; as shown with the descriptions of several new species of stygarctids (Hansen et al. 2012).