Isohypsibiidae

Marley, Nigel J., Mcinnes, Sandra J. & Sands, Chester J., 2011, Phylum Tardigrada: A re-evaluation of the Parachela, Zootaxa 2819, pp. 51-64 : 59

Family: Isohypsibiidae fam. nov.

Remarks. With the establishment of the superfamily, Isohypsibioidea, a familial title is required under ICZN (1999) and we propose the familial name of Isohypsibiidae derived from the genus Isohypsibius .

At the core of this group Isohypsibius , Thulinius and Halobiotus directly match the clade clearly demonstrated in Kiehl et al. (2007), Sands et al. (2008b) and Figure 2. While the AISM of Halobiotus have been described as hooks ( Pilato and Binda 2010), original descriptions and images suggest modified ridges with dorsal hook and ventral fenestra ( Kristensen, 1982; Crisp and Kristensen, 1983). Pilato and Binda (2010) ascribe Isohypsibius - type claws to Pseudobiotus and Doryphoribius Pilato 1969 (in Pilato, 1969b), the former having a ridged AISM but the latter an elongated ventral ridge AISM extended into a ventral lamina. They also describe Isohypsibius - type claws and ridged AISM for Eremobiotus Biserov, 1992 , which is aligned with Isohypsibius in Figure 2, and the elongated ridged AISM to Ramajendas Pilato and Binda, 1990 , though this genus has a combination of Isohypsibius- and Hypsibius- type claws ( Pilato and Binda 2010). We agree with these points and therefore include these genera within the new superfamily and family.

We are less certain as to the familial position of Mixibius (type species, formally Isohypsibius saracenus Pilato, 1973 ). This taxon was described as having modified Isohypsibius - type claws which would support moving it into the new family and superfamily. The AISM was however described as a modified hook ( Pilato 1992, Pilato and Binda 2010), but other evidence suggests this modified hook is markedly different from the Hypsibius form and is, sensu stricto, actually a small gap between the apophysis and the elongated longitudinal thickening. We therefore consider the overall shape of the AISM to be a modified ridge rather than hook and tentatively place Mixibius in the Isohypsibiidae , but advocate only molecular evidence can confirm this position. Similarly, claw morphology would also place Thalerius Dastych, 2009 in this group, though AISM data are not yet available for this taxon.

We envisage further morphological and molecular work will be required to clarify the interrelationships between these seven (or eight) genera.

Diagnosis. Isohypsibioidea. Claw pairs of similar size and shape. External and internal claws exhibiting articulation (the basal section and secondary branch form a solid unit while the primary branch and secondary branch articulate). Claws Isohypsibius - type, forming a right-angle between basal section and secondary branch. AISM ridge-like.

Composition. Based on the criteria discussed above: Isohypsibius Thulin, 1928 , Doryphoribius Pilato, 1969 , Pseudobiotus Nelson, 1980 (in Schuster, Nelson, Grigarick and Christenberry 1980), Thulinius ( Bertolani, 2003) , Halobiotus Kristensen, 1982 , Ramajendas Pilato and Binda, 1990 , and Eremobiotus Biserov, 1992 ( Mixibius Pilato, 1992 and Thalerius Dastych, 2009).

Etymology. As the Isohypsibius - type claw structure defines the superfamily, we propose the familial name of Isohypsibiidae , with the type genus of Isohypsibius .