Tenuibiotus, Pilato & Lisi, 2011

Pilato, Giovanni & Lisi, Oscar, 2011, Tenuibiotus, a new genus of Macrobiotidae (Eutardigrada), Zootaxa 2761 (1), pp. 34-40 : 39

Tenuibiotus gen. nov.

Genus of Macrobiotidae characterised by claws of the tenuis - type ( Figs. 1A and 2A–C ), i.e. with a stalk, a long common section in which primary and secondary branches are joined, and distal free sections of both the secondary branch (shorter than the primary) and primary branch forming almost a right angle.

The bucco-pharyngeal apparatus is of the ‘ Macrobiotus type’. Species attributed to this group share additional characters: narrow rigid buccal tube; small buccal cavity and poorly developed buccal armature; eggs of the known species laid freely and with conical or trunco-conical processes with more or less wide basal diameter.

Type species: Macrobiotus tenuis Binda & Pilato, 1972 .

Etymology: The name refers to the type of claws ( tenuis - type) which is the main characteristic of the new taxon.

Composition: the following species, previously ascribed to the genus Macrobiotus , have to be transferred to the new genus: M. tenuis , M. willardi , M. hystricogenitus , M. hyperonyx , M. higginsi , M. mongolicus , M. bondavallii , M. kozharai , M. tenuiformis , M. danilovi , M. voronkovi and M. ciprianoi .

We agree with Tumanov (2005) that M. ariekammensis ( Fig. 3C ) and M. kirghizicus ( Fig. 3D ) do not have claws of tenuis - type (their claws have primary and secondary branches joined over a much shorter distance than in the typical tenuis - type) and therefore they cannot be ascribed to the genus Tenuibiotus .

Unfortunately we did not have the chance to examine Macrobiotus caelicola that shares some characters with species of the tenuis group, but in Guil et al. (2007) Fig. 4F, the common portion of the claws of this species appears shorter than in the claws of the tenuis - type; as a consequence, we have doubts about its attribution to the new genus Tenuibiotus , but the problem needs further study.

Figures

FIGURE 1. A, Stylised drawing of the tenuis-type claws. As the primary and secondary branches are joined over a long distance, the remaining free portion of the secondary branch is clearly shorter than the primary branch, and the branches nearly form an almost right angle. B, Stylised drawing of the Macrobiotus hufelandi-type claws. Primary and secondary branches are joined over a shorter distance than in the claws of tenuis-type; the remaining free portion of the secondary branch forms with the primary branch an acute angle. ap = accessory points; l = lunules; pb = primary branch; s = stalk; sb = secondary branch.

FIGURE 2. A, Typical claws of the tenuis-type (the claws of the third pair of legs of the holotype of M. tenuis are shown). The arrow indicates the characteristic long common tract. B, C: Claws of the third pair of legs of a paratype of M. tenuiformis. In B an anterior appendage seems to be present (arrow) in the basal portion of the claws, but this appearance is due to the marked difference in the sclerotisation between the distal and the proximal tracts of the margin of the basal portion of the claws; in C the less sclerotised portion of the margin is focused (arrow) and it is evident that no true appendage is present; D, bucco-pharyngeal apparatus of Macrobiotus tenuis (holotype). (Scale bar = 10 µm).

FIGURE 3. A, B, claws of the first (A) and second (B) pair of legs of Tenuibiotus sp. It is clear that, due to the orientation of the claws, the angle between primary and secondary branches and the length of the common tracts may appear different in claws of the same pair of legs. C, D, claws of the fourth pair of legs of a paratype of Macrobiotus ariekammensis (C) and Macrobiotus kirghizicus (D). The arrows indicate that in both species the common tract of each claw is clearly shorter than that of the typical claws of tenuis-type. (Scale bar = 10 µm).