Mixibius schnurae, Pilato & Lisi & Binda, 2010

Pilato, Giovanni, Lisi, Oscar & Binda, Maria Grazia, 2010, Tardigrades of Israel with description of four new species, Zootaxa 2665, pp. 1-28 : 21-24

Mixibius schnurae sp. nov.

( Figs. 10, 11)

Material examined. Locality No. 1 ( Mt. Hermon : Makam Ibraim el Khalil): holotype (slide No. 5420) and 12 paratypes (Nos. 5419-20) .

Type repository. Holotype and paratypes are deposited in the collection of Binda & Pilato, Museum of the Department of Animal Biology “Marcello La Greca”, University of Catania .

Specific diagnosis. Dorsal cuticle rugose: transverse bands with faint, irregular reticular mesh design more elongate in some bands, less elongate in others. The ridges are more or less thick and also form small tubercles more visible in the posterior part of the body.

Stylet supports inserted on the buccal tube at c. 62–64 % of its length. Pharyngeal bulb with apophyses and two macroplacoids; microplacoid absent. Main branches of the claws with accessory points; small smooth lunules present; no other cuticular thickening present on the legs.

Description of the holotype. Body length 230 µm; colourless; eye spots not visible (however, the specimens sent by Chanan Dimentman were fixed in ethanol 70% and we were unable to examine living specimens). Body surface is rough ( Fig. 10 A–C) and we noted two forms of transverse bands, one where ridges form an irregular reticular design with transversely elongate meshes ( Fig. 10A), and the other where thin ridges form an irregular reticular design with almost isodiametric meshes ( Fig. 10C, arrows). The ridges are more or less thick and also form small tubercles ( Fig. 10A) more visible in the posterior part of the body ( Fig. 10B, arrow). The ventral surface showed an almost invisible granulation. The mouth, antero-ventral, has no peribuccal lamellae or papulae; other structures are not visible. Buccal tube 26.6 µm long, and when examined on the dorsal or ventral view, appeared slightly narrower in the anterior portion and wider in the caudal one ( Fig. 11A); it is 2.7 µm wide at the anterior extremity (pt = 10.2) and 3.3 µm (pt = 12.4) in the caudal portion. Apophyses for the insertion of the stylet muscles, as in the other species of this genus, "hook" shaped, but slightly asymmetrical with respect to the frontal plane; both apophyses with two caudal processes pointing backwards and sideways ( Fig. 11A). Stylet supports inserted at 62.8 % of the buccal tube length (pt = 62.8). Pharyngeal bulb with apophyses and two macroplacoids; microplacoid absent ( Fig. 11A); entire placoid row 9.4 µm long (pt = 35.3), first macroplacoid, with a central narrowing, 5.1 µm long (pt = 19.2); second macroplacoid 3.1 µm long (pt = 11.7).

Claws of ‘ Mixibius type’ and well developed; the basal portion of the internal claws very short ( Fig. 11B, C, D). Internal and external claws of the second pair of legs 12.0 µm (pt = 45.1) and 14.7 µm long (pt = 55.3), respectively; the orientation of the claws of the fourth pair of legs did not allow their measurement; in a paratype of the same body length ( Table 5) the anterior and posterior claws were 13.1 µm (pt = 46.8) and 17.0 µm (pt = 60.7), respectively. Main claw branches with accessory points ( Fig.11C); small, smooth lunules were present ( Fig. 11D). No other cuticular thickening present on the legs. Eggs not found.

The paratypes are similar to the holotype in both qualitative and metric characters. Measurements of structures of the holotype and of the smallest and largest specimens are indicated in Table 8.

Etymology. The name is in honour of our colleague Heather Schnur (Jerusalem).

Differential diagnosis. Until now only seven species are known of the genus Mixibius ; four have ornamented cuticle: M. tibetanus Li & Li, 2008 , M. ornatus , M. sutirae and M. ninguidus Biserov, 1999 . The new species differs from M. tibetanus in the characters of the cuticular ornamentation, in having only two macroplacoids, in lacking both the microplacoid, and cuticular bar on the legs I–III.

The new species differs from M. ornatus in having different cuticular ornamentation ( Figs 10A,C and 12A). In M. schnurae sp. nov. the stylet supports are inserted on the buccal tube in a more cephalic position (pt values from 62.4 to 64.3 in M. schnurae sp. nov., from 69.1 to 70.5 in M. ornatus ,), the buccal tube is slightly wider, and placoids and claws are slightly longer ( Table 8).

Mixibius schnurae sp. nov. differs from M. sutirae in having a different cuticular ornamentation ( Figs 10A, C and 12D), in having the stylet supports inserted on the buccal tube in a more cephalic position (pt values from 62.4 to 64.3 in M. schnurae sp. nov., from 70.5 to 70.8 in M. sutirae ) and slightly longer placoids ( Table 8).

The new species differs from M. ninguidus in having a different cuticular ornamentation, longer buccal tube and shorter second placoid ( Table 8).

One may hypothesize that before the genus Mixibius was created and described, some species belonging to this genus had been attributed to Isohypsibius . For this reason we compared Mixibius schnurae sp. nov. with species of Isohypsibius possessing ornamented cuticles. We noted that in some characters the new species is similar to Isohypsibius gilvus . However, we noted difference in the cuticular ornamentation and, in addition, the new species has wider buccal tube, shorter second macroplacoid (though the values of the pt index are not that different due to the I. gilvus buccal tube being slightly shorter with respect to the body size), and small lunules are present.