Isohypsibius rusticus, Pilato, Giovanni, Sabella, Giorgio & Lisi, Oscar, 2015

Pilato, Giovanni, Sabella, Giorgio & Lisi, Oscar, 2015, Two new freshwater eutardigrade species from Sicily, Zootaxa 3918 (2), pp. 273-284 : 274-278

publication ID	https://doi.org/ 10.11646/zootaxa.3918.2.8
publication LSID	lsid:zoobank.org:pub:5FFF0A8B-839E-45E3-A510-0E7D32C9D8AA
DOI	https://doi.org/10.5281/zenodo.5660071
persistent identifier	https://treatment.plazi.org/id/CE22D104-1E63-CF5F-FF13-FB0EB906D687
treatment provided by	Plazi
scientific name	Isohypsibius rusticus
status	sp. nov.

Treatment

Isohypsibius rusticus sp. nov.

Type locality. Saracena Torrent (Maniace, Catania); 37°52′N, 14°48′E; 750 m. a.s.l.

Material examined. Holotype (slide N. 5540) collected by Angelo Zappalà 17.11.1974.

Specific diagnosis. Aquatic; colourless; eye spots present; the body surface is ornamented with many variously sized tubercles; pharyngeal bulb with apophyses and two rod-shaped macroplacoids; microplacoid absent; claws of the Isohypsibius type, long, slender with a long, thin common basal portion; accessory points on all main branches joined to branch and unexposed, small flexible lunules present; no cuticular bars on the legs.

Description of the holotype. Body length 318 µm, colourless; eye spots present before mounting; the entire body surface is ornamented: many, variously sized small tubercles that do not form a reticular design, are present; the largest (diameter up to 2.4 µm) are present on the dorsal body surface and are intermingled with numerous, much smaller which appears almost as dots ( Fig. 1A, B View FIGURE 1. A – D ). All these tubercles are external, prominent structures, not pillars. The ornamentation is present both on the dorsal and on the ventral surface, but on the latter it is less showy ( Fig. 1C View FIGURE 1. A – D ).

Bucco-pharyngeal apparatus of the Isohypsibius type ( Fig. 1D View FIGURE 1. A – D ): mouth without peribuccal lamellae, buccal tube rigid without ventral lamina; apophyses for the insertion of the stylet muscles ridge-shaped. Buccal armature, today no longer visible but observed immediately after mounting, consisting of dorsal and ventral transverse ridges, present in the caudal portion of the buccal cavity, and subdivided into teeth: anterior to the transverse ridges are a band of very small teeth. Buccal tube 32.9 µm long and 3.9 µm wide externally (pt = 11.9); stylet supports inserted on the buccal tube wall at 76.0 % of its length (pt = 76.0). Pharyngeal bulb with apophyses and two rodshaped macroplacoids; microplacoid absent. First macroplacoid with a central constriction ( Fig. 1A, D View FIGURE 1. A – D ) 9.6 µm long (pt = 29.2), second 5.8 µm long (pt = 17.6). Macroplacoid row 15.8 µm long (pt = 48.0).

Claws, well developed, of the Isohypsibius type ( Fig. 1A View FIGURE 1. A – D and Fig. 2 View FIGURE 2. A – D ); external and internal claws of each leg different in length, the external having longer main branches. The basal common portion of the claws is long and thin ( Fig. 2 View FIGURE 2. A – D ). The orientation, as it is frequent in the species with very long claws, made the measurements of the total claw length difficult, for this reason we include separate measurements for the main branch length. The orientation of the holotype meant we were only able to measure the external claw of the second pair of legs and the claws of the hind legs ( Table 1). Accessory points on all main branches joined to branch and unexposed; very thin, flexible lunules, but no cuticular bars, present on the legs ( Fig. 2C View FIGURE 2. A – D ).

We did not find eggs attributable to the species.

Isohypsibius rusticus Isohypsibius verae Isohypsibius zappalai sp. nov. sp. nov.

Slide No. 5540 holotype 3679 holotype 5551 holotype µm pt % µm pt % µm pt % Differential diagnosis. Excluding species of Isohypsibius with smooth cuticle, those with gibbosities or regular, reticular cuticular ornamentation, those with three macroplacoids or with microplacoid, and those with leg bars, leaves relatively few Isohypsibius species for comparison. These are: Isohypsibius gilvus , Isohypsibius verae , Isohypsibius barbarae , Isohypsibius annulatus ( Murray, 1905) , Isohypsibius pauper (Mihelčič, 1971) , Isohypsibius sculptus ( Ramazzotti, 1962) and Isohypsibius fuscus (Mihelčič, 1971/72).

We ascertained that the new species differs from these seven species in characteristics of the cuticular ornamentation. In particular, Isohypsibius rusticus sp. nov. differs from Isohypsibius gilvus in having cuticular tubercles that do not form transverse bands alternating with smooth bands, ( Figs. 1A, B View FIGURE 1. A – D and 3A View FIGURE 3. A – C ); stylet supports inserted on the buccal tube in a more caudal position (pt = 76.0 in the new species, 64.3 in I. gilvus ); first macroplacoid clearly longer than the second ( Fig. 1D View FIGURE 1. A – D and 3B View FIGURE 3. A – C ), and claws clearly different in the shape, those of the new species being longer and more slender and without obvious accessory points ( Figs. 2 A–D View FIGURE 2. A – D and 3C View FIGURE 3. A – C ).

Isohypsibius rusticus sp. nov. differs from I. verae in having cuticular tubercles while I. verae has dots; stylet supports inserted on the buccal tube in a more caudal position (pt = 76.0 in the new species, 66.6 in I. verae ); a presumably higher difference in length between first and second macroplacoid ( Figs. 1A View FIGURE 1. A – D and 3 View FIGURE 3. A – C D; Table 1); a shorter common basal portion to each claw ( Figs. 2A–D View FIGURE 2. A – D and 3 View FIGURE 3. A – C E), higher percent value between the main branch length and the total claw length ( Table 1); and presence of lunules.

The new species differs from I. barbarae in having differently shaped cuticular tubercles that are also present on the ventral surface ( Fig. 1C View FIGURE 1. A – D ); the absence of the transverse undulations that are present in I. barbarae ( Fig. 4A View FIGURE 4. A ); the stylet supports are inserted on the buccal tube in a more caudal position (pt = 76 in the new species, 67.9 in I. barbarae ); the claws are longer and more slender ( Figs. 2 A–D View FIGURE 2. A – D and 4 View FIGURE 4. A C, D), and without obvious accessory points, which are present in I. barbarae ( Fig. 4 View FIGURE 4. A D).

Isohypsibius rusticus sp. nov. differs from I. annulatus in having variously sized and irregularly distributed cuticular tubercles, ( annulatus was named for the regular lines of papillae running round the body); in addition, the external and internal claws seem to be of different length and exposed accessory points are lacking, while these are clearly shown in I. annulatus (see Murray, 1905, plate III fig. 14c).

The new species differs from I. pauper in having cuticular tubercles of various sizes; in addition, the eye spots are present, the buccal tube is longer than the pharyngeal bulb, and the claws lack accessory points. Mihelčič (1971/72) in the description of I. pauper did not record or draw lunules, which are present in Isohypsibius rusticus sp. nov.

Isohypsibius rusticus sp. nov. differs from I. sculptus in having proper cuticular tubercles and not pillars as reported by Dastych (1997) for the latter species; eye spots present, higher pt value relative to the stylet supports (76 in the new species, 69–70 in I. sculptus ) and probably longer claws.

Isohypsibius rusticus sp. nov. differs from I. fuscus in having variously sized, well spaced cuticular tubercles; in addition, the buccal tube is longer than the pharyngeal bulb, first macroplacoid length is clearly not three times larger than the second macroplacoid. Mihelčič (1971) in the description of I. fuscus did not record or draw lunules, which are present in the new species.

Etymology: The specific name rusticus = unrefined, refers to the look of the cuticular ornamentation.