Isohypsibius occultus, Pilato & D’Urso & Sabella & Lisi, 2019

Pilato, Giovanni, D’Urso, Vera, Sabella, Giorgio & Lisi, Oscar, 2019, A new species of Isohypsibiid (Eutardigrada) from Sicily, Zootaxa 4608 (3), pp. 543-554 : 545-547

Isohypsibius occultus sp. nov.

Figs. 1 , 2. Table 1

Type locality: Sicily : Mirabella Imbaccari: wet mosses at the side of the river “Fiume del Ferro” .

Material examined: Holotype and one paratype (slide N. 5608) collected in wet mosses in October 1980 in the type locality; 21 paratypes (slides Nos. 1201–1204; 2774; 5548–5550) extracted from sediment of Flascio River in the territory of Randazzo.

Specific diagnosis: cuticle smooth or with ornamentation fading to invisibility, often difficult to see, similar to that of Isohypsibius monoicus. Eyes present. Buccal apparatus of the Isohypsibius type; buccal armature with well-developed medial transverse ridges. Claws, of the Isohypsibius type, well developed; internal claws I–III and anterior claws IV with the main branch thinning gradually; common basal portion thin; flexible lunules present, often rolled down under the claw base; no cuticular bar is present on the legs but, in some cases, a cuticular bulge is present simulating the presence of a bar-like thickening. Smooth eggs laid in the exuviae.

Description of the holotype: Body length 411 µm, yellowish. Eyes present. Cuticle with ornamentation fading to invisibility, very difficult to see, more easily recognizable in the caudal portion of the body; tubercles give to the cuticle, as in Isohypsibius monoicus, a “Persian lamb”-like pattern (Figs. 1 A, B, arrows). In a paratype 383 µm long, the largest caudal tubercles have a diameter up to 2.7 µm, but most are smaller The buccal apparatus is of the Isohypsibius type, i.e. the mouth has no peribuccal lamellae, the buccal tube is rigid without ventral lamina, and with ridge-shaped apophyses for the insertion of the stylet muscles, symmetrical with respect to the frontal plane ( Fig. 1 C , arrows a). Buccal armature ( Pilato 1974) without bands of teeth but with a long dorsal and a long ventral transverse ridge in the caudal portion of the buccal cavity; the median portion of those ridges is well developed ( Fig. 1D , arrow a), the lateral portions are subdivided into teeth. The buccal tube is 41.7 µm long and 4.9 µm wide (pt = 11.7); the stylet supports are short and stout ( Figs. 1C,D , arrows b), inserted on the buccal tube at 70.6 percent of its length (pt = 70.6); each stylet has a well-developed furca, the terminal branches of which have very evident swollen apices ( Figs. 1 C,D , arrows c). The pharyngeal bulb has apophyses and three short and stout macroplacoids without lateral incisions; microplacoid and septulum absent ( Figs. 1C,D ). The first macroplacoid, with a short triangular anterior portion, is 5.0 µm (pt = 12.0), the second 4.8 µm (pt = 11.6), the third 5.9 µm (pt = 14.2), the entire placoid row is 16.8 µm (pt = 40.5). By coverslip compression, the placoids may assume ( Figs. 1C,D ) the appearance described by Ramazzotti (1966) for Isohypsibius granulifer baicalensis (see Ramazzotti 1966 Fig.1B , and Fig. 5B ).

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The claws, of the Isohypsibius type ( Fig. 2 ), are well developed. The external claws I are 25.4 µm (pt = 61.2); internal claws I was not measurable; external and internal claws II, 27.7 µm (pt = 66.7) and 18.1 µm (pt = 43.6) respectively; external and internal claws III were not measurable; posterior and anterior claws IV, 33.0 µm (pt =79.5) and 22.9 µm (pt = 55.2) respectively.

Small, flexible lunules are present ( Fig. 2 B , arrow; and 2 C, arrow ‘a’), often rolled down under the claw base, and concealed. No cuticular bar is present on the legs, but in some cases, as described and shown by Dastych in Isohypsibius asper ( Dastych, 2016: figures 19 and 21), a cuticular bulge is present ( Fig. 2 C , arrow ‘b’) simulating the presence of a bar-like thickening.

Smooth eggs laid in the exuviae (we found with up 8 eggs). Remarks: The paratypes are similar to the holotype in both qualitative and quantitative characters ( Table 1 ). In the buccal armature of some paratypes, the medio-dorsal ridge may have the anterior margin with incisions, and appears indented.

Figures

FIGURE 1. Isohypsibius occultus sp. nov. A, B, The arrows indicate details of the cuticular ornamentation (A: paratype, slide No. 5548. B: paratype, slide No. 5608). C, Bucco-pharyngeal apparatus in lateral view (paratype, slide No. 1203). The ridge- shaped apophyses for the insertion of the stylet muscles (arrow a), the short and stout stylet supports (arrow b), and the very developed stylet furcae (arrows c) are evident. D, Bucco-pharyngeal apparatus in dorsal view (holotype, slide No. 5608). The well-developed medio-dorsal transversal ridge of the buccal armature (arrow a), the short and stout stylet supports (arrow b) and the well-developed stylet furcae (arrow c) are evident. Scale bars = 10 µm.

FIGURE 2. Isohypsibius occultus sp. nov. A, Claws of the second pair of legs (paratype, slide No. 2774). B, Claws of the fourth pair of legs of the holotype; the arrow indicates the lunule of the internal claw (slide No. 5608). C, Claws of the second pair of legs (paratype, slide No. 2774); arrow ‘a’ indicates a lunule: arrow ‘b’ a cuticular bulge simulating the presence of a bar-like thickening. D, Claws of the hind legs (paratype. slide No. 1203); the arrow indicates the accessory points of a posterior claw. Scale bars = 10 µm.

FIGURE 5. Isohypsibius baicalensis, A, Detail of the cuticular ornamentation. B, Bucco-pharyngeal apparatus. C, Claws of the second pairs of legs. D, Claws of the hind legs. Scale bars = 10 µm. The photographs of Isohypsibius baicalensis, were kindly furnished by Prof. Roberto Bertolani, from a specimen in the Ramazzotti Collection preserved in the Museum of Natural His- tory of Verona, who had kindly gave permission for the examination and photography.