Crenubiotus crenulatus (Richters, 1904) Lisi & Londoño & Quiroga, 2020

Lisi, Oscar, Londoño, Rosana & Quiroga, Sigmer, 2020, Description of a new genus and species (Eutardigrada: Richtersiidae) from Colombia, with comments on the family Richtersiidae, Zootaxa 4822 (4), pp. 531-550 : 540-543

Redescription of Crenubiotus crenulatus comb. nov. ( Richters, 1904a)

( Figs 6–7 , Table 2)

Material examined: neotype, 4 neoparatypes and 3 eggs, deposited in the Pilato and Binda collection (slide Nos. 2284 and 2285) at the University of Catania. Type locality: Valtellina (Northern Italy), Palabione, 1700 m asl (these are the only data available from Binda 1974) .

Description: Body length up to 320 µm, colourless after mounting. Eye-spots present before mounting. Cuticle with circular and elliptical pores probably present in all life stages, global diameter pt range about 0.7–9.2; the largest pores are a very cephalic pair, constantly present in all specimens lateral to the mouth, which are elliptical (minor × major diameter of these pores 2.5 µm × 2.9 µm; pt = 7.4 × 8.5, measurable only in one specimen 254 µm long); apart from that pair of cephalic pores, the largest, elliptical, are present in the caudal portion of the body (major diameter range 2.9–3.1 µm, pt = 9.1–9.2); the smallest pores, instead, sparsely distributed on the cuticle, are rounded and have diameter starting from more than about 0.7 µm (it was difficult to measure precisely such small structures; pt more than about 2.1). Examining the available material, it seems the pores are present in all life stages and do not show allometric growth. Very small cuticular tubercles present in a dorso-lateral caudal band just anterior to the hind legs ( Fig. 6E in the evidenced polygon), as well as on the dorsal cuticle of legs IV ( Fig. 6E arrow); legs very probably also provided with smaller tubercles/granules (Pilato, pers. comm.) but no longer visible due to the micropreparation age.

Bucco-pharyngeal apparatus ( Fig. 6A ) of modified ‘ Macrobiotus type’, i.e. with ten peribuccal lamellae, rigid buccal tube with ventral lamina which is provided with an additional ventral thickening on its anterior portion ( Fig. 6A arrow, 6D arrow); dorsal apophysis absent or very reduced into a small thickening ( Fig. 1B arrow b, but this detail should be ascertained and also depends on interpretation).

Oral cavity armature ( Fig. 6B, C ) seemingly without anterior and posterior bands of teeth (not visible, at least in light microscopy), but provided of the crest system, which is represented only by the lateral crests (no medial crests or teeth present); each latero-dorsal crest forms at its medial extremity a rounded thickening appearing like a tooth ( Fig. 6B arrow); the ventral crests ( Fig. 6C , arrow indicating one crest), instead, simply continue medially in the ventral lamina.

Big stylet furcae with the thickened, swollen apices of the branches very developed and elongated laterally as described for the genus.

Two rod-shaped macroplacoids plus a microplacoid in the pharynx; the first macroplacoid is longer and shows a medial incision, the second, shorter, with subterminal incision ( Fig. 6A ).

Symmetric, slightly robust doubled claw Y-shaped ( Fig. 6F, G ), with a long stalk system, proximally forming a laminar peduncle while distally it has a round section, separated by a septum from a subsequent intermediate tract; from this, a distal incomplete septum, closing only the main branch base, leads to a following common tract of the two branches where their suture is visible; claw branches diverging quite high in the whole claw height and forming a nearly acute angle. Large lunules on all legs, indented in a regular pattern by long, narrow teeth equal to one another ( Fig. 6 F–G).

Egg ( Fig. 7 ), non-areolated, with conical processes (about 15–18 in the optical section, 46–47 in the hemisphere). The processes are usually short and wide cones which form abruptly a long, narrower terminal portion quite variable in shape (from relatively thick to narrow) and irregular either: only in some cases it is a simple slender cone, while in the others it is variously branched and/or show an uneven surface which gives an irregular shape, though remaining relatively transparent.

We noticed also the following details under the microscope, but they are barely visible due to the slide age and cannot be shown clearly on photos: only in few processes, there can be observed a single internal “bubble” at the base of this distal portion (with similar appearance to Fig. 8G arrow, in Crenubiotus revelator sp. nov.). The process tips usually end with a very delicate filament variously frayed. Very fine, delicate reticulation on the main body of the processes (distal portion excluded), difficult to see (drawn by Binda 1974); the process base forms short, narrow projections on the egg shell, drawn as dots by Binda (1974), which are not long enough to continue on the egg shell between the processes and connect to one another ( Binda 1988 described the egg shell as “perfectly smooth”).

Figures

FIGURE 1. Buccal tube of Crenubiotus gen. nov. and Mesobiotus sp. A. Lateral view of the buccal tube showing the detail of the buccal tube apophyses in a paratype of Crenubiotus revelator sp. nov. (slide CBUMAG:TAR: 00067). Arrow “a” points to the ventral apophysis and the arrow “b” to the putative dorsal residual apophysis. B. Detail of the buccal tube apophyses in a neoparatype of Crenubiotus crenulatus comb. nov. (slide No. 2284 from Pilato and Binda collection); arrows same as in A. C. Ventral view showing the trapezoidal appearance of the ventral thickening (arrow, pointing at the caudal base of the “trapeze”) in Crenubiotus revelator sp. nov. (slide CBUMAG:TAR: 00096). D. Ventral view of the typical arrow-shaped ventral lamina (arrow) in a Mesobiotus sp. E. Detail of the stylet furca in Crenubiotus revelator sp. nov., the arrow indicates a lateral process of the furca (slide CBUMAG:TAR: 00067). Scale bars 10 µm.

FIGURE 6. Crenubiotus crenulatus comb. nov. A. Bucco-pharyngeal apparatus of the neotype (Slide No. 2284 of Pilato and Binda collection). The arrow indicates the additional ridge of the ventral lamina. Scale bar 10 µm. B. Oral cavity of a neoparatype (Slide No. 2285 of Pilato and Binda collection) in dorsal view; the arrow indicates one of the two median teeth formed by the dorsal lateral crests. C. Oral cavity of the same neoparatype in ventral view; the arrow indicates one ventral lateral crest. D. Ventral view of the buccal tube of the same neoparatype showing the additional ventral thickening (arrow). E. Detail of the caudal tubercles in another neoparatype (Slide No. 2284 of Pilato and Binda collection): the evidenced polygon indicates the caudal band, the arrow indicates the area with tubercles over legs IV; F. Claws of legs II and III of the neotype. G. Claws of legs IV of a neoparatype (Slide No. 2284 of Pilato and Binda collection). Scale bars 10 µm.

FIGURE 7. Egg of Crenubiotus crenulatus comb nov. Slide No. 2284 from Pilato and Binda collection. Scale bars 10 µm.

FIGURE 8. Crenubiotus revelator sp. nov. A. Bucco-pharyngeal apparatus of the holotype. Scale bar 10 µm. B. Oral cavity of a paratype in dorsal view; the arrow indicates the two median teeth formed by the dorsal lateral crests. C. Oral cavity of the same paratype in ventral view; the arrow indicates the central tooth in between the ventral lateral crests. B, C, slide CBUMAG: TAR: 00094, scale bars 5 µm D. Detail of the caudal tubercles in the holotype: arrows “a” indicate the caudal band, arrow “b” indicates the tubercles over legs IV; scale bar 10 µm. E. Egg in toto, scale bar 10 µm. F. Detail of the processes showing the tips and basal projections. Arrow “a” points at the papillous/hairy surface of the tip. Arrow “b” points at the thin projections on the eggshell. G. Detail of the faint reticular design (barely visible only at the process base) and the internal septum forming a bubble in the process (arrow). H. Detail of the digitations at the base of the processes, notice how in this case they are long and connected (arrow). F–H common scale bar 10 µm. E-H slide CBUMAG:TAR: 00403.