Crenubiotus revelator, 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 : 543-547

Crenubiotus revelator sp. nov.

( Figs 8–9 , Table 3)

Material examined: 65 specimens deposited in the Centro de Colecciones Científicas de la Universidad del Magdalena: CBUMAG:TAR:00067 (4 specimens), 00069 (1 specimen), 00073 (10 specimens), 00074 (2 specimens), 00075 (1 specimen), 00076 (1 specimen), 00092 (10 specimens), 00093 (10 specimens), 00094 (13 specimens), 00096 (12 specimens), and 00403 (1 egg). Localities: San Lorenzo 11°06’20.0’’N, 74°03’50.0’’W, 2284 m asl (type locality), and Bella Vista 11°05’47.8’’N, 74°05’04.4’’W, 1930 m asl. Complete information with correspondence between localities, sample kinds, type material and slide numbers, is given in Table 1.

Type repositories: Holotype, CBUMAG:TAR:00092-1. 32 Paratypes: CBUMAG:TAR:00092 (9 specimens), 00093 (10 specimens), 00094 (13 specimens), 00403 (1 egg).

Species diagnosis: Colourless after mounting, eye-spots present. Cuticle with circular and elliptical pores, in all life stages, of various sizes, global diameter pt range about 0.5–6.3; the smallest pores are rounded and sparse on the body, while the biggest are elliptical and present caudally as well as a cephalic pair present laterally to the mouth. Small cuticular tubercles present in a dorso-lateral caudal band just anterior to the hind legs, on the dorsal cuticle of such legs, and, less evident, on all legs on the dorsal and lateral leg cuticle (both externally and internally) and some between the claws. Simple buccal armature: no anterior or posterior bands of teeth visible under light microscopy, only lateral transverse crests, dorsal and ventral, the former ending each into a tooth in their median extremity; a medio-ventral tooth present between the two crests. Slender buccal tube, pt of its width about 10, pt of the stylet supports insertion point about 74. Two macroplacoids plus microplacoid. Claws typical for the genus, slender; large lunules on all legs with long, thin teeth equal to one another and uniformly distributed.

Eggs with conical, very finely and delicately reticulated processes. They are constituted by a main body and a tip more slender provided with darker papillous surface; tip sometimes containing internal septa delimiting a single proximal “bubble” plus eventual smaller, more distal ones. Tips sometimes ending with a filament. Base of processes with narrow projections on the egg shell, frequently connecting to each other from different adjacent processes.

Description of the holotype: Body length 359 µm, colourless after mounting. Eye-spots present. Cuticle with circular and elliptical pores, the largest are a very cephalic pair, elliptical, lateral to the mouth (minor × major diameter 1.51 µm × 2.22 µm; pt = 3.8 × 5.6) and the very the caudal, also elliptical (major diameter up to 1.61 µm, pt = 4.2); the smallest pores, instead, rounded and sparsely distributed on the cuticle, have diameter starting from less than about 0.5 µm (it was difficult to measure precisely such small structures; pt less than about 1.3). The pores are present in all life stages and seem not to show allometric growth.

Small cuticular tubercles form a dorso-caudal band ( Fig. 8D arrows a), on the dorsal side of legs IV ( Fig. 8D arrow b), and, smaller, on all legs ( Fig. 9A arrows, 9C arrow), giving a dotted appearance, on the dorsal and lateral leg cuticle (both externally and internally) and some between the claws. Bucco-pharyngeal apparatus ( Fig. 8A ) 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, appearing as a ridge, laterally ( Fig. 1A arrow a, in a paratype), as an elongated trapezoidal structure pointing forward ventrally ( Fig. 1C arrow, in a paratype); stylet furcae with the thickened, swollen apices of the branches very developed and elongated laterally ( Fig. 1E arrow, in a paratype). Buccal armature ( Fig. 8B, C ) seemingly without anterior and posterior bands of teeth (not visible, at least under light microscopy); crest system present but represented only by the lateral crests, with dorsal lateral crests which form each at the medial extremity a thickening similar to a tooth ( Fig. 8B arrow, in a paratype). A proper median tooth present only ventrally between the crests, slightly in a more anterior position ( Fig. 8C arrow, in a paratype).

Pharynx with apophysis, two rod-shaped macroplacoids, the first with central constriction, the second with slight, subterminal constriction, and microplacoid ( Fig. 8A ).

Claws typical of the genus, slender with long base and common portion; main branches with accessory points; very big lunulae, typically indented (long and thin teeth equal to one another and uniformly distributed) ( Figs 2 , 3 , 9 ).

Egg ( Fig. 8E ) white, spherical, with conical processes constituted by a main body and a distal portion more slender provided with darker, minutely papillous/hairy surface ( Fig. 8F arrow a); the tips sometimes end with a filament eventually frayed ( Fig. 8 E-G). The distal portion may contain internal septa delimiting a single proximal “bubble” plus eventual smaller more distal ones ( Fig. 8G arrow). A very minute, delicate reticular design, difficult to see and to show on photos, can be observed on the main body of the processes (barely visible in Fig. 8G ), while their bases form thin projections on the eggshell, usually long, that may in some cases connect to one another between adjacent processes ( Fig. 8F arrow b, H arrow), but without forming areolation or reticulation.

The only egg found has a diameter of 97.8 µm including the processes, 78.1 µm excluding them; 45 processes are present on the hemisphere, 16 on the optical section; the processes are high 14.0– 16.8 µm and have a basal diameter of 10.6–14.0 µm (most processes are about 15 µm high and 11 µm wide at their base).

In Table 3 the measurements of selected morphological structures of the holotype, and relative pt indices, and the ranges among the measured type specimens, are provided.

Taxonomic remarks: The paratypes show the same characteristics of the holotype in both qualitative and metric characters, with very low morphometric variability ( Table 3). The only egg found is not embryonated but it is definitely the same type as that of C. crenulatus , with just minor differences at sibling species level, and the absence of other Macrobiotoidea taxa in the sample allowed us to attribute it to the specimens found.

Differential diagnosis: C. revelator sp. nov. is very similar to C. crenulatus comb. nov., but it differs from it in having smaller cuticular pores on all the body; in particular, C. revelator has pt of minor × major diameter of the cephalic elliptical pore pair 3.8 × 5.6 (holotype; vs 7.4 × 8.5 in the neotype of C. crenulatus comb. nov.), pt of the diameter of the smallest pores (it was difficult to measure precisely such small structures) less than 0.5 (vs at least 0.7 in C. crenulatus comb. nov.), pt of major diameter of the biggest elliptical pores (which were located posteriorly) 4.0–6.3 vs 7.5–9.9 in C. crenulatus comb. nov. The new species has a medio-ventral tooth in the buccal armature (absent in C. crenulatus comb. nov.), more slender buccal tube (pt = 9.6–11.0 in the new species, about 13.2–14.4 in C. crenulatus comb. nov.), slightly more caudal stylet supports (pt = 73.2–74.8 in the new species, vs. about 71.9–72.8, slightly more slender claws (compare Figs. 2 and 3A, B for the new species with Figs. 3C and 6F, G for C. crenulatus comb. nov.) and in details of the egg (compare Fig. 7 with Fig 8 E–H): the processes are usually more slender in the new species and more often the main body of the process continues gradually in the tip, without the abrupt passage observed in C. crenulatus comb. nov.; the tips are more regular being very slender cones without irregularities or branches; these tips appears less transparent in the new species, being usually covered by a sort of extremely fine down, and often show internally a basal “bubble” eventually followed by other smaller (the basal bubble is more rare in the egg processes of C. crenulatus comb. nov., and additional smaller bubbles were not observed in this species). The distal filament is thicker and usually not frayed, while it is instead very often in C. crenulatus comb. nov. Process bases forms projections on the shell which are more developed in the new species and are frequently connected (not so in C. crenulatus comb. nov.).

See the end of former paragraph “Remarks on Crenubiotus crenulatus comb. nov. ” about possible confusion between the egg of the new species with eggs of the Mesobiotus coronatus group.

Etymology: The specific name “ revelator ” (= one who reveals) refers to the fact that the specimens of the new species revealed the existence of the new genus and the belonging to it of the former M. crenulatus .

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 2. Claw structure in Crenubiotus gen. nov. (from the holotype of C. revelator sp. nov., slide No. CBUMAG: TAR:00092-1). Arrow “a”: basal portion of the stalk system in the shape of a laminar peduncle; arrow “b”: distal, enlarged, portion of the stalk system; arrow “c”: intermediate portion of the claw without suture; arrow “d”: complete septum; arrow “e”: incomplete septum; arrow “f”: distal portion of the common portion with the suture between the claw branches.

FIGURE 3. Claws of Crenubiotus gen. nov. A. Claws of legs I of a paratype of Crenubiotus revelator sp. nov., arrows “d” indicate the complete septum between stalk and common portion of the claw in different views; slide CBUMAG:TAR: 00094. B. Claws of legs II of the holotype of Crenubiotus revelator sp. nov., arrow “d” indicates again the complete septum, “a” the basal peduncle. C. Claws of legs IV of a neoparatype of Crenubiotus crenulatus comb. nov., arrow “a” indicates the shape of the stalk system in frontal view; “f” indicates the suture between the two branches, “g” the claw base continuing into the lunule margin; slide No. 2284 from Pilato and Binda collection. Scale bars 10 µm. The letters of the various arrows are not in alphabetic order but follows the same denomination of Fig. 2 for easier comparison.

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.

FIGURE 9. Claws and cuticular tubercles of Crenubiotus revelator sp. nov. A. Leg II of the holotype, the arrows indicate the cuticular tubercles. B. Leg I of a paratype (slide No. CBUMAG:TAR:00094). C. Legs IV of another paratype (slide No. CBU- MAG:TAR:00092), the arrow indicates some tubercles. Scale bars 10 µm.