Onychiurus arbailakensis Arbea, Beruete & Jordana, 2021

Beruete, Enrique, Arbea, Javier I., Baquero, Enrique & Jordana, Rafael, 2021, The family Onychiuridae (Collembola) from karst caves of the Basque biospeleologic district, with description of four new species, Zootaxa 5040 (2), pp. 151-194 : 175-178

Onychiurus arbailakensis Arbea, Beruete & Jordana sp. nov.

Figs 26−34 , Tables 7 and 13

Syn. Onychiurus rectospinatus: Jordana et al., 1997 nec Stach, 1922

Type Locality. Oxibar caves, 420m asl, coordinates 43.109916, -0.927993 ; Etchekertia cave , 1024m asl, coordinates 43.13264773, -0,99845122 ; Macizo de Arbailak , Zuberoa-Soule, Atlantic Pyrenees, France .

Type Material. Holotype female, slide MZNA717040, Oxibar cave (Loc. 33), Arbailak Massif , Zuberoa-Soule, Atlantic Pyrenees, France, 1.X.1988, E. Beruete leg. Paratypes: 2 males (MZNA717042 and MZNA717043), Etchekertia cave (Loc. 18), Arbailak Massif , Zuberoa-Soule, Atlantic Pyrenees, France, 24.XI.1985, J.P. Besson leg.

Etymology. The specific name derives from Arbailak, the name of the massif where the caves in which this species has been found are located.

Description. Whitish body. Length (without antennae): female holotype 1.9 mm, male paratypes 1.7−1.9 mm. Cuticular granulation is relatively thick, especially on the cephalic dorsum and Th I–III and AbdVI tergites.

Pso formula 3,2/1,3,3/3,3,3,5,3 dorsally and 1,1/0,0,0/2,1,1,2 ventrally ( Figs 26−28 ). Each subcoxa 1 of the legs I−III with 2 pso. Neither psx nor psp could be distinguished.

Head. Antennae slightly shorter than the head; ratio length of the antenna/cephalic diagonal 0.80–0.85. Ant IV with subapical organite and ms basolateral, relatively large, located above the first proximal row of chaetae. AIIIO composed of 5 papillae, 5 guard chaetae, 2 small internal sensilla, and 2 curved, smooth and ribbed sensory clubs; the lateral ms is situated just behind the sensory organ ( Fig. 31 ). Ant I−III with 7–8, 14, and 16 ordinary chaetae, respectively. Well-defined antennal base, with finer granulation. PAO with 15–18 compound vesicles arranged in two rows ( Fig. 29 ). Dorsal cephalic chaeta d 0 present ( Fig. 26 ). Maxillary palp simple, with 1 basal and 2 sublobal chaetae. Labral formula 4/542 ( Fig. 30 ). Labium type AB, with 6 proximal, 4 basomedial (E, F, G, f) and 5 basolateral (b, c, d, e, e ‘) chaetae. 4 +4 postlabial chaetae along the ventral groove.

Dorsal body chaetotaxy as in Table 7 and Fig. 26 . Chaetae-s are similar to ordinary ones. Th II–III tergites with lateral ms. Axial Th II to AbdV chaetotaxy as 3,3/3,3,3,2,1 pairs of pointed microchaetae ( Fig. 26 ). Abd IV tergite with an axial unpair chaeta (p 0); AbdV without axial unpaired chaetae; AbdVI with a blunt axial macrochaeta a 0 ( Fig. 26 ). Relatively short AS, on well-differentiated papillae, 0.5–0.6 times as long as the inner edge of the claw of leg III.

Ventral body chaetataxy as in Fig. 27 . Th I–III sternites without chaetae. VT with 5 +5 distal chaetae, anterior and basal chaetae absent. Furcal vestige reduced to a finely granulated area, with 4 posterior dental microchaetae and two irregular rows of manubrial chaetae: mm row with 2 +2 and mp row with 2+ 2 chaetae, of which the outer ones are macrochaetae ( Fig. 33 ). Genital plate with 16 chaetae and 2 posterior microchaetae in the female, and 50–60 chaetae in the males. Males with ventral organ formed by short and thick chaetae: 2 in the Abd II and 16 in the Abd III sternites ( Fig. 34 ). Anal valves with numerous acuminate chaetae; each lateral valve with chaetae a 0 and 2a 1; posterior valves with chaetae a 0, 2b 1, 2b 2, c 0, 2c 1 and 2c 2.

Legs. Subcoxae 1 of legs I–III with 4,4,4-5 chaetae, subcoxae 2 with 0,4,3, coxa with 2–3,10,11–12, trochanters with 9,9,8 and femurs with 16,16,14 chaetae, respectively. Tibiotarsi of legs I−III with 18 (9,8,1), 19 (9,8,2), and 17−18 (9,7,1−2) chaetae, respectively ( Fig. 32 ). Claw without internal or lateral teeth. The empodium reaches 70% of the inner edge of the claw, with a narrow basal lamella, which reaches 40% of its length ( Fig. 32 ).

Discussion. O. arbailakensis sp. nov. is close to a group of six species, mainly cave-dwelling, with 3,2/1,3,3/3,3,3,5,3 pairs of dorsal pso from head to the AbdV tergite, whose main diagnostic differences are summarised in Table 13. By the shape of the male ventral organ, the new species resembles O. confugiens Gama, 1962 , O. dissimulans Gisin, 1952 ( Gisin 1952b) and O. rectospinatus Stach, 1922 . O. dissimulans is separated by the number of ventral cephalic pso and the shape of the empodium (3 +3 pso and empodial lamella developed in O. dissimulans compared with 2+ 2 pso and narrow or absent empodial lamella in the other species). Furthermore, they are differentiated by the number of pso in the Abd I–IV sternites (2,1,1,2 in O. dissimulans and the new species compared with 1,1, 1,2 in O. confugiens and O. rectospinatus ). It can be differentiated from O. furcisetosus Pomorski, Furgoł & Christiansen, 2009 , O. reluctus Christiansen, 1961 and O. subambulans Denis, 1935 by the number of ventral pso (1,2,1,2 in O. furcisetosus , 1,1, 1,2 in O. reluctus , 2,1, 1,1 in O. subambulans and 2,1, 1,2 in the new species), the presence of the empodial lamella (absent in the other species), and the shape of the male ventral organ (absent in O. furcisetosus and O. reluctus , fine chaetae between Abd II and II sternites in O. subambulans , and thick chaetae on Abd II and III in the new species).

Figures

FIGURES 26−30. Onychiurus arbailakensis sp. nov. 26, dorsal view; 27, abdominal ventral view; 28, head ventral view; 29, PAO; 30, labrum. Scales: 0.2mm (26−28), 0.05mm (29−30).

FIGURES 31−34. Onychiurus arbailakensis sp. nov. 31, AIIIO and AntIV microsensillum; 32, tibiotarsus and claw of leg III; 33, furcal area; 34, male ventral organ. Scales: 0.02 mm (31, 34), 0.05 mm (32−33).