Arrhopalites potapovi, Vargovitsh, Robert S., 2015

Vargovitsh, Robert S., 2015, Arrhopalites potapovi sp. nov. (Collembola, Symphypleona) from Russia, Zootaxa 3955 (1), pp. 101-112 : 102-111

Arrhopalites potapovi sp. nov.

Figs 1–35 , Table 1 .

Diagnosis. Body length up to 0.88 mm. White or very slightly pigmented with reddish spots. Trichobothria ABC form right angle and AB =2 BC. Antenna about 1.3× of head length; Ant IV not subdivided or with about 5 pseudosubsegments, with 12 whorls of setae. Head dorsum with 13 spine-like setae. All claws with inner tooth, claws II and III usually with weak tunica. Tip of empodium I–II reaching tip of corresponding claw, empodia I and II with normal and III with reduced or rarely normal corner tooth. Tenaculum with 1 seta. Manubrium with 5 + 5 setae; dens with 3, 2, 1, 1, 1 thick anterior setae, Ia moderately spine-like; posterior side with 8 spine-like setae, seta Vpe absent. Tip of mucro swollen. Circumanal setae long, broad, lamellate and basally serrated; cuticular spines of Abd VI strongly differentiated; appendices anales spatulate, apically serrated.

Type material. Holotype on slide “20R(5)”: female, 55.47217o N, 109.11945 o E, 702 m alt., Buryat Republic, ~ 25 km SW Severobaykalsk, near Slyudyanskoye Lake, steep SE slope, near former micaceous mine, pine forest with cowberry, under looser bark of dead pine-tree, 19.viii.2013, leg. Potapov M. and Gulgenova Ay. (point “20R” on Fig. 23 ).

Paratypes: Nine females and 1 juv. on slides and 9 specimens in alcohol, same data as in holotype. Holotype and 7 paratypes are deposited in the collection of the Schmalhausen Institute of Zoology, National Academy of Sciences of Ukraine, Kiev. Two paratypes are deposited in the collection of Moscow Pedagogical State University, Moscow.

Other material. Five females on slides and 8 specimens in alcohol: Irkutsk Oblast, W Khamar-Daban Range, Slyudyanka River, taiga belt, mixed forest, under loose bark of tree, 753 m alt., 29.viii.2008, leg. Potapov M. (point “45R” on Fig. 23 ).

Description. Female: Body length 0.6–0.8 mm, habitus as in Fig. 24 . Pigmentation varies: a) totally unpigmented (most specimens); b) only eyes slightly pigmented; c) eyes, head dorsum and sometimes anterior part of thorax with weak spotted reddish pigmentation.

Head ( Figs 1 , 33 ). Eyes 1 + 1, ~7 µm in diameter. Clypeal area (rows a to f) with axial seta in row a. Interantennal area (rows α and β) with axial seta in row β. Dorsal area (rows A to D): 3 axial setae in rows A, B and C; 13 setae spine-like ( Fig. 12 ) with broadened sockets (in row A: 1 + 1, B: 1 + 1, C: 2 + axial + 2, D: 2 + 2); other setae are not modified.

Mouthparts. Prelabral / labral chaetotaxy: 6 / 4 5 5 ( Fig. 27 ). Proximal / basomedian / basolateral fields of labium with 5 / 4 / 5 setae. Maxillary outer lobe with 3 sublobal hairs ( Fig. 16 ). Labial palp as in Fig. 17 . Maxilla as in Fig. 32 .

Antenna ( Fig. 19 ) short, 1.2–1.4× of head (1.3 in holotype). Mean length ratio of antennal segments I: II: III: IV = 1: 2.7: 3.5: 7.3 (1: 2.3: 3.4: 7.2 in holotype). Ant I with 6 thick anterior setae and small posterior microseta (3 µm in holotype). Ant II with 14 setae. Ant III with moderate subbasal swelling and with following chaetotaxy: 17 simple setae of which Api and Ape short and thin, 2 sense rods in shallow pits (3.6 µm in holotype) and Aai as small (2.8 µm in holotype) bent and blunt sensillum ( Fig. 26 ). Ant IV entirely undivided (as in Fig. 19 ) or with 5–6 pseudosubsegments without distinct separation (as in Fig. 25 ) or rarely with weak constriction separating whorls in middle of segment. Ant IV bears 12 whorls of setae. Sensory hairs in middle and subapical parts of subsegment modified into somewhat broadened sensilla ( Fig. 9 ).

Foreleg ( Fig. 20 ): precoxae 1, 2 and coxa with 1, 0, 1 setae respectively ( Fig. 2 ). Trochanter with 3 anterior and 1 posterior setae. Femur with 12 setae, a4 turned perpendicularly to the longitudinal axis of the segment, p3 a microseta. Tibiotarsus with 44 setae: whorl I with 9, whorls II–V with 8 setae each and region F with 3 primary setae (e, ae, pe). Pretarsus with 1 anterior and 1 posterior setulae. Foot complex ( Fig. 31 a). Claw: with weak (in holotype) or without tunica; with inner tooth and two pairs of lateral teeth, 4× shorter than tibiotarsus. Empodium: thin, with distinct corner tooth, 1.1– 1.3× shorter than claw; tip of empodial filament visually reaching tip of claw (sometimes not quite reaching claw, other times surpassing it).

Mid leg ( Fig. 21 ): precoxae 1 and 2 with 1, 1 setae respectively, precoxal process present, coxa with 3 setae and microsensillum ( Fig. 2 ). Trochanter with 4 setae including 2 simple anterior and 1 posterior setae and anterior trochanteral organ. Femur with 13 setae, 2 posterior ones as microsetae. Tibiotarsus with 43 setae: distal whorl I with 9 setae, whorls II–IV with 8 setae, whorl V with 7 setae (Vp absent), basal region F with 3 FP setae. Foot complex ( Fig. 31 b). Claw: with or without visible tunica, inner tooth and 2 pairs of small lateral teeth present, 3.9– 4.3× shorter than tibiotarsus (4.2 in holotype). Empodium: broader than in foreleg, with distinct corner tooth, 1.3– 1.5× (1.3 in holotype) shorter than claw; tip of empodial filament visually reaching tip of claw (sometimes not quite reaching claw, other times surpassing it).

Hind leg ( Fig. 22 ): precoxae 1 and 2 with 1, 1 setae respectively, process on precoxa 1 present, coxa with 3 setae and microsensillum ( Fig. 2 ). Trochanter with 5 setae: anterior trochanteral organ, 3 anterior and 1 posterior simple setae. Femur with 13 setae, 2 posterior ones as microsetae. Tibiotarsus with 44 setae: whorl I with 9 setae, whorls II–IV with 8 setae, whorl V with 7 setae (Vp absent), region F with 3 primary setae FP and secondary seta FSa. Foot complex ( Fig. 31 c). Claw: usually with visible tunica, with inner tooth and 2 pairs of lateral teeth, 5.1– 5.7× shorter than tibiotarsus (5.5 in holotype). Empodium: broad, corner tooth vanishingly small or absent ( Fig. 22 ), rarely normal ( Fig. 31 c), 1.4–1.7× shorter than claw; tip of empodial filament not reaching or sometimes almost reaching tip of claw.

Mean lengths ratio of tibiotarsi I: II: III = 1: 1: 1.3 (as in holotype). Tibiotarsus I about 2× shorter than head.

Ventral tube ( Fig. 2 ) with 1 + 1 subapical microsetae. Tenaculum ( Fig. 14 ): each ramus with 3 teeth and a basal process; anterior lobe with 1 apical seta.

Furca ( Fig. 18 ). Manubrium with 5 + 5 posterior setae. Dens with 23 setae. 3,2,1,1,1 setae on anterior side, Ia – moderately spine-like ( Fig. 10 ), a and ae setae of other rows are heavy. Posterior side with 8 spine-like setae: Ie ( Fig. 11 ), Ipe–IVpe, Ii, IIIpi, IVpi; seta Vpe absent. Mucro heavily serrated, with globular apex ( Fig. 35 ). Dens 1.5–1.7× as long as mucro (1.46 in holotype).

Great abdomen ( Fig. 2 ). Holotype with sutures (not granulated transversal lines, represented by hatched lines in Fig. 2 ) demarcating thorax II, III and abdomen I ( Fig. 29 ). Segments Th II and III bearing single seta-sensillum in row a and 3 setae in row m with m1 and m2 moderately spine-like ( Figs 6–7 ). Abd I bears single row with 5 setae. Trichobothrial complex ( Fig. 30 ): ABC form about right angle (88°–100°; 90° in holotype; mean—91°) and AB is 2–2.4× of BC (2.0 in holotype; mean—2.2); p seta is located much above the level of trichobothrium B; seta b1 lies almost on line BC, closer to C; microseta c1 (1.4–2 µm, possibly the shortest seta of entire body) lies in front of trichobothrium C and seta c2 —below C. Posterior lateral complex with 3 + 3 and furca base complex with 8 setae. Central dorsal complex with 3 subequal setae. Posterior dorsal complex with about 22 setae arranged in 3 longitudinal rows, the longest of which (dI-1 = 30 µm in holotype) is subequal to hind claw ( Fig. 5 ). Ventral complex with 2 or 3 setae.

Fifth abdominal segment ( Fig. 2 ) with 2 setae and trichobothrium D in row a, and 2 setae in row p. Genital field with 3 + 3 short setae along anterior margin of genital opening.

Sixth abdominal segment ( Figs 15 , 34 ) with 4 + 4 differentiated cuticular spines, 2 + 2 per side: 1 small (mean 3 µm) + 1 big (mean 10.2 µm) on dorsal valve and 1 big (mean 8.2 µm) + 1 small (mean 2.1 µm) on lateral valve. Dorsal valve with 11 + 2 axial + 11 setae. Each of lateral valve bears 20 setae. Circumanal row with 7 modified setae per side: long (~50–70 µm, about 2× longer than posterior setae of great abdomen), broad, mps1–mps3 and mpi1–mpi3 lamellate and serrated basally ( Fig. 4 ). Appendices anales ( Figs 13 , 28 ) (mean 22.3 µm) spatulate, ~3.2× as long as width of distal margin, apically distinctly serrated with few deeper cuts; sitting on semiglobular papilla. In total, normally 64 setae and 8 cuticular spines on Abd VI are present.

Male not seen.

Variability. Ant IV with 5 indistinct pseudosubsegments or totally undivided without signs of annulations. Ventral complex of great abdomen with 2 or 3 setae. Claws with or without visible tunica. Empodia with apical filament reaching claws tip but sometimes a little longer or shorter. Empodium III corner tooth usually minute or absent but sometimes normally developed. In one specimen (slide “20R(3)”) double seta b 1 in trichobothrial complex and double axial seta ms1 on Abd VI were observed.

Bionomy and distribution. Specimens of Arrhopalites potapovi sp. nov. were sampled from two sites over 550 km from each other, both over 700 m altitude, not far from opposite NE and SW points of the Lake Baikal ( Fig. 23 ). Apparently, its distribution should be much broader. The findings of many specimens are restricted to the special habitat exclusively under the loose bark of trees in the pine and mixed forest; small body size and short antennae quite correspond to tight under-bark habitat (M. Potapov, pers. com.).

Etymology. The new species is dedicated to distinguished collembologist Mikhail Potapov (Moscow) who collected the material and kindly provided it for study.

Discussion. According to the anterior dens chaetotaxy (3, 2, 1, 1, 1) the new species belongs to the caecus group of species (sensu: Vargovitsh 2013).

A. potapovi sp. nov. seems to be very closely related to A. caecus auct. (for example, as described by Stach (1945, 1956), Fjellberg (2007)), but: a) bears empodia I–II reaching or surpassing claws tip (vs distinctly shorter); b) cuticular spines of Abd VI are strongly differentiated (vs subequal); c) shape of appendices anales is spatulate (vs rodlike) and ratio of its length: width = 3.2 (vs 6–10); d) body size is somewhat smaller. Other characters also seem to be somewhat different from A. caecus (presence of thick sensilla (sense hairs) on Ant IV, etc.) but possibly they could be variable and thus are not considered here as diagnostic.

The new species is also similar to the Japanese A. minutus Yosii but differs from it by: a) lesser Ant/head ratio (~1.3× vs ~2×); b) Ant III swollen basally (vs not swollen); c) empodia II and III with corner tooth (vs untoothed); d) terminal part of appendices anales (deeply serrated vs finely ciliated); e) strong differentiation of cuticular spines on Abd VI (vs subequal); f) manubrium with 5 + 5 setae (vs 4 + 4); g) 6 setae on outer surface of dens (vs 5); and possibly h) Abd VI chaetotaxy (as seen from Yosii 1970).

Nearctic Arrhopalites incertus Zeppelini & Christiansen, 2003 (Colorado, USA) as well as A. potapovi sp. nov. has differentiated (but not so strongly) circumanal spines. The new species can be readily separated from A. incertus by absence of distinct Ant IV subsegmentation (vs 4 distinctly ringed subsegments), 6 setae on outer surface of dens (vs 7) and shape of appendices anales (spatulate vs rod-like).

Strong differentiation of circumanal spines, similar to that in the new species, was shown in A. caecus from the Wind Cave: South Dakota, USA ( Moore et al. 2005, Fig. 2 F). Identification of this species is undoubtedly valid accordingly to existing keys, but possibly its correspondence to typical A. caecus should be verified (e.g. thinner setae on dens, longer inner tooth of claws, shape of cuticular spines etc.). Gough (1973) interprets wide differences in the shape of cephalic and dens setae and also Abd VI cuticular spines in different European populations just as variations of the certain character. On the other hand, it is quite possible that widely distributed A. caecus is rather a superspecies with several local species or subspecies, especially in the caves and other isolated natural habitats.

Figures

FIGURES 1 – 14. Arrhopalites potapovi sp. nov.: 1, chaetotaxy of head, frontal view; 2, chaetotaxy of great abdomen, lateral view; 3 – 13, shape of setae: 3, ms 1 of Abd VI; 4, mps 3 of Abd VI; 5, dII- 1 of great abdomen; 6, m 1 of mesothorax; 7, m 2 of mesothorax; 8, dorsal seta of abdomen; 9, sensilla of Ant IV; 10, Ia of dens; 11, Ie of dens; 12, spine-like seta of head vertex; 13, appendices anales; 14, tenaculum.

FIGURES 15 – 19. Arrhopalites potapovi sp. nov.: 15 chaetotaxy of Abd VI, lateral view, setae of circumanal row are filled with gray colour; 16, maxillary outer lobe; 17, chaetotaxy of labial palp, each papilla and associate setae marked with different colour; 18, chaetotaxy of furca; 19, chaetotaxy of antenna.

FIGURES 20 – 22. Arrhopalites potapovi sp. nov.: chaetotaxy of legs, anterior view: 20, foreleg; 21, mid leg; 22, hind leg.

FIGURES 23 – 24. Arrhopalites potapovi sp. nov.: 23, places of findings, type locality marked as “ 20 R ”; 24, habitus of female, on slide.

FIGURES 25 – 30. Arrhopalites potapovi sp. nov.: 25, Ant IV; 26, Ant III; 27, labrum; 28, appendices anales; 29, fragment of great abdomen, sutures between segments marked with arrows; 30, chaetotaxy of trichobothrial complex.

FIGURES 31 – 35. Arrhopalites potapovi sp. nov.: 31, foot complex (a—foreleg, b—mid leg, c—hind leg); 32, maxilla; 33, fragment of head with eye; 34, fragment of female Abd VI with winged circumanal setae and 4 cuticular spines (marked with arrows), lateral view; 35, mucro and distal part of dens, lateral view.

Tables

TABLE 1. Lengths (in µm) for body parts of type specimens (10 females) of Arrhopalites potapovi sp. nov.

Body part	min–max	mean
Body total	560–880	777
Head	240–310	271
Eye diameter	6.5–9.0	7.7
Antenna	290–410	346
Ant I	21–34	26
Ant II	57–78	69
Ant III	73–110	89
Ant IV	169–212	185
Tibiotarsus I	120–162	137
Tibiotarsus II	117–162	138
Tibiotarsus III	154–206	177
Claw I	30–39	34
Claw II	28–37	33
Claw III	28–39	33
Empodium I	22–30	27
Empodium II	20–27	24
Empodium III	17–25	21
Manubrium	100–128	119
Dens	113–147	132
Mucro	77–93	84
AO-III rods	3.0–3.9	3.6
Head longest spiny seta	15–21	18.1
Abd seta c1	1.4-2.0	1.8
Abd seta dI-1	28–38	32
Abd VI longest seta	55–72	64
Circumanal spine s1	2.4–3.8	3.0
Circumanal spine s2	8.7–12.2	10.2
Circumanal spine s3	5–9.4	8.2
Circumanal spine s4	2.0–2.4	2.1
Appendices anales	19–26	22
Dens spiny seta Ia	15–18	17