Lithobius (Monotarsobius) tanagolus, Gordana & Ambros, 2018

Farzalieva, G. Sh., 2018, Lithobius (Monotarsobius) tanagolus sp. n., a new lithobiid species (Chilopoda, Lithobiomorpha) from southern Siberia, with remarks on the closely related L. (M.) holstii (Pocock, 1895), Arthropoda Selecta 27 (1), pp. 22-30 : 23-27

Lithobius (Monotarsobius) tanagolus sp.n.

Figs 1–14, 19, Map 1.

DIAGNOSIS. A Lithobius (Monotarsobius) species with body 6.3–10.0 mm long, antennae composed of 17–21 articles, commonly 19+19; 7–11 ocelli on each side on head, commonly 8–9, arranged in 3 rows; Tömösváry’s organ as large as nearest ocellus, 2+2 forcipular coxosternal teeth and setiform porodonts; unipartite tarsi of legs 1–13, posterior angles of all tergites without triangular projections; number of coxal pores varying from 3 to 5, commonly 4; ♀ 1 st gonopodal segment with 2+2 coniform spurs and a single distodorsal spine; terminal claw tridentate; ♂ with a poorly-expressed dorsal sulcus on Ti 15; in both sexes, legs 15 more densely setose ventrally than dorsally ( Figs 4, 6–7).

TYPES. Holotype ♀ ( ZMMU) Russia, Altai Republic, Lake Teletskoye, near Lake Chiri , 51°22′N, 87°50′E, subalpine belt (= goltsy), 1750–2000 m a.s.l., 29–30.VII.1997, S.I. Golovatch & A.V. Tanasevitch. Paratypes: 15 ♂♂, 4 ♀♀ ( ZMMU), 5 ♂♂, 2 ♀♀ ( PSU), together with holotype; 2 ♂♂, 2 ♀♀ ( ZMMU), same locality, upper timberline of Picea obovata and Pinus sibirica taiga, mainly near water, 1700–1750 m a.s.l., 29.VII.–1.VIII.1997; 11 ♂♂, 6 ♀♀ ( ZMMU), Lake Teletskoye, Altai Nature Reserve, Chiri, upper reaches of Chiri River , Picea obovata and Pinus sibirica taiga forest, 1350 m a.s.l., 28–29.VII. and 2.VIII.1997, all leg. S.I. Golovatch & A.V. Tanasevitch.

NON-TYPE MATERIAL. 2 ♀♀ ( ZMMU), Altai Republic, Lake Teletskoye , near Artybash, 51°47′N, 87°14′E, Picea obovata , Abies sibirica and Pinus sibirica taiga, 500–800 m a.s.l., 13–24.VII.1997; 5 ♂♂, 2 ♀♀ ( PSU), same locality, high bog in Picea obovata , Abies sibirica and Pinus sibirica taiga forest, 800 m a.s.l., 20.VII. 1997, all leg. S.I. Golovatch & A.V. Tanasevitch; 20 ♂♂, 18 ♀♀ ( ZMMU), 1 ♂, 1 ♀ ( PSU), Altai Republic, Altai Nature Reserve , litter, IX.1969, leg. A.L. Tikhomirova; 3 ♂♂, 7 ♀♀ ( PSU), Kemerovo Area, Shorsky National Park , near Verkhniy Taymet, 52° 29′N, 88°16′E, Abies forest with Tilia , Pinus sibirica taiga with Vaccinium and Betula forest, 20.VII.–11.VIII.2016; 2 ♀♀ ( ZMMU), Kemerovo Area, Biyskaya Griva Mt. Range , Pinus sibirica taiga 11.VIII.2016, all leg. L.A. Trilikauskas.

NAME. The species is a combined abbreviation named after Andrei V. Tana sevitch (an expert in Linyphiidae spiders), and Sergei I. Gol ovatch (an expert in Diplopoda) who collected the type material.

DESCRIPTION. Holotype ♀. Body ca 9.7 mm long, 1.2 mm wide (at T10 ); colour in alcohol yellow-brownish. Tergites: almost smooth, with short and long setae, T15 indistinct; posterior margin of TT1, 3, 5, 8, 10, 12, 14 and intermediate T slightly sinuate, as in Fig 2; intermediate T slightly broadened, breadth/length ratio 1.04 (length 0.68 mm, breadth 0.70 mm). Cephalic plate: breadth/length ratio 1.02 (breadth 1.02 mm, length 1.00 mm); breadth/breadth ratio of cephalic plate and Tf 1.22 (breadth of Tf 0.83 mm). Antennae short, reaching the middle of T5 , composed of 19+19 short articles, first two slightly enlarged ( Fig. 5). Ocelli: 8 on each side, dark, arranged in three rows; posterior and posterosuperior ocelli poorly distinguished in size from other seriate ocelli. Tömösváry’s organ as large as nearest ocellus, rounded ( Fig. 1). Forcipular coxosternite: dental margin slightly concave, with 2+2 acute teeth and setiform porodonts, median diastema Vshaped; shoulders of coxosternite strongly sloping, as in Figs 3, 19.

Tarsal articulation of legs 1–13 indistinct, tarsi distinctly longer than tibiae. Legs 14 and 15 slightly incrassate, with glandular pores on lateral and ventral surfaces. Legs 15 with DaC. Accessory spine on leg 15 large, well-developed. Plectrotaxy as in Table. Coxal pores: present on legs 12–15, large and rounded; inner pores smaller than neighbouring ones; distance between pores varying, but generally not exceeding the diameter of neighboring pore ( Fig. 4); formula 3,4,4(5),4(5). Gonopods without setae on internal face, with 2+2 slender and sharp spurs separated from one another by distances greater than diameter of the widest part of a spur ( Fig. 14). First segment of gonopod with one spine, second with 3, third with one dorsal spine ( Fig. 11). Claw of gonopod tridentate, lateral denticles unequal: external lateral denticle displaced to the middle of external ridge ( Fig. 13), whereas internal denticle located closer to tip of apical claw ( Fig. 12).

Paratype ♀♀. Length 6.3–9.9 mm, breadth 1.0– 1.3 mm. All other characters as in holotype, but ocelli 7– 11, usually 8–9 in three rows ( Fig. 1). Posterosuperior and posterior ocelli in some specimens slightly larger than seriate ones. Antennomeres varying from 15 to 19, mainly 19+19 antennomeres. Intermediate T either slightly broadened as in holotype or equal in breadth and length. Legs 12 with 3 pores in all specimens, number of coxal pores on legs 13–15 varying from 3 to 5. Gonopods: second segment usually with 3 dorsal spines (in two specimens second segment with 4 spines on one of gonopod); gonopodal claws tridentate, but in some specimens external lateral denticles poorly-expressed.

Paratype ♂♂. All characters as in ♀♀, but body length 6.5–10.0 mm; intermediate T slightly elongate or equal in breadth and length. Legs 14 and 15 slightly incrassate, without clearly expressed secondary sexual characters, with glandular pores on lateral and ventral surfaces. Ti 15 in adult ♂♂ (large and well-sclerotized) with a poorly-developed distodorsal sulcus, the latter never crossing entire Ti ( Figs 7–8). In most ♂♂, sulcus visible from half to 2/3 tibia and extending to its distal margin (when viewed from above, the sulcus is poorly visible, as in Fig. 9). In young ♂♂ (but with developed gonopods) no such sulcus is visible. Plectrotaxy as in holotype, but some specimens with 14VpF. Coxal pores as in holotype, their number varying from 2 to 5. Gonopods 1-segmented, small and low, with a single seta.

VARIATION. Some specimens show an asymmetric number of antennomeres, ocelli and spinulations on the right and left ♀ gonopods. Thus, the most common situation is a different number of antennomeres on the left and right antennae (usually, one of the antennae consists of 19 antennomeres) and a variable number of ocelli (the difference is usually 1, rarely 2 ocelli). The structure of the ♀ gonopods is relatively stable: in most ♀♀ the 2 nd gonopodal segment is with 3, rarely 4 dorsal spines ( Fig. 11); the claws are three-dentated, and the internal lateral denticle is always well-developed, while the external lateral denticle is shifted from the apex to the middle of the claw and is poorly-expressed in some specimens.

Plectrotaxy is relatively stable, but in some specimens DaP begin from leg-pair 9 and VaF from leg-pair 3.

REMARKS. The new species belongs to the subgenus Monotarsobius , based on the clearly unipartite tarsi of legs 1–13, 19-segmented antennae, the absence of posterior triangular projections on the tergites, 2+2 forcipular coxosternal teeth and setiform porodonts.

Lithobius tanagolus sp.n. show no apomorphies, but differs from other species by a unique combination of characters. Thus, both sexes of L. tanagolus sp.n. differ from all Palaearctic Monotarsobius species by (1) 19-segmented antennae, (2) the large accessory spine on leg 15, (3) the usually 8–9 (rarely 7, 10–11) dark ocelli arranged in three rows, (4) the large Tömösváry’s organ that is slightly larger than or equal to the neighboring ocellus, (5) 2+2 acute teeth and (6) the sloping shoulders of the forcipular coxosternite. In addition, ♀♀ have a rare feature, i.e. the dorsal spine on the 1 st gonopodal segment. ♂♂ are characterized by a poorly-expressed sulcus in the distodorsal part of 15Ti. The sulcus is clearly visible in well-sclerotized mature ♂♂, but in young ♂♂ with fully developed gonopods it may be absent.

Lithobius tanagolus sp.n. is especially similar to L. (Monotarsobius) holstii ( Pocock, 1895) , recorded from the Kurile Islands [ Eason, 1996], China and Japan [ Takakuwa, 1941; Pei et al., 2011], but differs in the sloping shoulders of the forcipular coxosternite (cp. Figs 19 and 20), the number of ocelli (7–11 in L. tanagolus sp.n. vs. 5–6, rarely as many as 9 in L. holstii [ Eason, 1996], cp. Figs 1 and 25 & 27), the number of antennomeres (usually, 19 in L. tanagolus sp.n. vs. 20 (our data) or 19–20 (rarely 17 or 21 in L. holstii [ Eason, 1996]) and some plectrotaxy details (14 VaTi and 14 DaC in L. holstii vs. without such in L. tanagolus sp.n.). The ♀ of L. tanagolus sp.n. differs well from L. holstii by (1) the presence of a distodorsal spine on the 1 st gonopodal segment (absent in L. holstii ) and (2) the armament of the 2 nd and 3 rd gonopodal segments (cp. Figs 11 and 15). In addition, the ♀ of L. tanagolus sp.n. is devoid both of setae and spines on the inner surface of the 1 st gonopodal segment (cp. Figs 14 and 16).

On the other hand, the ♀ of L. tanagolus sp.n. is similar to the ♀♀ of L. (Monotarsobius) insolens Dányi et Tuf, 2012 and L. (Monotarsobius) worogowensis Eason, 1976 by the structure of the gonopod, but differs by the 19-segmented antennae (vs. 20-segmented in L. insolens and L. worogowensis ) and plectrotaxy, especially, 15 DaC in the new species vs. 9–15 DaC in L. insolens and 13–15 in L. worogowensis (for details see [ Farzalieva, 2006: 107]).

Finally, L. tanagolus sp.n. is also somewhat similar to further two Lithobius (Monotarsobius) , namely, L. songi Pei, Ma, Shi, Wu et Zhou, 2011 , from Hebei Province, and L. zhangi Ma, Pei, Hou et Zhu, 2014 , from Shandong Province, both showing a close body length, 19+19 antennomeres, 2+2 coxosternal teeth, 2+2 spurs and a tridentate ♀ gonopodal claw. However, L. tanagolus sp.n. is well-distinguished from the latter two species by the presence of an accessory spine on leg 15 (leg 15 devoid of such in L. songi and L. zhangi ) and 3–5 coxal pores (vs. 1–2 in L. songi and L. zhangi ). In addition, the new species differs from L. songi and L. zhangi by the number of ocelli (8–9 vs. 6–7 in L. songi and 5–6 ocelli in L. zhangi ), the leg plectrotaxy (e.g. 15 DaC in L. tanagolus sp.n. vs. 14–15 DaC in L. songi and in L. zhangi ; for more details see [ Pei et al., 2011; Ma et al., 2014b]), as well as in the presence of a dorsolateral spine on the ♀ first gonopodal segment (absent in L. songi and L. zhangi ).

DISTRIBUTION ( Map 1). The Altai Republic and Kemerovo Region.