Tonkinodentus lestes Schileyko, 1992

A. Schileyko, Arkady & N. Solovyeva, Evgeniya, 2019, On the taxonomic position of the enigmatic genus Tonkinodentus Schileyko, 1992 (Chilopoda, Scolopendromorpha): the first molecular data, ZooKeys 840, pp. 133-155 : 139-141

Tonkinodentus lestes Schileyko, 1992 Figures 2-4, 5-9, 10-14, 15-19

Tonkinodentus lestes Schileyko 1992: 13.

Tonkinodentus lestes : Schileyko 1995: 74.

Tonkinodentus lestes : Schileyko 2007: 83.

Locus typicus.

Central Vietnam, Dak Lak (Darlak) Province, environs of Boun Ma Thuot.

Material.

Dak Lak (Darlak) Province, ca 15 km of Buon Ma Thuot, Eakmat, 450 m, 1-5.05.1986, col. L.N. Medvedev, 1 spec. (holotype, Rc 6358); Dong Nai Province, Ma Da Forest, Dipterocarpus area, soil samples, 19.10.1994, col. N.V. Beliaeva, 1 spec. (Rc 6555).

Diagnosis.

Cephalic plate lacking any sutures, its posterior margin overlapped by tergite 1; eyes absent (Figs 4, 13). Forcipular tooth-plates well developed and relatively short, with 7 teeth arranged in 2 parallel rows in a chess-board pattern (Fig. 5); trochanteroprefemoral process bisected sagittally (Figs 5, 6). Sternites 2-20 with paramedian sutures (Figs 7, 14). Pleuron with intersclerite membrane clearly visible; spiracles triangular with a 3-part “flap”, slit-like entrance and deep atrium. 21 LBS; the ultimate one visibly shorter than penultimate (Fig. 15). Leg with tarsus 1 considerably longer than tarsus 2, with both tarsal spur and pretarsal accessory spines. Ultimate sternite with poorly developed longitudinal median depression in caudal half. Cylindrical coxopleural process well developed, with spines (Figs 10, 16, 17). Ultimate legs of “common” shape (sensu Schileyko 2009; Figs 8, 12); femur, tibia, and tarsus 1 each with an apically rounded distal ventro-lateral process (Figs 8, 12, 18).

Composite redescription.

[data concerning the non-type specimen in square brackets]

Length of body ca 45 [34] mm. Color in ethanol: entire animal uniformly yellow-brownish (Figs 2, 3) [pale yellow, nearly white; Fig. 8]. Body and legs with a very few minute setae.

Antennae of 19 articles (in the both specimens left antenna of 19 and right one of 18, as the corresponding apical article seems to be broken off), reaching the anterior margin of tergite 5 [5.5-6] when reflexed. Basal articles 6 or 7, with a very few long setae, subsequent articles densely pilose. Basal antennal articles flattened.

Cephalic plate (Figs 4, 13) without any sutures, rounded and remarkably narrower than tergite 1; its posterior margin covered by the latter. No light spots at the place of ocelli.

Maxillae 2: the second article of telopodite distally with dorsal spur. Dorsal brush very poorly visible, consisting of short, delicate and transparent setae; apical setae no longer than pretarsus. Uniformly brown pretarsus (Fig. 19) simple (not pectinate) and claw-shaped, as long as 1/3-1/4 of the length of the apical article of telopodite; pretarsus with 2 thin accessory spines.

Forcipular segment: coxosternite with shortly branched medial suture which is as long as 1/3 of coxosternal length; 2 short sutures stretched caudo-laterad from median diastema (Fig. 5) [all coxosternal sutures very hardly visible] in the form of an angle of ca 60° [ca 70°]; chitin-lines short but well developed (Fig. 6). Tooth-plates definitely wider than long [visibly higher than in the holotype]; height of tooth margin increasing medially. Each tooth-plate with 7 teeth, fused to various degrees and arranged in 2 parallel rows in a chess-board pattern (Fig. 5), the lateral tooth is the shortest and the most isolated. Basal sutures of tooth-plates form a nearly straight line. Trochanteroprefemural process well developed, divided sagittally into 2 (dorsal and ventral) halves (Figs 5, 6), each half with 2 or 3 lateral tubercles [dorsal halves of both processes with 3, ventral ones (which are visibly smaller) with 2]; the apical end of this process is considerably higher than corresponding tooth-plate. Tarsungula (Fig. 6) of normal length (left one broken off apically in the holotype), ventrally with 2 blunt ridges.

Tergite 1 without sutures (Figs 4, 13), tergite 2 with visible incomplete paramedian sutures, tergites 3-20 with well-developed and complete ones (Fig. 15), tergite 21 with complete median suture. Tergites 15/16-20 with poorly developed lateral margination posteriorly; only tergite 21 definitely marginate. Tergite 21 nearly as wide as long and not narrowed caudad (Fig. 15); its lateral sides slightly rounded and posterior margin evidently rounded. Tergites lacking any median keel.

Sternites 2-20 (Figs 7, 14) with lateral sides practically parallel; 2-20 with complete paramedian sutures; sternites 6/7-18/19 with a well-developed longitudinal median depression, which is wide and deep [very shallow]. Ultimate sternite long and very narrow (Fig. 11), at least twice as long as wide at base [1.5:1; Fig. 17], very slightly narrowing caudad; its posterior margin practically straight [with strongly rounded corners]. Endosternites not recognizable.

Composition of pleuron (Fig. 9) usual for Scolopendrinae, intersclerite membrane well visible. Elongated spiracles triangular with a typical for this subfamily 3-valved “flap” which covers slit-like entrance in a well-developed atrium (Fig. 9).

Legs (Figs 7, 9) with tarsus 1 considerably longer than tarsus 2, legs 1-18 [1-19] with tarsal spur (legs 19-21 of the holotype are lost). Pretarsus long (approximately as long as ¾ of tarsus 2), legs 1-20 with well-developed accessory spines.

Ultimate LBS visibly shorter than penultimate (Fig. 15). Coxopleuron (excluding coxopleural process) visibly longer than sternite 21 (Figs 11, 16), its coxal part very densely pierced with coxal pores of various size, only this coxopleural process and a narrow posterior area remaining poreless [this posterior area visibly broader than in the holotype]. Short, cylindrical coxopleural process (Figs 10, 16) slightly curved dorsad [definitely curved medially and very slightly dorsad], with 2 apical, 2 subapical, and 2 ventral spines close to its base [with 3 apical, 1 subapical, and 1 lateral spine]; 1 or 2 [1] spines at posterior margin of coxopleuron. Coxopleural process practically reaches the caudal margin of the ultimate tergite. Caudal margin of ultimate pleuron virtually straight and lacking spines; coxopleural surface with scattered minute setae. Gonopods well developed (Figs 11, 17).

[Ultimate legs (Figs 8, 12) ca 7 mm long, relatively slender (width of prefemur ca 0.7 mm), prefemur definitely flattened dorsally, other articles cylindrical. Prefemur, femur and tibia practically of the same length (ca 1.7 mm), tarsus 1 considerably longer than tarsus 2 (Figs 8, 12, 18), the latter twice as long as pretarsus. Ventral surface of prefemur spineless, left prefemur with 23 and right one with 20 small ventrolateral spines, remaining ones (23 on left prefemur, 22 on right) disposed ventromedially, medially and dorsomedially (Figs 12, 16, 17). The spines grouped in very indistinct rows or scattered chaotically; corner spine well developed (Figs 12, 16), with 2 apical spines. No tarsal spur; pretarsus slender, sharply contrasting to much thicker tarsus 2, accessory spines absent. Tarsus 1 and tibia visibly broadened apically; femur, tibia and tarsus 1 each with a characteristic distal process ventro-laterally, the latter short and rounded apically (Fig. 8, 12, 18)].

Remarks.

The known material consists of two specimens only, neither of which are in perfect condition. More material is needed to investigate the anatomy (e.g. peristomatic structures, foregut, gizzard).

All differences between the holotype and the second specimen are explicable by the latter being a subadult. The much paler and considerably softer cuticle the second specimen suggests that it is newly moulted. Because of this, some delicate structures (e.g. forcipular sutures, leg spurs) are less evident than in the holotype. The most delicate parts (maxillae, antennae, legs) are somewhat deformed (wrinkled) in the holotype, but in the second specimen, the ventral surfaces of the apical articles of the ultimate legs are deformed (unnaturally concave).

Eight specimens of Cormocephalus dentipes Pocock, 1891 (Rc 7518, 7013, 7028, 7231, 7233) from India (Assam and Punjab states), Western Nepal and Indonesia (Sumatra, Medan) demonstrate virtually the same structure of the sagittaly bisected process of the forcipular trochanteroprefemur (Fig. 20). As for the chess-board pattern of the arrangement of the teeth of the forcipular tooth-plates in Tonkinodentus (Fig. 5), it is unique among the Scolopendromorpha .

Discussion.

The genus Tonkinodentus conforms to the Scolopendrinae and differs from members of both the Plutoniumidae and Cryptopidae Kohlrausch, 1881 by: (1) the presence of paired sternal longitudinal sutures (Figs 7, 14) vs single median suture, (2) the slit-like spiracles are covered by a “flap” (a synapomorphy that is unique for Scolopendrinae; Fig. 9), with the longitudinal axis of the spiracle parallel to the such of the body vs open oval spiracles, (3) the well-developed, spinulated coxopleural process (Figs 10, 16) vs its virtual absence, and (4) the ultimate legs of “common” shape (sensu Schileyko 2009; Figs 8, 12) vs enlarged, “pincer-shaped” ones in Plutoniumidae or "pocket knife-shaped" ones in Cryptopidae . Tonkinodentus also sharply differs from the typical cryptopids (= Cryptops Leach, 1814) by having: (1) well-developed forcipular tooth-plates with strongly chitinized teeth, (2) a forcipular trochanteroprefemur with a well-developed process, (3) sternites without transversal sutures, and (4) prefemur of ultimate legs with numerous spines (Fig. 17).

Summing up, the genus Tonkinodentus is morphologically the typical representative of the subfamily Scolopendrinae (and namely of the former tribe Scolopendrini Leach, 1814) and is the most similar to the genus Scolopendra L., 1758, but differs readily from the latter by the absence of eyes and the peculiarities of the forcipular segment.