Siamaxytes bifurca Srisonchai and Panha, 2024

Srisonchai, Ruttapon, Enghoff, Henrik, Likhitrakarn, Natdanai, Jeratthitikul, Ekgachai, Jirapatrasilp, Parin, Panha, Somsak & Sutcharit, Chirasak, 2024, Molecular phylogeny of dragon millipedes (Diplopoda: Polydesmida: Paradoxosomatidae) from mainland SouthEast Asia, with description of a new genus and species, Zoological Journal of the Linnean Society 202 (1), pp. 1-33 : 23-28

Siamaxytes bifurca Srisonchai and Panha sp. nov.

( Figs 6–9 )

Zoobank registration: urn:lsid:zoobank.org:act:F8B9D6B5-C21F-45AC-B645-B3C877973F22 .

Type specimens

Holotype: ♂ ( CUMZ-Px0231 ) THAILAND, Kanchanaburi Province, Sai Yok District, Tham Sue Dao (Sue Dao Cave) , 14°06 ʹ 05.0 ʹʹ N, 99°13 ʹ 39.3 ʹʹ E, c. 120 m a.s.l., 16 August 2016, R. Srisonchai and C. Sutcharit leg.

Paratypes: 20♂♂ 3♀♀ (CUMZ-Px0232) 2♂♂ ( NHMD1184660 ) 1♂ ( NHMW) 1♂ ( ZMUM), same data as holotype . 5 ♂♂, 1 ♂ THAILAND, Kanchanaburi Province, Tha Muang District, Wat Tham Fad , 13°57 ʹ 48.1 ʹʹ N, 99°34 ʹ 59.1 ʹʹ E, c. 100 m a.s.l., 16 August 2016, R. Srisonchai and C. Sutcharit leg.

Etymology

The name is a Latin adjective and refers to the branching of the lamina medialis (lm) into two processes.

Diagnosis

Same as genus, genus monotypic.

Description

Size: Length 32–34 mm (male), 36 mm (female); width of midbody metazona c. 2.2 mm (male), 3.0 mm (female). Width of head = collum = body rings 2 = 3 <4 <5–16, thereafter body gradually tapering towards telson.

Colour ( Fig. 6A–D ): Specimens in life brown or pinkish brown; head, antennae, legs, sterna, epiproct brown; collum, metaterga, surface below paraterga brown or pinkish brown; paraterga pale brown or pink; epiproct pale brown; a few basal podomeres of legs whitish brown. Colour in alcohol: after 7 years changed to brown.

Head ( Figs 6A–D , 7A, D ): With a sparse cover of long setae. Epicranial suture conspicuous, groove shallow. Mouth parts not dissected.

Antennae ( Fig. 6A–D ): Very long and slender, reaching back to body ring 6 or 7 (male) and 5 or 6 (female) when stretched dorsally.

Collum ( Fig. 7A, D, G ): With two transverse rows of setiferous cones/spines; 3 + 3 cones/spines in anterior row and 3 + 3 cones/spines in posterior row; paraterga of collum elevated at c. 40°, directed caudolaterad, with two conspicuous setiferous notches at lateral margin.

Tegument ( Figs 7 , 8A–K ): Quite dull; frontal region of head, collum, metazona, paraterga, surface below paraterga, anterior part of epiproct, sterna, and legs with microgranulation; clypeus, epicranium, posterior part of epiproct smooth; prozona finely shagreened.Stricturebetweenprozonaandmetazonashallow,wide.

Metaterga ( Fig. 7A–C ): With two transverse rows of setiferous spines; 3 + 3 spines in anterior row, 3 + 3 spines in posterior row; spines in posterior row larger than anterior one.

Pleurosternal carinae ( Figs 7D , 8C ): On body ring 2 conspicuous, crest-like; on body ring 3 small, inconspicuous; thereafter missing.

Limbus ( Fig. 8J ): With a continuous fringe of finger/hairlike processes. Surface in front of limbus smooth.

Paraterga ( Figs 7A–F, H , 8D, E ): Very long and slender; elevated at c. 50°–60° (male) 40°–50° (female); with two conspicuous notches; tip directed increasingly caudad on body rings 18 and 19.

Ozopores ( Fig. 8D ): Oval; present only on rings 5 and 7; located on dorsal-lateral margin.

Telson ( Figs 7I–K , 8L ): Preanal ring (epiproct) quite long; tip slightly concave; lateral setiferous tubercles visible, short; apical tubercles inconspicuous. Posterior tip with four long spinnerets arranged at corners of a square, each surrounded by crownlike collar. Hypoproct subtriangular; caudal margin concave, with conspicuous setiferous tubercles.

Sterna ( Fig. 8K ): Cross-impressions quite deep, wide. Sternal lobe between male coxae 4 swollen, separated into two small lobes by conspicuous pore.

Legs ( Fig. 8M ): Very long and slender. Relative length of podomeres: femur ≥ tibia> tarsus ≥ postfemur> prefemur> coxa> claw. Male femora 6 with hump/apophysis ventrally in distal part. Male femora 7 with hump/apophysis ventrally in distal part, but smaller than in male femora 6.

Gonopods ( Fig. 9 ): Coxa (cx) with microgranulation on surface in lateral view. Cannula (ca) quite stout. Gonopod telopodite quite long and slender. Prefemoral part (pfe) subequal in length to prefemur and femur. Femur (fe) slightly curved. Mesal sulcus (ms) conspicuous, quite deep, wide; lateral sulcus (ls) inconspicuous. Seminal groove running on mesal surface of femur. Postfemoral part (pof) quite short, conspicuous in mesal view. Solenophore (sph) well developed, consisting of lamina lateralis and lamina medialis. Lamina lateralis (ll) large, divided into two lobes—the first spatulate lobe clearly seen in ventral view and the second lobe almost enveloping solenomere. Lamina medialis (lm) branched into two processes—first process slightly longer than the second one, directed mesoventrad, apically expanded and fringed with several small spines; the second lobe more slender, tip sharp and directed ventrad. Solenomere (sl) quite long, slightly curved, tip directed mesad.

Distribution and habitat

This monotypic genus is currently known only from the western part of Thailand at Kanchanaburi Province (Mueang, Sai Yok, and Tha Muang districts) ( Fig. 1C ). Based on our observations during fieldwork, the new species seems to be locally endemic, and highly restricted to limestone habitats. The type locality is inside a temple, and is within a cave currently used as a tourist attraction that people can easily access.

Remarks

In all other dragon millipede species, the defensive glands and their ozopores are found on body rings 5, 7, 9, 10, 12, 13, and 15–19, but the new species described here is an exception, having defensive glands and ozopores only on body rings 5 and 7. Because Siamaxytes gen. nov. is monotypic, it is impossible to know whether the reduced ozopore formula is a generic or a specific character. The formula 5, 7, 9, 10, 12, 13, 15–19 is by far the commonest in the entire order Polydesmida ( Makarov 2015) , although there are numerous examples of reduction, including some genera in which some species have a normal formula, while others have a reduced one. Examples of this are the oxydesmid genus Iringius Hoffman, 1967 ( Hoffman 1990), the pyrgodesmid genus Myrmecodesmus Silvestri, 1910 ( Shear 1977), and the star millipedes genus genus Eutrichodesmus Silvestri, 1910 ( Liu et al. 2017b). In addition, several systematically scattered millipedes, e.g. some Sphaeriodesmidae of North and Central America and some Chelodesmidae and Cryptodesmidae from East Africa, completely lack pores.

The reduction of defensive glands can be used to distinguish the new species from other dragon millipede species. The branching of lamina medialis of the solenophore is also a unique characteristic, confirming the recognition as a new species and new genus. No variation has been found.

Figures

Figure 1. Distribution areas of dragon millipede genera based on all relevant data. A, Gigaxytes; B, Desmoxytes; C, Burmaxytes and Siamaxytes gen.nov.; D, Hylomus; E, Nagaxytes; F, Spinaxytes.

Figure 6. Photographs of live specimens and habitat of Siamaxytes bifurca gen. nov.and sp.nov.(CUMZ-Px0232). A, B, male paratypes; C, female paratype; D, mating couple; E, F, habitat at the type locality.

Figure 7. Siamaxytes bifurca gen.nov.and sp. nov., male paratype (CUMZ-Px0232)—SEM.A–C, dorsal view; D–F, lateral view. A, D, anterior body part; B, E, body rings 8–10; C, F, posteriormost body rings and telson; G, collum in dorsal view; H body ring 10 in posterior view; I–K, telson in lateral, ventral and dorsal views, respectively.

Figure 8. Siamaxytesbifurca gen.nov.and sp.nov.,male paratype (CUMZ-Px0232)—SEM.A, head and mouthparts;B, antennal sensilla on antennomere 7;C, pleurosternal keels on rings 2–4,D, paraterga of ring 5 with ozopore; E, paraterga ofring 10; F,surface belowparaterga of midbody ring;G, suture between prozona andmetazona ofmidbody ring;H, surface of prozona in midbody ring;I, surface of metaterga in midbody ring;J,limbus of midbody ring; K,sternal lobe onmale coxae 4; L, tip of epiproct;M, male legs 6, 7 and10; N, tip oftarsus and clawof leg 14.

Figure 9. Siamaxytes bifurca gen. nov. and sp. nov., male paratype (CUMZ-Px0232)—SEM, right gonopod.A, mesal view (cx, coxa; ca, cannula; fe, femoral part; pfe, prefemoral part; pof, postfemoral part; sg, seminal groove; sl, solenomere; sph, solenophore); B, lateral view; C, dorsal view; D, ventral view; E, F, subdorsal views; G, H, subventral views (ms, mesal sulcus; ll, lamina lateralis; lm, lamina medialis).Scale bar A, C, 0.2 mm. Scale bar B, D, E, F, 0.1 mm.