Vietpetalum marmoratum Le, Akkari & Nguyen sp. nov.

Figs 1, 2, 3, 4, 5, 6, 7, 8, 16

Material examined.

Holotype: Vietnam – Tuyen Quang Province • male; Bach Xa commune, Cao Duong village, Bai Soi cave; 22.2878°N, 104.9885°E; 630–700 m a. s. l.; 20 June 2026; Anh D. Nguyen, Yen T. Phan, Vu H. La leg.; IEBR-Myr 1081 H.

Paratypes: Vietnam • 1 female, 1 juvenile; same data as holotype; (IEBR-Myr 1081 P).

Non-type material: Vietnam – Tuyen Quang Province • 1 male, 1 female, 1 subadult male; Bach Xa commune, Cao Duong village, cave near end of village; 22.3021°N, 104.9915°E, 630–700 m a. s. l.; 19 June 2026; Anh D. Nguyen, Yen T. Phan, Vu H. La leg.; IEBR-Myr 1080 • 2 females; ibid.; 17 December 2022; Anh D. Nguyen leg.; IEBR-Myr 1014 • 1 female, 3 juvenile; ibid. 21 April 2019; Anh D. Nguyen leg.; IEBR-Myr 799.

Differential diagnosis.

This species of Vietpetalum differs from congeners in having each gonopod with two clavate prefemoroidal processes (Pf) and the telopodite (T) distally curved at a 90 ° angle, with the apex downturned and with no distomesal spine.

Etymology.

The epithet marmoratum is from a Latin adjective, meaning “marbled”, used to emphasize the marbled pattern on collum and tergites 2–4.

Description.

Male holotype: length about 70.6 mm, width and height at midbody PT 2.7–2.8 mm and 2.9–3.0 mm, respectively; 72 PT + telson.

Male paratype: 73 PT + telson.

Colour: living specimens brownish grey (Fig. 1 D). Ethanol-preserved specimens (Figs 2, 3, 4) generally reddish brown, with whitish-yellow marbled spots near primary crest 3; posterior part of metazonites with a brownish-yellow margin; head, pleurotergites, antennae, and telson yellowish brown; legs brownish yellow; body crests paler.

Head (Fig. 2 A – C) modified; frons with a strong projection; forehead and vertex concave.

Antennae (Figs 2 A – C, 3 A) long, extending beyond posterior edge of PT 7 when folded backwards; ratio antenna / body length about 1 / 7; all antennomeres white; length of antennomeres: 1 = 0.5 mm; 2 = 1.5 mm; 3 = 1.9 mm; 4 = 1.6 mm; 5 = 1.8 mm; 6 = 1.3 mm; 7 = 0.5 mm; tip of antennomere 7 with four cones protruding well beyond the edge (not visible in Fig. 3 A).

Field of ommatidia (Fig. 3 B) black, well delineated, composed of 48 ommatidia in eight vertical rows. Tömösváry’s organ about two times larger than the largest ommatidium, placed between eye and base of antenna (Fig. 3 B).

Width of PT: 6 >> 7> 8–14> 5> 4 = 3 = 2> 1. PT slightly higher than broad; height of 10 th PT: 3.00 mm, width 2.8 mm.

Collum (Fig. 2 B, C) much narrower than head; pleurotergite 6 in males strongly enlarged (Fig. 2 A – D). Crests on collum (Fig. 2 C) moderately expressed mostly in posterior part of ring. Complete crests series appearing from PT 2 onwards. Above ozopores, midbody PT with 3 + 3 primary crests and with 3–5 + 3 – 5 secondary slightly shorter crests between primary crests (Figs 2 C, 2 D, 3 C, 3 D, 4 B, 4 C); 3 rd primary crest strongly enlarged, other primary crests not flattened, almost equally broad along metazonal length; secondary crests slightly shorter, but strong as primary crests. Ozopores lying on primary crest 3, visible from sixth to last but one PT (Figs 2 C, 2 D, 3 C, 3 D, 4 B, 4 C).

Below ozopores, midbody PT with 2 + 2 primary crests and 2 + 2 shorter and thinner secondary crests between primary crests, and 9–10 lower crests down to ventral pleurotergal edge (Figs 2 B, 3 D, 4 C).

Midbody pleurotergal setae 5 + 5, located at caudal edges of primary crests (Figs 2, 3, 4); setal pattern as in Table 1. Axial line obviously distinct.

Epiproct (ep) (Fig. 4 B, C) simple, with 2 + 2 setae on lateral sides and 2 + 2 setae in transverse rows on dorsum. Hypoproct (hp) (Figs 4 D, 5 A) tripartite, medial sclerite largest, subtrapeziform, bearing two paramedian macroseta; each lateral sclerite with a single macroseta born on a large tubercle. Paraprocts (pp) (= anal valves) (Figs 4 C, 4 D, 5 A). smooth, each divided into a small upper and a large lower sclerite, both with a pair of macrosetae. Spinnerets long and slender, tube-shaped, each ending with a long seta. All setae on telson brown, contrasting with yellowish background.

Male leg-pairs 1 and 2 much shorter, with strong setae on ventral side of femorite and tibia; leg-pair 3 slightly shorter than following legs; tarsal pads large visible on pregonopodal legs, then gradually thinner and eventually absent on subsequent legs. All legs ending with a rather slender, long, curved claw. Coxal sacs present from legs 3–23.

Coxa 2 with a pair of gonopores placed on small cones (Fig. 5 B). Coxa 6 normal, without processes or modifications. Coxa 7 (Fig. 5 C, D) with anterior round tuberculiform process (rp) directed ventrad and an angular process (ap) directed posteriad. Coxae of the remaining legs normal.

Gonopods (Figs 6, 7) brownish yellow, some parts (seminal groove, distal part of telopodite) dark brown to black. Gonopods protruding well beyond the gonocoel, stems of telopodites long, thin, subparallel, and diverging, pointing laterad (Figs 5 D, 6 A – D). Each gonopod with a long, subfalcate prefemoroidal process (pf) densely apically covered with long macrosetae (Fig. 6 B – D). Coxa with a round lobe (Ca) and a long, falcate spiniform process (b) (Fig. 6 A, B), reaching the distal part of the telopodite. Telopodite (T) long, slender, apically twisted laterad (Figs 6 B – D, 7 A, 7 B). Distal part of telopodite rather sinuous with a reduced lamella (dl), smoothly narrowing towards apex, bifurcating into solenomere (sl) and parasolenomere (ps) (Figs 6, 7). Seminal groove (sg) terminating in solenomere (Fig. 7).

Female: head unmodified (Fig. 8 A, B). Length about 73.2 mm. 10 th PT ca 2.9 mm wide and 3.1 mm high; 73–78 PT + telson. Leg-pair 2 strongly modified (Fig. 8 B – D); coxa well developed, large, trapeziform, with a small, round tubercle, a highly elevated, chimney-shaped process, and anteriorly large spine-like process (Fig. 8 C); other podomeres strongly modified as large, bilobed processes (Fig. 8 C). Leg-pairs 1–3 with tarsal brushes. Cyphopods large and round (Fig. 8 D). Coxae 7 normal, without processes.

DNA barcode.

The COI barcode is uploaded to GenBank with the accession number PQ 685116. The new species has a genetic similarity of 82.86 % with Abacion magnum (Loomis, 1943) (JN 656584).

Cave habitat.

Millipede specimens were collected from two somewhat horizontal caves located approximately 1.5 km apart. Both caves are located at an elevation of 600–700 m a. s. l. Both caves have small, narrow entrances that widen inside. Darkness begins about 10 m from the entrance. The cave floor is mostly wet and covered with small rocks. Clay deposits were observed in the area where the species was discovered. The new species was found on clay ground and large rocks 100–200 m from the cave entrances. Callipodidans, glyphiulid millipedes, and ground beetles were also present in the caves alongside the new species.

Distribution.

The species is known only from its type locality.

Remarks.

We collected specimens of this species on three occasions. During the first survey (April 2019), only subadult males were found. In the second survey (December 2022), only females were collected. In the third survey (June 2026), both mature males and females were present. These observations suggest that the maturation period is likely to extend from June to October or November each year.