Sphaerobelum onyx Srikampha & Srisonchai, 2025

Sphaerobelum onyx Srikampha & Srisonchai , sp. nov.

Figs 6 View Figure 6 , 7 View Figure 7 , 8 View Figure 8 , 9 View Figure 9 , 14 C, D View Figure 14 , 15 G, H View Figure 15 , 16 View Figure 16

Sphaerobelum sp. L 10 — Wesener, 2019: 239.

Type material.

Holotype. Thailand • ♂ ( MZKKU -MYR 0003 ), Bueng Kan Province, Mueang District, Wat Phu Ngam (Wat Singhanat Banphot), 18°11'24.2"N, 103°50'40"E, ca. 180 m a. s. l., 11 August 2022, K. Srikampha, R. Srisonchai, and MZKKU students coll GoogleMaps . Paratypes. THAILAND • 6 ♂♂, 5 ♀♀ ( MZKKU -MYR 0004 ), same data as holotype GoogleMaps . • 4 ♂♂, 9 ♀♀ ( MZKKU -MYR 0004 ), 3 ♂♂, ♀ for SEM ( MZKKU -MYR 0004 ), Bueng Kan Province, Bueng Khong Long District, Wat Tham Puang , 17°58'10.9"N, 104°6'35.8"E, ca. 180 m a. s. l., 12 August 2022, K. Srikampha coll. GoogleMaps • ♂ ( CUMZ - MYR 0032 ), same data as holotype GoogleMaps . 1 ♂ ( NHM), same data as holotype GoogleMaps . • ♂ ( NHMD), same data as holotype GoogleMaps . • ♂ ( NHMW), same data as holotype GoogleMaps . • ♂, ♀ ( ZFMK), same data as holotype GoogleMaps .

Additional material examined — non-type.

Thailand • 4 ♂♂ ( MZKKU), Nakhon Phanom Province, Ban Phaeng District, Nakee Cave, Phu Langka National Park , 17°59'5.8"N, 104°7'38.3"E, ca. 320 m a. s. l., 12 August 2022, K. Srikampha coll. GoogleMaps • ♂, 12 ♀♀ ( MZKKU), Bueng Kan Province, Seka District, Wat Tham Chum Chang ( Nam Yad Cliff ), 18°11'29.6"N, 103°54'47"E, ca. 200 m a. s. l., 11 August 2022, K. Srikampha coll. GoogleMaps • 7 ♂♂, 3 ♀♀ ( MZKKU), Bueng Kan Province, Si Wilai District, Wat Pradu Nam Thip , 18°9'43"N, 103°51'34.9"E, ca. 200 m a. s. l., 11 August 2022, K. Srikampha coll. GoogleMaps LAOS • ♀ ( SMF), Vientiane Province, Vang Vieng, W. of Nam Song, Tham Nam or Khem , 18°55'46.86"N, 102°20'56.82"E, ca. 320 m a. s. l., 28 July 2014, P. Jäger & S. Münnich coll. GoogleMaps

Diagnosis.

S. onyx sp. nov. differs in the femur of the legs, in which only the apical margin carries a few teeth (no teeth or teeth at the entire margin in the other known Sphaerobelum species), a character only shared with S. bicorne Attems, 1938 , S. bolavensis Wesener, 2019 , S. nonghinensis sp. nov., as well as S. petramurum sp. nov. described below. S. onyx sp. nov. differs from both S. bicorne and S. bolavensis in the presence of a “ hook ” on telopoditomere 4 of the posterior telopods. S. onyx sp. nov. differs by the glabrous tertgites (vs. hairy) from both S. nonghinensis sp. nov. and S. petramurum sp. nov. The black body colour with red appendages of S. onyx sp. nov. is unique for known Thai members of the genus but does also occur in S. schwendingeri Wesener, 2019 , and S. laoticum Wesener, 2019 , and potentially (known specimens are faded in ethanol) S. peterjaegeri Wesener, 2019 , from Laos. S. onyx sp. nov. shares only with S. clavigerum , S. hirsutum , S. laoticum , S. nonghinensis sp. nov., S. petramurum sp. nov., S. schwendingeri , S. separatum , and S. splendidum the presence of a hook-like tip on telopoditomere 4 of the posterior telopods. S. onyx sp. nov. differs from S. clavigerum by having a shorter locking carina on anal shield (vs. 3 × long), from S. hirsutum and S. separatum by glabrous tergites (vs. hairy), from S. laoticum , S. nonghinensis sp. nov., S. petramurum sp. nov., S. schwendingeri , and S. splendidum by the presence of 5–6 rows of marginal bristles and marginal bristles covering 3 / 4 of outer area (vs. 3–4 rows and 1 / 4 covered area).

Description.

Measurements: Male holotype; body length 26.3 mm; width (broadest) of thoracic shield 13.5 mm of tergite 7 = 13.6 mm; height of tergite 7 = 7.2 mm. Males: body length = 23.7–26.1 mm; width (broadest) of thoracic shield = 11.9–13.3 mm, of tergite 7 = 12.2–13.7 mm; height of tergite 7 = 6.3–8.0 mm. Females: body length = 25.7–32.4 mm; width (broadest) of thoracic shield = 12.4–16.4 mm, of tergite 7 = 13.3–17.3 mm; height of tergite 7 = 8.2–10.0 mm.

Colouration (Fig. 6 A – F View Figure 6 ): Live specimens with shiny black colour. Head, collum, thoracic shield, tergites, and anal shield black. Antennae, legs, and venter contrastingly brownish orange. Some specimens in alcohol after 3 years faded to dark brown; anterior margin of tergites and venter dark olive; legs brown.

Head (Fig. 7 A, E View Figure 7 ): Trapeziform; with long and sparse setae, each seta located inside small pit. With 59–78 ommatidia (ocelli) in males and 71–85 in females. Aberrant ommatidium situated at brim of antennal groove. Organ of Tömösváry located at brim near the base of antenna, separated from eye field. No sclerotised crest / ridge between antennal socket and eye field.

Antennae (Figs 6 B, C View Figure 6 , 7 A – D View Figure 7 ): Quite short; covered by long and dense setae; last antennomere extending back to leg pair 3 or 4. Lengths of antennomeres 6> 1 = 2 = 3 = 4 = 5. Antennomere 6 slightly rounded apically, oval; apically with sensilla basiconica. Apical disc slightly convex, with 34–59 apical cones in male or 31–42 in female.

Epipharynx (Fig. 7 F View Figure 7 ): With a regular central tooth (ct); laterally with abundant external teeth (et), short, triangular; inner area of each side with a row of dentate spines (rsp).

Gnathochilarium (Fig. 7 G, H View Figure 7 ): Structure typical as for Sphaerotheriida . Lamellae linguales (ll) rectangular, apically truncate. Central pads (Cp) modified, with numerous sensory cones. Stipites (st) large; densely setose; located laterally to lamellae linguales. Mentum (me) large; fused at base; with dense and long setae. Lateral palpi inconspicuous. Inner palpi (ip) with sensory cones (sc) arranged in three fields (clusters).

Mandibles (gnathal lobe) (Fig. 7 I, J View Figure 7 ): With undivided external tooth (Et) and with conspicuous 3 - combed inner tooth (3 it). With 5–6 rows of pectinate lamellae (pl). Inner area (Ia) with group of tiny teeth. Molar plate (mp) flat, velvet-like; lacking a membranous fringe. Condylus (co) conspicuous, apically with one distinct ridge.

Tegument (Fig. 6 A – F View Figure 6 ): Shiny and smooth; all tergites sparsely microscopic setose; each seta located in an inconspicuous pit. Anterior margins of midbody tergite and anal shield with a few rows of long setae.

Collum (Figs 6 B, C View Figure 6 , 7 A View Figure 7 ): Subsemicircular; tip of lateral margin obtuse; sparsely long setose.

Thoracic shield: With large and shallow groove demarcated by a large and long ridge at anterior edge. Groove and ridge smooth, without setae. Sloped towards groove with 3 inconspicuous (but traceable) keels.

Midbody tergite: With a row of oval impressions at anterior margin. Tips of midbody paratergites projecting posteroventrad.

Paratergites: Paratergites 3 and 4 slender, slightly attenuate; tip sharp. Paratergites 5–12 wide; tip obtuse.

Anal shield: Slightly sexually dimorphic, in female large and well-rounded, in male slenderer. With a row of oval impressions at anterior edge. Underside without or with a single short or dot-like, black locking carina.

Endotergum of midbody tergite (Fig. 14 C, D View Figure 14 ): Posterior margin (pm) unmodified, flat, regular. Outer area (oa) narrow; smooth, without setae. Marginal bristles arranged in five or six rows; tips of the longest bristles reaching to posterior margin (but not reaching above the margin). Middle area (ma) with several tiny cuticular impressions (cp), tubercle-like. Inner area (ia) without tubercles or setae.

Pleurites (laterotergites): First pleurite slender, boomeranglike; apical margin slightly attenuated, strongly projecting into a wide tip. Pleurite 2 wider than the first one, tip obtuse. All remaining pleurites flat and broad, apical margin slightly extended.

Subanal plate (Fig. 8 H View Figure 8 ): Densely setose; large and wide; subsemicircular; heartlike; apical; apical margin strongly concave.

Stigmatic plates (Fig. 8 C, D View Figure 8 ): First stigmatic plate slender, apex rounded. Second stigmatic plate in both sexes not curved.

Legs (Fig. 8 A – G View Figure 8 ): All podomeres sparsely setose. Coxa (cx) large; coxal process absent in first legs; each side of legs 2–21 laterally with a dentate ridge. Prefemur (pre) quite short; apico-mesally with short but conspicuous projection. Femur (fe) 1.8 times longer than wide, with a long ridge in all leg pairs; apico-mesally with inconspicuous dentate margin, carrying inconspicuous teeth (Sp). Postfemur (po) and tibia (ti) relatively short. Tarsus (ta) of midbody legs quite long, 3.9 times longer than wide, as long as length of femur + postfemur; first two leg pairs without apical spine; leg-pair 1 with 2 ventral spines; leg-pair 2 with 4 ventral spines; leg-pair 3 with 6 or 7 ventral spines and 1 apical spine; leg pairs 4–21 with 6 or 8 ventral spines and 1 apical spine. Claw normal, with a small notch at base.

Male gonopore (Fig. 8 F View Figure 8 ): Small, triangular; covered by long setae.

Anterior telopods (Fig. 9 A, C, E – G View Figure 9 ): First telopoditomere rectangular. Telopoditomere 2 large and stout, with process as long as telopoditomere 1. Immovable finger (process of telopoditomere 2) slightly long; almost as long as telopoditomere 3; strongly curved; tip obtuse, inner margin with single spine. Telopoditomere 3 longer than telopoditomere 4, clearly demarcated from telopoditomere 4 by suture when seen in ventral view, apically with one spine. Tepoloditomere 4 short, less than half as long as telopoditomere 3, with two small spines; tip directed mesad.

Posterior telopods (Figs 9 A – D View Figure 9 , 15 G, H View Figure 15 ): Consisting of 4 telopoditomeres. First telopoditomere rectangular, length = width. Telopoditomere 2 large and stout. Immovable finger (process of telopoditomere 2) quite long, hammerlike; 2 times longer than wide, with a characteristic, extremely swollen, apically round apex; tip obtuse; with thick and dark spot near apex; tip in situ, curving ventrad; antero-apical margin a bit collapsed to accommodate tip of telopoditomere 4. Telopoditomere 3 quite short, 2 times longer than wide, with a single spine at excavated inner margin. Telopoditomere 4 short, 3 times shorter than telopoditomere 3, with two spines, strongly tapering toward apex and slightly curved near apex by forming a digitiform tip. Telopoditomeres 1 and 2 in anterior and posterior views mostly covered by setae. Telopoditomeres 3 and 4 mostly glabrous, except small area at basal part of telopoditomere 3 with long setae. Inner horns with sharp-edged tips.

Female sexual characters (Fig. 8 G View Figure 8 ): Vulva short and stout; sparsely setose; covering almost 1 / 3 of coxa; projecting mesally to base of prefemur. Operculum (op) narrow, flattened dorso-ventrally when seen in posterior view; mesal margin protruding into a small lobe on each side. Bursa (bu) short and stout, demarcated from operculum by a triangular groove.

Etymology.

The name is a noun in apposition and refers to the remarkable black body colour, which somewhat resembles the chalcedony mineral “ onyx. ”

Distribution and habitat

(Fig. 6 G, H View Figure 6 ). Sphaerobelum onyx sp. nov. is currently known from the Mekong River basin, specifically in Laos and Thailand. All examined specimens in Thailand (Bueng Khan and Nakhon Phanom Districts) were observed during the daytime on rocky sandstone beds that were covered with thick leaf litter in evergreen forests. Notably, a single female previously reported by Wesener (2019) was found in limestone habitats in the Vang Vieng district (18°55'46.9"N, 102°20'56.8"E), indicating some habitat variability within its distribution.

Remarks.

Wesener (2019) identified a single female specimen from Vang Vieng, Laos, as Sphaerobelum sp. L 10, although it has not yet been formally named. The morphology of all the newly collected specimens from Thailand corresponds closely with the description of this female specimen, showing a genetic divergence of 5.02 % based on the COI genetic divergence.

In this species, females typically exhibit a larger body size compared to males. Additionally, some specimens display variation in the locking carina, which may be absent or consist of a single short or dot-like structure.