Prionobelum inthanonense Donworth & Wesener, new species

Figs 2A, B, 3–5

Material examined.

Holotype: Male, MHNG 4 E-2, Thailand (Prov. Chiang Mai): Doi Inthanon National Park ( Chomthong Distr.), evergreen lower montane forest, cloud forest, 2150 m, 15.X.1993, leg. P. Schwendinger.

Paratypes: 1 female, MHNG 4 E-2B, same data as previous; 1 female, MHNG 7 A, Thailand ( Prov. Chiang Mai): Doi Inthanon (Distr. Chomthong), 2250 m. 18.VI.1986 , leg. P. Schwendinger; 1 male, NHMD 1184674, Thailand, Chiang Mai Province, Doi Inthanon NP, main road, 2200 m, coll. Zool. Museum Copenhagen, 15.X.1981; 1 male, 1 female, same data as previous, but ZFMK MYR13661; 1 male, 1 female, NHMD 1184675, Thailand, Chiang Mai Province, Doi Inthanon NP, main road, 2200 m, coll. Zool. Museum Copenhagen, 7.X.1981 .

Derivatio nominis. inthanonense, adjective, after the type locality.

Diagnosis. Prionobelum inthanonense n. sp. is a medium-sized brown-chestnut colored species with a glabrous, shiny surface. The antenna is cylindrical, the legs with a short well-rounded coxal process (Fig. 3A), midbody legs with a single apical and 8 or 9 ventral spines. P. inthanonense n. sp. differs from all other known Prionobelum species in the greatly enlarged vulva, with the operculum covering the whole of the prefemur and the mesal corner of the operculum further elevated (Fig. 3C). A membranous spot on the immovable finger of the posterior telopod (Fig. 4A) is otherwise only present in P. hainani and P. joliveti (Mauriès 2001), but also occurs in some Thai species tentatively placed in the genera Sphaerobelum and Zephronia (Rosenmejer et al. 2021; Bhansali & Wesener 2022). P. inthanonense n. sp. differs from all other known species of the genus in the anterior telopod having a strong hook with only three crenulated teeth (Fig. 3D–F).

Description (based on holotype).

Size: Length: 17.7 mm. Width of thoracic shield 8.5 mm, of widest segment (7th) 9.0 mm. Height of thoracic shield 5 mm, Height of highest segment (7th) 5.7 mm. Female: Length: 24.2 mm. Width of thoracic shield 11 mm, of widest segment (8th) 11.7 mm. Height of thoracic shield 6.1 mm, Height of highest segment (8th) 7.1 mm.

Colour: Faded after 30 years in ethanol (see intraspecific variation below). Shiny (Fig. 2A, B). Head chestnut, anteriorly mahogany to black. Antennomeres tan, distal margin chestnut. Antennal disc black. Collum dark mahogany with black spots. Thoracic shield chestnut, with extensive black spots. Tergites tan with irregular black spots, posterior margins chestnut (Fig. 2A). Anal shield tan with central gray discoloration. Legs tan to gray with dark brown stripe on femur. Tarsi apically chestnut, spines and claws black.

Head: Number of ommatidia 60. Organ of Tömösváry located within antennal groove.

Antennae (Fig. 5A, B): Antennomere lengths: 6>1>2=3>4=5 (Fig. 5A).Antennomere 6 as long as antennomeres 4 and 5 combined.Antennae short, barely reaching first leg pair. Sixth antennomere subcylindrical (Fig. 5A), number of apical cones 22/21 (Fig. 5B). Roughly eight sensilla basiconica located along both dorsal and ventral sides of antennal disc (Fig. 5B).

Mandible: Not examined.

Gnathochilarium: Gnathochilarial palpi with sensory cones arranged in pads.

Collum: Mostly glabrous with two or three rows of sparse setae at the anterior margin.

Thoracic shield: Thoracic shield grooves wide and deep, with three sclerotized ledges along inner ridge (Fig. 2A, B).

Tergites: Paratergite tips on posterior half almost straight, very slightly projecting backwards. Tergites glabrous except for paratergite depressions. Shiny (Fig. 2A, B).

Endotergum (Fig. 5C, D): With a regular flat margin. Outer zone with two or three rows of dense, irregular marginal setae (Fig. 5D), extending two thirds of the distance from setal base to posterior margin. Cuticular impressions approximately 20 µm in diameter separated by approximately 40 µm. Intersegmental membrane (Fig. 5C, ma) smooth, without cones but with setae with large glabrous gaps. Setae with tiny scales (Fig. 5D).

First stigmatic plate: With a well-rounded apex.

Pleurites: Pleurite 1 strongly elongated with a well-rounded apex. Pleurite 2 projecting slightly, also well-rounded. Midbody pleurites typical for the family (see Wesener & VandenSpiegel 2009), well rounded with a sharp edge point laterally (Fig. 3B).

Legs: Ventral spines on leg 1: 2/3, on 2 4/?, on 3 5/6. Short apical spine present on leg 3. Single apical (Fig. 3A, arrow) and 8 or 9 ventral spines on midbody legs. Femur not extended, lacking teeth, prefemur lacking processes. Femur 1.8, tarsus 4.1 times longer than wide. Coxae with conspicuous well-rounded mesal process (Fig. 3A).

Anal shield: Well-rounded and glabrous. Ventral side with single marginal locking carina, 5 times longer than those on tergites, located halfway between tergite margin and last pleurite.

Male sexual characters: Gonopore covered by simple apically membranous plate.

Anterior telopods (Fig. 3D–F): Syncoxite without any peculiarities (Fig. 3D). Podomere 1 rectangular, as long as wide, covered with setae anteriorly, with extra-long setae mesally, and posteriorly almost glabrous (Fig. 3D, F). Podomere 2 with long posteriorly protruding immovable process visible laterally in anterior view (Fig. 3D, F, arrow). Immovable process curving inwards against apex of podomere 3. Podomere 3 cylindrical apically tapering, 2–3 times as long as wide, with three crenulated teeth on the underside of tip (Fig. 3E, F, arrow), two posteriorly visible spines near base and one large spine on apex (Fig. 3E). Apex of podomere 3 strongly bent backwards with a sharp tip (Fig. 3E).

Posterior telopods (Fig. 4A, B): Inner horns elongated, protruding into a slender tip with a wide whitish membranous projection (not drawn). Podomere 1 wider than long, covered in setae anteriorly, and nearly glabrous posteriorly (4B). Podomere 2 with wide immovable finger, tapering only slightly near apex and bearing an ovoid membranous spot on posterior side (Fig. 4A, arrow). Apex pointed and curved towards podomere 4. Immovable finger shorter than movable finger, only reaching apex of podomere 3. Membrane between immovable and movable finger with two strongly angled membranous lobes (Fig. 4A, B). Podomere 3 with sparse setation on anterior side, glabrous posteriorly. Podomere 3 ca. 3 times longer than wide, towards immovable finger with membranous ledge and one spine, posterior side with row of 10 black crenulated teeth (Fig. 4A, arrow). Podomere 4 short, slightly curved, ca. 3 times longer than wide, with a short membranous ledge and 2 spines facing towards immovable finger (Fig. 4B).

Female sexual characters (based on paratype; Fig. 3C): Vulva large, covering 2/3 of coxa, with the massive operculum covering 1/2 of prefemur. Operculum larger than bursa. Operculum sparsely setose, apical margin extending into a small mesal lobe, which covers mesal prefemur. Subanal plate mesally invaginated, creating two distinct lobes separated by a suture, both lobes well-rounded.

Intraspecific variation (Fig. 2A, B). Head mahogany or chestnut, in some individuals faded to gray and tan. Collum black, mahogany or dark chestnut, in some individuals faded to gray and tan. Thoracic shield tan to chestnut (Fig. 2B), in some individuals faded to light tan (Fig. 2A), with black or faded gray spots. Tergites dark tan, in some individuals faded to a light tan or beige, with spots ranging from black to gray to chestnut. Anal shield tan to buff often with extensive gray spotting. Posterior margins of collum, thoracic shield, tergites and anal shield black, often faded to dark chestnut. Antennae beige, tan or light brown. Legs beige, tan, or gray, sometimes with black spots. Claws and spines black, sometimes faded to chestnut. Apical spine on leg 3 absent in one female (MHNG 7A).

Distribution. This species is apparently only occurring at the summit of Doi Inthanon above 2.000 m above sea level (Fig. 6A). There it appears to be common and regularly collected. A second unidentified Zephroniidae species (ZMUC K56x3B, K56x7B) was collected in sympatry with P. inthanonense n. sp.