Prionobelum naevium Donworth & Wesener, 2024

Donworth, Patrick & Wesener, Thomas, 2024, The first record of the giant pill-millipede genus Prionobelum Verhoeff, 1924 from Thailand, with the integrative description of two species (Diplopoda, Sphaerotheriida, Zephroniidae), Zootaxa 5419 (4), pp. 545-562 : 555-558

publication ID	https://doi.org/ 10.11646/zootaxa.5419.4.4
publication LSID	lsid:zoobank.org:pub:6882F668-F897-4BD1-B35C-71D1AF6B6AE2
DOI	https://doi.org/10.5281/zenodo.10798759
persistent identifier	https://treatment.plazi.org/id/433C87F8-1D62-EE33-FF54-FA43FC80F81A
treatment provided by	Plazi
scientific name	Prionobelum naevium Donworth & Wesener
status	sp. nov.

Treatment

Prionobelum naevium Donworth & Wesener , new species

Figs 2C View FIGURE 2 , 6B View FIGURE 6 , 7 View FIGURE 7 , 8 View FIGURE 8

Material examined. Holotype: Male, MHNG 4B-1 , Thailand (Province Yala): Distr. Than To, Bang Lang National Park ( Than To Waterfall ), 150 m, 1.II.1991, leg. P. Schwendinger.

Paratypes: 1 male, NHMD 1184671 , Thailand, Yala Province, Bang Lang NP , lowland rainforest, <400 m, 6°04’N, 101°11’E, coll. M. Andersen, O. Martin & N. Scharff, 20.X.1991 GoogleMaps ; 1 female, NHMD 1184672 , Thailand, Yala Province, Bang Lang NP , lowland rainforest, <400 m, 6°04’N, 101°11’E, coll. M. Andersen, O. Martin & N. Scharff, 20.X.1991 GoogleMaps ; 1 male, NHMD 1184673 , Thailand, Yala Province, Bang Lang NP , lowland rainforest, 270 m, 6°11’47.5”N; 101°9’50.9”E, coll. ATOL Expedition 2003, 15.X.2003 GoogleMaps .

Derivatio nominis. Latin adjective meaning ‘having moles or spots’. Named after the irregular black spots covering the tergites ( Fig. 2C View FIGURE 2 ), first thought to be artifacts of bleaching in ethanol, but also visible in living specimens ( Fig. 6B View FIGURE 6 ).

Diagnosis. Prionobelum naevium n. sp. is a large (> 35 mm length,> 20 mm width) giant pill-millipede species with a shiny, glabrous surface and a reddish-brown-black coloration pattern. P. naevium n. sp. is far larger than all other known Prionobelum species, none of which are larger than 30 mm in body length. The axe-shaped antennomere 6 with>100 apical cones ( Fig. 8B View FIGURE 8 ) is unique for this species among Prionobelum , with only P. durum showing a non-cylindrical antenna (which is swollen but not axe-shaped). The posterior telopod with telopoditomere 4 strongly projecting above the immovable finger ( Fig. 7E, F View FIGURE 7 ) is shared with P. durum , P. joliveti , P. leve and P. multidentata , but P. naevium n. sp. differs from all of the latter species in the shape and dentition of the anterior telopods ( Fig. 7B–D View FIGURE 7 ).

Description (based on holotype).

Size: Length: 36.8 mm. Width of thoracic shield 21 mm, of widest segment (9th) 21.3 mm. Height of thoracic shield 11.4 mm, of highest segment (9th) 12.1 mm.

Colour ( Fig. 2C View FIGURE 2 ): Faded after 20 years in alcohol. Head black. Antennae olive green with dark brown spots. Legs medium brown, tarsi dark brown and olive green. Tarsal claws apically dark brown. Collum black. Thoracic shield black, in some areas faded to dark brown. Tergites light brown with chestnut spots, posterior margin black. Anal shield light brown with extensive chestnut spotting ( Fig. 2C View FIGURE 2 ).

Head: Number of ommatidia ca. 70. Tömösváry organ located in antennal groove.

Antennae ( Fig. 8A–C View FIGURE 8 ): Antennomere lengths: 6>1>2>3>4>5 ( Fig. 8A, B View FIGURE 8 ). Antennae reaches leg pair 3. Antennomere 6 strongly apically swollen, axe shaped, number of apical cones 106/123 ( Fig. 8B View FIGURE 8 ).

Gnathochilarium: Lamellae linguales with numerous long setae, medially glabrous. Sensory cones on gnathochilarium palps in pads.

Mandible: Not examined.

Collum: Largely glabrous with one row of setae on posterior margin and 2–3 rows near the anterior margin.

Thoracic shield: Thoracic shield grooves anteriorly narrow and steep, laterally wide ( Fig. 2C View FIGURE 2 ), with 9 crests (sclerotized ledges?) on each side.

First stigmatic plate: rounded, with a sub-triangular apex.

Tergites: Tergites glabrous, shiny, at (100x magnification) sparse tiny pores become visible. Paratergite tips on posterior half straight ( Fig. 2C View FIGURE 2 ).

Pleurites: Pleurite 1 with a slightly elongated and very rounded tip. Pleurite 2 projecting less than 1 and with a very rounded apex. Pleurite 3 and following rectangular with no tip.

Endotergum ( Fig. 8D, E View FIGURE 8 ): with a regular flat margin. Outer zone with two or three dense rows of irregular marginal setae extending up to two thirds of the distance from setal base to posterior margin ( Fig. 8D, E View FIGURE 8 ). A single row of rounded cuticular impressions 30 µm in diameter present next to marginal ridge, distance between impressions 30 to 45 µm ( Fig. 8D View FIGURE 8 ). Intersegmental membrane smooth, without cones and with very few setae ( Fig. 8D View FIGURE 8 ). Setae with tiny scales ( Fig. 8E View FIGURE 8 ).

Legs: Ventral spines on leg pair 1 3/4, on 2 7/8, on 3 10/11. Apical spine on leg 3 present. A single apical spine and 12 to 14 ventral spines on midbody legs ( Fig. 7A View FIGURE 7 , arrow). Femur regularly shaped, 1.9 times longer than wide. ( Fig. 7A View FIGURE 7 ). Tarsus 4.5 times longer than wide ( Fig. 7A View FIGURE 7 ).

Anal shield: Glabrous. One medium-sized locking carina 3 times the length of those on tergites, located close to margin.

Male sexual characteristics: Gonopore inconspicuous, consisting of large membranous opening located directly at mesal margin.

Anterior telopods ( Fig. 7B–D View FIGURE 7 ): Syncoxite without any peculiarities ( Fig. 7D View FIGURE 7 ). Podomere 1 rectangular, as long as wide ( Fig. 7D View FIGURE 7 ). Long setae covering both medial and lateral sides of the first 2 podomeres, as well as much of the posterior side of podomere 2 ( Fig. 7B, D View FIGURE 7 ). Podomere 2 with a large, well-rounded immovable process protruding inward towards podomere 3 ( Fig. 7B, D View FIGURE 7 , arrow), which does not extend to podomere 4 ( Fig 7B View FIGURE 7 ). Podomere 3 and 4 irregularly fused, suture visible in lateral but not in anterior view ( Fig. 7C, D View FIGURE 7 ). Podomere 3 and 4 strongly curved backwards, with a pointed, sharp tip towards process of podomere 2. Podomere 3 with sparse setation, bending towards immovable finger. Podomere 4 very short, with one laterally protruding spine and three nodules near tip on mesal side ( Fig. 7B, C View FIGURE 7 ).

Posterior telopods ( Fig. 7E, F View FIGURE 7 ): Inner horns projecting into white triangular membranous tip (not drawn). Podomere 1 slightly longer than wide, clusters of setae on lateral and mesal margins ( Fig. 7E View FIGURE 7 ). Podomere 2 setose, with especially dense setation on immovable finger. Immovable finger straight and long, apically tapering in a well-rounded projection, reaching but shorter than podomere 4. Membranous lobe extending from immovable finger bearing two elongated processes, fused at base. Podomere 3 posteriorly glabrous, with sparse setation on anterior side and 20 or 21 small crenulated teeth on posterior side ( Fig. 7F View FIGURE 7 , arrow). Membranous ledges on podomeres 3 and 4. Podomere 4 glabrous, curved and overlapping tip of immovable finger and bearing a posteriorly visible spine ( Fig. 7F View FIGURE 7 ).

Distribution. Currently, this large and conspicuous species is only known from the lowland rainforests of the Bang Lang National Park where it appears to be relatively widespread ( Fig. 6A View FIGURE 6 ). The smaller species Sphaerobelum meridionalis Bhansali & Wesener, 2022 occurs in direct sympatry.