Sphaerobelum bicorne Attems, 1938

Semenyuk, Irina, Golovatch, Sergei I. & Wesener, Thomas, 2020, Some new or poorly-known Zephroniidae (Diplopoda, Sphaerotheriida) from Vietnam, ZooKeys 930, pp. 37-60 : 37

Sphaerobelum bicorne Attems, 1938 Figs 1A-C , 3A , 4A , 5

Sphaerobelum bicorne Attems, 1938: 200; Enghoff et al. 2004: 32 (list); Jeekel 2001: 17 (list); Wongthamwanich et al. 2012: 34 (key); Wesener 2019: 211 (key).

Material examined.

1 ♂, 1 ♀ (ZFMK MYR8860), 2 ♂, 5 ♀, 2 juv. (ZMUM Rd 4636), Vietnam, Quang Nam Prov., Song Thanh National Park, 15°33'N, 107°23'E, 1000 m a.s.l., tropical forest in a narrow river valley, on forest floor (♂) and in leaf litter (♀), daytime, V.2019, I. I. Semenyuk leg. Syntypes 1 ♂, 1 ♀ (NHMW 2196), Vietnam, South Annam (Tourane = Da Nang), Ba Na Hills, C. Dawydoff leg. Studied only from numerous photographs by author TW.

New diagnosis.

Sphaerobelum bicorne belongs to the group of congeners in which the mesal margin of the femur is extended into several teeth. Sphaerobelum bicorne shares only with S. bolavensis Wesener, 2019, from Laos ( Wesener 2019), the presence of such an extension in the apical part of the femur, but differs from the latter species in several characters: ♀ operculum projecting into two conspicuous processes (Fig. 5H ) (vs. one process in S. bolavensis ), telopoditomere 4 of posterior telopod straight, apically with a recessed hook (Fig. 5A, B ) (vs. no hook in S. bolavensis ), and locking carina of anal shield long (vs. short in S. bolavensis ).

Redescription (mostly based on ZFMK material).

Body length: ♂ length ca. 40.9 mm, width of thoracic shield 21.3 mm, of tergite 8, 21.9 mm (= broadest), height of thoracic shield, 12.1 mm, of tergite 8, 13.3 mm (= highest); ♀ length ca. 42.7 mm, width of thoracic shield, 23.5 mm, of tergite 7, 24.3 mm (= broadest), height of thoracic shield 11.9 mm, of tergite 8, 15.1 mm (= highest). ZMUM adults 18 (♂) to 23 mm wide (♀). Coloration: both in vivo and in vitro, after several months of preservation in ethanol, uniformly black to blackish, shining. Head and collum also black. Antennae orange, legs in life mainly blackish as well (Fig. 1D-F ), but in alcohol dark olive, usually with several basal segments and tarsi or their distal halves orange, only juveniles a little lighter, dark brown to blackish, some with very vague variegated tergal patterns (Fig. 1G, H ). Head: eyes with>70 ocelli. Aberrant ocellus located inside antennal groove. Antennae short (Fig. 5G ), with rounded joints, protruding posteriorly to leg-pair 3. All antennomeres densely pubescent, sensilla basiconica surrounding apical disc. Shape of antennae sexually dimorphic, cylindrical in ♀, thickened, apically broadened and slightly flattened in ♂. Apical disc with ca. 74/76 (♂) or 56/51 (♀) apical cones, respectively. Apical cones typical of Diplopoda. Organ of Tömösváry located inside antennal groove. Gnathochilarium: structure typical of the order. Palpi with sensory cones arranged in clusters. Mandibles : not dissected. Stigmatic plates: first stigmatic plate broadly rounded, apex clearly rounded, weakly curved towards coxa 1. Laterotergites : laterotergite 1 strongly projecting into a well-rounded tip. Laterotergite 2 well-rounded, like following laterotergites. Collum: with a glabrous surface, margins with few isolated setae. Thoracic shield: surface glabrous like tergites, setae only in grooves. Shallow grooves beset with numerous long setae, sloping towards groove with 5 or 6 continuous lateral and posterior keels. Tergites: surface of anterior half of tergites setose, with very small setae and small pits, posterior half of tergite smooth (Fig. 4A ). Tips of midbody paratergites projecting posteriorly. Endotergum: inner section lacking any spines or setae. Middle area with a single row of large, dense, elliptical, cuticular impressions. Distance between impressions shorter than half their diameter. Apically, 3-4 dense rows of long marginal bristles, tips of longest setae clearly protruding beyond tergal margin (Fig. 3A ). Bristles not smooth, but with numerous small spinicles. Anal shield: large, sexually dimorphic: in ♀ well-rounded, in ♂ weakly bell-shaped. Surface in ♀ only in anterior half, in ♂ completely covered with tiny setae. Underside with a single, long, black, locking carina, this being slightly longer than width of last laterotergite, locking carina located close to last laterotergite. Legs: leg 1 with 4, leg 2 with 5, leg 3 with 6 or 7 ventral spines. First two leg-pairs each without an apical spine. Leg-pairs 4-21 with 7-9 ventral spines and one dorso-apical spine (Fig. 5F ). In leg 9, femur 1.7, tarsus 3.8 times longer than wide (Fig. 5F ). All podomeres densely setose. Coxa with a large and well-rounded process. Coxa process sharp in legs 1 and 2. Prefemur apico-mesally with a weak projection. Femur in apical part extended mesally into a dentate margin featuring 4-6 teeth. Female sexual characters: vulva large, covering 2/3 of coxa, extending mesally to anterior half of prefemur (Fig. 5H ). Operculum centrally deeply recessed, apical margin projecting into two rounded lobes, 2-3 times as high as remaining operculum (Fig. 5H ). Subanal plate well-rounded, almost circular. Male sexual characters: gonopore covered with a single, undivided, circular, sclerotized plate. Anterior telopods (Fig. 5C-E ): consisting of only 3 telopoditomeres distal to syncoxite, telopoditomeres 3 and 4 partly fused. Telopoditomere 1 cylindrical, slightly longer than wide. Telopoditomere 2 large, without process as long as telopoditomere 3. Process of telopoditomere 2 located posteriorly, visible in anterior view. Process slender, projecting to 2/3 of telopoditomere 3, conspicuously curved, with an almost sharp apex. Telopoditomere 3 massive, cylindrical, straight, apically slightly tapering. Posterior side with a black sclerotized spot and a small, triangular spine. Telopoditomere 1 in apical view covered with long setae. In posterior view all telopoditomeres setose. Posterior telopods (Fig. 5A, B ): telopoditomere 1 large and cylindrical, twice as long as wide, reaching the length of telopoditomere 3. Immovable finger (process of telopoditomere 2) shorter than movable finger, consisting of telopoditomeres 3 and 4. Immovable finger with a characteristic, distally swollen apex, clearly rounded, apex therefore wider as base, projecting especially strongly at lower margin. Telopoditomere 3 rectangular, clearly rounded, with a sharp process directed towards immovable finger. Telopoditomere 4 as long as, but slightly more slender than, telopoditomere 3, 2.5 times longer than wide, apically weakly tapering, with a tiny curved hook directed towards immovable finger. Telopoditomere 1 on both sides covered with setae, remaining telopoditomeres in posterior view almost glabrous, in anterior view with few isolated setae except for immovable finger which is more densely setose.

Remarks.

In the field, these millipedes were found in a very wide range of habitats, from 700 to 1200 m a.s.l., including extremely humid forest on river banks and in valleys with abundant Cyathea sp. tree ferns, on sandy soils and in sparse leaf litter; on hill slopes covered with rich broadleaved tropical forest and a thick leaf litter layer; as well as on very dry ridges and interfluves with broadleaved forest with admixtures of coniferous trees, and in open places colonized by Dicranopteris sp. ferns and Melastoma sp. bushes. A similar number of males and females were recorded during the expedition (30 adult individuals in total). Two-thirds of the females were hidden in leaf litter inside their "living chambers", the remaining were spotted walking on the forest floor. All males were likewise walking on the forest floor, most probably searching for mates. The few recorded juveniles of both sexes were hidden in leaf litter. During the expedition, the day temperature on the leaf litter surface averaged 24 °C, compared to 19 °C in the night, with occasional nights when the temperature dropped down to 17.5 °C. Heavy, but rather short showers took place almost every day, quite often also with fogs in the evening. The abundance of the millipedes did not change drastically under rains, only slightly decreasing on non-rainy days in open habitats.

According to local knowledge, April is the driest month in the Park, while the rest of the year is extremely humid. Surprisingly, we noticed the lack of Diplopoda during the expedition with very little millipede activity, but S. bicorne was abundant at different age stadia. It may be a strategy for avoiding competition with other millipede species, as Sphaerobelum is a quite robust and well-protected diplopod capable of surviving difficult conditions.

Figures

Figure 1. Live Sphaerobelum pumatense sp. nov. (A-C) and Sphaerobelum bicorne Attems, 1938 (D-H) in the field A-C adult, enrolled, ventral view and walking, respectively D-F adults, ventral view, and enrolled, respectively G, H juvenile, enrolled and unrolling, respectively. Pictures taken not to scale.

Figure 3. Endoterga of midbody segments, SEM micrographs. A Sphaerobelum bicorne Attems, 1938, ♂ (ZFMK) B Sphaerobelum pumatense sp. nov., ♂ holotype C Sphaeropoeus maculatus (Verhoeff, 1924), ♂ lectotype D Sphaeropoeus bidoupensis sp. nov., ♂ holotype E Sphaeropoeus honbaensis sp. nov., ♂ holotype. Scale bars: 0.2 mm.

Figure 4. Tergal surface of midbody segments, SEM micrographs. A Sphaerobelum bicorne Attems, 1938, ♂ (ZFMK) B Sphaeropoeus bidoupensis sp. nov., ♂ holotype. Scale bars: 0.2 mm.

Figure 5. Sphaerobelum bicorne Attems, 1938, ♂ (A-G) and ♀ (H) from Song Thanh National Park. A, B Right posterior telopod, anterior and posterior views, respectively C, D right anterior telopod, posterior and anterior views, respectively E telopoditomeres 2 and 3 of right anterior telopod, lateral view F left leg 9, anterior view G left antenna H left coxa and prefemur 2 with vulva, posterior view. Scale bars: 1.0 mm, E drawn not to scale.