Alluviobolus omega sp. nov.

Figs 5–9

Material examined. Holotype: 1 M, FMNH-INS 5458, Madagascar, Province Toliara, Forêt de Vohibasia #3, 59 km NE Sakaraha, tropical dry forest, 780 m, 22°27.5’ S, 044°50.5’ E, coll. S. Goodman, 10–16.i.1996.

Paratypes: 1 F, FMNH-INS 5458, same data as holotype; 3 M, 1 F, FMNH-INS 5462, Province de Toliara, Forêt de Vohibasia, 59 km NE Sakaraha, 780 m, 22°27.5’ S, 44°50.5’ E, leg. S. Goodman, 10–16.i.1996 ; 1 M, FMNH-INS 5403, Province de Toliara, Forêt de Vohibasia, 59 km NE Sakaraha, 780 m, 22°27.5’ S, 44°50.5’ E, coll. S.M. Goodman, 10.i.1996 .

Other material: 1 M, FMNH-INS 5396, Province de Toliara, Forêt de Vohimena, 35 km SE Sakahara, 780 m, 22°41.0’ S, 44°49.8’ E, coll. S.M. Goodman, pitfalls, 17–24.i.1996 ; 10 M, 2 F, CAS BLF 7381, Madagascar, Province Fianarantsoa, Forêt d’Analalava, 29.6 km 280° W Ranohira, tropical dry forest, 700 m, 22°35’30” S, 045°07’42” E, coll. Fisher, Griswold et al., pitfall trap, 1–5.ii.2003 ; 1 M, CAS BLF 7306, Madagascar, Province Fianarantsoa, Parc National d’Isalo, 9.1 km 354°N Ranohira, gallery forest, 725 m, 22°28’54” S, 045°27’42” E, coll. Fisher, Griswold et al., pitfall trap, 27–31.i.2003 .

Derivatio nominis. omega, noun in apposition, after the last letter of the Greek alphabet.The posterior gonopods resemble the letter “Z”, the last letter in our Lain alphabet.

Diagnosis. The gnathochilarium with the division of the mentum and the sclerotized ledges on the stipites and mentum identify this species a member of a group uniting several genera of small-bodied Malagasy Pachybolidae (see Wesener et al. 2009a). This species is placed in the genus Alluviobolus because of the posterior telopods, in which the coxite and telopodite are clearly separated, the telopodite with a torsion so that the opening of the spermatic groove (or sperm channel) discharges apico-laterally. A. omega sp. nov. differs strongly from the other three Alluviobolus species distributed in the SE of Madagascar: the anterior telopod has a weaker telopodite process, the posterior telopod is unique, almost resembling the letter ‘Z’ with a hole in anterior view and numerous large membranous folds apico-mesally.

Description

Measurements: holotype male with 45+0 body rings, ca. 36 mm long, midbody rings 3.1 mm wide. Other males with 45 or 46+0 body rings, length up to 39 mm, midbody ring width up to 3.4 mm. Females larger, large paratype female with eggs ca. 56 mm long, at midbody rings 5.1 mm wide, with 46+0 body rings.

Colour: Head and collum black, only on margins red (Fig. 5A), legs, antennae (Fig. 5B) and anal valves (Fig. 5C) red. Telson and body black, dorsally with a thin red stripe.

Head:Eyes with 30 ommatidia arranged in 4–5 rows (Fig.5A).Antennae, length of antennomeres1<<2>3>4>5=6 (Fig 7A), with fields on sensilla basiconica on 5th and 6th (Figs 7B, C), 4 apical cones (Fig. 7B). Antennae in male long, reaching back to 5th body ring (Fig. 5A), in female much shorter, protruding back to body ring 2. Head with 2/2 labral grooves and 2/2 setae on lamellae linguales of gnathochilarium (Fig. 5A). Gnathochilarium with a mentum divided by a suture, stipites each with three apical setae (Fig. 8A). Central pads of gnathochilarium with two sets of sensory cones, one rounded spot with 6 or 7 located more apically and an oval field with cones in 3–4 rows closer to the endochilarium (Fig. 8B). Mandible with a 3-combed inner tooth, pectinate lamellae with teeth in 5–6 rows, molar plate relatively small, with 6 ridges (Fig. 8C).

Ozopore starting at 6th ring (Fig. 5A), located on suture between meso- and metazonite (Figs 5C, 9B).

Legs in both sexes long, longer than width of body rings (Fig. 6F, G). Male legs without tarsal pads (Figs 6F, 8D, E). Male legs 3–5 with cylindrical coxa processes, tip broadly rounded. Process of coxae 3 and 4 bent posteriorly, 3rd tip protruding to 4th, 4th tip protruding to 5th coxa. 5th coxa process not bent, short. 6th and 7th coxae flat & broad (Fig. 5B). Legs 8+ in male with a cylindrical, basally tapering coxa, femur longest podomere, length of podomeres: coxa <prefemur<femur>postfemur>tibia<tarsus, tarsus as long as prefemur. Each podomere in both sexes with an apical spine (Fig. 6F, G). Male tarsus with short sharp claw with small paronychium (Fig. 8D, E), single short apical spine above claw (Figs 6F, 8E) and 5 or 6 short ventral spines. Female leg similar to male leg, with four ventral spines (Fig. 6G).

Anal valves not invaginated. No pre-anal processes (Fig. 5C).

Female vulva simple, bivalve-like, with a small, poorly sclerotized operculum at base (Fig. 8F). Posterior valve apically overlapping part of anterior one. Basally on each valve towards opening with two or three rows of setae

Anterior gonopods massive and wide (Figs 5D, E, 6A, B). Median sternal projection triangular and elongated with a well-rounded, rectangular tip (Figs 5D, E, 6A, B). Sternal process always far longer than coxite and telopodite, except for telopodite process. Coxite process weakly developed, broadly rounded mesally and barely visible behind massive sternite (Fig. 6A, B). Telopodite mesally with a slender, apically tapering process (Figs 5D, E, 6A, B). Tip with a small, sharp-edged, retrorse process (Fig. 6B).

Posterior gonopods in situ almost completely covered by coxite and telopodite of anterior gonopod. Coxite and telopodite of posterior gonopod clearly separated, with telopodite located at different level and angle than coxite (Figs 5F, G). Sternite sclerotized and well-visible (Figs 5G, 6E). Coxite mesally with a single groove,protruding into a short stem towards telopodite. Telopodite longer than coxite, curved posteriorly (Figs 5F, G, 6 C–E). Telopodites arranged parallel to one another. A torsion present in telopodites, sperm canal discharging apico-laterally (Fig. 5F, G), telopodites resembling the letter ‘Z’. Telopodite in anterior view centrally with a ‘hole-like’ structure (Fig. 6C), apex with four specific areas labelled a–d: (a) is a spinose membranous area, (b) the lateral opening of the sperm channel, (c) a membranous fringe below the apex and (d) a large membranous area located mesally (Fig. 6C, D).

Distribution. Intermediate rain-dry forests (Moat & Smith 2007) in Vohibasia, Isalo and Vohimena.

Intraspecific variation. The three populations at Vohibasia, Isalo and Vohimena differ from one another slightly in their size, ring number and gonopods. The population from Vohimena has 47 body rings, differs slightly in the colour pattern (Fig. 9A, B), missing a coxal processes on male coxa 5 (Fig. 9C), and in a completely red telson (Fig. 9D). The anterior (Fig. 9E, F) and posterior gonopods (Fig. 9G, H) appear very similar to those of the type series from Vohibasia. Future studies should elucidate if these are three different species, like what was observed in the giant pill-millipede genus Zoosphaerium, where similar but distinct species can be found in Vohibasia, Isalo and Vohimena (Wesener 2009; Wesener & Anilkumar 2020).