Malayorthomorpha halabala, Likhitrakarn & Golovatch & Sittichaya, 2022

Likhitrakarn, Natdanai, Golovatch, Sergei I. & Sittichaya, Wisut, 2022, Review of the millipede genus Malayorthomorpha Mrsic, 1996 (Diplopoda, Polydesmida, Paradoxosomatidae), with descriptions of two new species from Thailand and a key to its species, ZooKeys 1118, pp. 1-19 : 1

Malayorthomorpha halabala sp. nov.

Figs 2A , 3 , 4 , 5

Material examined.

Holotype: Thailand - Yala Province • ♂; Betong District , hill in evergreen forest, on forest floor; 1440 m a.s.l.; 5°55'N, 101°26'E; 22 May 2021; Wisut Sittichaya leg.; CUMZ . Paratype: Thailand - Yala Province • ♀; same District, elfin montane forest ( Malaya Phytochorion province ); 1430 m a.s.l.; 25 May 2022; Wisut Sittichaya leg.; CUMZ .

Diagnosis.

This new species seems to be particularly similar to M. siveci Mršić, 1996, with which it shares most of the gonopodal characters. It differs from M. siveci by the wider body, 2.7-3.2 mm (vs smaller, 1.2 mm), the colour pattern which is uniformly red brown with lighter red brown paraterga (Fig. 3A-F ) (vs a light brown body with the collum and caudal edges of metazonae margined darker brown; Fig. 1A ), as well as the pleurosternal carinae present until segment 11 (vs until segment 5), the sternal lobe between ♂ coxae 4 with a pair of small cones laterally near base (Fig. 3E, H, I ) (vs absent, Fig. 1D ), and the tip of the gonopod with a denticulate margin (Figs 4A, B , 5C, D ) (vs smooth and rounded; Fig. 1E-G ).

Description.

Length 29.3 (♂) or 36.2 mm (♀), width of midbody pro- and metazonae 2.1 and 2.7 mm (♂) or 2.7 and 3.2 mm (♀), respectively.

Colouration of live animal rusty red (Fig. 2A ), edges of paraterga light red brown; antennae dark brownish, legs and venter contrasting light yellow (Fig. 2A ); colouration in alcohol, after one week of preservation, red brown (Fig. 3A-F ); edges of paraterga light red brown, head and antennae brown, legs, venter and a few basal antennomeres contrasting light yellow (Fig. 3A-G ).

Clypeolabral region sparsely setose; epicranial suture distinct. Antennae long, extending caudally past metaterga 5 (♂) or metaterga 3 (♀) when stretched dorsally. In width, segment 3 <4 = collum <segment 2 = head <segment 5 <6-17, body gently and gradually tapering thereafter.

Collum with three transverse rows of setae: 4+4 in anterior, 2+2 in intermediate, and 3+3 in posterior row, all mostly abraded, but still traceable as insertion points; lateral incisions absent; caudal corner of paraterga very broadly rounded, declined ventrad, produced slightly past rear tergal margin (Fig. 3A, B ).

Tegument generally smooth and shining, prozonae finely shagreened, metaterga finely leathery and faintly rugulose (Fig. 3A, C, F ), surface below paraterga leathery and rugose (Fig. 3B, D, E ). Postcollum metaterga with two transverse rows of setae traceable at least as insertion points when setae broken off: 2+2 in anterior (presulcus) and 3+3 in posterior (post-sulcus) row. Tergal setae simple, slender, ca. 1/3 as long as metaterga. Axial line barely traceable both on pro- and metazonae.

Paraterga rather well developed (Fig. 3A, C, F ), lying rather high (at upper 1/3 of body), slightly upturned, but lying below dorsum; anterior edge broadly rounded and narrowly bordered, fused to callus; lateral edge without incisions; caudal corner very narrowly rounded, not produced past rear tergal margin except in rings 2 and 3 (Fig. 3A, B ); posterior edge nearly straight. Paraterga 2 broad, anterior edge angular and rounded, lateral edge without incisions (Fig. 3A ).

Calluses on paraterga rather narrow, delimited by a sulcus fully on dorsal side and in about posterior 2/3 on ventral side; on poreless rings more narrow than on pore-bearing ones in dorsal view (Fig. 3B, D, E ). Ozopores evident, lateral, lying in an ovoid groove at about 1/3 in front of posterior edge of metaterga.

Transverse sulcus usually distinct (Fig. 3A, C, F ), complete on metaterga 5-17, narrow, line-shaped, rather deep, not reaching the bases of paraterga, very faintly ribbed at bottom, incomplete and nearly wanting on segment 18. Stricture between pro- and metazona wide, deep, ribbed at bottom down to base of paraterga starting with segment 5 (Fig. 3A-E, F ). Pleurosternal carinae complete crests with a sharp caudal tooth on rings 2-4, increasingly reduced and retaining a sharp caudal tooth on rings 5 and 6 thereafter, further retained as a small caudal tooth and increasingly reduced until segment 11, absent from segment 12 on (♂, ♀) (Fig. 3B, D, E ).

Epiproct (Fig. 3E-G ) conical, flattened dorsoventrally, with two evident, but small, rounded, apical papillae; tip subtruncate; pre-apical papillae small, but evident, lying close to tip. Paraprocts regularly convex, each with premarginal sulci medially and two pairs of setigerous knobs at medial margin (Fig. 3G ). Hypoproct roundly subtrapeziform, setigerous knobs at caudal edge very small and well-separated (Fig. 3G ).

Sterna sparsely setose, shining, cross-impressions shallow, without modifications; a single, linguiform, medially rather deeply notched sternal lobe between ♂ coxae 4, with a pair of small cones laterally near base (Fig. 3E, H, I ). A conspicuous and high ridge present in front of gonopod aperture. Legs long and slender (Fig. 3B ), midbody ones ca. 1.4-1.6 (♂) or 1.2-1.3 (♀) times as long as body height, without modifications, ♂ tarsal brushes absent.

Gonopods (Figs 4A-D , 5 ) simple; coxa a little curved caudad, densely setose distoventrally. Prefemur as usual, densely setose, about 1/3 as long as femorite + postfemoral part. Femorite rather stout, wider than prefemur or postfemur, slightly expanded distad, suberect, showing a distinct mesal groove/hollow (g), with a sulcus demarcating a postfemoral part; seminal groove running entirely mesally along fermorite, solenomere (sl) flagelliform, almost fully sheathed by solenophore (sph). Lamina medialis (lm) well developed, short and unciform, terminal lobe sheathing the tip of solenomerite. Lamina lateralis (ll) elevated, prominent, stout, expanded apically, denticulate at caudal edge (Figs 3A, B , 4C, D ).

Etymology.

To emphasize Hala-Bala Wildlife Sanctuary, the type locality. Noun in apposition.

Remarks.

A comparison of these two species shows only a few differences, but they are sufficient to distinguish both. The type locality of M. siveci , Park Belum, is located quite far away (ca. 50 km) from this new place. In addition, because the elevations between the two localities are greater than 1000 meters above sea-level, it seems improbable that the species is one and the same. Consequently, we conclude that the two are obviously distinct species.

The specimens were collected in a primary sub-elfin montane forest with no significant disturbance due to human activity, in a high mountainous area of southernmost Thailand (Fig. 2B, C ). The area is dominated by a single plant species, Dacrydium elatum . The canopy of Dacrydium elatum is low (ca. 10-15 m above ground), flat and continuously covering the area. The understorey is dense and covered with dwarf branches of small hardwood trees and teeming with bryophytes, lichens, orchids and ferns. The forest floor is with abundant orchids, ferns, liverworts, and thick slowly degraded bio-litters. The female specimen was easy to spot on the substrate and observed crawling on the leaf litter surface (Fig. 1A ).

Figures

Figure 1. Malayorthomorpha siveci Mrsic, 1996, ♂ holotype A, B anterior part of body, lateral and dorsal views, respectively C anal segment, ventral view D sternal process and left anterior leg of body segment 5, suboral view E-G right gonopod, mesal, lateral and suboral views, respectively. Photos not to scale (after Mrsic 1996).

Figure 2. Habitat at the type locality of Malayorthomorpha halabala sp. nov., ♀ A live colouration B, C elfin montane forest floor and collecting the specimens B, C pictures taken not to scale.

Figure 3. Malayorthomorpha halabala sp. nov., ♂ holotype A, B anterior part of body, dorsal and lateral views, respectively C, D segments 10 and 11, dorsal and lateral views, respectively E-G posterior part of body, lateral, dorsal and subventral views, respectively H, I sternal cones between coxae 4, subcaudal and sublateral views, respectively.

Figure 4. Malayorthomorpha halabala sp. nov., ♂ holotype, right gonopod A-D lateral, mesal, suboral and subcaudal views, respectively E sternal cones between coxae 4, subcaudal view. Abbreviations: ll lamina lateralis, lm lamina medialis, sl solenomere, sph = solenophore. Scale bars: 0.5 mm.

Figure 5. Malayorthomorpha halabala sp. nov., ♂ holotype, right gonopod A-D submesal, oral, subsuperior and sublateral views, respectively. Scale bars: 0.2 mm.