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 Author Likhitrakarn, Natdanai https://orcid.org/0000-0002-1306-317X Program of Agriculture, Faculty of Agricultural Production, Maejo University, Chiang Mai, 50290, Thailand Author Golovatch, Sergei I. Biodiversity and Utilization Research Center of Maejo University, Maejo University, Chiang Mai, 50290, Thailand Author Sittichaya, Wisut https://orcid.org/0000-0001-6200-1285 Institute for Problems of Ecology and Evolution, Russian Academy of Sciences, Leninsky pr. 33, Moscow 119071, Russia wisut.s@psu.ac.th text ZooKeys 2022 2022-08-16 1118 1 19 http://dx.doi.org/10.3897/zookeys.1118.89593 journal article http://dx.doi.org/10.3897/zookeys.1118.89593 1313-2970-1118-1 B1B42B9E1CCA4E85A22E39710CFA755E BAC22F9CBE275EE788FFC573D610E645 Malayorthomorpha hulutbeeda sp. nov. Figs 6 , 7 , 8 Material examined. Holotype : Thailand - Yala Province • ♂ ; Betong District , elfin montane forest ( Malaya Phytochorion province ); 1430 m a.s.l. ; 25 May 2022 ; Wisut Sittichaya leg.; CUMZ. Diagnosis. This new species is distinguished from its two congeners in sternal process between male coxae 4 linguiform with a rounded tip, and lamina lateralis of gonopodal solenophore triangular, apically bifid and protruded laterally. Description. Length of holotype 31.5 mm, width of midbody pro- and metazonae 2.7 and 3.0 mm, respectively. Colouration of alcohol material after one week of preservation dark red brown (Fig. 6A-F ); paraterga paler, head and antennae light brown to brown (Fig. 6A, B ), legs and venter contrasting light yellow to brown (Fig. 6 ), antennae and legs increasingly darker brown distally (Fig. 6B, E, G ). Figure 6. Malayorthomorpha hulutbeeda 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 All characters as in M. halabala sp. nov., except as follows. Antennae rather long, extending caudally past metaterga 4 when stretched dorsally. Collum with three transverse rows of setae: 4+4 in anterior, 2+2 in intermediate, and 3+3 in posterior row; with a small lateral setigerous incision near midway (Fig. 6A, B ). Paraterga 2 broad, anterior edge angular and rounded, lateral edge with a small notch at about 1/4 in front of caudal corner (Fig. 6A ). Calluses on paraterga rather narrow, delimited by a sulcus fully on dorsal side and in posterior half on ventral side; on poreless rings narrower than on pore-bearing ones in dorsal view (Fig. 6B, D, E ). Transverse sulcus distinct (Fig. 6A, C, F ), complete on metaterga 5-17, narrow, line-shaped, rather deep, not reaching the bases of paraterga, smooth at bottom, incomplete and nearly wanting on ring 18. Stricture between pro- and metazona wide, deep, beaded at bottom down to base of paraterga starting with segment 5 (Fig. 6A-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, retaining a small caudal tooth on ring 7, missing further on (Fig. 6B, D, E ). Hypoproct roundly subtriangular, setigerous knobs at caudal edge very small and well-separated (Fig. 6G ). Sterna moderately setose, shining, cross-impressions shallow, without modifications; an entire, large, linguiform, sternal lobe between ♂ coxae 4, with a pair of small denticles laterally near base (Figs 6H, I , 7E ). An inconspicuous and low ridge present in front of gonopod aperture. Legs long and slender, midbody ones ca. 1.6-1.9 times as long as body height, without modifications, ♂ tarsal brushes absent. Gonopods (Figs 7A-D , 8 ) rather simple; coxa almost straight caudad, densely setose distoventrally. Prefemur as usual, densely setose, about 1/3 as long as femorite + postfemoral part. Femorite stout, 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, thick and large, unciform, terminal lobe sheathing the tip of solenomere. Lamina lateralis ( ll ) triangular in shape, protruding laterally, tapered apically, bifid at tip (Figs 7C, D , 8A , 8C-D ). Figure 7. Malayorthomorpha hulutbeeda sp. nov., ♂ holotype, right gonopod A-D lateral, mesal, oral and caudal views, respectively E sternal cones between coxae 4, subcaudal view. Abbreviations: ll lamina lateralis, lm lamina medialis, sl solenomere, sph solenophore. Scale bars: 0.2 mm. Figure 8. Malayorthomorpha hulutbeeda sp. nov., ♂ holotype, right gonopod A, B mesal and lateral views, respectively C-F submesal, subsuperior, oral and subcaudal views, respectively. Scale bars: 0.2 mm Etymology. To emphasize " Malayorthomorpha hulutbeeda " which means "flat-back millipede" in Malay dialect, a noun in apposition. A Malay dialect language is mainly used in three provinces of southern Thailand where the holotype was obtained. Remark. This species was found living together with M. halabala sp. nov. Moreover, according to our observations, they may even occur syntopically, sharing the same habitat: leaf litter surface, branches of trees and tree trunks.