Orthomorpha rotundicollis subrotundicollis (Attems, 1937),

Likhitrakarn, Natdanai, Golovatch, Sergei I., Semenyuk, Irina, Efeykin, Boris D. & Panha, Somsak, 2019, Review of the millipede genus Orthomorpha Bollman, 1893 (Diplopoda, Polydesmida, Paradoxosomatidae) in Vietnam, with several new records and descriptions of two new species, ZooKeys 898, pp. 121-158 : 121

Orthomorpha rotundicollis subrotundicollis (Attems, 1937), var. nov. Figs 9 , 10 , 11

Material examined.

1 ♂ (ZMUMRd 4209), 1 ♀ (ZMUMRd 4201), Vietnam, Gia Lai Province, Kon Ka Kinh National Park, near the village of Krong, 14°18'03"N, 108°26'42"E, 600 m a.s.l., mixed tropical forest, on forest floor, night time, 9.V.2017; 1 ♂ (ZMUM Rd 4210), same locality, forest near the Park’s headquarters, mixed tropical forest on hill slope, 14°11'34"N, 108°19'23"E, 1,200 m a.s.l., on forest floor, daytime, 29.V.2017; 2 ♂ (ZMUM Rd 4284, Rd 4285), same locality, on log; 1 ♀ (ZMUM Rd 4283), same locality, 14°18'24"N, 108°27'13"E, 750 m a.s.l., on forest floor, daytime, 12.V.2017, all leg. I. Semenyuk.

Name.

To emphasize the strong similarity to the typical O. rotundicollis (Attems, 1937). Normally, no Latin names are to be applied to varieties as infrasubspecific categories, but because this new variety had first been qualified and described as a new species based on purely morphological grounds before the molecular evidence showed it to be the same as O. rotundicollis , we allot it the previously chosen name subrotundicollis and treat it separately in our analyses, key, and map.

Diagnosis.

Using the latest key ( Likhitrakarn et al. 2011), this new variety keys out and seems to be especially similar to the typical O. rotundicollis , but it differs in the smaller size (up to 23 mm (♂) or 29 mm (♀) long and 2.9-3.2 mm (♂) or 3.3-3.9 mm (♀) wide, respectively), and the pleurosternal carinae being complete crests until segment 7 (♂) or 5 (♀), each crest supplied with an evident sharp denticle caudally, thereafter increasingly strongly reduced until segment 16 (♂, ♀), coupled with tarsal brushes being traced until ♂ legs 11.

Description.

Length 20.0-23.0 mm (♂) and 21.5-29.0 mm (♀), width of midbody pro- and metazonae 1.7-1.9 and 2.9-3.2 mm (♂) or 2.3-2.6 and 3.3-3.9 mm (♀), respectively.

Colouration of live animals blackish ( Fig. 9A ), paraterga and epiproct contrasting yellow-orange, head and antennae dark brownish, legs pale brownish; colouration in alcohol, after one year of preservation, blackish or faded to black-brown ( Fig. 9 B–H ), paraterga and epiproct pale whitish yellow to light yellow, legs and sterna light yellow to pale brown, antennae light yellow to dark brownish distally.

Clypeolabral and vertigial regions sparsely setose; epicranial suture distinct. Antennae rather short ( Fig. 9A, B ), reaching behind body segment 3 when stretched dorsally, with a pair of lighter, yellowish, oblong spots above antennal sockets. In width, head <collum <segment 3 <4 <<2 <5-17 (♂, ♀), body gently and gradually tapering thereafter. Collum with three transverse rows of setae: 3+3 in anterior, 2+2 in intermediate, and 3+3 in posterior row; a very faint incision laterally in posterior 1/3; caudal corner of paraterga a minute, dentiform, slightly declined knob not drawn behind rear margin.

Tegument smooth and shining, prozonae finely shagreened, metaterga smooth and delicately rugulose, leathery; surface below paraterga finely microgranulate. Postcollum metaterga each with two transverse rows of setae: anterior (pre-sulcus) row with 2+2 setae traceable at least as insertion points when setae broken off; posterior (postsulcus) row with 3+3 setae borne on minute to small tubercles growing a little larger laterally, in addition to fully obliterated knobs with insertion points of abraded setae near axial line. Tergal setae long, strong, slender, ca. 1/3 of metatergal length. Axial line visible on collum and both on following pro- and metazonae.

Paraterga 2 broad, anterior edge angular, lateral edge with two small, but evident incisions in anterior 1/3; posterior edge slightly oblique ( Fig. 9B, C ). Following paraterga strongly developed ( Fig. 9 B–H ), especially well so in ♂, slightly upturned caudally, all lying below dorsum, set at ca. upper 1/3 of midbody height, subhorizontal, caudal corner almost or fully pointed, increasingly spiniform and produced behind rear tergal margin; anterior edge well-developed, slightly convex to rounded, bordered and fused to callus. Lateral edge of paraterga with two small, but evident incisions, one in anterior 1/3, the other in posterior 1/3 on following poreless segments, but only one (at front 1/4) on following pore-bearing segments. Calluses on paraterga 2-4 delimited by a sulcus only dorsally, on following paraterga both dorsally and ventrally, rather narrow, modestly enlarged in pore-bearing segments, thinner in poreless ones ( Fig. 9 B–H ). Posterior edge of paraterga clearly concave, especially well so in segments 17-19 ( Fig. 9F ). Ozopores evident, lateral, lying in an ovoid groove at ca. 1/3 in front of caudal corner. Transverse sulcus usually distinct ( Fig. 9B, C, F ), complete on metaterga 5-18, incomplete on segments 4 and 19 (♂, ♀), deep, line-shaped, nearly reaching the bases of paraterga, evidently ribbed at bottom. Stricture between pro- and metazona wide, clearly ribbed at bottom down to base of paraterga ( Fig. 9B, C, F ). Pleurosternal carinae complete crests with a sharp caudal tooth on segments 2-7 (♂) or 2-5 (♀), a front bulge and a caudal tooth until segment 10, each with a small sharp tooth caudally, thereafter tooth increasingly strongly reduced until segment 16 (♂, ♀) ( Fig. 9C, E, H ).

Epiproct ( Fig. 9 F–H ) conical, rounded dorsoventrally, with two evident apical papillae; tip subtruncate; pre-apical papillae evident, lying rather close to tip. Hypoproct roundly subtriangular, setiferous knobs at caudal edge evident and well-separated.

Sterna sparsely setose, without modifications except for two rather large, fully separated, setose sternal cones between ♂ coxae 4 ( Fig. 9I, J ). A paramedian pair of evident tubercles in front of gonopod aperture. Legs moderately long and slender; midbody ones ca. 1.1-1.2 (♂) or 0.8-0.9 (♀) times as long as body height, prefemora without modifications, ♂ tarsal brushes present until legs 11.

Gonopods ( Figs 10 , 11 ) simple. Coxa long and slender, with several setae distoventrally. Prefemur densely setose, nearly 3 times shorter than femorite + “postfemoral” part. Femorite very slender, moderately curved, very slightly enlarged distad, “postfemoral” part demarcated by an oblique lateral sulcus; tip of solenophore small, trifid, with two subequal denticles (one lower terminal, the other middle) and a broader upper, sharp, subterminal lobule.

Remarks.

Based on morphological characters alone (see Diagnosis), this variety had first been qualified and distinguished as a full new species before the molecular analyses unequivocally showed it to be genetically the same as O. rotundicollis . Indeed, the average genetic distance (Di) of subrotundicollis from the typical, morphologically closest and sympatric O. rodundicollis is null (Table 2 ). In one of the phylograms ( Fig. 20 ), subrotundicollis falls out between the two individuals of rotundicollis , and overall the genetic variation is strikingly scant. This is one of the direct consequences of the molecular analyses accepted in our study.

Adults of this variety were found only in May during a short expedition to Kon Ka Kinh National Park, as part of IS’ research on the diversity, biology, and ecology of millipedes in Vietnam. The previous trip to the same area in 2016 failed in finding this species. In 2017, millipedes were very abundant in many types of forest ranging from native to highly disturbed ones, up to even forestless hills with farmed crops. The activity was mainly noted in the night time in forest, but walking millipedes appeared even in daylight in open areas. Mating was recorded in May.

Figures

Figure 9. Orthomorpha rotundicollis (Attems, 1937), subrotundicollis var. nov., ♂ A habitus and live colouration B, C anterior part of body, dorsal and lateral views, respectively D, E segments 10 and 11, dorsal and lateral views, respectively F-H posterior part of body, dorsal, ventral and lateral views, respectively I, J sternal cones between coxae 4, subcaudal and sublateral views, respectively.

Figure 10. Orthomorpha rotundicollis (Attems, 1937), subrotundicollis var. nov., ♂, left gonopod A, B mesal and lateral views, respectively C distal part, submesal view. Scale bars: 0.2 mm.

Figure 11. Orthomorpha rotundicollis (Attems, 1937), subrotundicollis var. nov., ♂, left gonopod A, B lateral and mesal views, respectively C-H distal part, caudal, mesal, suboral, oral, caudal and sublateral views, respectively.

Figure 20. A rooted phylogram based on COI sequences obtained from the relevant literature on Paradoxosomatidae (Nguyen et al. 2017, 2018) and available in GenBank (all given in black, yet with several name updates according to modern taxonomy), combined with new haplotypes (six species and two varieties, these latter put in quotation marks and all highlighted in red). Tree topology was reconstructed using MrBayes software. The values of statistical support are given above the branches only when these exceed 65 %.