Orthomorpha enghoffi sp. n.

Figs 1, 2, 3 A & B, 4.

Material examined: Holotype male (CUMZ), Thailand, Nakhon Ratchasima Province, Pak Chong District, Khao Rup Chang, evergreen forest, 14°31´33˝ N, 104°21´36˝ E, 26 April 2009, leg. S. Panha, C. Sutcharit and N. Likhitrakarn. Paratypes: 10 males, 3 females (CUMZ), 2 males (ZMUC), 2 males (ZMUM), same data as holotype.

Name: Honours Henrik Enghoff, a globally renowned specialist in Diplopoda and an enthusiastic researcher of the millipedes of Thailand.

Diagnosis: Differs from congeners in the particularly roughly microgranulate, rugulose and dull vertex and metaterga, coupled with the black-and-yellow live colour pattern, the especially prominent anterior incision at the lateral edge of paraterga, and the irregularly axe-shaped tip of the solenophore.

Description: Length 21–24 mm (male), 22–25 mm (female), width of midbody pro- and metazona 1.8– 2.3 and 2.9–3.3 mm (male), 2.4–2.5 and 3.3–3.6 mm (female), respectively. Holotype 23 mm long 1.9 and 3.1 mm wide on pro- and metazona, respectively.

Live coloration (Fig. 1 A) blackish, head and antennae blackish as well, paraterga and epiproct contrastingly yellow, legs and venter dark brown; coloration in alcohol somewhat faded to pale yellow paraterga and epiproct, as well as to brown head, venter and legs after one year of preservation.

Head usual, clypeolabral region densely setose, surface of vertex rather roughly microgranulate and rugulose (much like that of metaterga), with a pair of lighter, yellowish, oblong knobs above antennal sockets; epicranial suture distinct. Antennae moderately long (Fig. 1 C), reaching end of body segment 4 (male) or 3 (female).

Head in width <collum <segments 3 and 4 <segment 2 <segments 5–16 in male, gently and gradually tapering thereafter, but head = collum in female. Collum with three transverse rows of setae, 4+4 anterior, 2+2 intermediate, and 1+1 posterior setae, latter row borne on very small paramedian cones; a very faint incision laterally near midway; caudal corner of paraterga like an elevated, upturned, subtriangular flap (Fig. 1 C).

Tegument dull, prozona very finely shagreened, metaterga unevenly, often roughly microgranulate and rugulose, leathery; surface below paraterga more delicately, but still evidently microgranulate and rugulose, a little more clearly so on several anteriormost segments. Metaterga with two transverse rows of setiferous cones or spines; 2+2, usually slightly smaller cones in anterior (pre-sulcus) row, normally 3+3, rarely 3+2 or 2+2, or even 4+4 (on a few posteriormost segments) longer cones in posterior (postsulcus) one; only metatergum 19 with 2+2 and 3+3 setae, but without their supporting cones. Tergal setae long, slender, often abraded, about as long as 1/3 of metazonum. Axial line not visible on metazona, only slightly so on prozona. Paraterga very strongly developed (Figs 1 A–H), especially so in male, usually slightly upturned, lying above dorsum on segments 3–18 in male, always below dorsum in female, caudal tip bent posteriad; paraterga very thin in lateral view, like blunt blades, a little thicker only on pore-bearing segments. Calluses developed only dorsally, thin, especially so on poreless segments. Paraterga 2 broad, anterior edge straight, lateral edge with 2–3 small, but evident incisions in anterior 1/3, lying well within contour, posterior edge slightly concave (Figs 1 B & C). Paraterga 3 and 4 subequal, anterior edge strongly convex and slightly bordered, lateral edge with two, even more evident incisions in anterior half, lying within contour, posterior edge slightly concave (Figs 1 B & C). Ventral surfaces of paraterga 2–4 with a few evident crests. Paraterga 5–13 (male) or 5–15 (female) lying within rear tergal contour, following paraterga increasingly well-produced behind. Paraterga 5– 14 (male) or 5–16 (female) with anterior edge similarly convex, lateral edge with a very strong anterior edge, on poreless segments, a slightly smaller midway incision, posterior edge delicately fringed and with a peculiar membranous, often clearly fringed to denticulate lobe near base (Figs 1 D & E). Paraterga 15–18 (male) or 17 and 18 (female) with anterior edge nearly straight, directed increasingly caudolaterad, lateral edge likewise with a very strong incision/tooth in anterior 1/3 and a slightly smaller incision in posterior 1/3, posterior edge increasingly concave, finely fringed and unilobate near midway (Figs 1 F–H). Paraterga 19 smaller, their posterior edge particularly concave, neither fringed nor lobate (Figs 1 F–H). Ozopores evident, dorsolateral, lying in an ovoid groove at about 3/4 of metazonital length. Transverse sulcus present on metaterga 5–18, shallow, line-shaped, reaching bases of paraterga, finely beaded at bottom, a little better developed in male than in female (Figs 1 B & D). Stricture between pro- and metazona narrow, evidently beaded at bottom down to base of paraterga (Figs 1 B, D, E & H). Pleurosternal carinae traceable only as small, caudal, round tooth on segments 2–15, a little more strongly developed on segments 2 and 3. Epiproct (Figs 1 F–H) conical, flattened dorsoventrally, apical papillae well-developed, tip narrowly emarginate; preapical papillae very small, almost missing. Hypoproct (Fig. 1 G) subtriangular, setiferous knobs at caudal edge well-separated.

Sterna delicately and sparsely setose, without modifications, but with pair of strong, acute, deeply separated, pointed cones between male coxae 4 (Figs 1 I & J). A conspicuous ridge in front of gonopod aperture. Legs moderately long and slender, slightly incrassate in male, about 1.5 (male) or 1.2–1.3 times (female) as long as midbody height, prefemora without modifications, tarsal brushes missing.

Gonopods (Figs 2 A–F, 3A & B) simple. Coxa long and slender, with several setae distodorsally. Prefemur as usual densely setose, less than half length of femorite. Latter slender, slightly curved and enlarged distad, without demarcated postfemoral part, tip of solenophore faintly bifid; solenomere about as long as solenophore, flagelliform.

Remarks. There is one sample which seems to be very similar to O. enghoffi sp. n. It comes from Thailand, Loei Province, Wang Saphung District, Huay E Loet, 1 male, 2 females (CUMZ), leg. P. Pimvichai on 27 April 2009. Since the differences between the populations from Khao Rup Chang and Huay E Loet are very few and minor, we prefer to treat the latter population as only a variety of O. enghoffi sp. n., as follows.