Oxidus gigas ( Attems, 1953 )

Anh D. Nguyen, Zoltán Korsós, Kuem-Hee Jang & Ui-Wook Hwang, 2017, A revision and phylogenetic analysis of the millipede genus Oxidus Cook, 1911 (Polydesmida, Paradoxosomatidae), European Journal of Taxonomy 293, pp. 1-22 : 8-11

Oxidus gigas ( Attems, 1953)

Figs 3–4

Kalorthomorpha gracilis gigas Attems, 1953: 165 , fg. 44.

Oxidus gracilis gigas – Jeekel 1963a: 20; Jeekel 1968: 60. — Golovatch 1983: 181.

Oxidus gracilis – Golovatch 1984: 54.

Oxidus gigas – Enghoff et al. 2004: 39. — Nguyen & Sierwald 2013: 1295.

Diagnosis

This species is particularly similar to Oxidus gracilis ( C.L. Koch, 1847) in body appearance and gonopod conformation, but differs in larger size and in details of gonopod structure: process h narrow and long, pointed at the end and not serrated at distolateral margin; bases of process h and spine z less distinctly separated.

Material examined

VIETNAM: 1 ♂, 1 ♀, Lao Cai Prov., Sa Pa, Ham Rong Mts., limestone mountain, 1600 m, 16 Jul. 2006, Anh D. Nguyen, IEBR-113; 1 ♂, 6 ♀♀ (IEBR-Myr 516), 7 ♀♀ (IEBR-Myr 517), Ha Giang Prov., Bac Quang Distr., Duc Xuan Commune, Na Po village, limestone forest, under logs, 14−15 Apr. 2013, leg. Anh D. Nguyen; 1 ♂, 3 ♀♀, Vinh Phuc Prov., Tam Dao National Park, forest, 900−1000 m, Mar. 2012, leg. Hoang Long, IEBR-Myr 518; 2 ♂♂, 1 ♀, Lao Cai Prov., Co xan, in and around a cave, 1971, leg. Gy. Topál & I. Matskási, IEBR-H133.

Redescription

SIZE. Body length 31−34.5 mm (♂♂), 29.9−30.2 mm (♀); width of midbody pro- and metazonae 1.9−2.2 mm (♂), 2.2 mm (♀) and 2.8−3.2 mm (♂), 3.1− 3.2 mm (♀), respectively.

COLORATION. Generally castaneous brown, but anterior half of metaterga and posterior margin of prozonae darkish brown. Posterior half of metaterga, anterior margin of prozonae and pleura castaneous brown; paraterga, sterna and legs brownish yellow.

HEAD. Slightly narrower than collum; labrum sparsely setose; epicranial suture distinct, dividing frons into two equal parts. Antennae long and slender, not claviform, reaching segment 3 if stretched posteriorly. Antennomere 1<7<<2=3=4=5=6 in length.

COLLUM. Subequal to, or slightly narrower than collum, trapeziform; surface shining and smooth, without rugosity; setae broken, but traces of two rows: 3+3 close to anterior margin and 1+1 in middle. Paraterga large, ear-shaped with broadly rounded laterocaudal corners; lateral side with a setiferous incision.

In width, segment 4≤3<2<5–17, thereafter gradually tapering towards telson. Prozonae and metaterga shining, smooth, without rugosity. Metaterga with two rows of setae: 2+2 close to anterior margin and 2+2 close to posterior margin. Transverse sulcus starting on metatergum 4, well developed, reaching base of paraterga on metaterga 5−19, beaded at bottom on some caudal segments. Stricture between pro- and metazonae clearly distinct, broad and striolate at bottom. Pleura shining, smooth; pleurosternal carinae completely absent or poorly developed only on pre-gonopodal segments.

PARATERGA. Well developed, lying subequal to or lower than metatergal surface. Calluses small, but obvious; lateral side with 2 setiferous incisions at ⅓ and ⅔ of its length.Anterior corner broadly rounded, but posterior corner acute, produced into a pointed projection on segments 15−17. Ozopores located behind second lateral incision of paraterga 5, 7, 9, 10, 12, 13, 15–19.

EPIPROCT. Long, but broadly truncated, dorsoventrally Fattened, with two minute apical tubercles. Tip with four spinnerets. Hypoproct trapeziform, with two well separated, distolateral, setiferous knobs.

STERNA. Modestly setose, without modifcations, but with a minute cone caudally near each coxa.

LEG. Long and slender, about 1.6−1.7 (♂), 1.4−1.5 (♀) times as long as midbody height. Tarsal brushes absent. Prefemora not swollen. Femora without modifcations.

GONOPOD. Relatively complicated. Coxite cylindrical, long, subequal to femorite in length; distoventral part sparsely setose. Prefemorite densely setose, separated laterally from femorite by a distinct oblique sulcus. Femorite weakly twisted, grooved mesally, more or less slightly enlarged distally, without modifcations and demarcated from postfemoral region by a lateral sulcus. Postfemoral region shorter than femorite, with a lateral sub-pentagonal lamina l; spine z pointed; process h long and pointed, not serrated laterally; bases of process h and spine z not separated. Solenophore strongly spiral; distomesal lobule well developed and distinctly separated from solenophore tip. Solenomere Fagelliform, completely sheathed by solenophore.

DNA

COI and 16S barcode data (partial) are deposited in GenBank ( Table 1).

Habitats

All material was found under leaf-litter, logs and decaying wood.

Distribution

The species has only been recorded from northern Vietnam (Lao Cai, Ha Giang and Vinh Phuc Provinces).

Remarks

Attems (1953) proposed a new subspecies Kalorthomorpha gracilis gigas with a short note. Enghoff et al. (2004) raised this subspecies to full rank as Oxidus gracilis , and also showed minor differences in size and gonopod process h. The species is fairly similar to O. gracilis , but the molecular data has provided strong evidence to separate the species.

Golovatch (1984) misidentifed O. gracilis in Vietnam (sample IEBR-H133), which is currently corrected as O. gigas in this paper.

Figures

Fig. 3. Oxidus gigas (Attems, 1953) from Duc Xuan Commune, Ha Giang Prov., Vietnam. A. Entire body, length ca 34 mm. B – C. Segments 8 – 9 – 10. B. ♂. C. ♀. Scale bars = 1 mm. (photo by Anh Nguyen)

Fig. 4. Right gonopod of Oxidus gigas (Attems, 1953), from sample IEBR-Myr 113. A. Lateral view. B. Ventral view. C. Mesal view. The picture has been Fipped horizontally. Scale bars = 1 um.