Unixenus moniqueae, Huynh, 2020

Huynh, Cuong, 2020, Three new species of penicillate millipedes from the Con Dao Islands of southeast Vietnam (Diplopoda, Lophoproctidae and Polyxenidae), Zootaxa 4759 (1), pp. 1-30 : 21-23

Unixenus moniqueae new species

Fig. 17–21

Material examined: Type specimens. Adult ♂ holotype ( QMS 109028),; 6 adult ♀ paratypes ( QMS 109029–34) from Vietnam, Con Dao archipelago, Con Son Island, Lo Voi beach, leaf litter in casuarina woodland, 8.691097°N, 106.620542°E, elevation 9 m; on 24th July 2015 (Collected by C. Huynh).

Diagnosis. Shares similar characteristics with U. mjoebergi and U. intragramineus : chaetotaxy (setae on leg articles) with one seta on pre-femur and two setae on femur, single seta on tibia and tarsus 2. Claw more similar to U. intragramineus in being slender, differs from U. mjoebergi . A posterior process shorter than half length of the claw in U. moniqueae compared to U. intragramineus with a posterior process longer than half length of the claw.

Description: Colour dark brown patch in eye area, same colour as transverse band in vertex. Body milky white, light brown pleural trichomes and darker colour in caudal bundle; dark brown marks on lateroposterior rosette trichomes form a dark band along each lateral side of body. Last tergite darkest in colour; white ventrally ( Fig. 17 ). Holotype, body length 2.2 mm; paratypes 2.2–2.4 mm. Male caudal bundle slightly narrower in width and longer (0.6 mm) compared to female (0.5 mm). Head: Each side with 8 ommatidia: 4 dorsal, 4 lateral (1 anterior, 2 medial and 1 posterior). Vertex with 2 posterior trichome groups with a large medial gap, each group with 2 rows. Anterior row curved slightly on an oblique angle, all trichome sockets of similar size, posterior row with varied trichome socket sizes. A narrow space between anterior and posterior rows. Holotype with vertex posterior trichome groups with 14+12 sockets in anterior rows and 8+6 sockets in posterior rows ( Fig. 18A ) (Variations are common in paratypes regardless of sex, from 12–18 sockets (anterior rows) and 6–10 (posterior rows)) ( Fig. 19A ). Trichobothria: trichobothrium a (posterior position), trichobothrium b (lateral position) and trichobothrium c (anterior position) typically thin sensory hairs with narrow cylindrical funicles. Trichobothria (a, b and c) equal in socket size, forming an isosceles triangle with equal distance between ab and bc ( Figs 18F and 19C ). Antennae: 8 antennomeres, 4 sensory cones ( Fig. 20A ), typical characteristics of Polyxenidae . Antennomere VI with 3 thick bacilliform sensilla (T), different lengths: A short bacilliform sensillum located in the anterior position (Ta), the longest intermediate long bacilliform sensillum (Ti), and a bacilliform sensillum of (Tp) medium length in posterior position. A setiform sensillum (s) between Ta and Ti and conical sensillum (c) in next to Tp. Antennomere VII with 2 thick bacilliform sensilla, Ta slightly longer than Tp; a setiform sensillum (s) between them and a conical sensillum (c) located next to Tp ( Fig. 20B ). (This pattern of sensilla on the antennomere VII is commonly seen in all Unixenus species). Clypeolabrum: Holotype with 10 setae along labrum posterior margin, these setae being half the width of labrum (setae in paratypes ranging from 10–13 in both sexes). Labral surface with spherical papillae with pointed ends, forming 3 rows of large size setae in anterior margin and reducing in size in posterior margin. Anterior margin of labrum with 4+4 lamellae on each side of median cleft ( Figs.18G and 19B, D ). Gnathochilarium: Lateral palp 2.5 times as long as medial palp. 13 conical sensilla on lateral palp, medial palp with 22, same in holotype and paratypes ( Fig. 18H ). Trunk: 10 tergites, 9 pleural projections, and telson excluding caudal bundle.13 pairs of legs. Collum (tergite 1) with trichome sockets arranged in 2 oval shapes in lateral position, opposite each other connected by a posterior row of trichome sockets forming a line with a gap in the middle. Holotype collum with 49 trichome sockets both sides, lateral protuberances with 5 trichome sockets on each side ( Fig.18B ) (Trichome sockets on collum varying in paratypes ranging from 54–60 sockets and 4–5 sockets on lateral protuberances). Tergites 2–10, each with pleural projections located in anterolateral positions. Tergal trichome socket arrangements from tergites 2–9 typically with 4 undefined rows of tergal trichomes arranged in two lateroposterior clusters, on either side of midline. Anterior row often uneven, intermediate rows rarely in defined rows and posterior row of trichomes continuous and evenly distributed, forming a line with a medial gap ( Fig. 19A ). Tergite 10 is the exception, with trichome sockets being smaller and denser. Almost no space between lateral rosette trichome sockets and those in posterior row. Trichome sockets of tergite 2 in holotype with 55 on both sides ( Fig. 18C ). Tergite 10 with 53 (L) and 54 (R) sockets ( Fig. 18D ) (In contrast, trichome sockets on tergite 2 in paratypes 50–65, whereas tergite 10 containing between 54–68 trichome sockets). Legs: Leg segmentation following Manton (1956). Legs 1 and 2 without trochanter, leg 1 lacking tarsus 1. Chaetotaxy (setae on leg articles): coxa 1: 1 seta, coxa 2: 2 setae, coxae 3–13: 2–6 setae; pre-femur, tibia and tarsus 2 with seta; femur with 2 setae ( Fig. 21A ). Setae on coxa, pre-femur, femur distally with with longitudinal ridges on basal funicle; each ridge extending distally into long thin spine, spines surrounding flagellum base ( Fig. 21B ). Seta in mid femur similar, but smaller ( Fig. 21C ), tibia and tarsus 2 each with setiform seta ( Figs. 21D and E ). Posterior edge of last sternite with 4 setae similar those present on coxa (Number of these setae same in paratypes). Sex organs in male: pair of penes present on coxa 2, 2 pairs of coxal glands on coxal plates of legs 8th and 9th. Telotarsus-Claw: A slender structure bearing a posterior lateral process that is shorter by half the length of claw. A small anterior lateral process and a lamella process both present, anterior setiform process slightly enlarged at base and longer than the claw ( Fig. 21F ). Telson: Dorsal ornamental trichome sockets arranged symmetrically on both side of telson with 5 trichomes a sockets in holotype (Paratypes with 5–6 trichomes a). A single trichome b socket and 3 trichome c with large protruding base sockets: c 1, c 2 and c 3, forming a triangular shape each side of telson. Circular indentation d apparent near exterior side of trichomes c ( Fig. 18E ). Caudal bundles: Male, caudal bundle with a single uniform large trichome socket of caudal trichomes. Female with two obvious distinguishing structures: a main dorsal structure similar to male, but with 2 latero-sternal bundles of smaller trichome sockets of nest trichomes ( Figs. 19E, F ). Caudal trichomes 2–4 hooks. (These caudal structures are like those observed in U. intragramineus ( Huynh and Veenstra 2018c) which is common to members of the genus Unixenus and is classified as caudal bundle type I ( Condé and Nguyen Duy-Jacquemin 2008))

Remarks: Unixenus moniqueae n. sp. was first identified as Unixenus sp. by Monique Nguyen Duy-Jacquemin and Condé (1967) based on two adult specimens (a male and a female), which were collected from Con Son Island, Vietnam. These specimens were part of the Indochinese collections of Dr C. Dawydoff ( Attems 1938). Formal naming of these specimens was deferred because of uncertainty around the specific diagnosis of Unixenus at that time, despite this species having similar characteristics to U. mjoebergi and other evidence that supported them belonging to the same genus ( Nguyen Duy-Jacquemin and Condé, 1967). The identification of Unixenus to species proved difficult due to similarities in the morphology of the main characteristics used for identification: the sensilla on antennomere VI, pointed spherical papillae of the labrum, 13 sensilla on the lateral palp of gnathochilarium, the arrangement of the tergal trichome sockets, chaetotaxy and the setiform sensillum on tarsus 2.

Etymology: The species is named in honour of Dr. Monique Nguyen Duy-Jacquemin who made a significant contribution to the study of penicillate millipedes since the 1960s. She was the first to identify this species collected from Con Son Island, Con Dao Islands in 1967 as Unixenus sp.

Figures

FIGURE 17. Digital image of Unixenus moniqueae n. sp.

FIGURE 18. Holotype Unixenus moniqueae n. sp., A. Head capsule with 8 ommatidia on each side, the posterior vertex trichome group (pv) and 3 sockets of trichobothria (trichobothria a, b and c); B. Collum (co) and lateral protuberances (Lp) showing the arrangement of trichomes sockets; C. Tergite 2 (T2); D. Tergite 10—the last tergite (T10); E. Dorsal ornamental trichome sockets of trichome a (a), trichome b (b), trichome c (c) and the circular indentation d (d); F. Trichobothria a, b and c (right hand side) showing the sensory hairs and sockets; G. Clypeo-labrum showing the pointed spherical papillate on its surface and the structures 4 + 4 lamellae; H. Gnathochilarium: lateral palp (LP) with 13 sensilla (a sensillum number 3 missing) and medial palp (MP) with 22 sensilla.

FIGURE 19. SEM images of Unixenus moniqueae n. sp., A. Dorsal view; head, the posterior vertex trichomes (pv), Collum (co), tergite 2 (T2) and tergite 3 (T3); B. Ventral view; head, f: frons, cl: clypeolabrum, g: gnathochilarium; C. Trichobothria a, b and c; D. Labrum showing the posterior setae (s) and pointed spherical papillate (Psp) on its surface; E. Caudal bundle (cb) with trichomes attached, T9: tergite 9, b: trichome b and ct: caudal trichomes; F. Female caudal bundle structure without trichomes; ots: ornamental trichome sockets, b: barbate trichome, bts: barbate trichome sockets, c: trichome c, cts: caudal trichome sockets, nts: nest trichome sockets, tsft: trichome socket-free tissue.

FIGURE 20. A. Unixenus moniqueae n. sp., Scanning electron microscope (SEM) image of antennomeres VI, VII and VIII with 4 sensory cones (sc); B. Arrangement of sensilla on the antennomeres VI and VII from the holotype. (c: conical sensillum, T: thick sensillum (a: anterior, i: intermediate, p: posterior), s: setiform sensillum)

FIGURE 21. A. Holotype Unixenus moniqueae n. sp., 2nd leg showing seven leg articles (co: coxa, pf: pre-femur, fe: femur, pof: post-femur, tib: tibia, T1: tarsus 1, T2: tarsus 2, c: claw) and sex organ—penis (P); B. Biarticulated seta with a ridged funicle present on the coxa, pre-femur, the distal edge of femur and the posterior edge of the last sternite; C. Similar smaller version of this seta is present in the middle of the femur; D. Seta on tibia; E. Setiform seta on tarsus 2; F. Telotarsus—claw structures, a ventral view (SEM image) from a specimen and drawing of the telotarsus from the holotype (lateral view), p: posterior lateral process, a: anterior lateral process, c: claw, l: lamella process and s: anterior setiform process.