Monographis panhai, Huynh & Likhitrakarn, 2023

Huynh, Cuong & Likhitrakarn, Natdanai, 2023, First records of penicillate millipedes (Diplopoda, Polyxenidae) from Thailand, with descriptions of two new species, Zootaxa 5383 (4), pp. 514-536 : 518-521

Monographis panhai sp. nov.

Figs 3–8

Material examined: Monographis panhai sp. nov. specimens were collected from three distinct locations across Thailand: Location A ( PM1.01 ): Pha Mon Cave , Pang Mapha District, Mae Hong Son Province, Thailand. 19.500825, 98.278439; elevation 680 m; collected by S. Panha, N. Likhitrakarn, and C. Sutcharit, 19 July 2008. Five female individuals were used for DNA extraction and the preparation of slides. The body lengths of the specimens, excluding the caudal bundle, ranged from 2.8–3.0 mm in males and 3.2–3.6 mm in females. Location B ( PM1.03 ): Thap Lan National Park , Wang Nam Khiao District, Nakhon Ratchasima Province, Thailand. 14.215292, 101.902894; elevation 357 m; collected by N. Likhitrakarn, 24 July 1999. Two males and four females were used for this study. The body lengths of the specimens were 3.3 mm in both sexes, and the length of the caudal bundles was 0.6 mm. Location C (Krabi): Near Khao Phueng Cave, East Krabi, Thailand. 8.2369 98.905981; elevation 123 m; collected by C. Huynh, 25 July 2017. Five specimens were collected, consisting of one adult male, one adult female, one female with 12 pairs of legs, and two females with 10 pairs of legs. Four individuals were mounted on slides, while one female with 10 pairs of legs was used for SEM imaging. The body lengths of the specimens ranged from 2.1 mm in the male to 2.6 mm in the adult females, the length of the caudal bundle was measured at 0.6 mm. An adult male, from Location B was designated as holotype, while the paratype specimens were from three locations A, B and C ( Fig. 1 ).

Diagnosis. Body length: 2.1–3.6 mm. Antennomere VI with 11 bacilliform sensilla forming crescent shape, followed by small gap and short thin bacilliform sensilla, with setiform sensillum in anterior position, and conical sensillum present. Labrum asetose, with slender anterior setae on anterior margin. Telotarsus with posterior lateral process equal to half-length of a claw, anterior setiform process shorter than a claw.

Description. Holotype male body: 3.3 mm; paratypes: males 2.1–3.3 mm, females 2.6–3.6 mm; caudal bundle of trichome: same length in both sexes: 0.6 mm, nest trichomes in females: 0.2 mm.

Colouration. Live specimens of Monographis from Krabi display a yellowish-brown colour and darker shading on the latero-posterior rosette trichomes, forming two distinct dark lateral bands. The eyes exhibit a brownish-red colouration. Two dark brown bands connecting between eye regions are visible in the vertex area. The last tergite shows the darkest colouration, extending into the telson region. The ventral side of the body has a white colour ( Fig. 2 ).

Head: Eye, each side 8 ommatidia: 4 dorsal, 4 lateral (1 anterior, 2 medial, and 1 posterior). Vertex with two groups of trichomes at posterior region (pv), separated by a middle gap. Each group comprises two rows, anterior row straight with trichome sockets of equal size, gradually decreasing in size towards both ends. Anterior rows with 17 trichome sockets; posterior rows with 8 sockets (left side) and 7 sockets (right side); narrow space between these rows ( Figs 3A, B ; 7A ). Paratypes showed variation in number of sockets in posterior vertex trichome groups, regardless of sex, ranging from 14–19 sockets in anterior rows, 7–10 sockets in posterior rows. Exception for paratypes from Krabi, fewer sockets in posterior vertex trichome groups, ranging from 10–14 in anterior rows, 2–3 in posterior rows. Trichobothria : Typically thin, sensory hairs with narrow cylindrical funicles; equal in socket size, forming isosceles triangle (ab and bc equal distance); trichobothrium a (interior), trichobothrium b (lateral), and trichobothrium c (exterior) of head capsule ( Figs 3A, C ; 7B ). Clypeo-labrum : Holotype: 11 setae (6 present, 5 sockets missing setae) in posterior margin of labrum (se), seta length equals labral width; paratypes: 10–12 setae in both sexes. Labral surface asetose, posterior margin with row of backward-pointing setae (sb). Lateral lamella (Ll) and single broad lamella (l) on each side of median cleft (mc); 8 (left: L) and 9 (right: R) slender setae (sa) on anterior margin of labrum. The number of these anterior slender setae varies among paratypes, ranging from 18–20 across both sides ( Figs 3E , 7D ). Gnathochilarium: Lateral palp 1.25 times medial palp; 11 conical sensilla on lateral palp, 22 on medial palp; same in holotype and paratypes ( Figs 3D , 7C ). Antennae: Antennomere VI with 10–11 bacilliform sensilla, followed by a small gap and 8–12 short thin bacilliform sensilla. Holotype with 11 bacilliform sensilla forming crescent shape with 3 thick ( T) and 8 thin bacilliform sensilla (t), a small gap, 9 short thin bacilliform sensilla (ts), setiform sensillum (s) located in anterior position, and conical sensillum (C) present in middle of thin bacilliform sensilla ( Figs 4A, B, D ; 8A–D ). Antennomere VII with 2 thick bacilliform sensilla ( T, Ta, and Tp), setiform sensillum (s) located between these two sensilla ( T), conical sensillum (C) located next to Tp ( Figs 4C , 8C ).

Body: 10 segments, 9 pleural projections, excluding telson and caudal bundle; 13 pairs of legs. Collum (first tergite) with lateral protuberances (Lp) bearing 5–7 trichomes on each side ( Fig. 5A ). Tergites 2 (T2) to 10 (T10), each connected with a pair of pleural projections (pp) located anterolaterally ( Fig. 5B ). Tergal trichome socket arrangements typically 2 broad oval shapes, slightly enlarged laterally, and a posterior row slightly upwardly curved towards centre with large gap between these trichome socket rows. Tergite T10—last tergite, trichome sockets dense and smaller ( Fig. 5C ).

Legs: typical of Polyxenida , naming of leg segments after Manton [1956]. Legs 1 and 2: Without trochanter, leg 1 without tarsus 1. Chaetotaxy: Coxa (co) 1 and 2: 2–4 setae. Coxae 3–13: 4–6 setae. Pre-femur (pf), post-femur (pof), tibia (tib) with 1 seta, femur (f) with 1–4 setae. Tarsus 1 (T1) and 2 (T2) with a spine. Coxa, pre-femur, femur with biarticulated seta and ridged funicle. Last sternite with 4 biarticulated setae ( Fig. 6F ). 1–3 smaller biarticulated setae in intermedio-posterior position of femur. Post-femur and tibia distally with setiform seta. Spine on tarsus 2: Sharply pointed, twice the length of a spine in the anterio-sternal position of tarsus 1 ( Figs 6A–E ).

Telotarsus: Claw slender with anterior lateral process (a), and posterior lateral process (p) equal to half the length of the claw (c); anterior setiform process (s) shorter than half the length of the claw; lamella process (la) present ( Figs 6G , 7E ). Sex organs in the male: A pair of penes on coxae 2 and 2 pairs of coxal glands located on the 8th–9th coxal plates.

Caudal bundles: Similar to congeners ( Huynh & Veenstra 2022) and classified as caudal bundle type I arrangement ( Condé & Nguyen Duy-Jacquemin 2008). Caudal trichomes with a series of 2–6 backward hooks ( Huynh & Veenstra 2013).

Telson: Dorsal ornamental trichome sockets arranged symmetrically on either side of the telson. Holotype with 17 sockets of trichomes a on each side of the telson (paratypes with 14–20). Trichome a sockets in 2 rows, top row with small sockets, bottom row with larger sockets. One trichome b socket, 3 large trichome c sockets with protruding bases: c1, c2 and c3, forming triangular shape located in ventroposterior positions in each arrangement. Circular indentation d apparent on each side near the exterior side of trichome c ( Fig. 6H ).

Figures

FIGURE 1. Collecting locations of Monographis panhai sp. nov. (white circles) and Unixenus thailandicus sp. nov. (white triangle) in Thailand. A: Pha Mon Cave, Pangmapa District, Mae Hong Son Province. B: Thap Lan NP., Wang Nam Khiao District, Nakhon Ratchasima Province. C: Near Khao Phueng Cave, East Krabi. D: Khao Cha-ang On, Bo Thong District, Chonburi Province.

FIGURE 2. Monographis panhai sp. nov. from Krabi, Thailand.

FIGURE 3. Monographis panhai sp. nov., holotype. A. The head capsule: eyes, trichobothria, and the vertex. B. Posterior vertex. C. Trichobothria. D. Right gnathochilarium. E. Clypeo-labrum. (Explanation of figure labels in the text).

FIGURE 4. Monographis panhai sp. nov., holotype. A. Antennomeres V–VIII, four sensory cones and sensilla. B. Sensilla arrangement on antennomere VI. C. Sensilla on antennomere VII. D. Sensilla on antennomere VI.

FIGURE 5. Trichome socket patterns of Monographis panhai sp. nov. A. Collum and lateral protuberances. B. Tergites 2 and the pleural projections. C. Tergite 10.

FIGURE 6. Monographis panhai sp. nov., holotype. A. Second leg with the chaetotaxy. B. Biarticulated setae with ridged funicles. C. A similar but smaller seta is on the intermedio-lateral position of the femur; D. Setiform setae are on the posterior postfemur and tibia. E. A spine on tarsus 2. G. Telotarsus and its structures; a setiform showing shorter than half the length of the claw (dot line indicated). F. Last sternite. H. Ornamental trichome sockets.

FIGURE 7. SEM images of Monographis panhai sp. nov. A. An image shows a head, antenna, and the body structures. B. A close-up image of the eye, trichobothria. C. The gnathochilarium. D. The clypeo-labrum. E. Telotarsus; a setiform showing shorter than half the length of the claw.

FIGURE 8. SEM images of Monographis panhai sp. nov. A. Antennomeres VI–VII. B. Antennomeres VI–VIII, and the sensory cones. C. The Krabi’s specimen shows different pattern in the thick bacilliform sensilla on antennomere VII. D. Another arrangement of the short thin bacilliform sensilla on the antennomere VI.