Dibamus tropcentr Kliukin & Nguyen & Le & Bragin & Tran & Gorin & Poyarkov 2023, sp. nov.
Creators: name: Kliukin, Nikita S.
name: Nguyen, Tan Van
name: Le, Son Xuan
name: Bragin, Andrey M.
name: Tran, Tin Trong Vo
name: Gorin, Vladislav A.
name: Poyarkov, Nikolay A.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Squamata
Dibamidae
Dibamus
Dibamus tropcentr

description: Dibamus tropcentr sp. nov. Kliukin, Nguyen, Bragin & Poyarkov
(Figs. 1, 2, 3A–F, 4; Tables 1, 2)
Holotype. Adult female (ZMMU Re-17443; field tag NAP-13228) collected along the trail to Ao Ho Pond area, ca. 300 m from #702 road, Da Vach Mountain, Da Vach Peninsula, Nui Chua National Park, Thai An Village, Vinh Hai Commune, Ninh Hai District, Ninh Thuan Province, southern Vietnam (11.736°N, 109.213°E; elevation 200 m a.s.l.) on January 7, 2023, at 08:30 h by N. A. Poyarkov and S. X. Le.
Paratypes. ZMMU Re-17444 (field tag NAP-13142 / VRTC.NC.053), adult male collected at the same locality as the holotype on September 10, 2022, by S. X. Le; ZMMU Re-17572 (field tag NAP-13530), ZMMU Re-17573 (field tag NAP-13531), and ZMMU Re-17574 (field tag NAP-13532), two adult females and one subadult female respectively, collected at the same locality as holotype on February 28, 2023, by N. A. Poyarkov and A. M. Bragin; and VRTC NAP-13639 (field tag NAP-13639) and ZMMU Re-17575 (field tag NAP-13712), adult female and adult male respectively, collected in the valley of Nuoc Ngot River (11.778°N, 109.176°E; elevation 280 m a.s.l.), ca. 3 km south-west from Nuoc Ngot Beach, on the territory of Nui Chua N.P., Thai An Village, Vinh Hai Commune, Ninh Hai District, Ninh Thuan Province, southern Vietnam, on February 7, 2023, by N. A. Poyarkov and A. M. Bragin.
Diagnosis. The new species is assigned to Dibamus based on the following morphological characters: (1) worm-like body shape, fore limbs absent, hind limbs rudimentary, present only in males, forming flap-like structures located near the base of the tail above the vent; (2) eyes rudimentary, completely covered by scales; (3) external ear openings absent; (4) enlarged plate-like scales on the head; (5) postorbital bone absent; (6) epipterygoid absent; (7) temporal bone absent; (8) rib of last presacral vertebra absent; (9) tail length less than 34.0% of SVL; (10) subcaudal scales in females reduced to 64; and (11) postsacral vertebrae reduced to 36 in a single male (Greer 1985). Dibamus tropcentr sp. nov. can be distinguished from all other congeners by the following combination of morphological characters: (1) maximum SVL of 96.2 mm; (2) tail comparatively long, TL comprising 24.4–30.0% of SVL; (3) labial, nasal and medial rostral sutures present but incomplete, lateral rostral sutures completely absent; (4) two postocular scales; (5) three to four scales bordering the posteromedial edge of the first infralabial; (6) the medial sublabial scale not enlarged; (7) 19–21 midbody scale rows; (8) 23–24 transverse scale rows just posterior to head; (9) 18–19 transverse scale rows just anterior to vent; (10) 198–227 ventral scales; (11) 64–65 subcaudal scales; (12) relative size of frontal to frontonasal 88.5–120.5%; (13) relative size of interparietal to surrounding scales 91.3–128.6%; and (14) the light colored band on the body generally present.
Description of holotype. An adult female in a good state of preservation (Fig. 2); SVL 81.5 mm; tail length 22.8 mm (28.0% of SVL); head longer (HL 2.20 mm) than wide (HW 1.64 mm); snout bluntly rounded, projecting beyond the jaw (Fig. 3A,D; E-S 1.26 mm; E-N 1.00 mm; IN 0.59 mm; OI 1.15 mm); labial, nasal, and rostral sutures present, but incomplete (Fig. 3D–F); rostral pad with a large number of evenly distributed sensory papillae; two postocular scales; ear opening absent; eyes barely visible below the single ocular scale; supralabial single, larger than ocular scale, bordering ocular ventrally; three scales posterior to supralabial (Fig. 3A,D); frontal scale slightly larger than frontonasal scale (FSW/FNSW 104.9%); frontonasal wider than long (FNSL/FNSW 84.2%); interparietal single, not enlarged, narrower than frontonasal and frontal, posteriorly bordered by three slightly smaller nuchal scales (Fig. 3C,F); infralabials lanceolate, separated by a smaller mental; mental narrow, trapezoid in shape, bordered by the first infralabial on each side; four scales contacting the first infralabial, a small medial scale posterior the mental, and three larger scales contacting the infralabial posteromedially (Fig. 3B,E). Body wormlike, almost cylindrical (Fig. 2); body scales smooth, subcycloid (Fig. 3); 20 midbody scale rows; 24 scale rows just posterior to head; 19 scale rows anterior to vent; scales near vent thick; 64 subcaudals; 227 ventrals; tail complete, rudimentary flap-like hind limbs absent; tail tip blunt, covered by a single rounded scale, not terminating in a spine (Fig. 2). Morphometric data of the holotype are presented in Table 1.
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TABLE 1. (Continued)
Coloration. In life, dorsum, flanks and tail light grayish-brown; ventral surface slightly lighter; snout and head pinkish; tail darker grayish-brown; anal region dull-white (Fig. 2). The labial, rostral and nasal plates pinkish-beige to opaque (Fig. 3A–C), a small incomplete transverse bluish-gray band about 5–7 body scales wide present on the nuchal scales just posterior to head. In preservative after nine months of storage in ethanol the general coloration pattern does not change, though pinkish and orange tints fade to dull-white or beige.
Variation. The measurements and counts of the type series is presented in Table 1. The male paratypes are generally similar to the holotype in morphology with the major difference being the presence of the two short flap-like hind limbs which anterior to vent (HLL 1.65–2.47 mm). This difference clearly reflects sexual dimorphism previously reported for Dibamus (Greer 1985; Neang et al. 2011; Quah et al. 2017; Koppetsch et al. 2019). Three female paratypes ZMMU Re-17572–17574 have 19 midbody scale rows, while the female paratype VRTC NAP-13639 has 21 midbody scale rows (MBSR, Table 1). Two male paratypes ZMMU Re-17444 and ZMMU Re-17575, and three female paratypes ZMMU Re-17572–17574 have 23 scales rows posterior to head (PHSR, Table 1). Three female paratypes ZMMU Re-17572–17574 and male paratype ZMMU Re-17575 have 18 scale rows anterior to vent (VSR, Table 1). In a single female specimen ZMMU Re-17573 tail is damaged and regenerated what can be noticed by a different structure of the sales at the tail tip (see Darevsky 1992 for details); this specimen has comparatively shorter tail length and lower number of subcaudal scales (SC 56 vs. 64–65 in other type specimens; Table 1); these values were not used in morphological comparisons of the new species. All members of the type series had three scales on the posteromedial edge of infralabials (PIS), but the female paratype VRTC NAP- 13639 in which PIS was equal to four (Table 1). Significant variation was observed in the presence and position of the light transverse band across the body: it was completely absent in female paratype ZMMU Re-17572, an incomplete band was present on neck in female holotype and ZMMU Re-17443 and female paratype ZMMU Re-17574, male paratype ZMMU Re-17444 and female paratype ZMMU Re-17573 had a complete band at tail base, male paratype ZMMU Re-17575 had a complete band at midbody, while female paratype VRTC NAP-13639 had two bands: a complete band at midbody and an incomplete band closer to vent (see Table 1). It seems that the presence and degree of development of the light transverse band is highly variable in the new species and might depend on physiological condition of a given specimen; it appears that the use of this character in Dibamus taxonomy is not advisable.
Etymology. The name of the new species is a noun in apposition and is therefore invariable; the species name is given in reference to the Joint Vietnam - Russia Tropical Science and Technology Research Centre (VRTC). This international organization has been conducting research on ecology and biodiversity of Vietnam for over 35 years (1989–2023). Herpetological studies by VRTC staff have resulted in the description of over 60 new taxa of amphibians and reptiles from Vietnam. We recommend the names “ Ninh Thuan Blind Skink ” “ Ninthuanskaya cherveobraznaya yascheritsa ”and “ Thằn lằn giun Ninh Thuận ” as common names of the new species in English, Russian, and Vietnamese, respectively.
Comparisons. Comparative morphological data for the new species and the currently recognized nominal species of the genus Dibamus is presented in Table 2. Morphologically, Dibamus tropcentr sp. nov. is most closely resembling D. smithi, and morphological comparisons with this species appear to be the most pertinent. The new species (Fig. 3A–F) differs from D. smithi (Fig. 3G–I) by the presence of rudimentary labial suture (vs. absence), by having larger number of subcaudal scales (64–65 vs. 59–61); by a comparatively longer tail (TL/SVL 24.4–30% vs. 21–24%); by generally larger number of midbody scale rows (MBSR 19–21 vs. 18–19); by having interparietal scale not enlarged, subequal to the nuchal scale (IPW/NSW 91.3%–128.6% vs. 130–200%); by having frontal and frontonasal scales of the same size as compared to almost twice larger frontal scale (FSW/FNSW 88.5%–120.5% vs. 150–230%); by having three scales posterior of interparietal (vs. four scales); by having the medial scale posterior to mental not enlarged (vs. distinctly larger than surrounding scales); by having three to four scales on the posteromedial edge of infralabials (vs. two scales); and by having supralabial scale larger than ocular scale (vs. smaller).
Regarding the remaining species of Dibamu s, by having the labial suture incomplete (rudimental) Dibamus tropcentr sp. nov. can be differentiated from those species which have complete labial suture, namely: D. bogadeki, D. bourreti, D. celebensis Schlegel, D. dalaiensis Neang, Holden, Eastoe, Seng, Ith & Grismer, D. dezwaani Das & Lim, D. ingeri Das & Lim, D. kondaoensis, D. manadotuaensis Koppetsch, Böhme & Koch, D. montanus, D. nicobaricus (Steindachner), D. novaeguineae Duméril & Bibron, D. seramensis Greer, D. somsaki Honda, Nabhitabhata, Ota & Hikida, D. taylori Greer, D. tebal Das & Lim, and D. tiomanensis Diaz, Leong, Grismer & Yaakob, as well as from two species in which this suture is completely absent: D. deharvengi and D. floweri Quah, Anuar, Grismer & Grassby-Lewis.
The presence of an incomplete nasal suture further differs Dibamus tropcentr sp. nov. from the species in which this suture is complete, including: D. bogadeki, D. bourreti, D. celebensis, D. dalaiensis, D. deharvengi, D. dezwaani, D. ingeri, D. kondaoensis, D. leucurus (Bleeker, 1860), D. manadotuaensis, D. montanus, D. nicobaricus, D. novaeguineae, D. seramensis, D. somsaki, D. taylori, D. tebal, and D. tiomanensis, as well as from D. floweri in which this suture is completely absent.
The absence of lateral rostral sutures further distinguishes the new species from D. bogadeki and D. bourreti, the only two species of Dibamus in which these sutures are present. By the presence of incomplete medial rostral suture Dibamus tropcentr sp. nov. can be differentiated from species which completely lack rostral suture, namely: D. alfredi Taylor, D. bogadeki, D. booliati Das & Yaakob, D. bourreti, D. celebensis, D. leucurus, D. novaeguineae, D. seramensis, D. smithi, and D. taylori, and also from the two species which have a complete rostral suture: D. montanus and D. somsaki. The new species can be further differentiated from D. vorisi Das & Lim by having a larger number of subcaudals (SC 64–65 vs. 33 in males; 64 vs. 11 in females) and by a notably longer tail (TL/SVL 24.4–30% vs. 6.1–16.8%).
Among the other congeners inhabiting southern Indochina (see Fig. 1), Dibamus tropcentr sp. nov. is further differentiated from D. dalaiensis by having: two postoculars (vs. one), by higher number of subcaudal scales (SC 64–65 vs. 48–52), and by slightly longer tail (TL/SVL 24.4–30% vs. 18–22%). The new species can be further distinguished from D. deharvengi by having: two postoculars (vs. one), by three to four scales on the posteromedial edge of infralabial (vs. two), by higher number of midbody scale rows (MBSR 19–21 vs. 16–17), and by higher number of subcaudal scales (SC 64–65 vs. 57–61). Dibamus tropcentr sp. nov. is further diagnosed from D. greeri by having: two postoculars (vs. one) and by higher number of subcaudal scales (SC 64–65 vs. 53–54). The new species can be further distinguished from D. montanus by having: two postoculars (vs. one), by three to four scales on the posteromedial edge of infralabial (vs. two), by lower number of midbody scale rows (MBSR 19–21 vs. 22), by lower number of subcaudal scales (SC 64–65 vs. 43–49), and by longer tail (TL/SVL 24.4–30% vs. 15–18%). Dibamus tropcentr sp. nov. further differs from D. somsaki by having: two postoculars (vs. one), by three to four scales on the posteromedial edge of infralabial (vs. two), by higher number of subcaudal scales (SC 64–65 vs. 57–58), and by generally longer tail (TL/SVL 24.4–30% vs. 18–24%).
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TABLE 2. (Continued)
TABLE 2. (Continued)
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TABLE 2. (Continued)
Osteological description. The following description of skeletal features of the new species is based on the microCT data obtained from the male paratype specimen ZMMU Re-17444. Skeletal morphology of this specimen is presented in Fig. 4; osteological terminology generally follows Greer (1985) and Rieppel (1984). Head small, elongated; shoulder girdle absent; pelvic girdle and rudiments of hind limbs present (Fig. 4A). Body with 118 presacral vertebrae, 2 sacral vertebrae, and 36 tail vertebrae (Fig. 4A). The pelvic girdle includes the ilium, ischium, and pubis; hind limbs include femur, tibia, fibula, and a rudimentary bony cap (Fig. 4E).
The premaxilla is an unpaired bone bearing seven teeth (Fig. 4B); the transverse process of premaxilla is pierced by paired apical foramina. Four labial foramina present on the left maxilla, three labial foramina present on the right maxilla. Each of the maxillary bones bearing seven teeth (Fig. 4D). The nasal bones distinct, perforated by 5–6 foramina on each side (Fig. 4C). The prefrontal represents a triangular bone forming the posterodorsal edge of the lacrimal foramen. The lacrimal, postfrontal, postorbital and jugal bones absent. The paired frontals form anteromedial processes dividing the posterior portions of the nasals (Fig. 4C), and narrow anetrolateral processes located between the maxilla and prefrontal. The unpaired parietal bone forms supratemporal processes which overlay the dorsal portions of the prootics and the wide posterior process which meets the supraoccipital in a suture (Fig. 4C). The sagittal ridge on the parietal is absent (Fig. 4C). The vomers, palatine, pterygoids, and ectopterygoids are paired bones (Fig. 4B) with morphology similar to that described for the genus Dibamus by Greer (1985).
The parabasisphenoid complex (corresponding to the ‘parasphenoid + basisphenoid’ of Rieppel 1984) forms a broad massive bone meeting the basioccipital in a distinct suture. Exoccipitals fused with respective opisthotics, while the basioccipital, supraoccipital and prootics are separate bones with morphology typical for the genus as described by Greer (1985) (Fig. 4B–D). The stapes is characterized by a broad stapedial footplate slightly elongated anteroposteriorly (Fig. 4D). The quadrate bone short and flattened; its vertical axis is slightly tilted posteriorly.
Two labial foramina present on the each side of the dentary (Fig. 4D). The dentary bears four teeth on the left and five teeth on the right side. Coronoid process of the dentary comparatively high; the distinct coronoid bone absent. Compound bone is formed by the fused splenial, articular, angular and supraangular bones; the retroarticular process of the compound bone comparatively short (Fig. 4D). The lower jaw with mandibular, anterior and posterior suprangular foramina.
Distribution and natural history notes. The Ninh Thuan Province is known as the driest and hottest place in Vietnam (Hoang et al. 2021); the area of the province receives the lowest rainfall with an average of 650 mm per year and average temperature ranges from 24.6 to 27.2°C. The dry season in Ninh Thuan extends for eight months from November or December to July or August (Hoang et al. 2021). The Nui Chua N.P. lies in the south-eastern edge of the Great Annamites Ecoregion; due the unique semi-arid climatic conditions, the coastal areas of the N.P. are covered by maritime dry forest ecosystem which is not found in the other parts of Vietnam (Vu et al. 2013; Hoang et al. 2021). Previously, three endemic reptile species were described from Nui Chua N.P., namely: Cyrtodactylus caovansungi Orlov, Nguyen, Nazarov, Ananjeva & Nguyen, C. sangi Pauwels, Nazarov, Bobrov & Poyarkov, and Dixonius aaronbaueri Ngo & Ziegler (Ngo & Ziegler 2009; Orlov et al. 2007; Pauwels et al. 2018).
Dibamus tropcentr sp. nov. is to date known only from two localities within Nui Chua N.P., Ninh Thuan Province, southern Vietnam (Fig. 5). The distribution limits of the new species are unknown. During our three surveys in September 2022, January 2023 and February – March 2023 we recorded the new species on the Da Vach Peninsula and within the Nuoc Ngot River Valley; these two localities are located within dry evergreen forest at approximately 7 km from each other at elevation from 200 to 280 m a.s.l. at Da Vach Peninsula, the individuals were collected at 200 m a.s.l. elevation within a dry maritime mixed low evergreen forest with the dominance of Buchanania reticulata Hance, Choerospondias axillaris (Roxb.) Burtt. & Hill, Pentaspadon annamense (Evrard & Tardieu) Ph ạmh., Spondias pinnata (L.f.) Kurz, and Ormosia sp., including occasional trees of Sindora siamensis Teijsm. ex Miq., Streblus ilicifolius (S. Vidal) Corner, and Eurya turfosa Gagnep, and with an undergrowth formed primarily by Pandanus cornifer H. St. John and Dracaena sp. (Fig 5A) (plant identification – A. N. Kuznetsov, pers. comm.).
All specimens of the new species were found during daytime (from 10:00 h to 14:00 h) while digging through leaf litter, soil and crushing rotten tree logs. The holotype was found inside a decayed fallen log 30 cm in diameter, where it occurred together with Globitermes sulphureus (Haviland) colony.The paratype male ZMMU Re-17444 was found during midday on the soil surface beneath a rotten log in maritime dry evergreen forest and was also observed together with Globitermes sulphureus. Two paratype females ZMMU Re-17572–17573 were found beneath rotten, fallen logs of 20–40 cm diameter in close proximity to the holotype. In Da Vach Mountain, Dibamus tropcentr sp. nov. specimens were not found in other adjacent parts of the forest and seemed to be locally concentrated in small areas approximately 10.000 m 2 in square; similar biology was also recorded in D. dalaiensis (Neang et al. 2011). In Nuoc Ngot River Valley the two specimens were found beneath a rotten tree log in loose soil approximately 50 m from each other sharing the same habitat. In almost all cases, the specimens of Dibamus tropcentr sp. nov. were recorded in the same microhabitats together with Globitermes sulphureus found in soil and fallen tree trunks. Other species of lizards recorded syntopically with the new species at the type locality included: Calotes bachae Hartmann, Geissler, Poyarkov, Ihlow, Galoyan, Rödder & Böhme, Cyrtodactylus sangi, C. caovansungi, Dixonius aaronbaueri, Gekko russelltraini Ngo, Bauer, Wood & Grismer; Gehyra mutilata (Wiegmann), and Scincella rufocaudata (Darevsky & Nguyen).
All specimens of Dibamus tropcentr sp. nov. raised the body scales when handled, what gave them a somewhat wrinkled appearance. This defensive behavior was previously described for several Dibamus species (see Das & Yaakob 2003; Diaz et al. 2004; Grismer 2011; Quah et al. 2017); and is generally interpreted as an anti-predator mechanism employed by the lizards to imitate a Megascolecidae worm, which are likely inedible for some potential predators like birds (Darevsky 1992; Quah et al. 2017).
Conservation status. Dibamus tropcentr sp. nov. to date is known only from seven specimens collected from two localities within the Nui Chua N.P., Ninh Thuan Province, Vietnam. Though these elusive lizards appear to be locally abundant, it seems that their populations are locally concentrated in quite small areas. Any specific threats to Dibamus tropcentr sp. nov. are not well known, however the new species is likely associated with the specific microhabitats found in low-elevation dry maritime evergreen forests. This type of habitat is one of the most endangered in Vietnam and is intensively modified and destroyed due to the fast development of agriculture, infrastructure, and tourism in Vietnam. Given the available information, we suggest Dibamus tropcentr sp. nov. be considered as a Vulnerable (VU) species following IUCN’s Red List categories (IUCN Standards and Petitions Subcommittee 2019).
description: Published as part of Kliukin, Nikita S., Nguyen, Tan Van, Le, Son Xuan, Bragin, Andrey M., Tran, Tin Trong Vo, Gorin, Vladislav A. & Poyarkov, Nikolay A., 2023, A new species of the genus Dibamus Duméril & Bibron, 1839 (Squamata: Dibamidae) from the driest and hottest place of Vietnam, pp. 301-320 in Zootaxa 5380 (4) on pages 304-317, DOI: 10.11646/zootaxa.5380.4.1, http://zenodo.org/record/10244908