Dibamus annae, Kliukin & Nguyen & Pawangkhanant & Pham & Le & Gorin & Bos & Krone & Poyarkov, 2025

Kliukin, Nikita S., Nguyen, Tan Van, Pawangkhanant, Parinya, Pham, Hieu Minh, Le, Son Xuan, Gorin, Vladislav A., Bos, Collin, Krone, Isaac W. & Poyarkov, Nikolay A., 2025, A new species of Dibamus from the Central Highlands of Vietnam with redescription of Dibamus montanus Smith, 1921 (Squamata: Dibamidae), Zootaxa 5693 (1), pp. 1-31 : 18-25

Dibamus annae sp. nov.

urn:lsid:zoobank.org:act:

( Figures. 4A–C , 6A–C , 7A , 10–11 ; Tables 4–5 )

Holotype. Adult male ( ZMMU Re-15720 ; field tag ABV-1519) collected from Kon Ka Kinh National Park, Gia Lai Province, central Vietnam (geographic coordinates N 14.20418°, E 108.31532°; elevation 873 m asl.) on June 01, 2017, by A. B. Vassilieva.

Suggested common names: Anna’s Blind Skink (English); Thằn lằn giun An-na (Vietnamese); Cherveobraznaya yascheritsa Anny (ЧервеобраЗнаЯ ЯЩерица Анны, Russian).

Diagnosis. Dibamus annae sp. nov. can be distinguished from all other congeners by the following combination of morphological characters: (1) maximum SVL of 92.7 mm; (2) tail comparatively long, TL comprising 18.9% of SVL in a single male; (3) labial and nasal sutures present and complete, rostral suture present and incomplete; (4) one postocular scale; (5) two scales bordering the posteromedial edge of the first infralabial; (6) the medial sublabial scale not enlarged; (7) 19 midbody scale rows; (8) 21 transverse scale rows just posterior to head; (9) 18 transverse scale rows just anterior to vent; (10) 180 ventral scales; (11) 45 subcaudal scales; (12) relative size of frontal to frontonasal 136.3%; (13) relative size of interparietal to nuchal scale 133.9%; and (14) the light-colored band on the body present closer to the head.

Description of holotype. An adult male in a good state of preservation ( Fig. 10 ); SVL 92.7 mm; tail length 17.5 mm (18.9% of SVL); head longer (HL 3.56 mm) than wide (HW 2.08 mm); snout bluntly rounded, projecting beyond the jaw ( Fig. 4A , Fig. 6A ; E-S 1.6 mm; E-N 1.2 mm; IN 0.66 mm; OI 1.59 mm); labial sutures complete; nasal suture rudimental; rostral suture rudimental ( Fig. 4A , Fig. 6A ); rostral pad with a large number of evenly distributed sensory papillae; one postocular scale on each side; ear opening absent; eyes barely visible below the single ocular scale; supralabial single ( Fig. 4A , Fig. 6A ); frontal scale slightly larger than frontonasal scale (FSW/FNSW 136.3%); frontonasal scale wider than long (FNSL/FNSW 49.5%); interparietal single, not enlarged, narrower than frontonasal and frontal, posteriorly bordered by three slightly smaller nuchals ( Fig. 4B , Fig. 6B ); infralabials lanceolate, separated by a smaller mental; mental narrow, trapezoid in shape, bordered by the first infralabial on each side; two scales contacting the first infralabial, a small medial scale posterior to the mental, and three larger scales contacting the infralabial posteromedially ( Fig. 4C , Fig. 6C ). Body wormlike, almost cylindrical ( Fig. 11 ); body scales smooth, subcycloid ( Fig. 4B , Fig. 6B ); 19 midbody scale rows; 21 scale rows just posterior to head; 18 scale rows anterior to vent; medial scales near vent thick, flattened ( Fig. 7A ); 45 subcaudals; 180 ventrals; tail complete, rudimentary flap-like hind limbs present, but the right hind limb damaged ( Fig. 7A ; HLL 2.95 mm); tail tip blunt, covered by a single rounded scale, not terminating in a spine. Morphometric and meristic data of the holotype are given in Tables 4–5 .

Coloration. Coloration in life is unknown. In preservation, dorsum, flanks, and tail light brown ( Fig. 10A–B ); ventral surface, snout, and head slightly paler; rostral and mental pads lighter ( Fig. 6A–C ). Scales on the tip of hind limbs and in the cloacal region light brown. A distinct transverse cream-colored band present, complete, and located just behind the head basis ( Fig. 10A–B ); other light bands or markings absent.

Variation. The new species is known only from a single specimen (the holotype); its measurements and counts are presented in Table 4 .

Hemipenial morphology. Unknown, as the hemipenial structures were not everted before the preservation of the specimen.

Osteological description. The following description of skeletal features of the new species is based on the microCT data obtained from the holotype specimen ZMMU Re-15720. The skeletal morphology of this specimen is presented in Fig. 11 . Skull small relative to the body, elongated; shoulder girdle absent; pelvic girdle and rudiments of hind limbs present ( Fig. 11A ). Body with 111 presacral vertebrae, 2 distinct sacral vertebrae, and 25 tail vertebrae ( Fig. 11A ). The pelvic girdle includes the fused ilium, ischium, and pubis; hind limbs include the femur, tibia, fibula, and a rudimentary bony cap ( Fig. 11 E-F).

The premaxilla is an unpaired bone ( Fig. 11 B-D); the transverse process of the premaxilla is pierced by paired apical foramina. Three labial foramina are present on the left maxilla, and five labial foramina are present on the right maxilla. Each of the maxillary bones bears seven slightly curved teeth ( Fig. 11D ). The nasal bones are distinct, perforated by three foramina on each side ( Fig. 11C ). The prefrontal is a triangular bone forming the posterodorsal edge of the lacrimal foramen. The lacrimal, postfrontal, postorbital, jugal, and epipterygoid bones are absent. The paired frontals form the anteromedial processes dividing the posterior portions of the nasals ( Fig. 11C ), with the anterolateral processes of the frontals absent. The unpaired parietal bone forms supratemporal processes that overlay the dorsal portions of the prootics and a wide posterior medial process that meets the supraoccipital in a suture ( Fig. 11C ). The medial (sagittal) ridge on the parietal is absent ( Fig. 11C ). The vomers, palatine, pterygoids, and ectopterygoids are paired bones ( Fig. 11B ) with morphology similar to that described for the other members of the genus Dibamus by Greer (1985) and Kliukin et al. (2023, 2024a, 2024b).

The parabasisphenoid complex (corresponding to the ‘parasphenoid + basisphenoid’ of Rieppel 1984) forms a broad, massive bone meeting the basioccipital in a distinct suture. Exoccipitals, basioccipitals, and supraoccipitals are separate bones, while prootics and opisthotics are fused ( Fig. 11 B-D). The stapes is characterized by a broad stapedial footplate slightly elongated anteroposteriorly ( Fig. 11D ). The quadrate bone is short and flattened; its vertical axis is slightly tilted posteriorly.

Four labial foramina present are on each side of the dentary ( Fig. 11D ). The dentary bears eight teeth on each side. The coronoid process of the dentary is comparatively high; a distinct coronoid bone is absent. The compound bone is formed by the fused splenial, articular, angular, and supraangular bones; the retroarticular process of the compound bone is comparatively short ( Fig. 11D ). The lower jaw bears the mandibular, anterior, and posterior supraangular foramina.

Etymology. The new species epithet honors Dr. Anna B. Vassilieva, a Russian herpetologist currently working at the A.N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences. Dr. Vassilieva collected the holotype of the new species; furthermore, she has also spent over 10 years researching the herpetofauna of Vietnam.

Comparisons. Comparative morphological data for the new species and the currently recognized nominal species of the genus Dibamus is presented in Table 5 . The new species was provisionally identified by A. B. Vassilieva as D. montanus , and morphological comparisons with this species appear to be the most pertinent. Dibamus annae sp. nov. can be easily distinguished from D. montanus by having incomplete medial rostral and labial sutures (vs. complete), by having three scales posterior to the interparietal (vs. four scales), by the presence of a complete band on the body (vs. absent), by a slightly lower number of midbody scale rows (MBSR 19 vs. 20–22), by a lower number of scale rows anterior to vent (VSR 18 vs. 21), by a notably lower number of ventrals (VEN 180 vs. 200– 225), and by having two scales posterior to the infralabial (vs. generally three in D. montanus ).

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When compared to D. greeri , another congener inhabiting Gia Lai Province, Dibamus annae sp. nov. can be easily differentiated by a lower number of supralabial scales (SL 1 vs. 2 in D. greeri ), by a slightly lower number of midbody scale rows (MBSR 19 vs. 20 in D. greeri ), by a lower number of subcaudal scales (SC 45 vs. 53 in D. greeri ), by a shorter tail (TL/SVL 18.9% vs. 23.8–28% in D. greeri ), and by a notably smaller interparietal scale.

Regarding the remaining species of Dibamu s, one postocular scale distinguishes the new species from D. alfredi Taylor , D. celebensis , D. deimontis , D. dezwaani Das & Lim , D. ingeri Das & Lim , D. kondaoensis , D. manadotuaensis Koppetsch, Böhme & Koch , D. novaeguineae , D. seramensis , D. smithi , D. taylori Greer , D. tebal Das & Lim , D. tropcentr , and D. vorisi Das & Lim. Dibamus annae sp. nov. is further diagnosed from D. bogadeki , D. booliati Das & Yaakob , D. bourreti , D. dalaiensis , D. deharvengi , D. elephantinus , D. floweri Quah, Anuar, Grismer & Grassby-Lewis , D. leucurus (Bleeker) , D. somsaki Honda, Nabhitabhata, Ota & Hikida , D. tiomanensis , and D. nicobaricus (Steindachner) by a lower number of subcaudal scales (vs. 45 in Dibamus annae sp. nov.; see Table 5 ). The absence of lateral rostral sutures 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 an incomplete medial rostral suture, Dibamus annae sp. nov. can be differentiated from species that completely lack a rostral suture, namely D. alfredi , D. bogadeki , D. booliati , D. bourreti , D. celebensis , D. leucurus , D. novaeguineae , D. seramensis , D. smithi , and D. taylori , and also from the two species that have a complete rostral suture: D. montanus and D. somsaki . The presence of an incomplete nasal suture further differentiates Dibamus annae sp. nov. from the species in which this suture is complete, including D. bourreti , D. celebensis , D. dalaiensis , D. deharvengi , D. dezwaani , D. elephantinus , D. ingeri , D. kondaoensis , D. leucurus , 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. By having the complete labial suture, Dibamus annae sp. nov. can be differentiated from those species that have an incomplete labial suture, namely, D. alfredi , D. deimontis , D. leucurus , D. smithi , D. tropcentr , and D. vorisi , as well as from three species in which this suture is typically absent: D. deharvengi , D. floweri , and D. smithi .

Finally, Dibamus annae sp. nov. is substantially different from D. montanus in a number of osteological traits. Dibamus annae sp. nov. has a slightly lower number of presacral vertebrae (111 vs. 116) and tail vertebrae (25 vs. 26). The pelvic girdle contains the same set of bones in both species, but in Dibamus annae sp. nov., the pubis, ischium, and ilium are fused ( Fig. 11 E-F), while in D. montanus all pelvic girdle bones remain separate ( Fig. 8 E-F). Dibamus annae sp. nov. can be further diagnosed from D. montanus by the slightly higher medial (sagittal) ridge on the parietal and by the presence of a posteromedial process on the prefrontal bone ( Fig. 11C ) (vs. an almost triangular prefrontal in D. montanus ; Fig. 11C ). The new species can be further distinguished from D. montanus by the fusion of prootics, opisthotics, and basioccipitals, while in D. montanus these bones remain separate. In both species, there is a distinct suture between the parabasisphenoid complex and the basioccipital. Dibamus annae sp. nov. and D. montanus have almost equal numbers of labial foramina on each side of the maxillary (four in D. montanus and three to five in Dibamus annae sp. nov.) and almost equal number of labial foramina on each side of the dentary (four to five in D. montanus and four in the new species). Finally, Dibamus annae sp. nov. remarkably differs from D. montanus by the absence of the separate coronoid ( Fig. 11D ) (vs. separate coronoid present in D. montanus ; Fig. 8D ).

Distribution and natural history notes. The only known specimen of Dibamus annae sp. nov. was collected on June 1, 2024, during the day, from under a rotten log in a polydominant evergreen montane forest within the Kon Ka Kinh N.P., Gia Lai Province, at an elevation of 973 m asl. The habitat represents a rich evergreen montane forest located in the valley of the A Yun River; the forest is dominated by broadleaf trees of the families Euphorbiaceae , Myrtaceae , Moraceae , Duabangaceae , Lauraceae , Fagaceae , Meliaceae , and Theaceae , with numerous lianas and thickets of ferns ( Fig. 12 ). The soil layer was covered with a quite thick layer of leaf litter in the area of specimen collection. Sympatric lizard species recorded in Kon Ka Kinh N.P. include Sphenomorphus veunsaiensis (Geissler, Hartmann & Neang) (identification follows Bragin et al. 2025), S. indicus (Gray) , Scincella rufocaudata (Darevsky & Nguyen) , Lygosoma corpulentum Smith , Eutropis multifasciata (Kuhl) , Lipinia microcercus (Boettger) (Sincidae), Gehyra mutilata (Wiegmann) , Cyrtodactylus taynguyenensis Nguyen, Le, Tran, Orlov, Lathrop, Macculloch, Le, Jin, Nguyen, Nguyen, Hoang, Che, Murphy & Zhang ( Gekkonidae ), Calotes emma Gray , Acanthosaura lepidogaster (Cuvier) , A. nataliae Orlov, Nguyen & Nguyen , Physignathus cocincinus Cuvier , and Paracalotes ziegleri (Hallermann, Nguyen, Orlov & Ananjeva) ( Agamidae ). Morphological variation, reproductive biology, diet, enemies, and parasites of Dibamus annae sp. nov. remain unknown.

Conservation status. To date, Dibamus annae sp. nov. is known only from a single specimen collected from one locality in Kon Ka Kinh N.P., Gia Lai Province, Vietnam. Any specific threats to Dibamus annae sp. nov. are unknown, and the area of specimen collection is comparatively well-protected by the National Park and the local authorities. According to the available information, we suggest Dibamus annae sp. nov. be regarded as a Data Deficient (DD) species following IUCN’s Red List categories criteria ( IUCN Standards and Petitions Subcommittee 2019).

Figures

FIGURE 4. Line drawings of head scalation of the holotype of Dibamus annae sp. nov. ZMMU Re-15720 (A–C), male specimen of D. montanus ZMMU Re-18136 (D–F), and male paralectotype of D. montanus BMNH 1946.8.3.2 (G–I). Head is shown in lateral (A, D, G), dorsal (B, E, H), and ventral (C, F, I) aspects. Scale bar equals 1 mm. Drawings A–F by Nikita S. Kliukin; figures G–I taken from Greer (1985; with permission).

FIGURE 6. Photographs of head scalation of the holotype of Dibamus annae sp. nov. ZMMU Re-15720 (A–C); and male specimen of D. montanus ZMMU Re-18136 (D–F). Head is shown in lateral (A, D, G), dorsal (B, E, H), and ventral (C, F, I) aspects. Scale bar equals 1 mm. Photographs by Nikita S. Kliukin.

FIGURE 7. Line drawings of cloacal region and hindlimbs of the holotype of Dibamus annae sp. nov. ZMMU Re-15720 (A); and male specimen of D. montanus ZMMU Re-18136 (B). Drawings by Nikita S. Kliukin.

FIGURE 8. Skeletal morphology of the male specimen of Dibamus montanus (ZMMU Re-18136). General view of the skeleton (A); skull in ventral (B), dorsal (C), and lateral (D) views; skeletal structures present in the cloacal region in lateral (E) and ventral (F) views, vertebral column shaded. Terminology follows Greer (1985) and Rieppel (1984). Notes: *—compound bone consists of fused splenial, articular, angular, and supraangular bones (Greer 1985); labial foramina (1)—labial foramina of the maxilla, labial foramina (2)—labial foramina of the dentary.

FIGURE 10. Male holotype of Dibamus annae sp. nov. (ZMMU Re-15720) in preservative. A—right lateral view; B—left lateral view; scale bar equals 5 mm. Photograph by Nikolay A. Poyarkov.

FIGURE 11. Skeletal morphology of the male holotype of Dibamus annae sp. nov. (ZMMU Re-15720). General view of the skeleton (A); skull in ventral (B), dorsal (C), and lateral (D) views; skeletal structures present in the cloacal region in lateral (E) and ventral (F) views, vertebral column shaded. Terminology follows Greer (1985) and Rieppel (1984). Notes: *—bones fused; **—compound bone consists of fused splenial, articular, angular, and supraangular bones (Greer 1985); labial foramina (1)—labial foramina of the maxilla, labial foramina (2)—labial foramina of the dentary.

FIGURE 12. Natural habitat of Dibamus annae sp. nov. at the type locality in Kon Ka Kinh National Park, Gia Lai Province, Vietnam. Photograph by Alina V. Alexandrova.