Hapalomys suntsovi, Abramov & Balakirev & Rozhnov, 2017

Abramov, A. V., Balakirev, A. E. & Rozhnov, V. V., 2017, New insights into the taxonomy of the marmoset rats Hapalomys (Rodentia: Muridae), Raffles Bulletin of Zoology 65, pp. 20-28 : 24-26

Hapalomys suntsovi , new species

Holotype. ZIN 99487, field no.26, male, skin, skull, collected 14 January 2010 by A. V. Abramov and A. V. Shchinov.

Type locality. Vietnam, c. 13 km NE of Bu Gia Map Village, Bu Gia Map National Park , Binh Phuoc Province, 12°12′N, 107°12′E, elevation 540 m above sea level .

Paratypes. ZIN 98922, field no.11, male, body in ethanol, skull extracted, collected 25 April 2009 ; ZIN 99483, field no.6, male, skin, skull, skeleton, collected 11 January 2010 ; ZIN 99484, field no.11, male, skin, skull, skeleton, collected 12 January 2010 ; ZIN 99485, field no.17, female, specimen in ethanol, collected 13 January 2010 ; ZIN 99486, field no.18, female, skin, skull, collected 13 January 2010 ; ZIN 99488, field no.31, male, skin, skull, collected 16 January 2010 ; ZIN 100410 , male, specimen in ethanol, collected 16 January 2010 (karyotyped, see Abramov et al., 2012) ; collected by A. V. Abramov and A . V. Shchinov from the same locality as the holotype ; ZMMU S-186111, field no. BZM-18, GenBank accession number (COI) KU 958011 , female, skull, skin, body in ethanol, collected 6 November 2009 by A. V. Shchinov and A.E. Balakirev from the same locality as the holotype .

Diagnosis. A medium-sized Hapalomys that on the average is smaller in its external and cranial measurements than H. longicaudatus . It is comparable to H. delacouri in its body and cranium size, but can be distinguished by the longer tail, the relatively short incisive foramina, and the cytochrome oxidase c subunit I (COI). Distinguished from both known species by the karyotype composition.

Description. A medium-sized marmoset rat with the head and body length of 135.6 mm (127.0–146.0 mm) and the tail length of 157.1 mm (150.0–165.0 mm). Pelage is soft and dense, dorsum grayish brown, ventral surface white, demarcation between upper parts and under parts colouration coloration is apparent ( Fig. 4 ; see also fig. 2 in Abramov et al., 2012). The tail is longer than the head and body length (~116%), its distal part covered with long hairs. The hallux is fully opposable, bearing a nail instead of a claw. Skull with short and broad rostrum. The braincase with prominent postorbital and temporal ridges. Incisive foramina relatively short. The upper and lower molars have three longitudinal cusp rows.

Comparisons. As compared with H. longicaudatus , H. suntsovi can be readily separated by its smaller size. By its size, the new species is most similar to H. delacouri , but has a longer tail. In H. suntsovi , the incisive foramina are absolutely shorter and shorter relative to the overall skull size in comparison to those of H. delacouri and H. longicaudatus . H. delacouri and H. suntsovi do not have additional cusps on the anterior margin of each upper first molar, H. longicaudatus has two small, but well developed and conspicuous cusps on the anterior margin (see Musser, 1972: fig. 10). In H. suntsovi and H. delacouri , the lingual row of cusps of each first upper molar are smaller in comparison with other cusps of the tooth ( Fig. 5 ), in contrast to H. longicaudatus has similar-sized cusps ( Musser, 1972: fig. 10).

H. suntsovi and H. delacouri are distinguished by the differences in COI gene sequences. H. suntsovi differs from H. delacouri and H. longicaudatus in the diploid number of chromosomes: 2n=38 (specimen ZIN 100410, Abramov et al., 2012), 2n=48 and 2n=50, respectively.

Etymology. The new species is dedicated to Dr Viktor V. Suntsov (A.N. Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow), in recognition of his many contributions to the study of rodents of Vietnam. During 1992–2010, Dr Suntsov headed the Southern Division of the Joint Russian-Vietnamese Tropical Research and Technological Centre in Ho Chi Minh City.

Distribution. Currently known from the type locality, the Bu Gia Map National Park, Binh Phuoc Province, Southern Vietnam. It is likely to occur in the adjacent forest regions of Eastern Cambodia.

Natural history. The series of type specimens was collected in old, mature, thick trunk bamboo thickets growing along a forest road ( Abramov et al., 2011). All specimens were taken by traps set 5–7 m over the ground surface. Two females caught on 13 January 2010 were pregnant (at early stage) bearing four and five small embryos.

Figures

Fig. 4. General appearance of Hapalomys suntsovi based on a specimen ZIN 99484, collected from the Bu Gia Map NP, Vietnam, on 12 January 2010.

Fig. 5. Ventral, dorsal and lateral views of skull and lingual side of mandibles: A – Hapalomys suntsovi (holotype, ZIN 99487, Binh Phuoc Province, Vietnam); B – Hapalomys delacouri (ZIN 103040, Ha Tinh Province, Vietnam). Scale bar =10 mm.