Arvicanthis Lesson, 1842

Denys, Christiane, Missoup, Alain Didier, Nicolas, Violaine, Sylla, Morlaye, Douno, Mory, Kadjo, Blaise, Lalis, Aude & Monadjem, Ara, 2025, Annotated checklist of rodents from a biodiversity hotspot, Mount Nimba (West Africa), Zoosystema 47 (27), pp. 617-689 : 633-635

Genus Arvicanthis Lesson, 1842 ( Tables 7 ; 8 )

REMARKS

In West Africa, grass rats of the genus Arvicanthis are represented by four clades, namely: A. ansorgei Thomas, 1910 ; A. niloticus (Desmarest, 1822) C2 & C4 clades and A. rufinus ( Temminck, 1853) ( Bryja et al. 2019) . These four species are not easy to distinguish morphologically, although some can be characterized by their karyotypes. Arvicanthis ansorgei is defined by 2N=62, FN= 74-76 and this cytotype was recorded in Benin and S. Mali. A. niloticus is also characterized by 2N= 62 but a FN =64 and is found from Senegal to Burkina Faso ( Ducroz et al. 1997). In Côte d’Ivoire (RCI) Tranier & Gautun (pers. comm.) reported a specimen with 2N =62. A cytotype of 2N =62, FN =76 from West of the Niger River was attributed to A. rufinus ( Volobouev et al. 2002) . We did not collect any new specimens of this genus, so we can only rely on morphological characters to describe the two previously collected specimens. Thus, species identification remains doubtful.

A single specimen (MNHN-ZM-2006-10), preserved in alcohol, was collected in Grassfield ( Liberia) by Xavier Françoise, who attributed it to A. ansorgei because it had a very rufous pelage. However, it was a juvenile individual and no external measurements were reported.

The other MNHN specimen (MNHN-ZM-AC-1955-660) was collected by Matthey. It displays an Arvicanthis morphology but looks small and is relatively young ( Table 7 ). This specimen displays the dorsal speckled pelage with brown-rufous hairs mixed with grey-black ones. The tail is incomplete. The HF is small compared with the description of A. rufinus in Rosevear (1969), and fits better with A. ansorgei . There is a rufous area at the base of the tail and the ventral pelage is white-grey with pale orange. The tail is bicolored black above and reddish-yellow below. The skull of this specimen is robust, the nasal bones are short and the IOC large and framed by two marked fronto-parietal crests. In ventral view the infraorbital foramen is long entering the palate between the molar rows reaching the first lobe of cusps of the upper M1. The molar row is long, as is the length of the tympanic bullae. This specimen corresponds to a young individual and is slightly smaller than the NHM type series of A. rufinus but fits within A. rufinus from Benin and A. ansorgei for LGT measurement. Its upper molar row length fits with A. ansorgei karyotyped specimens rather than with A. rufinus ( Table 8 ).