Hylomys Müller, 1840

Hinckley, Arlo, Camacho-Sanchez, Miguel, Chua, Marcus A H, Ruedi, Manuel, Lunde, Darrin, Maldonado, Jesús E, Omar, Hasmahzaiti, Leonard, Jennifer A & Hawkins, Melissa T R, 2024, An integrative taxonomic revision of lesser gymnures (Eulipotyphla: Hylomys) reveals five new species and emerging patterns of local endemism in Tropical East Asia, Zoological Journal of the Linnean Society 202 (2), pp. 1-33 : 10-13

Hylomys Müller, 1840

Type species: Hylomys suillus Müller, 1840: 436 .

Included species: The type species, plus H. parvus , H. engesseri , H. macarong sp. nov., H. vorax sp. nov., and H. dorsalis , H. maxi , and H. peguensis (recognized at species rank, below).

Distribution: Currently known from Sundaland (including Borneo, Java, Sumatra, and the Malay peninsula) and Indochina (including Myanmar, Thailand, Cambodia, Lao P.D. R., Viet Nam, and southern China).

Emended diagnosis: The genus Hylomys is defined phylogenetically as the most recent common ancestor of extant H. parvus , H. dorsalis , H. maxi , H. peguensis , H. macarong sp. nov., and H. vorax sp. nov., and extinct H. engesseri , and by the following combination of morphological characters. Small-sized gymnures, HB from c. 98–157 mm, W c. 40–80 g, GLS from c. 29–39 mm ( Table 1 ). Hylomys is characterized by brown fur that can range from harsh to moderately soft. The dorsum fur is characterized by long and thick spinous black guard hairs and golden-brown guard hairs that produce a golden-streaked appearance. Black guard hairs are stiff and black tipped, gradually turning to a light silvered grey towards its proximal end. Golden-brown guard hairs are stiff and have a short black tip followed by a narrow yellow to golden band which can be more or less expanded and that sharply transitions to a proximal dark silvered grey. Hylomys parvus is an exception to this general appearance as its soft dorsal fur lacks spinous/stiff guard hairs ( Ruedi et al. 1994). Dorsum coloration generally acquires a more ochraceous coloration towards the rump and face, and a yellow hue in the shoulder area. The dorsal coloration has limited variation, with only the Bornean population adults exhibiting a moderately distinct to faint black sagittal stripe (but less marked than that of Neohylomys hainanensis ), generally restricted to the nape/shoulder area, but which can extend to the rump. Variation on dorsum fur length, guard hair thickness and coloration is slight. Higher elevation individuals seem darker and to have a softer and more dense fur, while lower elevation individuals can be harsher and more colourful (e.g. become very reddish in H. maxi at 100 m a.s.l.; Ruedi et al. 1994). Golden-brown guard hairs are paler, longer, and thicker in Indochinese populations, conferring the dorsum fur a lighter and more yellow appearance than that of Sundaic populations. Ventral coloration is grey/brown, paler than the dorsum, buff or white tipped with a grey base, and can be subject to seasonal, elevational, sexual, and/or ontogenetic variation within populations. In fact, this variation within populations seems generally greater than that between most species. Only H. peguensis is distinct from the other recognized or putative species, regardless of sex or season, as it exhibits buff coloration throughout most of its range. Adults can have a pale brown or ochraceous throat coloration, generally during spring or summer, possibly part of the breeding season. This darker coloration can extend across all the venter in males of Bornean and Da Lat populations, making these seasonally distinct to the other species. As with dorsal pelage, fore- and hindfeet are lighter in Indochinese than Sundaic populations. The legs are short and the feet plantigrade. Tails are bicoloured in all species but H. vorax sp. nov. and one H. maxi specimen from north Sumatra. The hindfoot sole and tarsal regions have short and applied hairs and have generally pale hair tufts over nails. Tail is very short (7–32 mm), 7–28% of head and body length and essentially naked with some short and applied hairs. Females have four axial and two inguinal mammae, the two upper axial are frequently hidden at the armpit area, perhaps suggesting why Anderson (1874) described just two axial and two inguinal mammae; adult males have a slight swelling in the uro-genital area and a penis with many spines; anal glands on anterior margin of anus.

The skull is relatively small with an elongate rostrum; posterior end of nasals spans the level of the antorbital rim in some species; antorbital fossae are moderately deep; maxilla and parietal are separated by a narrow frontal bone strip; supraorbital processes absent to well developed; frontals not inflated to strongly inflated; interorbital region minimally constricted; anterior parietal process is well developed or at least distinct; braincase inflated; sagittal crest inconspicuous to prominent, generally restricted to interparietal but can extend anteriorly to frontal in H. macarong sp. nov.; nuchal crest of varying height that originates laterally as low projections from dorsal margin of each mastoid that meet mid-dorsally to form a broadly tapered arch with which the sagittal crest converges [as described for Podogymnura in Balete et al. (2023)]; occipital crest absent to prominent, generally does not extend ventrally more than a third of the occipital bone; zygomatic arch complete and moderately developed, posteroventral process on zygoma absent or indistinct, deep nasolabialis fossa, small jugal bone; epipterygoid process moderately developed; basioccipital–petrosal suture closed forming distinct foramen, bullae incomplete, condylar foramen in condyle emargination; posterodorsal region of the premaxilla is rarely in contact with the anterodorsal region of the frontal (0–4.15 mm). Anterior palatine foramina positioned slightly anteriorly/posteriorly or at level of maxilla/palatine suture. Anterior opening of infraorbital canal dorsal to P4. Paraoccipital process almost indistinct to somewhat prominent. Dental formula: 3/3 1/1 4/4 3/3 = 44; I1 large and caniniform, C1 larger than adjacent teeth, P1 present, P3 slightly larger or equal to P2, P2 larger or equal to P1. P3 has one root or two roots that are fused in most species; molariform and tribosphenic P4, quadrate M1 and M2; M3 c. half the crown area of M1 and M2; lower incisors spatulate and procumbent, relatively small i1, i1 longer than i2 and i3, i2 longer than i3; c1 procumbent and larger than adjacent teeth; p1 present, crown generally extended anteriorly, p3 can have one or two roots and is larger or equal in size to p2. Mandible relatively elongated, with coronoid process long and narrow to moderately wide, condyloid process elongated, angular process narrow and average to long.

As Ruedi et al. (1994) pointed out, the morphological distinction among the taxa of H. suillus was historically almost exclusively based on variations in colour, despite the apparently high craniodental geographically structured differentiation exhibited by this genus. In the following accounts, we unite these two lines of morphological evidence and diagnose the two species named by Müller (1840) and Robinson and Kloss (1916), give species-level recognition to three subspecies, provide emended diagnoses, and describe two new species. To facilitate taxonomic comparisons, we group sympatric or parapatric taxa based on their distribution (mainland Asia and Sumatra), and allopatric taxa, based on phylogenetic relatedness and geographical proximity (Sundaland clade).