Nectomys apicalis Peters, 1861

PATTON, JAMES L., DA SILVA, MARIA NAZARETH F. & MALCOLM, JAY R., 2000, Mammals Of The Rio Juruá And The Evolutionary And Ecological Diversification Of Amazonia, Bulletin of the American Museum of Natural History 2000 (244), pp. 1-306 : 116-118

Nectomys apicalis Peters, 1861

TYPE LOCALITY: ‘‘southwestern Ecuador, Guayaquil’ ’; restricted by Hershkovitz (1944: 53) to Tena, Provincia de Napo, Ecuador, altitude 512 m.

DESCRIPTION: This is a large­bodied rat with soft, moderately long, and glossy dark brown upperparts finely mixed with yellow and black, with a tendency for a darker middorsal region, paling down the sides, without demarcation, to a gray venter washed with buff. The tail is longer than the head and body, robust, furred at the base but otherwise appears naked along its length. However, three short, stout hairs are associated with each scale. These hairs become slightly longer towards the tip, which ends with a very slight pencil. The hindfeet are wedge­shaped with a narrow heel and a broad palm at the base of the toes; the toes are partly webbed, and the sides possess a fringe of silver hairs. The sole of the foot is uniquely covered by roundish appearing scales. Females have four pairs of mammae.

The skull is large and robust, with a relatively short and broad rostrum, diverging zygomatic arches, an elongated cranium, and a broad interorbital region with strongly developed supraorbital ridges diverging posteriorly and extending on the temporal region as distinct ridges (fig. 80). The zygomatic notches are deep and the zygomatic plate has a prominent anterior extension, when viewed from above. The interparietal is shallow and broad, with an average length/width ratio of 0.484 (range 0.414 –0.579) for those specimens from the Rio Juruá (table 26). There is no alisphenoid strut separating the buccinator­masticatory foramen from the foramen ovale acessorius. The stapedial foramen is tiny to absent, and there is no squamosalalisphenoid groove, or sphenofrontal foramen (cephalic arterial pattern 3; Voss, 1988 Carleton and Musser, 1989). The bullae are small and uninflated, the mesopterygoid fossa is broad and without sphenopalatine vacuities in its roof, the parapterygoid fossae are long and narrow but relatively deeply excavated. The diastema is long, with a short and somewhat teardrop­shaped incisive foramen that ends well in front of the first molar; the palate is deeply grooved and ends with large, deep, and complex posterior pits The teeth are pentalophodont with well­developed cusps and somewhat more highcrowned than relatives, such as Oryzomys The third molar is particularly large and complex.

SELECTED MEASUREMENTS: Means and ranges for selected external and cranial measurements of adult individuals of both sexes are summarized in table 27.

DISTRIBUTION AND HABITAT: Within the Rio Jurua´, specimens were taken only in the central portion of the river, at localities within the Upper and Lower Central Regions and at one minor locality between these regions (locality i). Given that the range of the genus comprises all of Amazonia (see Emmons and Feer, 1997), one can expect to find this species throughout the Juruá drainage. Specimens were obtained mostly along streams in undisturbed or second­growth forest, or in garden plots adjacent to such forest. At Altamira (locality 9), we caught Nectomys in second­growth edge along a small stream while Holochilus was taken in the dense grasses that bordered the river. At Penedo (locality 7), we found both genera in a relatively small patch of inundated dense grass inland from the river’s edge (fig. 7).

REPRODUCTION: All specimens from the Rio Juruá were taken during the dry season = ×2. in the months of August through November At this time, adult males were scrotal with enlarged testes and vesicular glands, adult females were either pregnant (one individual with 3 embryos) or lactating (one individual with 3 placental scars), or juveniles with unerupted or unworn third molars (four individuals).

KARYOTYPE: 2n = 42, FN = 40. We karyotyped four specimens, one from Condor (locality 6; JLP 15565), one from Jainu (locality 11; MNFS 793) and two from Barro Vermelho (locality 12; JLP 15891 and MNFS 795). All had completely acrocentric autosomal complements with acrocentric sex­chromosomes. This is the same karyotype as recorded by Gardner and Patton (1976) from Balta , on the Río Curanja , Departamento de Ucayali, in eastern Peru´ . Bonvicino et al. (1996) examined one of our specimens ( JLP 15565, Condor) and listed its diploid number as 52 ; this specimen is clearly 2n = 42, however.

COMMENTS: Nectomys is superficially similar to Holochilus , in size, in general color and color pattern, and in wedge­shaped and slightly webbed hind feet. Fieldworkers conducting mark­and­release studies need to be cognizant that both taxa can be trapped together, and that their superficial resemblance can lead to misidentification. However, Nectomys can be readily distinguished in the hand by its shorter, less sleek and darker dorsal fur, and grayer venter; the proportionately longer and more readily apparent scaled tail; and especially the granular scales on the soles of the hind feet.

SPECIMENS EXAMINED (n = 11): (6) 1m — JLP 15565; (f) 1 unknown — MNFS 525; (7) 2f — JLP 15505, 15514; (i) 1m — DMN 3; (9) 1m, 1f — JLP 15966, MNFS 892; (10) 1f — MNFS 867; (11) 1m — MNFS 793; (12) 2f — JLP 15891, MNFS 795.