Chironectes minimus (Zimmermann)

VOSS, ROBERT S., LUNDE, DARRIN P. & SIMMONS, NANCY B., 2001, The Mammals Of Paracou, French Guiana: A Neotropical Lowland Rainforest Fauna Part 2. Nonvolant Species, Bulletin of the American Museum of Natural History 2001 (263), pp. 1-236 : 20-23

Chironectes minimus (Zimmermann)

VOUCHER MATERIAL: AMNH 266477 , 266478 ; MNHN 1998.672 . Total = 3 specimens .

IDENTIFICATION: Our voucher material conforms closely to most published descriptions of this widespread and distinctive species (e.g., Thomas, 1888; Cabrera, 1919; Krumbiegel, 1940a; Augustiny, 1942; Mondolfi and Medina, 1957; Husson, 1978; Marshall, 1978b; Emmons, 1990, 1997), but a few discrepancies and supplementary observations merit comment. Persistent references (op. cit.) to brownish and yellowish tints in the pelage of Chironectes minimus are probably based on old (faded or stained) museum skins; living animals and fresh skins have clear black­and­gray dorsal markings and pure white venters, with no trace of other hues. According to Cabrera (1919), the digits of the manus are webbed to the ends of the first phalanges, but our specimens (and those illustrated by Augustiny [1942: fig. 14] and Mondolfi and Medina [1957: fig. 1]) have unwebbed manual digits. The ‘‘supernumerary facial bristles’’ mentioned by Marshall (1978b) are the usual superciliary, genal, and interramal vibrissae (Brown, 1971), which are well developed (Augustiny, 1942: fig. 11) but otherwise unremarkable in C. minimus . Apparently, the only postcranial vibrissae in this species consist of a prominent tuft of long carpal hairs at the wrist.

Our only adult voucher (AMNH 266477), an old male, had external measurements of 286 Χ 345 Χ 63 Χ 31 mm and weighed 620 g. Selected craniodental measurements of this specimen fall within the known range of morphometric variation for the species (Marshall, 1978b): condylobasal length, 65.7 mm; length of molars, 14.5 mm; palatal breadth, 23.5 mm; palatal length, 42.7 mm; least interorbital breadth, 13.1 mm; least postorbital breadth, 8.4 mm; zygomatic breadth, 39.0 mm; length of nasals, 31.8 mm. Both of our other vouchers are juveniles.

REMARKS: Lutra minima Zimmermann (1780) was based on Buffon’s (1776) description of the ‘‘petite loutre d’eau douce de Cayenne’’, so our specimens are practically topotypes. Krumbiegel (1940a) and Marshall (1978b) both recognized four subspecies, but the necessity for a trinomial nomenclature for water opossums has yet to be demonstrat­ ed by any substantive analysis of character data. In the event that any subspecific distinctions are warranted, the Paracou population would obviously be referable to the nominate form.

FIELD OBSERVATIONS: Water opossums were commonly seen in all of the four named stream systems that have their headwaters in our study area; even the smallest and shallowest creeks were frequented (fig. 9). Because this species has bright eyeshine, is boldly marked, and splashes noisily while swimming or wading, it is not difficult to observe despite its nocturnal habits. Nevertheless, the occurrence of Chironectes at Paracou was previously unsuspected by the forestry workers and local hunters whom we interviewed.

One of our three vouchers was taken in a large (ca. 25 Χ 30 Χ 81 cm) wire live trap set in a small (ca. 2 m wide) shallow (ca. 15 cm deep) stream in primary forest; the trap was unbaited, but rows of stakes were driven unto the streambed on either side to funnel animals moving downstream into the trap opening. The other two vouchers were collected by shooting. In addition, we recorded 23 unvouchered observations of water opossums, of which 2 were based on juveniles trapped in small (145 Χ 145 Χ 410 mm) wire live traps set in streams, and 21 were sightings of free­ranging individuals.

All of our 26 (vouchered and unvouchered) records of water opossums at Paracou were of animals trapped or sighted while they waded or swam in primary forest streams at night. Most free­ranging individuals alarmed by our presence quickly swam away, but two animals left the water and disappeared in dense streamside vegetation, and another entered a burrow near the water’s edge. With the exception of a pair of animals apparently engaged in an aggressive interaction, all of our sightings were of solitary individuals.