IUCN threat status:

Endangered (EN)

Comprehensive Description

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Description

This is a large, sexually dimorphic species; adult standard length averages 26.3 mm in nine males (range 21.7-29.7) and 28.5 mm in 16 females (range 25.2-31.9). The head is relatively narrow; SL averages 8.0 times head width in males (range 7.1-8.3) and 8.3 times head width in females (range 7.6-9.4). Snout is bluntly pointed. Nostril shape is highly variable; the mean ratio of major axis to minor axis is 1.6 in males (range 1.3-2.0) and 1.5 in females (range 1.2-2.7). There appears to be an ontogenetic shift in nostril size and shape; most large adults have a small, comma-shaped nostril, whereas many smaller individuals have a relatively large, oval nostril. Large males with well developed mental glands have a swollen upper lip and enlarged nasolabial protuberances. Eyes are small; they either do not or just barely reach the margin of the jaw in dorsal view. A suborbital groove intersects the lip on each side of the head. There are 2-3 premaxillary teeth in males (mean 2.2) and 1-4 in females (mean 2.1). Vomerine teeth average 13.0 in males (range 10-16) and 9.9 in females (range 7-17). There are no maxillary teeth. Limbs are moderately long; limb interval averages 4.6 in males (range 4-5) and 5.3 in females (range 4-6). Hands and feet are relatively large with well demarcated digits. Only the two longest fingers and three longest toes are free at their tips, which are rounded rather than pointed in adults. Fingers, in order of decreasing length, are 3-2-4-1; toes are 3-(2-4)-1-5. There are marked subdigital pads on digits 2-4; they are also evident on digits 1 and 5 of the largest specimens. The tail is relatively long and exceeds standard length in most specimens; mean SL divided by tail length equals 0.89 in males (range 0.75-1.07) and 0.88 in females (range 0.66-1.52). The mental gland is white; the postiliac gland is visible.

Overall coloration is very dark. A dark-brown to brownish-tan dorsal band is conspicuous on some specimens but obscure on others. Many specimens have white flecks limited to the gular region; some have additional faint, tiny white spots on the snout, limbs, and, rarely, the venter. The iris is blackish brown.Based on field notes by J. Hanken for MVZ 183279-310 and 186963-79 (Texmola): some specimens display the dorsal stripe characteristic of Thorius, but others are almost completely dark above and below. For MVZ 185403-18 and 187103 (Xometla): faint, brassy dorsal stripe; faint whitish speckling on dark venter; no lateral flecking. D. B. Wake (2 April 1970) also noted two color morphs of this species at Xometla: one very dark dorsally and ventrally, with brassy iridophores that form an indistinct dorsal stripe; the second with a brown stripe and a uniformly black belly (Hanken and Wake 1998).

Etymology. The species name is a conjunction of two Latin words, lunaris (crescent-shaped) and naris (nostril), in reference to the distinctive and characteristic nostril shape (Hanken and Wake 1998).

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