XENODONTINAE, Bonaparte, 1845

Myers, Charles W., 2011, A New Genus and New Tribe for Enicognathus melanauchen Jan, 1863, a Neglected South American Snake (Colubridae: Xenodontinae), with Taxonomic Notes on Some Dipsadinae, American Museum Novitates 2011 (3715), pp. 1-36 : 18-20

XENODONTINAE

An undivided sulcus spermaticus is unknown in the South American “xenodontine” clade except in one species of Taeniophallus , as reported by Myers and Cadle (1994). Zaher (1999: 97) assigned Taeniophallus to Dipsadinae incertae sedis, but limited molecular data suggest that Taeniophallus brevirostris and T. occipitalis ( Cadle, 1984b, under “ Rhadinaea ”), and T. nicagus (Vidal et al., 2000, as “ Taeniophallus brevirostris ” 12) belong with Xenodontinae sensu stricto. This placement has now been corroborated by Zaher et al. (2009: 125, 144), based on mitochondrial data from T. affinis and T. brevirostris . 13 The generic name Taeniophallus ( Cope, 1895) was resurrected by Myers and Cadle (1994: 4), who included seven species that later were distributed by Schargel et al. (2005: 14–16) among three groups for discussion: (1) Taeniophallus brevirostris and T. nicagus ; (2) T. occipitalis ; (3) T. affinis group. Schargel et al. (2005) also added an eighth species—the enigmatic new T. nebularis —which arguably is related to T. brevirostris and T. nicagus . And the monotypic T. occipitalis group was enlarged with addition of the new T. quadriocellatus by Santos-Jr. et al. (2008); this species is close to occipitalis , with which it shares the diagnostic large median spine in the interspinal gap on the asulcate side of the hemipenis. These nine species constitute Taeniophallus sensu lato, for which there is no explicit evidence of monophyly. The first two groups comprise Taeniophallus sensu stricto ( nicagus is the generic type species). Amnesteophis is appropriately compared with Taeniophallus sensu stricto following the lead of Jan himself. In a key to the old snake genus Enicognathus , 14 Jan (1863a: 266; 1863b: 56) paired “ E. ” melanauchen with “ E. ” occipitalis , and Jan and Sordelli illustrated both species together (reproduced herein as fig. 6 ). Both are characterized by 15 rows of dorsal scales and have somewhat similar color patterns, or at least similar enough for Amaral (1929b [1930]: 173; 1936: 115) to suggest that “ Liophis ” melanauchen was based on an anomalous example of “ L.” [ Taeniophallus ] occipitalis . The hemipenis of T. occipitalis shares with Amnesteophis the characters of weak bilobation (some specimens) and large flaplike papillae (on asulcate side of

12 Based on voucher specimen MNHN 1996.4240 from French Guiana (not examined).

13 Zaher et al. (2009: 144) assigned Taeniophallus and Echinanthera (molecular data not available for the last) to their new tribe Echinantherini , but the tribal diagnosis is unsatisfactory on several points. (1) The “unilobed” hemipenis actually is distinctly bilobed in T. nebularis and weakly bilobed in some T. occipitalis . (2) The sulcus spermaticus does not divide “relatively distally, within the calyculate region,” but divides roughly halfway up the organ at the base of, or slightly below, the calyculate region; also it should be noted that the sulcus is unforked in the type species of Taeniophallus ( nicagus ). (3) The “large nude region present on asulcate side of the hemipenial body” refers to the asulcate interspinal gap, which is distinctly nude only in a few species (e.g., T. nebularis ). Although often distinctly expanded on everted organs, the interspinal gap usually bears a median line of tiny spines or spinelike papillae in the T. affinis group and some Echinanthera ; there is a very large median spine interrupting the gap in T. occipitalis and the related T. quadriocellatus ); there is no interspinal gap in T. nicagus and T. brevirostris , in which the asulcate side is spinose. See Schargel et al. (2005) for some illustrations.

14 Enicognathus Duméril et al. (1854: 328) is a junior homonym of the avian genus Enicognathus Gray (1840: 51) . The homonymous emendations Henicognathus were proposed by Agassiz (1846: 138, 178) and Cope (1868: 132) for the bird and snake names, respectively. The derivations are Gk. Enico- / Henic- (“single” or

“singular”) + Gk. gnathos (“jaw”).

capitulum). The occipitalis hemipenis otherwise is very different from that of Amnesteophis , since it has a calyculate capitulum, a deeply bifurcate sulcus, and a distinctive arrangement of spines (compare fig. 5 with Myers, 1974, fig. 47B, and Schargel et al., 2005, fig. 9D). Taeniophallus occipitalis seems to be related to T. brevirostris based on a few pertinent similarities (Myers, 1974: 211, and Schargel et al., 2005: 15). A close relationship between T. brevirostris and the partly sympatric T. nicagus is inferred from remarkable resemblances in color pattern, external morphology, and condition of the sulcus spermaticus (Myers and Cadle, 1994: 4–6; Myers and Cadle, unpubl.). The everted hemipenes of brevirostris and nicagus are compared in Schargel et al. (2005: fig. 8 ). The former is highly unusual among “xenodontines” in having one branch of the sulcus spermaticus noticeably shorter than the other branch, a condition also occurring in the two species of the North American Rhadinaea flavilata group (Myers, 1974: 49). I earlier suggested that shortening of a single branch was one way of evolving a simple sulcus spermaticus, which appears to have happened in Taeniophallus nicagus , in which there is no sign of a fork.

Nonetheless, except for the simple sulcus, the calyculate hemipenis of Taeniophallus nicagus is very different from the acalyculate Amnesteophis organ, which is ornamented with small spines proximally and flat papillae distally, with the sulcus extending past a nude area and onto one lobe in centripetal orientation.

Figures

FIG. 6. Portion of plate 1, livraison 16, in the Iconographie générale des ophidiens (Jan and Sordelli, 1866 [1860–1881]), shown 0.77× original folio size. 1. Syntype of Enicognathus occipitalis Jan 1863, now = Taeniophallus occipitalis. 2. Holotype of Enicognathus melanauchen Jan 1863, type species of Amnesteophis as proposed herein (see also figs. 1–3 and text for comments on faded color pattern).

FIG. 5. Hemipenis of Amnesteophis melanauchen (Jan 1863). Manually everted left organ of holotype of Enicognathus melanauchen, in sulcate (left), apical (top), and asulcate (right) views. (Basal half of organ is split and spread flat; the inflated distal half is fully everted but probably not maximally expanded.) The basally spinulate hemipenis is mostly spinose (spines emphasized by stippling); the spines are replaced on the small lobes by larger, soft flat- tened papillae; the unforked sulcus spermaticus extends centripetally to apex of the left lobe (sinistral sulcus) without entering a nude area in the lobular crotch; calyces are lacking (scale line = 1 mm).

FIG. 8. Examples of field-everted hemipenes showing diminution (A) or loss (B–C) of distal forks after expansion of capitulum. Pliable tissue separating the sulcus branches before eversion is stretched flat in B and C. (Scale line = 1 mm.) A. Leptodeira annulata cussiliris (AMNH R-107291, right organ); fork slightly widened (cf., fig. 7B), with very short branch terminations concealed in calyces. B. Leptodeira annulata annulata (AMNH R-133340, right organ); a pronounced fork on field-everted organ expanded into this shape after softening in KOH and injection with petroleum jelly (shape is triangular, the heart-shaped appearance imparted by overhanging calyces at top). C. Leptodeira maculata (AMNH R-82150, right organ), showing extreme flattening and loss of terminal fork.