Xenochrophis

Cadle, John E., 2011, Hemipenial morphology in the North American snake genus Phyllorhynchus (Serpentes: Colubridae), with a review of and comparisons with natricid hemipenes, Zootaxa 3092 (1), pp. 1-25 : 14-15

Xenochrophis

Xenochrophis cerasogaster (Cantor) (CAS 245195; Figs. 8C , 9A , 10B ). Hemipenis bilobed, the lobes relatively short and narrow; the left lobe slightly shorter and narrower than the right. A pair of large rounded basal lobes, one on each side of the sulcus spermaticus, is present on the proximal half of the hemipenial body. Sulcus spermaticus extends in centrolineal position to the sulcate edge of the crotch, where the sulcus lips diverge abruptly, the sulcus groove at this point broadening and extending laterally along the sulcate base of each lobe. These broad grooves shortly turn distad, broadening still further and forming a nude area extending up the sulcate face of each lobe to the edge of the tip (tip itself is spinose). Each divergent sulcus lip extends about half way up the proximal edge of its respective nude area, then peters out. The expanded sulcus groove in the crotch and its extensions along the lobes have no definitive border comparable to the divergent sulcus lips along the proximal edges of the groove. At the point of sulcus division in the crotch is a squarish nude area but otherwise the crotch is spinose (medial surfaces of lobes are spinose with the spines continuous across the asulcate side of the crotch between the lobes). The nude area on the right lobe of the organ bears a peculiar pocket, which is described more fully in the next section. Spines on the hemipenial body are recessed in small depressions, with the intervening tissue somewhat rugose.

Xenochrophis flavipunctatus (Hallowell) (CAS 210529; Fig. 9B ). Hemipenis with short bulbous lobes, more or less equal in size. Sulcus spermaticus extends up the middle of the sulcate surface of the hemipenial body to the crotch, where it divides; the branches thence extend in centripetal position to the distal tips of the lobes (toward to the tips of the lobes is a gradual curve toward the sulcate side). The entire sulcus, including the branches, is typical in form (no divergent lips or nude areas). Very narrow nude strips alongside the sulcus up to its point of division (these strips appear to be the lips of the sulcus, though not so thickened as in some snakes). Spines occupy elongate lobes or ridges alongside these nude strips.

Considerable morphological differences distinguish the hemipenes of Xenochrophis flavipunctatus and X. piscator (described immediately below; see Figs. 9B–C ), confirming that the two species are not synonymous. Zug et al. (2006) documented that the two differ in color patterns and scale counts despite a long history of confusion. Dissection of one side of the contralateral everted organ of CAS 210529 confirmed that no small “nipple” remained inverted at the lobe tips. Thus, the apical morphology of this species is quite distinct from the other Xenochrophis hemipenes examined.

Xenochrophis piscator (Schneider) (CAS 208428; Figs. 8D and 9C ). Hemipenis bilobed, lobes bulbous at the base but with long narrow ‘nipples’ at their tips (left nipple seemingly slightly longer but narrower than the right). Sulcus extends distally up the middle of the sulcate surface of the hemipenial body to a point in the crotch (closer to the sulcate than the asulcate side), where it divides. The branches extend in centripetal position up the medial face of each lobe but quickly curve abruptly toward the sulcate side. At the junction of the bulbous part of the lobes and the nipple the sulcus branches abruptly turn distad and extend further along the sulcate face of each nipple. At this final turn (at base of the nipples) each sulcus branch also abruptly widens (lips diverge), forming a broad nude area extending to the tip of each nipple (arrow in Fig 8D ); there are a few tiny spines on the otherwise nude tip of each nipple. This nude area seems clearly to be the floor of a greatly broadened sulcus spermaticus (the lips of each branch peter out abruptly soon after they diverge and the nude area has no distinct flanking borders). All other parts of the lobes are spinose. The hemipenis of Xenochrophis punctulatus (Günther) (CAS 211966) is similar in form and sulcus morphology to that of X. piscator except the “nipples” are shorter; the sulcus branches show a similar orientation on the sulcate face of lobes, where there is a small nude area. Some variability in the size of the nude area is suggested by another specimen of X. punctulatus, CAS 240075, in which the nude area is much smaller and narrower than in CAS 211966.

This characterization of the sulcus and apical morphology of Xenochrophis piscator differs from previous accounts. Rossman & Eberle (1977) stated that the sulcus in X. piscator was centripetal and neither they nor McDowell (1987: 40) mentioned the sulcate nude areas on the narrow part (“nipples”) of each lobe ( Fig. 8D ). While it is true that the sulcus is centripetal just after its point of division, the sulcus quickly reorients to the sulcate surface and thence extends distad (as in X. cerasogaster and X. punctulatus ). It is also clear (contra Zaher 1999: 32) that some Xenochrophis ( X. cerasogaster , X. piscator , X. punctulatus ) do develop apical nude areas but their orientation is on the sulcate (rather than medial) surfaces of the lobes. This morphology seems not to have been explicitly articulated for any natricids. It remains possible that some differences in interpretation could be due to unassessed variation in hemipenial morphology, as indicated by the variable size of the nude areas mentioned above for X. punctulatus .

Figures

FIGURE 8. Details of apical morphology of Rhabdophis and Xenochrophis hemipenes. A, Rhabdophis nuchalis (CAS 242054), crotch and medial surface of the right lobe showing broad sulcus groove within a nude expanse. B, Rhabdophis subminiatus (CAS 206565), tip of the right lobe showing divergence of the sulcus lips to form a small nude area. C, Xenochrophis cerasogaster (CAS 245195), left lobe, sulcate surface showing expansion of the sulcus spermaticus to form a nude surface. D, Xenochrophis piscator (CAS 208428), sulcate surface of the right lobe showing divergence of the sulcus lips to form a nude strip covering virtually the entire sulcate surface of the narrow part (“nipple”) of the lobe (the nipple is somewhat twisted). Arrow indicates the point at which the sulcus lips diverge.

FIGURE 9. Everted hemipenes of Xenochrophis in sulcate view. A, X. cerasogaster (CAS 245195) (detail of apex shown in Figs. 8C, 10B). B, X. flavipunctatus (CAS 210529). C, X. piscator (CAS 208428) (detail of apex shown in Fig. 8D). The right lobe in A is twisted to the right; the typical position is shown by the left lobe, in which the sulcus forms a broad nude area on the sulcate face of the lobe. A similar sulcus and lobe morphology is exhibited in C; again, the lobes are somewhat twisted. In B the sulcus spermaticus passes to the crotch between the lobes, where it divides and each branch passes centripetally up the medial face of its respective lobe.

FIGURE 10. Details of natricid apical morphology. A, Rhabdophis tigrinus (CAS 166939) showing well developed calyces on the lobes. Although not clear in this photo, each calyx has a single spine protruding from its center. B, Xenochrophis cerasogaster (CAS 245195), right lobe showing pocket at the distal end of the nude area (shadowed paraboloid area). The nude area is on the sulcate face of the lobe (right lobe twisted laterally); compare Figs. 8C and 9A.