Rhabdophis, Fitzinger, 1843

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 : 12-14

Rhabdophis

Rhabdophis nuchalis (Boulenger) (CAS 242054; Figs. 7A and 8A ). Lobes intermediate in length between those of R. subminiatus (relatively longer) and R. tigrinus (shorter), asymmetrical (left lobe slightly shorter and narrower than the right); overall shape of the lobes fingerlike, narrower at the apex than basally. Lobes spinose all around except for their nude medial (crotch) surfaces and a narrow nude band extending all around the tip of each lobe. Sulcus extends straight to the sulcate edge of the crotch, where it bifurcates, each branch extending about three quarters of the way along the medial surface of its lobe in centripetal orientation; the tip of each branch is separated from the tip of the lobe by a narrow band of spines. At the division of the sulcus is a small depression or basin, which has a thin floor and a slight ridge delimiting its distal border in the crotch. The branches of the sulcus are broad and open, each with a distinct border formed by thick rounded ridges and bordered on each side by an expanse of nude tissue. These broad open sulcus branches are the “nude grooves” of Rossman & Eberle (1977). The grooves appear continuous with the single part of the sulcus at the crotch but the floor of the grooves is thicker; the single part has a translucent floor through which the injected colored jelly is easily seen, whereas the grooves have opaque floors ( Fig. 8A ). Grooves in R. nuchalis are slightly deeper and more distinct than in R. tigrinus .

Rhabdophis subminiatus (Schlegel) (CAS 206565; Figs. 7B and 8B ). Hemipenis bilobed, each lobe bulbous and rounded distally, slightly broader at the tip than at the base; left lobe seemingly very slightly shorter and smaller than the right. Lobes spinose but spinose areas of the lobes do not meet in the crotch. Short proximal single portion of the sulcus spermaticus extends to the sulcate edge of the crotch, where it divides. After division, each branch of the sulcus passes distally somewhat closer toward the medial surface of its lobe but the entire length of each branch is clearly visible from the sulcate side. Terminus of each branch is slightly expanded, the lips diverging at the edge of the lobe tip and extending a short distance, but ending short of the center of the lobe ( Fig. 8B ). Proximal to the crotch, the lips of the sulcus are thickened and rugose, with spines protruding through the thickened tissue. Another specimen of Rhabdophis subminiatus, CAS 233144, has a hemipenis similar to CAS 206565 but the sulcus lips diverge more gradually and the nude areas at the tips of the sulcus branches are less discrete.

Rhabdophis tigrinus (Boie) (CAS 166939; Fig. 7C ). Hemipenial lobes short, cylindrical, seemingly of the same length and width (symmetrical). Crotch and medial side of each lobe nude. Sulcus divides just proximal to the crotch, each branch extending centripetally to the edge of the tip of its lobe (spines cover the tip of each lobe). Branches of the sulcus are very shallow grooves just discernible against the nude tissue of the lobes, with a similar structure and thick floor as described above for R. nuchalis but without a distinct bounding ridge. At the point of bifurcation of the sulcus, the sulcus lips diverge greatly and extend a short distance along each lobe before being reduced and incorporated into the nude strips alongside the sulcus branches; distally, the sulcus groove itself remains distinct (though broad and open) within a broader nude area. The nude strips bordering the grooves are occupied by the bases of spines (visible through the translucent tissue), which are directed away from the grooves; under magnification this appears like a well defined part in a shock of hair, with the groove representing a part where hair (spines) was combed away on each side. The grooves are continuous with the undivided part of the sulcus spermaticus. (The short, closely appressed lobes prevented obtaining a photograph of the sulcus branches without severe distortion, but they are similar to those in R. nuchalis , Fig. 8A ).

In contrast to Rossman & Eberle (1977) I interpret the sulcus morphology of Rhabdophis tigrinus as bifurcate and the “nude grooves” (their terminology) extending partway up each lobe as true branches of the sulcus spermaticus. This interpretation, which agrees with Malnate (1960) and McDowell (1961; but not McDowell 1987: 40), seems clear through comparing the generalized sulcus morphology in R. subminiatus with those of R. nuchalis (more modified) and R. tigrinus (most modified). The broad, shallow, thickened grooves in the last two species are continuous with the proximal (single) part of the sulcus spermaticus and seem clearly to be modified sulcus branches. The overall hemipenial morphology and details of sulcus morphology of R. leonardi (Wall) (CAS 234494) are similar to R. tigrinus or R. nuchalis (with broad centripetal grooves extending nearly to the tips of the lobes).

An unusual feature of the hemipenis of Rhabdophis tigrinus , and to a lesser extent those of R. nuchalis and R. subminiatus , is that the distal half of the hemipenial body and the lobes (except for the nude medial portions) are covered by a reticulating network of ridges closely resembling calyces, which are taken up in the general discussion below (see Fig. 10A ). These ridges lack ornamentation (i.e., no evident spinules or papillae) but from the center of each ‘calyx’ protrudes a single spine (spines being the primary ornamentation of the entire hemipenial body). The calyx-like network is present also on the more proximal portions of the hemipenial body except that they become progressively less organized (sometimes appearing as longitudinal ridges rather than a network). These calyces are best developed on the lobes. In R. subminiatus and R. nuchalis these structures are not as well-developed (but they are better developed in R. nuchalis than in R. subminiatus , especially on the lobes). No other natricid hemipenes I examined have similar structures, although several have very fine low ridges among the spines.

Figures

FIGURE 7. Everted hemipenes of Rhabdophis in sulcate view. A, R. nuchalis (CAS 242054) (detail of apex shown in Fig. 8A). B, R. subminiatus (CAS 206565) (detail of apex shown in Fig. 8B). C, R. tigrinus (CAS 166939). The sulcus spermaticus in A and C passes to the crotch, where it divides and each branch passes centripetally up the medial face of its respective lobe. In B the sulcus spermaticus passes to the edge of the crotch, divides, and each branch then passes toward the tip of its respective lobe in a position mainly on the sulcate face of the lobe.

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 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.