Nerodia

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 : 11

Nerodia

Nerodia erythrogaster (Catesby) (CAS 237700; Fig. 6 ). Hemipenis T-shaped, the crossbar of the T very broad, robust. Entire distal surface of the hemipenis and most of sulcate and asulcate sides of the crossbar nude. Sulcus spermaticus extending up the middle of the sulcate side and seemingly simple, but with an odd terminating basin and ridges within the nude area. The distal end of the sulcus is expanded into an oblong diamond-shaped basin, the distal part of which is bounded completely a thick fleshy border (proximal part bounded by the divergent sulcus lips). Within the nude area is a pair of large oval depressions, one on each side of the terminus of the sulcus, which extend laterally and distally to the edge of the apex; the depression on the right side is easily seen in Fig. 6B . Nude area lacks a distinct border; set off only by presence of very tiny spines all around (spines are very small compared to other natricid hemipenes examined).

I interpret the apparent simple condition of the sulcus spermaticus as a secondary modification of a sulcus primarily characterized by widely divergent sulcus lips. Close inspection ( Fig. 6B ) reveals that the sulcus lips begin to diverge within the spinose part of the hemipenial body well proximal to the nude region; at the edge of the nude area the lips diverge abruptly laterally, similar to the condition in Amphiesma stolatum described above. Furthermore, the sulcus terminus enclosed by a bounding ridge is very unusual. In typical simple sulci spermatici the sulcus lips simply fade out at the tip, leaving the sulcus groove opening onto the apex without any boundary (see, for example, Fig. 11 ). Nerodia erythrogaster shows the condition seen in other natricids with widely divergent sulcus lips leading to an apical nude area (such as Amphiesma stolatum or Xenochrophis cerasogaster ), with the addition of a novel sulcus terminus comprising a basin and bounding ridge within the nude area. I interpret these last features as added evolutionary novelties. Thus, the sulcus of Nerodia erythrogaster is not a classically simple sulcus, as often interpreted (e.g., Dowling & Savage 1960: Fig. 4D ; Rossman & Eberle 1977). Whether this characterizes other Thamnophiini or a more restricted taxon set needs study.

Figures

FIGURE 4. Everted hemipenes of natricids in sulcate view. A, Afronatrix anoscopus (CAS 230205). B, Amphiesma bitaeniatum (CAS 215037) (detail of apex shown in Fig. 5A). C, Natrix tessellata (CAS 183115) (detail of apex shown in Fig. 5D).

FIGURE 6. Everted hemipenis of Nerodia erythrogaster (CAS 237700). A, sulcate view of the organ. B, detail of the point at which the sulcus reaches the nude apex showing the diamond-shaped basin bordered by ridges.

FIGURE 11. Everted hemipenes of Salvadora in sulcate views. A, S. hexalepis (CAS 190805). B, S. grahamiae (CAS 190878). C, apical tip of S. hexalepis. D, apical tip of S. grahamiae. Arrows in C and D indicate the tip of the sulcus spermaticus.