Boiruna and

Scott Jr., Norman J., Giraudo, Alejandro R., Scrocchi, Gustavo, Aquino, Aida Luz, Cacciali, Pier & Motte, Martha, 2006, THE GENERA BOIRUNA AND CLELIA (SERPENTES: PSEUDOBOINI) IN PARAGUAY AND ARGENTINA, Papéis Avulsos de Zoologia (São Paulo) 46 (9), pp. 77-105 : 78-79

Boiruna and Clelia

Boiruna and Clelia are small to large snakes-the smallest species is generally less than 1 m ( C. bicolor ), and the largest approach 2.5 m in total length ( C. clelia , C. plumbea ). The larger species, well-known by the Brazilian common name of mussurana, are famous for consuming even large venomous Crotalus and Bothrops .

Most species have the normal configuration of colubrid scales. Diagnostic variation occurs in the number of body segments (reflected in ventral and subcaudal scale counts), and in the relative length of the snout, as seen in differing numbers of supralabials and in the varying proportions and positions of the loreal scale. There are two anterior temporals on each side of the head, the lower of which may or may not contact the postoculars. Species in the genera may have 17 or 19 midbody scale rows, but all of the species in the study area have 19. Dorsal scales are smooth, many with one or (usually) two apical pits ( Underwood, 1993).

The species of Clelia and Boiruna generally show a striking ontogenetic color change, from hatchlings with much orange or red to adults that are dark gray or black. In our area, Clelia rustica is the only exception; hatchlings may have a trace of a light collar, but otherwise are colored like the adults, which usually have a ground color of some shade of olive.

The hemipenes of the species of Boiruna and Clelia have a similar shape: a long basal portion that divides distally into two equal lobes. The single basal portion is 2-3 times the length of the terminal lobes. The lobes terminate in calyculate capitula. The sulcus spermaticus, basally single, divides into two branches at about the middle of the organ, each branch terminating in a separate lobe. The hemipenes may have large spines or enlarged spines may be lacking ( Zaher, 1996, 1999).

Study Area

The study area lies between the Tropic of Capricorn and cold temperate Patagonia. The northern portion west of the Río Paraná-Paraguay is generally dry Andean foothills, intermontane Monte desert valleys, or Chaco. The latter refers to the geological formation formed by the flat outwash plain of Andean erosion. Undisturbed vegetation in the Dry Chaco is thorn forest; the Humid Chaco is palm savannah subject to seasonal flooding from large rivers, with islands of thorn forest ( Cabrera, 1994). Much of the Humid Chaco has been cleared for cattle grazing .

East of the Río Paraná-Paraguay , the land is uplifted a few hundred meters above the level of the Chaco to produce rolling hills and broad river valleys originally covered with mesic, subtropical, semideciduous forest grading into wet Interior Atlantic Forest on the eastern margin. These forests have been greatly decimated, and only isolated remnants persist. An even west to east rainfall gradient in the study area (400 to 1700 mm /yr) produces deserts in the west and wet tall forests on the eastern margin .

In Argentina south of the mouth of the Río Paraná/ Río de La Plata , the native vegetation of the western Andean foothills grades into the eastern temperate Pampas grasslands or Patagonian shrublands in the extreme south.

We use the following nomenclature for the different reaches of the Paraná River ( Giraudo & Arzamendia, 2004): Alto Paraná above Posadas, Misiones Province, Argentina, Upper Paraná between Posadas and the junction with the Paraguay River, and Lower Paraná below this point.