ECHINOCEPHALUS-JANZENI N. SP. (NEMATODA, GNATHOSTOMATIDAE) IN HIMANTURA-PACIFICA (CHONDRICHTHYES, MYLIOBATIFORMES) FROM THE PACIFIC COAST OF COSTA-RICA AND MEXICO, WITH HISTORICAL BIOGEOGRAPHIC ANALYSIS OF THEGENUS

Echinocephalus janzeni n. sp. in the stingray, Himantura pacifica, is described from the eastern Pacific Ocean off the coasts of Costa Rica and southern Mexico. On the basis of the presence of 6 postanal caudal papillae, and modified annules anterior to the caudal alae in males, E. janzeni is most similar to Echinocephalus daileyi and Echinocephalu s diazi. Specimens of E. janzeni are distinguished from those of E. di aleyi by bilobed caudal alae and long cervical sacs that extend up to 65% of the length of the esophagus; E. janzeni is differentiated from E. diazi by the number of rows of cephalic spines (30-38 vs. 26-27), a rrangement of the postanal caudal papillae, 3 rather than 2 preanal pa pillae, relative position and distance between the anus and vulva (395 -460 mu m vs. 70 mu m), the digitiform female tail with a terminal cut icular fold, and the length of the female tail (450-480 mu m vs. 270 m u m). Cladistic analysis of the 10 Echinocephalus spp. resulted in a s ingle most parsimonious tree (consistency index = 0.893) and placed E. janzeni in a highly derived subclade where E. daileyi is the sister s pecies of E. diazi + E. janzeni. Historical biogeographic analysis of hosts and parasites provides support for origins in the Pacific rather than the Atlantic for the potamotrygonid stingrays.