EVOLUTION OF THE RADIOLARIAN SPECIES-COMPLEX PTEROCANIUM: A PRELIMINARY SURVEY

A global taxonomic and biometric study of the radiolarian genus Pterocanium defines 5 major lineages over the last 6 million years: Pterocanium charybdeum, P. praetextum, P. korot- nevi, P. prismatium, and P. audax. P. charybdeum is divided into 4 subspecies: P. charybdeum charybdeum (n. comb.), P. charybdeum trilobum (n. comb.), P. charybdeum grandiporus (n. comb.), and P. charybdeum allium (n. subsp.). Sympatric or parapatric speciation of P. prismatium and P. praetextum from ancestral P. cha- rybdeum was observed over a one-half million year interval in the latest Miocene and early Pliocene. Measurements of thoracic dimensions and qualitative observations suggest substantial, gradual phyletic evolution in the 5 lineages studied. Morphological intermediates between formerly distinct lineages were observed and suggest the possibility of hybridization and reticulate evolution in Pterocanium.