Contribution to the knowledge of the Entactinaria radiolarian family Rhizosphaeridae Haeckel and description of some new genera and species

This paper is a contribution to the knowledge of the family Rhizosphaeridae. Based on the study of several Late Jurassic (early Tithonian), Paleocene, Miocene and Quaternary species, I tried to understand its evolution and to establish its taxonomic basis. Based on the structure of the microsphere, the family is divided into two subfamilies: Praerhizosphaerinae nov. subfam., represented by a single genus (Praerhizosphaera nov. gen.) of Late Jurassic age and Rhizosphaerinae Haeckel of Cenozoic age, represented by 3 genera: Haliommilla Haeckel, with single medullary shell, Rhizosphaera Haeckel, with double medullary shell, and Hexarhizacontium nov. gen., with equally double medullary shell but with only 6 radial interconnecting bars between the microsphere and the cortical shell. The latter structure appears to be the result of a horizontal gene transfer between a species of Haliommilla and a species of Hexacontium. No species was until present recorded in the Cretaceous sediments. Nine species are described as new, four of which from the early Tithonian and five other from the Cenozoic.