Abstract
In the Gavrovo-Tripolitza zone of Greece, the «Faciès à imperforés indicates a peculiar back-reef to lagoonal sedimentation episode succeeding a bauxitogenous emersion. The foraminiferal association comprises several arenaceous conical taxa, a lot of miliolids, a species close to Praebullalveolina afyonica, various Peneroplis and/or Dendritina, Spirolina and Praerhapydionina species, scarce small Orbitolites and Rhabdorites malatyaensis. The similarity of this association with others from various parts of the Tethyan area gives evidence for a generalized regressive episode linked to the terminal Middle Eocene tectonic phase. From this association, presence of a new taxon is emphasized : Paraspirolina gigantea n. gen., n. sp. is characterized by an external aspect of a large Spirolina, a single dendritic terminal aperture and the very unusual association of external ribs with sub-epidermal partitions. Both of these last features appearing as independent adaptive devices related to algal symbiosis, their conjunction seems to characterized a singular evolutionary grade in a particular lineage. A single terminal aperture, together with a common tendency to develop an uniserial evolute rectilinear final part (PRU) seems to show a link between the new taxon, several Eocene soritids of the Old World, namely various Spirolina species (devoid of sub-epidermal partitions) and various species assigned to Praerhapydionina (with sub-epidermal partitions, one of them, P. huberi, being reported as ribbed); they are thought to constitute a natural group (a plexus or a sub-family).
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