Evolutionary trends of the pliocene silicoflagellate group Dictyocha fibula from Marathitis section, central Crete (Greece)

Abstract

A rich opal phytoplankton assemblage of Upper Zanclean to Lower Piacenzian age, containing diatoms and silicoflagellates, occurs in finely laminated diatomite beds in the north-central part of the Island of Crete (Marathitis section, Heraklion District, Greece). We are here mainly concerned with the stratigraphic distribution and evolutionary trends of the Dictyocha fibula silicoflagellates group. In addition to the two well established subspecies Dictyocha fibula ausonia ( Deflandre) and Dictyocha fibula mutabilis ( Deflandre), identified in our material, two new species/subspecies — Dictyocha hellenica n.sp. and D. fibula minos n.subsp.— are here described for the first time. Their distinction is also supported by a statistical analysis of morphometric data concerning the length (L) and width (W) of the inner diameter of both the major and minor axes, the L/W ratio, radius of curvature (Cr) and lateral portal diameter (dlp) of these taxons.