PSEUDOPODOSIRA KOSUGII: A NEW HOLOCENE DIATOM FOUND TO BE A USEFUL INDICATOR TO IDENTIFY FORMER SEA-LEVELS

Abstract

A heavily silicified sub-spherical diatom occurring abundantly close to the upper limits of marine facies in the sedimentary sequences recording a Holocene transgression is named and described; Pseudopodosira kosugii sp. nov. Observations on this form in a recent habitat and growing in cultures show that it grows vegetatively by normal cell division, although its thick spiny hemispherical valves in the Holocene sequences are suggestive of resting spore valves rather than valves of vegetative cells. Variation in frustule morphology is revealed and discussed. This new species is highly variable in morphology, and a pair of watch-glass shaped spiny valves is the most common combination of vegetative cells. Its peak abundances being close to marine limits have made the species a useful indicator of the former sea-level during the Holocene.