Thalassiosira fryxelliae nov. spec. (Bacillariophyceae) from Argentinian coastal waters

Abstract

The new marine nanoplanktonic diatom, Thalassiosira fryxelliae, is described with light and scanning electron microscopy from material collected in Argentinian coastal waters. T. fryxelliae is a morphologically distinctive species with: 1) cells embedded in irregular gelatinous masses, 2) absence of central, sub-central and scattered strutted processes on the valve surface, 3) one marginal ring of strutted processes with external tubes, 4) one marginal labiate process included in the ring of the strutted processes, 5) areolation pattern variable linear, sublinear, eccentric or irregular. Externally, the marginal strutted processes have double tubes, at least in the distal part, cut distally and with the half-cylinder bent vertically with crenulated distal edges and the labiate process has a simple tube. Internally, the strutted processes are short with four operculate satellite pores and the labiate process is sessile and radially located. Thalassiosira fryxelliae is similar to T. angulata and T. nanolineata in morphology and distribution pattern of the marginal strutted processes and in the location of the labiate process and to T. leptopus and some specimens of T. guillardii and T. pseudonana in lacking one central strutted process.