OBSERVATIONS ON THE FRUSTULE ARCHITECTURE OF MASTOGLOIA SMITHU, WITH PARTICULAR REFERENCE TO THE VALVOCOPULAE AND ITS INTEGRATION WITH THE VALVE

Abstract

Frustules of Mastogloia smithii from the Rabenhorst collection were studied in light and scanning electron microscopy. The valvocopula is composed of three elements: the band-like pars exterior, the septum, and the partectal ring, which contains a porous intrapartectal cylinder similar to that of Mastogloia grevillei and M. lanceolata. Pseudopartecta are interposed between the partectal ring and the apices of the septum; these are structures that bear an external resemblance to the partecta but apparently lack siliceous partitions. An undulate siliceous crest runs around the advalvar face of the partectal ring and seems to account for the integration between the valvocopula and the lateral margins of the valve mantle. Evidence is given of additional integration, in the form of a “tongue and groove” interaction between the septum and the pseudoseptum present inside the valve apices.