SEQUENTIAL VALVE DEVELOPMENT IN THE MONORAPHID DIATOMACHNANTHES MINUTISSIMAVAR.SAPROPHILA

Abstract

Valve development has been examined in Achnanthes minutissima var. saprophila H. Kobayasi & Mayama. The formation of the raphid valve (RV) proceeds in the same sequence as has previously been described for Navicula. Early development of the araphid yalve (AV) is remarkably similar to that of the RV, in that a primary central rib and primordial central nodule are initiated, followed by the development of secondary arms from the centre and the recurring of the primary rib at the poles. Therefore raphe slits appear both at the centre and poles during the early development of the AV. However, thin fin-like depositions arise along the primary central rib between the secondary arms extending out from the centre and the centripetal extensions of the primary central rib recurring from the poles. The fins then fuse with the secondary arms and the in-turned primary central rib, so that the initially-formed raphe slits do not develop any further and are filled in: an axial area devoid of a raphe is thus formed. The ...