Achnanthidium chitrakootense spec. nov. from rivers of Northern and Central India

Abstract

The group of diatoms morphologically similar to Achnanthidium pyrenaicum (Hustedt) Kobayasi includes a number of ecologically important taxa. The restricted distribution patterns of some Achnanthidium Kutzing species have become more obvious after detailed studies of this relatively small group. It has been characterized as having terminal raphe fi ssures curved to the same side, slit-like external areola openings, and internal hymenate areola occlusions. Unlike the rest of Achnanthidium, the new species A. chitrakootense possesses areola occlusions of an unusual type. It is also characterized by a raphe with ter- minals externally curved towards the same side of the valve, crossing the hyaline rim between the valve face and valve mantle, and internally undulate raphe terminals. The new member of the Achnanthidium pyrenaicum group is described from rivers of northern and central India. The species is documented with LM and SEM micrographs, and the frustule morphology of this species and similar taxa is compared and briefl y discussed.