MORPHOLOGICAL OBSERVATIONS OF NEIDIUM SPECIES WITH SAGITTATE APICES, INCLUDING THE DESCRIPTION OF N. CAPE-CODII SP. NOV.

Abstract

Nedium cape-codii Siver & Hamilton sp. nov. is described from a small glacial kettle lake situated on the Cape Cod peninsula, Massachusetts, U.S.A. Nedium cape-codii is a large diatom with slightly bowed margins, a single longitudinal canal along each valve margin and sagittate apices. Each areola is covered externally by volae and internally with a flat, thin, perforated hymen. In addition, small kidney bean-shaped structures, termed here renilimbi, are associated with specific rows of areolae on the internal valve surface. We also present SEM-based morphological descriptions of N. tokyoense Kobayasi, N. pseudogracilis Kobayasi and N. gracile Hustedt, the three species with sagittate apices morphologically most similar to N. cape-codii, from either type material or new material collected from the type localities. The relationships of N. cape-codii to other species with sagittate apices are also discussed.