Gyrosigma orbitum sp nov (Bacillariophyta) from a salt marsh in the Bay of Fundy, eastern Canada

An undescribed species of tube-dwelling sigmoid diatoms, Gyrosigma orbitum sp. nov., was found in the surface sediments of a salt marsh in Peck's Cove, Bay of Fundy, Atlantic Canada. The specimens belong to the section Strigiles sensu H. Peragallo and they are characterized by very fine longitudinal striation (34-45 in 10 mm), isomorphic proximal raphe endings and two large oval pits within the central area. While recorded in adjacent tidal mudflats, this species reached its highest abundances in the salt marsh, particularly within the cordgrass Spartina patens where it occurred in association with other epipelic taxa, including Diploneis cf. smithii, Surirella spp., Gyrosigma limosum, Nitzschia epithemioides, N. ligowskii, N. sigma, and a number of small sigmoid Nitzschia species. Gyrosigma orbitum is found mainly at sites with high sediment temperature and water content, but a shallow anoxic layer.