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Abstract
The taxonomy and biostratigraphy of the fossil marine diatom resting spore genera Dicladia Ehrenberg, Monocladia Suto and Syndendrium Ehrenberg are discussed. The three genera are probably the fossil resting spores of Chaetoceros and Chaetoceros-related genera, and are characterized by dichotomous branching processes on their valves. They were studied by examining samples from DSDP Sites 436, 438 (northwest Pacific) and 338 (Norwegian Sea) and the Newport Beach Section (California).
The genus Dicladia is characterized by having an epivalve with two conical elevations, and includes three species: D. capreola Ehrenberg, D. mitra Bailey and D. japonica Pantocsek. The genus occurs in the Neogene. The genus Monocladia possesses four species including two new species: M. humilis Suto, M alta Suto, M. perizoma sp. nov., and M. norvegica sp. nov. The occurrence of this genus is restricted to the Miocene. Monocladia differs from Dicladia by having only one elevation and a single hyaline, branching process on the epivalve. The genus Syndendrium holds seven species including five new species: S. akibae Suto, S. diadema Ehrenberg, S. medusae sp. nov., S. scarabaeum sp. nov., S. rugosum sp. nov., S. altantemna sp. nov., and S. humiliantemna sp. nov. This genus occurs from the early Oligecene to the Recent. This genus is characterized by two or more hyaline, branching processes that arise from the central portion of the epivalve.
Seven new species M. perizoma, M. norvegica, S. medusae, S. scarabaeum, S. rugosum, S. altantemna and S. humiliantenma are described in this paper. Some species have short-ranging occurrences and specific characteristics allowing for easy identification, and they may be biostratigraphically useful.