Bibliographic Detail
Komura, S., 2001
Reference:
Komura, S. (2001). Comments on some new diatoms from the Miocene Morito Formation,
central Japan. Diatom 17: 69-89.
Abstract:
Four new taxa are describedStelodiscus obscurus n. gen. et n. sp., Heterangion
orbiculatum n. gen. et n. sp., Diommatetras grossa n. gen. et n. sp. and Dimeractis
vicconstricta n. gen. et n. sp. They are based on specimens from the marine sediment of
the Morito Formation, early Miocene in age, distributed in the Miura Peninsula south of
Tokyo.
Stelodiscus obscurus has discoidal valves thin-walled with highly columnar areolae
encased by the hypocaist that allows the valvar wall to be empty to a great extent. The
loculate areolae are wholly veiled by a single, homogeneous sheet of extremely fine
reticulum.
Heterangion orbiculatum is a biddulphioid with circular valves that are bipolar by a
pair of marginal elevations of different sizes, and with poroid areolae aligned in
radiating rows with repeated furcations. The elevations project from the valve face,
each with an unlamellated ocellus at its summit.
Diommatetras grossa is another biddulphioid with quadrate valves that have
pseudocellate fields at the rostrate corners and equal-sized elevations paired at
opposing corners.
Finally, Dimeractis vicconstricta is a panduriform diploneid. The solid axial sternum
bears a plicate raphe alongside which are longitudinal canals, one on each side. The
canal opens to the frustular cavity through unocculuded pores and to the outside via
veiled poroids.
Between the sternum and the valvar margin are alveolar chambers that open to both
sides in bilateral rows, each with a mid-depth occlusion.
A taxonomic discussion concludes that the first taxon is comparable to Actinocyclus by
the marginal ring of fan-shaped rimoportules rising from the porous valvar wall ; the
second and the third are comparable to the Ceratoneis/Pleurosira complex due to the
pericentral rimoportule(s) and the presence of the polar elevations bearing topmost
ocelliand the fouth and final one is separated from Diploneis on the basis of the
distinctive canals associated with the dualness of areolar pattern.
