ABSTRACT
Silicified ostracods were recovered from Cisuralian micritic limestones of the Ryozensan Limestone Formation from the southwestern part of Ryozensan Mountain, Taga City located in Shiga Prefecture, Central Japan. Twenty-seven species belonging to 19 genera were obtained, of which six species are new and are described here: Bairdia tagaensis Tanaka sp. nov., Bairdiacypris ikeyanoriyukii Tanaka sp. nov., Kellettina noriyukii Tanaka sp. nov., Microcheilinella shigensis Tanaka sp. nov., Oliganisus ryozensannensis Tanaka sp. nov., and Pustulobairdia ohmiensis Tanaka sp. nov. Some Palaeozoic limestone localities in Japan cap greenstones and are surrounded by younger cherts (such as Mino Terrane of this study). They represent a characteristic reef and reef-slope environment around a seamount surrounded by deep sea ocean floor. This result is concordant with the ostracod assemblage. After this report, a Panthalassan ostracod fauna could be defined for the Cisuralian.
Subject(s)
Crustacea , Animals , Japan , Oceans and SeasABSTRACT
The carapace of some Archaeostraca exhibits two kinds of structures that are best interpreted as corresponding to sensory organs. Dorsal ones are located either along the dorsal margin of the valves of the carapace, or on the median dorsal plate. Anterolateral ones are located in the anterior region of both valves. Both structures are respectively homologous of the anterior and posterior sensory organs known from extant Leptostraca and other Crustacea. These structures are described in adult Archaeostraca from the Ordovician to the Carboniferous. It is expected that they could have baroreceptor, mechanoreceptor, and/or chemoreceptor functions in some cases, and a function in osmotic regulation in others.
