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Amphistegina
''Amphistegina'' is a foraminiferal protist 〔(Short Treatise on Foraminiferology )〕 included in the Rotaliida with a stritigraphic range extending from the Eocene to recent and a cosmopolitan distribution. The test is an asymmetrically biconvex trochospiral that may be bi-involute or partially evolute on the spiral side. Chambers are numerous, broad. and low, strongly curved back at the periphery to form chamber prolongations. The umbilical side is stellate, like that of ''Asterigerina'', and has a distinct umbilical plug. The wall is calcareous, optically radial; the surfacce finely perforate and smooth overall. The periphery angular to carinate (keeled); the aperture an interiomarginal slit on the umbilical side, bordered by a lip.〔(Loeblrich & Tappan 1988. Modern Foraminifera at )〕
Loeblich and Tappan, 1964 〔Treatise on Invertebrate Paleontology, Part C, Protista 2(2)〕 included ''Amphistegina'' in the Amphisteginidae along with related ''Boreloides'', ''Eoconuloides'', and ''Tremastegina''; the Amphisteginidae at that time included in the Orbitoidacea, the Asterigerinidae in the Discorbacea.
''Amphistegina'' prefers warm and shallow water (less than 30 m) and mainly inhabits the seafloor between the coastline and coral reefs. Also, the test is quite hard compared with many other more fragile foram tests which allows them to survive in wave agitated water.〔(The most common foram of Hawaii )〕
==References==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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