MILIOLINELLA-SUBROTUNDA (MONTAGU), A MILIOLID FORAMINIFER BUILDING LARGE DETRITIC TUBES FOR A TEMPORARY EPIBENTHIC LIFE-STYLE

Live observations, cytological characteristics and biometrical measurements on Miliolinella subrotunda (Montagu, 1803) sampled from the northern and southern Atlantic Ocean are presented. M. subrotunda facultatively constructs a long, detritic tube lifting the test several millimeters above the sediment surface. A thickened conical base anchors the construction on the sediment surface and a long, flexible tube protrudes into the velocity profile of the bottom currents. The miliolid test is placed on top, surrounded by the uppermost part of the tube. This construction allows the organisms to feed in the particle stream above the sediment surface. In comparison to species living in and on the surface sediments, M. subrotunda apparently shows higher nutritional values in food ingested and larger amounts of reserve substances. Characteristics of the shape and structure that reduce drag on the tubes include a broadened conical base, a flexible tube, and a rounded top. From biometrical measurements it is concluded, that the tubes are constructed over a short period of their ontogeny.