FINE STRUCTURE, REPRODUCTION AND PHYLOGENETIC PLACEMENT OF A SPECIES OF PSAMMOPHAGA (FORAMINIFERA) FROM COASTAL GEORGIA, USA
Psammophaga sapela is of moderate size (up to ~ 550 µm), generally pyriform in shape and has a single, flexible aperture at the end of a short neck. The flexible test is composed of a relatively thick (10-15 μm), outer agglutinated layer of fine clay particles arranged loosely parallel with respect to the plasma membrane of the cell body. It is highly selective with regard to the materials used in test construction. The agglutinated layer is underlain by a fairly thick (2–5 μm), inner organic lining (IOL), which is in direct contact with the cell membrane. Small vesicles just below the membrane function in the release of test construction materials to the IOL, indicating that growth occurs along the entire inner margin of the test. The vegetative nucleus in uninucleate individuals has a distinct cortical ring of densely packed chromatin as seen in some, but not all allogromids. Psammophaga spp. are well-known for ingesting large amounts of sediment. X-ray diffraction analysis identifies cytoplasmic inclusions as orthoclase, zircon, pyrrhotite, basaluminite, and pseudobrookite, along with the iron and/or titanium bearing minerals ilmenite and anatase, rendering this taxon magnetic. P. magnetica, described from Antarctica, is also magnetic.
Reproduction is gametogamous where gamonts release biflagellated gametes directly through the aperture into surrounding seawater. Alternatively membrane-bound packets are expelled through the aperture and subsequently open releasing swarms of gametes into the seawater. Reproduction by budding also occurs.