APATITE PARTICLES IN THE TEST WALL OF THE LARGE AGGLUTINATED FORAMINIFER BATHYSIPHON MAJOR (PROTISTA)

In the North Atlantic, the tubular agglutinated foraminifer Bathysipho n major occurs at bathyal depths off the coasts of North Carolina and north-west Africa. Apart from its large size (up to almost 10 cm long) , the most distinctive feature of this species is the appearance of th e test wall which has a sooty black outer layer, about 20 mu m thick, overlying a much thicker layer, pure white in colour and consisting of sponge spicules and small quartz grains. The black layer is composed of irregularly shaped, plate-like particles, 1-25 mu m in size. The na ture and composition of these particles has been studied using light a nd electron microscopy, x-ray microanalysis, electron diffraction anal ysis and infrared spectroscopy. The particles contain calcium and phos phorous and have electron diffraction patterns and infrared spectra co nsistent with a hydroxyapatite composition. Minor amounts of iron are probably responsible for their black colour. We believe that this repr esents the first report of apatite-like (phosphorite) particles occurr ing in the test of an agglutinated foraminifer. The particles are most likely to originate as phosphorite grains which are agglutinated by t he foraminifer, although the possibility of authigenic precipitation c annot be eliminated. The function of the outer black layer is unknown.