Apatite Particles in the Test Wall of the Large Agglutinated ForaminiferBathysiphon Major(Protista)

Abstract

In the North Atlantic, the tubular agglutinated foraminiferBathysiphon majoroccurs 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 the test wall which has a sooty black outer layer, about 20μm 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 (xm in size. The nature and composition of these particles has been studied using light and electron microscopy, x-ray microanalysis, electron diffraction analysis and infrared spectroscopy. The particles contain calcium and phosphorous and have electron diffraction patterns and infrared spectra consistent with a hydroxyapatite composition. Minor amounts of iron are probably responsible for their black colour. We believe that this represents the first report of apatite-like (phosphorite) particles occurring in the test of an agglutinated foraminifer. The particles are most likely to originate as phosphorite grains which are agglutinated by the foraminifer, although the possibility of authigenic precipitation cannot be eliminated. The function of the outer black layer is unknown.