Bathysiphon rusticus de Folin, 1886 and Bathysiphon folini n. sp.; two large agglutinated foraminifers abundant in abyssal NE Atlantic epibenthic sledge samples

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Abstract
Two species of large agglutinated foraminifers belonging to Bathysiphon, are described. B. rusticus de Folin, hitherto known only from the type locality, and B. folini sp. nov. which is a unique because its test is densely studded with large Globigerina shells. The material was obtained in the northeast Atlantic. Specimens of B. rusticus range in size from tiny tubes a few mm long to giant specimens up to almost 60 mm in length. The smallest tubes of this species are morphologically identical to fully developed individuals; in particular there is no indication of an initial chamber. In large specimens, the early part of the test is consistently missing and it is speculated that this loss may occur during life. B. rusticus is abundant in most samples from 2900-4000 m in the tropical northeast Atlantic and occurs in vast numbers in one remarkable 4000 m sample. It is usually less common in the Porcupine Seabight off southwest Ireland. Estimates of its density on the seafloor are generally < 20 specimens/100 m2. The distribution of B. folini complements that of B. rusticus. This species is abundant in samples obtained at depths of 2400-3000 m in the Porcupine Seabight but generally rare off the coast of Africa. Estimated seafloor densities are between 290-1640/100 m2. In certain samples, B. rusticus and B. folini are the dominant, large foraminifers and the msot abundant macrofaunal animals present. Since most foraminifers are too small to be collected efficiently by the sledge, these large species presumably represent only a relatively minor component of the total foraminiferal fauna. B. rusticus, and probably B. folini, live embedded vertically in the sediment with the upper end protruding. There is some photographic evidence for this life orientation. They are probably suspension feeders, trapping minute organisms on a knob of protoplasm extruding from the aperture.