Intracellular mineral grains in the xenophyophore Nazareammina tenera (Rhizaria, Foraminifera) from the Nazaré Canyon (Portuguese margin, NE Atlantic)
Xenophyophores, a group of large agglutinated foraminifera, are characterized by the presence of numerous intracellular barite grains, termed granellae, the function and origin of which is unclear. The recently described xenophyophore Nazareammina tenera ( Gooday et al., in press), from abyssal depth (4300 m) in the Nazaré Canyon contains an unusually dense concentration of mineral grains in its cytoplasm. Uniquely among known xenophyophores, the intracellular grains in this species comprise a variety of different mineral types in addition to barite. They exhibit a wide range of morphologies and energy dispersive X-ray analysis indicated that they include Ti-bearing minerals, many of them rod-shaped (probably rutile), as well as those containing Fe and Ti (possibly ilmenite and anatase), and Al and Si (probably clay minerals). While the function of intracellular particles in xenophyophores remains unclear, the presence of numerous particles of various types in the cytoplasm suggests that they originate from the sediment. This suite of intracellular mineral grains is completely different from that used to construct the agglutinated test of N. tenera, suggesting that this species is able to discriminate between different kinds of particles. A second xenophyophore species, Reticulammina cerebreformis ( Gooday et al., in press), which is abundant at the same site as N. tenera, is devoid of intracellular particles, suggesting that their presence in N. tenera is a species-specific characteristic.