(^) Foraminifera (“forams”) are amoeba-like protists, moving and feeding by extension
of cytoplasmic strands (pseudopodia). They are progressively more important with
depth, reaching up to 30% of the benthont biomass below 2000 m (Shirayama &
Horikoshi 1989). Most benthic forams have shells of calcite, protein, or adhered
sediment particles surrounding their nuclei. Their shells, that are useful in
paleoecological reconstructions, are found abundantly as fossils in cores and uplifted
deposits. They provide useful contrasts with any planktonic forams preserved with
them, and both provide mineral proxies for the composition of seawater in the past
(e.g. Cd/Ca ratio as an approximate measure of phosphate concentration at shell
deposition; Boyle 1988). There are more than 34,000 extant benthic species described
in a still-expanding systematics, plus many extinct species. Reaching out through the
sediment with networks of pseudopodia, they feed on bacteria, heterotrophic benthic
diatoms (also “meiofauna”, actually), detrital particles, and other meiofauna. Other
amoeboid protozoa and an array of ciliates also live in sediments as meiofauna or
microfauna. At least one foram genus, Bathysiphon, reaches a size included in the
macrofauna. The cells construct tubular shells of aggregated minerals, usually
including sponge spicules, up to 11 cm long and 2.3 mm in diameter (1.2 mm lumen).
About 1 cm is buried in the sediment, the rest stands erect. As tubular networks, they
can extend across the sediment to a meter or more. They are abundant at mid-slope
depths in zones with very little disturbance. The cytoplasm is loaded with diatom
frustules and various organic bits (Gooday et al. 1992). Even larger are the foram-
related (based on DNA sequences; Pawlowski et al., 2003) Xenophyophorea,
ff
(ff)
#1