Sunday sand: more forams

Walking on a beach in Bali is, more often than not, a delightful experience, even idyllic. But occasionally it can be a challenge to the balance, a sensation of walking on ball-bearings. This problem arises from the composition of the sand – it is essentially ball-bearings, dominated by myriads of minute spherical shells of foraminifera. The samples above were sent to me by another old arenokleptomaniac friend with whom I worked for many years.

Forams are remarkable creatures (I wrote of some Indian ones a while ago), thriving in more or less every marine environment on earth, including deep sea hot hydrothermal vents. They have a long history, going back hundreds of millions of years: hundreds of thousands of species represent that record. Today there are around 4000 living species, although that is only an estimate: judging from the astonishing results of the international collaboration of the Census of Marine Life in which 6000 new species of marine organisms are reported, we actually have no idea how many varieties of foraminifera there are. They come in all shapes and sizes, some with shells made of just one chamber, others with multiple chambers, constructed in spirals and seemingly endless other designs. The University of California at Berkeley has a great foram site, and the most common forms of this wonderful spectrum of shell design are described there as follows:

unilocular -- a single chamber

uniserial -- chambers added in a single linear series

biserial -- chambers added in a double linear series

triserial -- chambers added in a triple linear series

planispiral -- chambers added in a coil within a single plane. The center of the coil is called the umbilicus. The coil may be either involute (only the chambers of the last coil visible) or evolute (all chambers visible).

trochospiral -- chambers added in a coil that forms a spire like a snail shell. The side on which all chambers are visible (evolute) is called the spiral side. On the other side only the final coil is visible (involute) and this is called the umbilical side.

milioline -- chambers arranged in a series where each chamber extends the length of the test, and each successive chamber is placed at an angle of up to 180 degrees from the previous one.

fusuline -- a planispiral coil which is elongated along the axis of coiling. Typically each chamber is subdivided by a complex set of internal partitions.

tubular -- a simple hollow tube.

arborescent -- an erect, branching series of tubes. These forms may live attached to a solid surface or "rooted" in sediment.

irregular -- without any definite arrangement of the chambers. These forms usually live attached to a solid surface.

Most of the shells are built of calcium carbonate, but, as we shall see, some forams use other construction methods. Their dazzling variety was recorded in detail by the first great oceanographic research voyage, that of the Challenger in the 1870s. As I have described, the entire set of reports of the expedition is available, wonderfully, online, including the lengthy chapter devoted to forams, illustrated by 115 plates, each one showing a dozen or so specimens. Perhaps the most dramatic illustration is this one of globigerina, a planktonic foram:

But I mentioned that some forams build their shells differently – they are the deliciously named agglutinated forams that simply use whatever is available as fragmentary material to glue together a shell. So, when we find these forams as in a sediment, they are sand grains made out of sand grains. And, as with other creatures that build with sand, the glue they use is of considerable interest to medical science.

The plates from the Challenger report include several of agglutinated forams, including, inevitably using the Greek for sand, psammophaera.

And, coming back to the continuing saga of the discovery of new species, it was reported earlier this year that “tiny single-celled creatures called foraminifera living at extreme depths of more than ten kilometres build their homes using material that sinks down from near the ocean surface.” Agglutinated forams happily living in the so-called “hadal” depths of the ocean. Where were these critters found? In the Challenger Deep.

[The Challenger reports are on line thanks to Dr. David C. Bossard, prepared from original documents in the library holdings of Dartmouth College, Hanover New Hampshire.]