Sunday sand: critters of Calangute

 

I have a small, but very select, band of arenokleptomaniacs, friends and family who never leave home without small plastic ziploc bags in which to collect sands on their travels - carefully labelled - to be added to my collection. One of my agents, a Dutch friend who had recently been in Goa, brought back a wonderful and very diverse selection from the beaches of the Arabian Sea, and this is one of them. Calangute is primarily a tourist destination, the lure being the usual endless sand and tropical balminess.

It’s clear from simply looking at the sand that it contains much organic debris, fragments and sand-sized grains of shells. But, down the microscope, its true beauty is revealed. Crowding out the scattered rock and quartz grains are countless little spiral shells of foraminifera, the incredibly diverse group of single-celled marine organisms, of which hundreds of thousands of species are known and which occupy essentially every marine habitat known. They are also survivors, boasting an evolutionary lineage that covers hundreds of millions of years. Most of them, like these from Goa, make their shells, or tests, from calcium carbonate and thus are key players in the great game of ocean chemistry. And they are among nature’s most creative and artistic designers, their shells demonstrating a seemingly endless variety of exquisite geometries. Below is one of the stunning illustrations of Ernst Haeckel, the nineteenth-century German biologist, philosopher, and artist – among the thousands of new species that he identified and named were large numbers of foraminifera.

 

But forams are not the only critters in these sands – there are all kinds of biogenic bits and pieces, and, in my microscopic browsing, I happened upon this perfect shell. What is perhaps remarkable is that, in spite of the daily buffeting and grinding of waves and tides, the onslaught of monsoon storms, and the crushing weight of sunbathing tourists, these shells survive intact – built to last. 

Comments

[Walter]

Beautiful. How large is shell?

[Sandglass]

The shell is a couple of millimeters, the forams less than a millimeter - amazing, huh?

[Walter]

Yes. Amazing. Knowing nearly nothing of such things, I find myself assuming that shell is that of a scallop. Correct? Is it that of a young one or of a small variety (species?).

[Sandglass]

Knowing nearly nothing of such things myself, it certainly would seem to be a bivalve, but whether it's a scallop (pecten)I'm not sure - the hinge shape (important, I believe, in such classification) doesn't look quite right. I suspect that it's a diminutive species, but, again, I'm not sure.

[Sean McKenna]

Both forams and Haeckel's illustrations thereof are fascinating. And your bottom image is absolutely lovely.

As to the top image - those shells are forams? I've never seen images of forams along with any other objects, and since I have no reference for grain size in the image, the forams(?) seem rather large to me.

Would it be safe to assume that foram shells found in beach sand would be of the planktonic variety, as opposed to benthic? I suppose fossil benthic type shells could wash down from eroding uplifted oceanic crust, though.

Since we are still ahead of the holiday season, these may be provide some holiday amusement: http://www.flickr.com/photos/28196673@N08/sets/72157611177529561/

[Sandglass]

Hi Sean - thanks for the comment. Re the size of the forams: the sand is generally fine-grained (with some larger chunks of shell fragments) - the forams are around a millimeter or slightly less in size, not visible to the naked eye. The amazing diversity of foraminifera also means that they occur in a wide range of sizes - the majority less than a millimeter, but the fossil nummulites can be several centimeters in diameter. There's a great foram site at:

http://www.ucl.ac.uk/GeolSci/micropal/foram.html

As for planktonic versus benthic, I'd have to agree with you and go for the former - but I fear that I am no expert! I don't believe that the local geology offers much of a source for fossil forams.

And thanks for the Haeckel Christmas link!

[f]

I had previously missed your comment and the link here, Michael. Thank you.