Wednesday, August 11, 2010

Shells At Hand

Every observer brings to his or her own science a unique perspective,
and I am no exception.
~ Geerat Vermeij, Privileged Hands: A Scientific Life (1997)

My little experiment in perception is inspired by Geerat Vermeij and takes place on a hot midsummer’s morning on the shore of Flanders Bay. Flanders Bay is at the beginning of a series of bays separating the North and South forks of the eastern end of Long Island, NY, these waters ultimately connect to Block Island Sound and the Atlantic Ocean (see map).

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It’s a shallow bay, and along with its big sisters, the Great Peconic and Little Peconic Bays was once rich in scallops, clams, and oysters. Recreation is its claim to fame now. The bay this day is its usual meek self, waves little more than ripples lapping at the sand. The receding tide has left a motley array of shells and other marine debris in a rough line extending along the beach.

At the water’s edge, I select three shells. Each is a very common shell here – in the picture below, the shell at the top is the top valve of the bivalve known as a Jingle Shell (Anomia simplex) (to provide a frame of reference, this shell is roughly 1 inch from edge to edge), the smaller shell immediately below it is, I am convinced, a little example of a valve of the bivalve Bay Scallop (Argopecten irradians), and the third is a Common Slipper Shell (Crepidula fornicata) from a gastropod (snail).

I then sit on dry sand, and try to answer the question,

What can I learn about these shells by touch alone?

Since I am by myself on this morning, I select the shells by sight. And, so, not unexpectedly, my experiment begins on a false note. Still, despite that, the experience of exploring each shell with my fingers is revealing. Even this brief effort suggests what I might miss relying almost solely on sight.

The differences between sight and touch emerge quickly.

Textures. The feel of the shell surfaces serve as the introduction for the exploring fingers. The exterior of the Slipper (or Boat) Shell has somewhat erratic ripples that work their way across the shell, they are relatively smooth. The apex is smoother and devoid of ripples. The interior is smooth though somewhat chalky once it has dried. The platform on the Slipper Shell’s underside (see picture below) is almost pearly to the touch with a subtle ridge that emerges from the underside of the apex and runs in an arc along that edge of the shell.  I wonder why the platform's surface should be different from the actual interior?  I assume a purpose for this difference though I don't know what it is.

The Scallop Shell is surprising because the interior and exterior surfaces are remarkably similar in feel but only primarily along the outer portion. The crenulated edges reflect the radiating ribs.  Why ribs?  What's gained by that, is it defensive architecture?  Though the ribs can be felt clearly on the interior along the outer edge, their definition fades as my fingers travel toward the underside of the apex.  The inner surface becomes coarse. Even with this very small shell, it’s relatively easy to feel that the each rib on the exterior is bumpy as is each of the grooves that separate the ribs. Once again, the apex is relatively smooth.

The Jingle Shell’s interior and exterior surfaces are, to the touch, a study in contrasts (despite how similar they appear to the eye). The exterior is bumpy and uneven, feeling as though it is made by a hand that paid little attention to symmetry, the grooves that surround the apex are only roughly concentric. The interior, on the other hand, is a fingertip’s delight – glassy in its texture with one ridge that runs parallel to the far edge.  Why should the interior be so smooth, so different from the exterior surface?

Edges and Thickness. Of course, I feel edges on all of these shells and quickly register whether the edge is thick, thin, strong, fragile. The Slipper Shell’s edges are ragged, sharp, and broken. The platform on the underside has lost a lot. The edges of this shell are relatively thick, suggesting that it takes some significant force to break it. Though the edges of the Scallop Shell are mostly complete, they are sharp to the touch and relatively thin, seemingly very breakable. The Jingle Shell’s edges are relatively smooth, though they do reveal some breakage. Curiously, the outer edge feels as though it has a lip that curls back under the shell.  To what end?  Protection for the much flatter bottom valve that is only infrequently found on the beach?

Weight. Though none of these shells weighs much, weight, as an attribute of each specimen, is registered almost immediately by my fingers and my palm.

Simultaneity. This is the most striking difference to me between examining by sight and examining by touch. By using my thumb and index finger I can simultaneously examine the inner and outer surfaces of each of these shells. This immediate sensation of contrasting textures highlights how very different or similar these surfaces can be. Is this of some value in trying to learn about and understand the creatures that made these shells? I don’t know, but it’s a lasting impression from this experiment.

Questions. Finally, I wonder if there isn’t some aspect of this exploring by touch that sparks questions. Perhaps it has to do with the inability to take in the totality of the object as one does with sight. The fingers identify pieces that need to be assembled into the whole, triggering questions of how does this fit with the other pieces I’ve felt, and, perhaps, why is this shaped, textured, sculptured in this particular way.

Obviously, there are attributes of these shells that touch alone cannot identify. Color, for example, is denied the fingers, not only the presence of color but the location and any changes in color. Also, the overall structure of the specimen is more quickly apparent using sight, though educated hands might do as well.

I began this posting with a quotation from evolutionary biologist Geerat Vermeij’s autobiography Privileged Hands. From early childhood, Vermeij has been blind. Though that attribute is one frequently used in identifying him, it is not the one that defines him.

Vermeij, professor of marine ecology and paleoecology at the University of California, Davis, and an expert on molluscs, has written extensively on the evolutionary consequences of the ancient and continuing arms race between molluscs and their predators, and among those predators. He has identified what he calls the Mesozoic marine revolution when some 200 million years ago marked innovations occurred in predation and in shell architecture resisting that predation, a revolution as “shallow-water marine communities underwent a profound general reorganization.” (Privileged Hands, p. 200).

There is a great deal out there by and about Vermeij.  An interesting profile of the scientist ran in 1995 in the New York Times. (Though the article suggests that he and I might not see eye to eye politically, so be it.) Among his myriad articles is a wonderful piece he wrote for Natural History (February, 2002) The title suggests its appeal – Why Are There No Lobsters on Lands or Bats at Sea?

It is apparent that, because Vermeij examines shells, from extant and extinct creatures, with his fingers, he gains a different and strikingly useful perspective. The quotation that began the posting comes from this paragraph which suggests some of what Vermeij derives from his fingers:

I cannot claim to observe shells better than others do, nor would I pretend to discriminate more easily among species on the basis of shell features than other malacologists do. Every observer brings to his or her own science a unique perspective, and I am no exception. Inspection of an object with fingertips, fingernails, and thin needles reveals not only the broad outlines but also the small-scale details – the number, relative size, and orientation of elements of sculpture; the placement of teeth and folds surrounding snail-shell apertures; the pattern and asymmetry of clam-valve serrations; and the like – that a casual observer is apt to overlook. (p. 265)

Privileged hands, indeed. His research has included an examination of the evidence of predator attacks on mollusc fossils from millions of years ago, an exploration where the sensitivity of his fingertips to the healed over scars left by failed assaults is crucial.

A moment in the 4th grade set him on his life’s course. His teacher brought in some shells gathered in Florida. When Vermeij held them and ran his fingers over them, he was struck by the differences between these shells and the cold-water ones he had collected previously in his native Netherlands. An apparently endless sequence of questions was engendered by this tactile encounter. He continues to grapple with versions of the question he asked as a 4th grader, concluding his autobiography with several, beginning with that first one:

Why are northern shells chalky and tropical ones so beautifully crafted and so finely textured? Why do some predatory snails have lip spines while others do not? Why did acorn barnacles replace other kinds of shore animals when they appeared some fifty million years ago? I do not know, but I shall ask. Nature will surprise us if we let her. (p. 272)

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