10 November 2010

A whole lotta Donax

436, to be exact. I collected these bivalve shells at a beach in Puerto Rico in 1994. I believe they are Donax variabilis.

224 of the shells are right valves and 212 are left valves. I did a chi-square test and the difference was not significant (P=0.565).

What else can I do with them? Some have drill holes or chipped edges, providing evidence for predation. There are a few very small, presumably juvenile, shells. Perhaps, I can measure them all and look at the distribution of shell sizes. Or, maybe I can measure the volumes of a subsample and look at the change in shell volume during growth. What else?


Cindy said...

I'm not sure what other sciencey stuff you could do, but here are instructions on making a Seashell Mosaic Flower Pot with them!

Anonymous said...

Ooooh, Caribbean marine mollusks! My current speciality!

Most Donax species do look rather similar to one another, being mostly wedge-shaped or bean-shaped, and almost all of them about the same size, but this is in fact Donax denticulatus, the common Caribbean species. D. variabilis on the other hand reaches only as far south as the Florida Keys and is much more colorful.

An rather old (1961) but good book you might want to get hold of is "Caribbean Seashells" by Warmke & Abbott, based on the Puerto Rico fauna. (Many secondhand "Dover" edition copies of this book are available very cheaply.) Another great source of info (no pictures) is Gary Rosenberg's online database of the marine mollusks of the Western Atlantic, "Malacolog".

If this is a true random sample, if you felt like it you could maybe try to look at the numerical distribution of the color forms in your sample (white, yellow, purple, with or without stripes)? Or a numerical distribution of height, length and/or width of the valves, which might turn out to be characteristic of this species of Donax? And I am curious, were any of them drilled by Naticids (predatory moon snails), which leave perfectly round countersunk holes?

And did you bring any other shells back, or was that it?

Susan J. Hewitt


Susan, I was hoping you would confirm or correct my identification. I used to have a copy of Warmke & Abbott, but I sold it off foolishly. I suppose I could get another copy.
I will try to post photos of the drilled shells.
Yes, I do have a few other shells from PR.

Anonymous said...

Hey me again. My mistake. I realize I should have said this is Donax striatus Linnaeus, 1767. The two species have been confused in the past. Note the strong keel on the posterior slope of the shell. These bivalves "stand on their heads" when in the sand, with the siphons protruding from the surface so they can respire. As is the case in any species of sand-dwelling bivalve, the relative size of the pallial sinus on the interior of the shell valves is an indication of the length of their siphons, and thus how deep they routinely bury themselves.

Susan J. Hewitt

Fred Schueler said...

You could spend a few years assembling the hardware and techniques that you'd need to do 3-d scans of the exterior of the shells, and then quantitatively describe the shapes of the exteriors and patterns of, and variation in, radial and concentric coloration (since you asked).

Anonymous said...

I have a spare copy of the softcover Dover edition (smaller format than the original hardback) and a spare copy of the original hardback too. I can send you one or other of them if you would like. Or if you prefer, you can order another copy of either the Dover edition or the original hardback (the plates are a bit better in the original) using Abebooks for about $5 or $6 plus shipping.

Susan J. Hewitt

forestwalk/laura k said...

i like to put my 'collections' (shells, rocks, stones, etc) in unusual shaped jars or glass bottles...add water (which makes the colors bright!)...cover...and set on shelf...mantle...

OR i'll do something more creative...make a shell 'picture' or wall hanging with driftwood...etcetc...

nice collection!! :]]