28 October 2009

In the bosom of a very distant relative

Among the numerous bone and mollusk shell fragments scattered throughout our yard is this old, thick clam shell. I have no recollection of where it came from and no idea what species it may have once represented.


The other day when I picked it up to move it elsewhere, I found these 3 slugs, Deroceras reticulatum, safely nestled on the underside of it.


The last common ancestor of gastropods and bivalves must have lived sometime in the Cambrian, more than 500 million years ago*. That makes them very distant relatives indeed. Nevertheless, I had no intention of interfering with their family union of sorts. I returned the clam shell with its inhabitants to its spot.

*Here is a brief intro to mollusk evolution.


Wallace Ward said...

Looks like a RANGIA: commonly used for shell pavement down here in SE TX. It tolerates brackish water well.

Anonymous said...

My guess would be a very old and very chipped Mercenaria mercenaria. Because that species has been a popular food item for not only hundreds of years but millenia, this old shell could easily pre-date your occupation of the house, and maybe even pre-date your house and perhaps be way older still. It looks as if it may have been long buried and then dug up at some point.

Susan J. Hewitt


The shell may indeed be older than the house, which is not that old (~25 yrs), but it was brought to the yard by us most likely either from the Tampa, FL area or from Chincoteague, VA within the last 10 yrs.

Anonymous said...

OK, well then Mercenaria mercenaria the hard clam or quahog lives as far south as Virginia. Mercenaria campechiensis the southern quahog, a closely-related species, lives in Florida.

Susan J. Hewitt

xoggoth said...

I fished out what appeared to be an empty pondsnail shell from my pond the other day and found a gigantic species of Ictheosaur, previously thought to be extinct for 150 million years, inside it.

I put it back in a hurry I can tell you.


You didn't even take a picture of it?!