Re: Is the shell of a mollusc considered to be a 'living thing' or 'non-living'

Hello Michael,

What an interesting question! I've never heard of a biological classification system based on whether the item is living, dead, or non-living. Fortunately, the molluscan shell about which you ask fits neatly into one of those categories.

A mollusc's shell is secreted by a layer of tissue called the mantle, usually located on the dorsal surface of the animal. The shell itself is acellular (i.e., non-living), consisting of layers of calcium carbonate often covered on the outside by a thin organic layer called periostracum. There are generally two kinds of layers of calcium carbonate: one type is thick and chalky, and the other is the thin nacreous (pearly) layer that you see on the inside of many shells.

As mentioned above, the shell does not contain cells and does not have a metabolism, so it may be safely classified as "non-living". I wouldn't consider it to be "dead" because it had never been "living" and it would have to have lived before it could die. Using the same logic, a leaf that has fallen from a tree could be classified as "dead" – it is composed of cells that at one point were alive and metabolically active, and when the metabolism stops the leaf dies.

It may be of interest to note that a mollusc is attached to its shell at only specific points. The muscles that attach the body to the shell are called adductor muscles. If you have ever tried to shuck an oyster you'll have noticed that there's a large adductor muscle that must be severed before you can open the shells, and that once you have cut through that muscle the shells open very easily.

I hope this answers your question!

Allison J. Gong
MAD Scientist

Reference: Brusca and Brusca, 2003. Invertebrates. Sinauer Associates, Inc.