Gastropods

Speaking “Seashell” Means Delving Into the Life of Mollusks

In my Florida life, a seashell was a seashell. Some were prettier than others, some were larger and I just called them shells and never knew they were actually mollusks. In fact, when I found a nice shell, I never gave much thought to what had once lived inside.

seashells in a big round bowl — My Seashell Collection

Now I have learned to speak seashell. At least to the degree that I know the difference between a gastropod and a bivalve and that animals in the phylum mollusca inhabit most every area of the earth, although I write about the marine mollusks, the ocean-dwelling ones. (In England mollusk is spelled “mollusc”.)

cropped-img_1948 — Fighting Conch – Gastropod

Mollusks are invertebrate animals and I am mostly interested in the ones that live inside their shell homes, but some mollusks don’t have shells (squid, cuttlefish and octopus). They consist of single shells that are all in one piece – gastropods or univalves, and shells that are hinged, or two pieces – bivalves. They all live in ocean water or brackish water, which is less salty as it is combined with fresh water.

disc dosinia seashells — Disc Dosinia Seashells – bivalves

I mainly use the common names of the shells when describing them, but the scientific names are important in identifying seashells and each shell will have a two-part name. Always the scientific name is italicized, with the first part being capitalized and the second is not.

Below is a beautiful Knobbed Whelk shell. Search as Busycon carica. And read more about this one on my blog post.

When reading the descriptions of a gastropod on a more scientific site or in my seashell ID book, I learn about the spire (top part of the shell), whorl (the way it twists), aperture (opening), lips (edges of the opening), canal, and operculum which seals the “door” when the animal retreats inside it’s shell. The bivalve descriptions could include describing the umbones, ligament and hinge teeth. Most descriptions will include colors and characteristics unique to that shell and the inside color along with the size and where it can be found.

Once you know this, you can speak seashell too.

Seashell Markings and Bore Holes

I have collected some shells and pieces of shells that are full of holes or have crazy lines etched in the top. Sometime a shell will have a perfect hole all the way through it, just as if it was meant to be hung on a wire to make a pretty necklace.

I never knew what caused these phenomenons until I read about “Shell Wars” in my new reference book, “Florida’s Living Beaches, A Guide For the Curious Beachcomber” (affiliate link to Amazon), by Blair and Don Witherington. In the mollusk section of the book they explain how some gastropods will bore holes through the shells of others to feed on them. In doing so, they leave a hole, or sometimes lots of holes as in the case of boring sponges that use acid to digest shells and actually leave them looking like a sponge – full of holes.

cross-barred venus clam — Shells with bore holes

How Are The Bore Holes Made

Meat eating mollusks will eat other mollusks and one way they do that is to bore a hole into the shell and suck out the snail inside.

With their tongue, or radula, they create the hole with the help of enzymes from their own body which soften the shell. They use their radula as a drill, and make the hole.

This is why some shells look like a hole was drilled perfectly into the top. That sea snail was killed by another snail.

Considering Sea Snails, There is Lots to Learn

When you find a beautiful shell on the beach, do you ever think about the creature that used to live inside? They are interesting organisms and the shell homes they create are even more so. Each mollusk makes it’s own type of shell, and within those varieties can be more varieties. Each seashell is unique, which is why we love collecting them so much.

Now that I have a boat, and can get out to the islands along the Indian River waterway, I’m constantly looking for unique mollusks and their seashells. Sometimes I even get to find a living shell like this huge horse conch and beautiful fighting conch.

I see plenty of empty shells with weird markings too, but now I know why they are there.

A List of Recent Blog Posts

The Frog Shell

The frog shell is not extremely pretty as it tends to be covered in “limy deposits”. The St. Thomas Frog Shell (Bursa thomae) got it’s name because it was first discovered in St. Thomas in the Virgin Islands. It’s a small shell, growing only to a little over an inch long.

Another frog shell – the California Frog Shell (Bursa californica) is commonly found in Baja California where it is frequently pulled up in crab and lobster traps. This species is larger and can be up to 5 inches in length.
Info taken from National Audubon Society’s Field Guide to Shells

See another photo of a frog shell – The Yellow Mouthed – here.