Look in the Dining Room!

by Peggy Williiams

Shells are the outer "skeleton" of living animals - molluscs - and to live and grow, like any animal, they must eat. However, unlike birds, mammals, insects, etc., they are relatively immobile (slow-moving), so they are usually found near their food source.

So, to find live shells, first find out what they eat!

Bivalves are easy - they're filter feeders, drawing food out of the water. This food is tiny planktonic (free-swimming) plants and animals. Few bivalves leave their havens if they can help it, essentially settling on the dining room table and waiting for the water (waiter?) to bring them dinner.

Some, however, prefer high-energy zones of the beach (the window seats), some would rather be in deeper, quieter water (back of the restaurant), and others hide deep inside rocks or holes (near the kitchen). Most of them attach to the substrate with either a cement of limestone (essentially growing on a rock) or a byssus of sticky threads that holds them down.

Mussels have this byssus and some prefer the high-energy zone. Thus, in northern waters you find huge colonies of blue mussels covering rocks where the tide surges in and out, bringing food to them.

Coquinas, on the other hand, prefer the sandy surf zone and have to burrow for their lives lest they get washed out with the next wave. In between waves they get to eat!

Among the gastropods there is much more variety to food preferences. Some eat tiny plants, some like worms, others eat sand dollars, coral, or clams. There's a great variety of food in the sea!

Some molluscs even eat jellyfish - and these molluscs spend their lives floating in the open ocean among the Man-O-War jellyfish, snacking as they float: Purple snails and some shell-less molluscs called nudibranchs.

Hereabouts (Florida) we can look in clam beds for whelks, which eat practically nothing else and horse conchs, which eat practically anything. Tulip shells also eat any molluscan meat that comes

their way. Find a quiet place in the bay where there's clean sand and a little turtle grass and see if you find clams. The other shells will be nearby.

Looking for crown conchs? They like oysters, so check out the oyster beds (oysters prefer muddy sand). There you also will find lots of smaller shells: mussels that hitchhike on the oysters, oyster drill shells (three or more varieties), and tiny, 1/4 inch odostomias and dove shells.

On the limbs of mangroves overhanging the water you'll find periwinkles that eat tiny plants growing on the mangrove branches. Other periwinkles like the plants that grow on seawalls and shore rocks.

If you can find rocks that come out of the water at low tide (in south Florida and the Bahamas for instance), you'll find shells that eat the mossy-looking plants in the splash zone: nerites, "false limpets" (siphonaria), limpets chitons and periwinkles. Many of these shells have a "home" in one particular spot and return to it when the tide is not right (either high or low depending on their preference) and leaving it to feed at other times.

How about helmet shells? They eat sea urchins, sand dollars, and their relatives, so they'll be where these food items are found: in sand and turtle grass areas (where their own food is). If there aren't any of these creatures around, there won't be any helmet shells; but if there are lots of them, and some are dead or broken, there probably are helmets nearby.

Chitons mostly eat vegetation. They don't move much but, like limpets, have a home place on the rock which they leave to graze and return to when

Nassas ("basket shells") and marginellas are mostly scavengers, cleaning up the sea bottom by eating fresh dead meat. If you find a dead fish or a fresh-dead clam you'll probably find lots of these molluscs dining on the leftovers. They crawl across the sand with their siphons extended, "sniffing" the water for the scent of fresh dead meat.

they're resting. Chitons are made of eight pieces of shell which is held together by a fleshy "girdle". One group has a girdle which is longer on the head end of the shell. This is because these animals eat small crabs and crustaceans that wander by. The chiton holds this part of the mantle up when hunting and when the crab goes under it, drops it quickly to catch its dinner.

If you're snorkeling around sea fans, look for coral-eating shells. Some species of coral snails live at the base of the large sea fans and sea whips, especially the purple ones. They are kind of lumpy and hard to spot. Slender, one-half to one-inch-long simnias eat the coral animals that make up sea whips (in our area they are purple) and may be found by careful searching, looking like a lump on the narrow "fronds" of the coral colony.

Terebras ("augers") eat worms, so they'll be found in sandy areas where worms can easily burrow. Olives eat worms, too, and other animals that live under the sand. These molluscs are made for burrowing, with long, slender shells. The olive shells are shiny, too, to cut down on resistance from the sand when they move through it.

Moon snails eat bivalves, and to get at the meat they bore a neat hole in the umbone (kind of the "shoulder") of the bivalve shell. If you find bivalves with neat holes in them you will probably find moon snails nearby. When the tide begins to come in they emerge from the sand where and start to wander around looking for bivavles just under the sand's surface.

I read in a shell book that some sundial shells eat sea anemones - the ones that grow in great numbers, or "mat anemones", in shallow water. I first found them on mat anemones in Mexico. Just as the low tide turned they began emerging from among the anemones (which were closed up until the water would cover them again) where they had been keeping wet during the low tide and began feeding. Now I look for them whenever I find mat anemones and have found three different species this way.

There are many more examples of specific foods that determine where molluscs live. Read the shell books to find more!