LOTSA MUSCLE

by Nancy Sefton

The vertical rock wall I paddled by in my kayak was exposed by low tide. It was covered with bumps, little rounded knobs of various colors... animals hanging on tenaciously to the sheer face, using suction and some incredibly strong muscles. Had I tried to pull one of these limpets off the wall, I’d have failed; it’s like they were stuck to the rock with super glue.

Among marine animals without backbones (invertebrates) there’s one group that qualifies as the Arnold Schwartzeneggers of the underwater world…excessively strong. It’s a diverse group as well. I’m always amazed that the little limpets with their conical shells, like Chinese hats, are close cousins of the octopus. Both are classified as mollusks, along with squid, cuttlefish, oysters and clams, and other marine snails of many kinds. Most species wear a shell on the outside, a few on the inside.

Besides the shell, what gives all these animals an odd kinship is muscle, pure muscle. That giant squid may never have let go of Capt. Nemo’s submarine (in Jules Verne’s “20,000 Leagues Under the Sea”) if the captain hadn’t applied about 20,000 volts of electricity to the metal hull. Likewise, it takes a screwdriver and some elbow grease to pry apart the shells of an oyster.

Snails such as top shells, whelks and turbans simply suction themselves onto the rocks using that muscular foot on the underside. When they hunker down, pulling their shells over all the soft parts, they’re fairly well protected from predators. They feed using their tongues, which have a rough surface, to scrape algae from the rocks.

The mussel secrets strong fibers called byssal threads, guy wires that tie it to the bottom and to its fellow mussels crowded together securely on the sometimes stormy rocky shore. Mussels pump water through their siphons, filtering food particles.

A clam like the geoduck uses its muscular foot as a shovel . It digs quickly, and must often relocate as sand gets shifted around by heavy waves. A “soft” beach is a very different habitat than a rocky shore, and any mollusk trying to make a living there must be equipped to burrow. Like the mussels, these bivalves pump water to feed.
limpet underside: This limpet underside shows off the strong muscular suction device that keeps the animal attached to rocks.


limpet top: This limpet is starting to rise up on its muscular foot, from its attached position.


mussels: These small mussels, common on docks and pilings, show off the twin siphons through which they filter plankton via a pumping action.

Perhaps the most popular mollusk is the octopus. Our local species, the giant Pacific octopus, reaches 100 lbs. when fully grown, with an armspread of up to 18 feet and more. The 8 muscular arms of these mollusks are lined with powerful suction cups. A scuba diver embraced enthusiastically by “Octopus dofleini” would simply have to wait for his new friend to lose interest and relax its grip.

In the octopus, the traditional mollusk shell is just an interior sliver, but it’s there nonetheless, as it is in the squid and cuttlefish. These smart cephalopods are carnivores, using speed and agility to capture crabs, fish and other prey items with those efficient tentacles.

So despite their differences…in size, shape, feeding habits and intelligence, all these animals and more are bound by family traits that make them the diverse and fascinating mollusks.