Know Your Neighbours: Essential Shells

June-July 1999

This is an article from WaveLength Magazine, available in print in North America and globally on the web

by Bryan Nichols

Few things symbolize the sea shore better than seashells, whether she sells them or not.

Alive, they are obvious and plentiful, often the most abundant intertidal critters we see. Recently dead, most are edible, a staple of coastal peoples worldwide and regulars on expensive seafood menus.

Long dead, we have collected and traded them for millennia, way back into our hairy prehistoric past. For whatever reason, we don't consider their bleached bones morbid. Quite the reverse-we have used them for romance, money, home décor, sports and even music. Traded far inland, big snail shells remind us of the ocean when we are landlocked; listen, can you hear it?

Though shells are familiar, the animal inside often isn't (even if we're eating it).

TAXONOMY

(What are they and who are they related to?)

Sea shells are made by molluscs, proud members of the Phylum Mollusca, which is a big one-perhaps one hundred thousand living species and lots of fossils' shells preserve well. Molluscs themselves are mushy, unsegmented critters that live a number of very different ways, from filter feeding clams to speedy predatory squid. From a shell perspective, most are either gastropods with a single shell (Class Gastropoda, the stomach foots) or bivalves with two (Class Bivalvia).

It's worth mentioning the lamp shells, since Northwest paddlers can bump into at least one type. Though they

look a bit like bivalve molluscs, they are actually brachiopods, remnants of a phylum (Brachiopods-the arm foots) that once had tens of thousands of species. Brachiopods hit their peak long before the dinosaurs were a glimmer in some amphibians eye. The evolution of predators made them obsolete long ago and now only a few hundred scattered species hang on.

ANATOMY

(How do they work?)

Mushy molluscs use a shell gland to take calcium from the water and grow their own protection; shells are like a heavy skeleton on the outside. Most gastropods have a muscular "foot" they can cruise around on and a tooth-like radula for scraping or spearing. The bivalves use a large muscle to keep their shells closed, and often have siphons to bring water in and out.

ECOLOGY

(What do they do?)

Bivalves lead boring lives, fixing themselves to rock or burying themselves in the sand. Most of them filter feed, pulling in water and straining the tasty bits out. This sort of lifestyle was initially very effective and filter feeders covered the bottoms of ancient oceans. Despite their protective shells, they were sitting ducks, and predators evolved to eat them. Now they are most common in the harsher interridal zone, where they are harder to get at.

Gastropods are more active-many are grazers, roaming about scraping algae off rocks. There are also lots of scavengers and predators--some tropical snails even use poison to help subdue their prey.

Though seemingly harmless, remember that filter feeders have a tendency to accumulate toxins. Never eat bivalves (oysters, mussels, clams etc) in polluted waters. Even in wilderness settings, toxic algae that cause red tides and paralytic shellfish poisoning may be present. PSP took out some of Captain Vancouver's crew, long before pulp mills, sewage effluent and fish farm residue became so popular along our coast. Before you eat any bivalve, be sure you've checked for red tide closures.

Now get out there and paddle around-you'll quickly discover the following shelly critters. For you inquisitive types, there are hundreds more shells on our coast.

Lifelist #5 - Shelled Molluscs

MUSSELS Mytilus species (mussel)
We're all familiar with the clusters of blue, black or brownish mussels that grow intertidally throughout the Northwest. Blue type mussels grow to 15cm and form dense mats on rocks, pilings and such. California mussels are bigger (to 26cm) and can completely cover stretches of surf-battered shoreline. Their sharp shells make launching and landing difficult-their tasty flesh can make remote campsites divine. Check for closures though-government scientists use mussels to predict red tides because they accumulate the toxins quickly.

HEART COCKLE Clinocardium nuttallii (nutty's sloped heart)
A big (to 14cm) and common cockle that is yellow and brown with about 35 ribs and thin wavy lines across them. Younger cockles usually have a mottled look. They live below the sand and gravel in protected bays-a sterile looking beach might hide oodles of these popular filter feeders just below the surface. Their empty shells often wash up, the victims of moon snails, sea stars, worms and other predators.

OLYMPIC AND PACIFIC OYSTERS Ostrea conchaphila (mussel-like bone) Crassostrea gigas (big thick bone, heh heh). White, irregular shells scattered across rocky or soft bottoms. The native olympics only grow to 9cm and prefer gravelly bottoms. The big Pacific oysters (to 30cm) were brought as "seed" from Japan and are constantly replenished by the commercial industry. As a naive and prudish biologist, I know oysters are supposed to enhance something but I'm not sure what.

LEAFY HORNMOUTH Ceratostoma foliatum (leafy hornmouth) These large (to 9cm) snails have a beautiful shape highlighted by three wavy frills and a long "tooth". They are common on rocky shores where they dine on mussels and barnacles. Motionless when dry, try watching them in (slow motion) action when they are just below the surface of tidepools or calm shores.

GEODUCK (pronounce it gooey duck) Panopea abrupta (abrupt all open) All you will see of a healthy geoduck is the top of the siphons, which is just as well. These large (the shells alone reach 12cm) clams cannot fully retract their dangling siphon and the resulting sight is not for the faint of heart or deeply religious. The world's largest intertidal clam lives in sand, mud or gravel and can weigh over four kilograms. Oddly enough it's also one of the Northwest's oldest animals-studies show they may live to 145 years. Sitting in mud for a century and a half-I figure they become deeply philosophical.

GIANT ROCK SCALLOP Crassadoma gigantea (giant thick house) The heavy shell is permanently at- tached to rocky bottoms and usually coated in critters, especially yellow boring sponges. When submerged, a row of eyes will peek at you from the open valves. The intertidal ones often fall victim to us hungry humans. I make it a practice never to eat any animal older than my illegitimate teenage offspring-alas, tasty rock scallops may reach 50 years.

WHITECAP LIMPET Acmaea mitra (ultimate cap) Unlike the hordes of confusing flat limpets, this one is nearly as high as it is , tall and usually covered in an attractive pink coating of coralline algae. They live on rocky shores, particularly where there is plenty of pink coralline algae to eat and wear.

HAIRY TRITON Fusitriton oregonensis (spindle shaped from Oregon) Snails got hair? This big snail (to 15cm) really is hairy looking, though of course it isn't true hair. It's known for eating sea urchins and laying eggs that look like white corn.

TUSK SHELLS Class Scaphopoda, Family Dentaliidae (toothy hollow foots) Another oddball shell, these long (to 13cm) white tubes are open at both ends - unique and a class unto themselves. Like tusks, some are slightly curved, some are straight. The live critters live under subtidal sand and filter feed but storms may wash up their shells, especially off the West Coast of Vancouver Island. Coastal tribes used them for jewelry and currency so finding them is like finding ancient money on the beach.

PURPLE-RING TOPSNAIL Calliostoma annulatum (ringed beautiful mouth) It's pretty hard to miss these outrageously beautiful snails, if you're lucky enough to paddle past one. A bright gold /yellow background with beaded rings of purple. Even the snail inside is a vivid orange. Look for them on rocky shores along the open coast. Low tide is your only chance and beware-once you've seen the Northwest's most beautiful snail, the others will all seem drab.

Copyight Bryan Nichols 1999 No reproduction without pemission of the author

For more info I recommend the book Shells & Shellfish of the Pacific Northwest A Field Guide. See my review of this book below.

Shells & Shellfish of the Pacific Northwest A Field Guide

Shells & Shellfish is exactly the sort of field guide we need more of. It is comprehensive - if you see a clam, chiton or snail out there, it's almost assuredly in this guide. It is colorful - there are excellent, full color photos for each species. And it is well written - Nanaimo biologist Rick Harbo has plenty of experience with field guides and writes clearly and concisely.

THE GOOD STUFF
The guide is full of bonuses. The color plates are attractive and well laid out. There are color coded sections for bivalves, siphons, gastropods, tusk shells and chitons. The section on siphons is unique - color photos and descriptions of the only part of a healthy, undisturbed clam you should see.

The text includes a smattering of biology with accompanying drawings - very helpful in understanding these odd creatures. The species accounts, which are divided taxonomically, include alternate names, size, range, habitat, a verbal description and occasional comments (including edibility). As usual, the comments often make for fascinating reading.

NITTY GRITTY
The standard Harbour field guide size of 14x22cm, it's a substantial 270 pages but still very packable. Color plates form the first third - text with line drawings and b&w photos makes up the rest.

The appendices are very helpful, starting with an excellent (ten page) checklist of all the molluscs that notes which are intertidal and/or edible. This is followed by a short but helpful list of further reading divided into categories and a list of contacts for harvesting and red tide info. There is a glossary of terms as well as a glossary of scientific names explained - not all of them, but still very helpful for remembering. Finally, the index is quite good.

IF I WERE EDITOR
This is an excellent book, but dividing color photos and text descriptions always makes a field guide a little harder to use. With digital printing technologies available now, I would consider putting color throughout (like Harbo's general guide "Whelks to Whales"). If that's too expensive, then instead of repeating habitat info in the color and text sections, I'd bump habitat to text only and include a couple key descriptive field marks so they are right there with the picture. That would make the guide quicker and easier to use for many species.

TAKE IT HOME?
From hardcore seashell freaks to occasional paddlers, this is a fine bookshelf reference that you can also pack on trips.

GORY DETAILS
Shells & Shellfish of the Pacific Northwest
A Field Guide
Rick M. Harbo
Harbour, 1997
270 pg, $24.95 cdn
1-55017-146-1

Shells and Shellfish of the Pacific Northwest can be bought at Amazon.com

Shells and Shellfish of the Pacific Northwest can be bought at Chapters.ca (Canadian site and Canadian dollars)

Bryan Nichols comes out of his shell to write this regular column.