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Northwest Wildlife Online
By John M. Regan
Phylum Mollusca
Clams, Oysters, Squids, Octopus, Slugs, and Snails
Protozoans Sponges Cnidarians Ctenophores Arthropods Echinoderms Mollusks Nematodes Flatworms Annelid Worms
Birds Mammals Reptiles Amphibians Fish Invertebrates Home
Mission Editor Bio Contact Wildlife Park Links Further Study Wild Employment Northwest Trek
On the left is the 5 inch long European Red Slug, Arion rufus. An introduced species, European slugs are enemies of gardeners everywhere. The slug on the right is a homegrown Pacific Banana Slug, Ariolimax columbianus. Found more often in the forest than the garden these members of the Mollusca phylum are reported to grow from 10 to 18 inches long. Most of the ones I've seen, however, are in the 3- 4 inch range. Banana slugs are seldom found in our gardens. They tend to keep to the forest where they happily munch mushrooms instead of tomato plants. ON the far right is one of the more unusual representatives of the Phylum Mollusca - a Nudibranch. Looking for all the world like the sea slug it is, these guys come in a variety of beautiful colors.
Some our most popular and least popular invertebrates are found in the phylum we call Mollusks. Ask anyone to name their favorite animal species and it is the rare person who names a slug or a snail. Hairless, cold, and slimy - these oozing, legless creature are pretty well shunned by humanity. But they do have their fans, and once you get past the ooze and slime you'll find an interesting creature.
Snails and slugs have some very popular and fascinating relations. Perhaps the most intriguing invertebrates to observe, squids and the octopods are also members of this group. And at the American dinner table clams and oysters are hardly strangers.
On the left is a color variation of a Banana Slug. To the right a pair of Gray Slugs demonstrate the hermaphroditic character of their species. The male part of one slug inseminates the female anatomy of the other and vice versa. Slug courtship is often elaborate, lengthy, and very unique.
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Let's start the largest class of mollusks, the
Gastropods, our snails and slugs. To begin with,
both have shells. In the slug, however, it's so small and recessed under the skin that we can't see it.
Slugs are hermaphroditic - like many worms they possess male and female sex
organs. If that were not odd enough, many slugs mate while hanging
together from a mucous strand of slime. Most slugs have complex,
almost bizarre mating behavior. In one species an actual sperm "dart" is
injected into the skin of the partner. Some actually caress each other for
extended periods prior to mating. And you thought they weren't lovable!
That slime trail we find so repulsive is not only a great help to slug transportation, it also serves as protection and a scent trail for other slugs to follow. Slugs and snails have four obvious tentacles protruding from their head. The uppermost ones are called cephalic tentacles and eye on the end of each. Beneath these cephalic tentacles are the smaller oral tentacles used for touch and smell. The swollen area behind the slug's head is called the mantle, and the large hole visible in the Red Slug above is the pneumostome, a breathing hole. Just about the entire length of the bottom, ventral, part of the slug is the foot and is responsible for locomotion.
The most common slugs in our area, in addition to those pictured above are the Gray Slug, (Limus maximus) and common Rufous Garden Slug (Arion ater). If you decide to research these guys, however, be ready for a wide variety of common names.
Pictured below is another European import, the European Black Slug. This slug is about the same size as the Banana Slug but with a striking black velvet color.
Snails share many of the same characteristics of slugs with one obvious exception - their noticeable shell. Typically it is a conic sphere that whorls upward and away from the animal. Each species of snail has a particular pattern to its shell. Snail shells spiral clockwise (to the right) or counter clockwise (to the left). The head and foot of the snail are drawn into the shell by a retractor muscle and the opening covered by a hard cover called the operculum.
Clams, oysters, scallops, and mussels are known collectively as Bivalves and our region fairly abounds with them. All of these animals display a clam like shape composed of a shell with two hinged valves that completely enclose the body. Of tremendous economic importance around the world for their edibility, most people do not realize that they make very interesting aquarium pets. I have raised freshwater clams and they are surprisingly active moving with the aid of a foot that protrudes from the shell. It's an amazing thing to see. Equally fascinating is their filter feeding mechanism, an easily observed activity in the aquarium. Of the thirty or so species in our area the Razor Clam, Siliqua patula, and the giant Goeduck, Panopea generosa, the largest burrowing clam in the world, are the most well known. (Pronounced "gooey-duck" for you out of staters.)
How did the Goeduck get its name? According to David George Gordon's book, "Field Guide to the Goeduck," there are two explanations. The likely explanation is that the name is a European corruption of the Nisqually Indian word, "gweduc," meaning dig deep. Another story says the the first white man to recognize the clam was John F. Gowey. Well known for his penchant for duck hunting Gowey would sometimes return from hinting forays with the big clams in his pouch. This led to the appellation "Gowey Ducks." The Goeduck, Panopea generosa, pictured above, is just one of several very large Pacific Coast bivalves. I've heard wild claims about Goeducks of three feet in length, but the largest I can verify was slightly less than a foot long, but still not a bad size for a clam. And I can testify that they do taste good.
Pacific Blue Mussel Mytilus edulis. Normally found bunched together in quite tide pool locations; edible; also called the blue Mussel. Known to man for a long time this mussel was first classified by the Linnaeus in 1758. On the right California Mussels, Mytilus californicus, cover a hug rock at Cannon Beach, OR. The green area to the left marks the boundary where Ochre Sea Stars can reach the mussels and feed on them.
The most active, interesting, and largest of the mollusks are in the Cephalopod Class. Squids and octopus are remarkable animals. Characterized by complex behavior and abilities we are constantly learning new things about cephalopods. This class of animals also includes some of the most brilliantly colored members of the animal kingdom. Expansion and contraction of specialized cells called chromatophores in many squids and ocotpods produce spectacular and dramatic color changes.
Once again we are blessed in the Northwest with an easily accessible variety of these creatures. The monarch of Pacific cephalopods is, of course, the Giant Pacific Octopus (Octopus dolfeini). With an arm span of 30 feet and a weight up to 600 pounds this true giant is the largest octopus in the world. They can be found in relatively shallow, intertidal zones. On the other end of the octopus size scale we have the 4 inch long Red Octopus (Octopus rubescens).
Looking more like an octopus than a squid is the Stubby Squid (Rosia pacifica). Also called the Short Squid, at an inch and a half long he is a cute little guy with an over sized head and large eyes. Favorite of the sportsman is the Opal or Opalescant Squid (Loligo opalescens). Eight inches long and the color of white pearl Opal Squids are caught at night by suspending a lantern over the side of a dock. The squid are attracted to the light and are then caught by yanking up on a jigging rig.
Take your pick among the mollusks as to which is the most interesting. Any one you choose to study will reward you with a lifetime of fascination - and you're in one of the prime regions of the world to do it.
Protozoans Sponges Cnidarians Ctenophores Arthropods Echinoderms Mollusks Nematodes Flatworms Annelid Worms
Birds Mammals Reptiles Amphibians Fish Invertebrates Home
Mission Editor Bio Contact Wildlife Park Links Further Study Wild Employment Northwest Trek
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