UC Davis Natural Reserve System
Stebbins Cold Canyon Reserve

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Mullusks of Cold Canyon

Mollusks (Phylum Mollusca) are the group that includes octopuses, squid, clams, oysters, and snails. Although these animals are all quite diverse in body form and lifestyle, they have certain commonalities that betray their shared evolutionary history. For instance, they all have a radula, a tongue-like organ lined with sharp teeth-like protrusions, used for feeding. Mollusks are a successful group in evolutionary terms, which means that they have evolved into a plethora of species. All mollusks share a soft, unsegmented body, and their skin is not covered by a chitinous external skeleton as in insects or a cuticle like our own skin. This means that they basically cannot control evaporation of water from their skins, a limitation which restricts most kinds of mollusks to an aquatic existence. Because they are vulnerable in dry environments, even terrestrial mollusks inhabit only moister areas.

The only mollusks that occur in Cold Canyon are snails and slugs. When most people think of snails, they think of the common garden snail, which eats holes in their petunias and young tomato plants and becomes a disconcertingly crunchy nuisance underfoot on garden paths at night. In fact, the brown gardensnail (Helix aspersa) is only one of an estimated 30,000 kinds of terrestrial snails worldwide and is unusual in its habit of feeding on green, living plants. Most snails are the size of a pebble and never make themselves known to gardeners and farmers. Instead, they live in moist, shady places, quietly feeding on dead and decaying plant material, thus reducing the detritus to ever-smaller particles, which speeds up decomposition and soil formation.

Snails have shells made out of calcium carbonate, into which their internal organs are coiled, and slugs are their somewhat tubular relatives that through evolution have ceased to have a shell. A small evolutionary remnant of the ancestral shell (a "vestigial" shell) sometimes occurs buried in the tissues of the slug's back. There are several hundred kinds of slugs worldwide, but they are mostly restricted to cool, humid, and generally forested regions.

Snails and slugs are hermaphroditic, which means that each individual can produce sperm and eggs at the same time. Nevertheless, to produce offspring, they usually seek to mate with other individuals of their species. Mating is often preceded by a lengthy "courtship" of mutual circling and touching, which scientists believe sends a message to its partner that it can produce healthy offspring, much like the message male birds send with their bright plumage.

Cold Canyon Reserve has not been studied by malacologists (mollusk biologists), so we do not know exactly what kinds live here. You may actually be the first person to discover that a species occurs in the reserve, and interested malacologists are encouraged to study this area. The following information is based on the distributions of snails and slugs elsewhere in the Coast Ranges of California.

Shoulderband (Helminthoglypta spp.). The shoulderband, a snail with a shell about an inch in diameter, may be a reserve inhabitant. Shoulderbands look similar to brown gardensnails (Helix aspersa) known from human-dominated California landscapes, but their tan shells have a single narrow dark band rather than a broad zone of dark, cloudy pigment. The name shoulderband refers to the narrow band on the "shoulder" of the shell. More than 60 species of Helminthoglypta are native to California.

Lancetooth snail (Haplotrema spp.). Lancetooth snails are flat-shelled snails without bands; the shell is greenish-yellow with a waxy luster and is about 0.5 to 0.75 in. (1.3 to 1.9 cm) in diameter. The head and foot of the animal are pale buff or cream-colored. Haplotrema spp. are unusual among snails in that their diet also includes other snails; the "teeth" of their radula are sharp and elongate (leading to the common name "lancetooth"), presumably as an adaptation to this food source.

Pacific bananaslug or leopard slug (Ariolimax columbianus). The only species of land mollusk already observed to occur in the reserve is a large yellowish or olive-brown slug, sometimes almost covered with black patches. This peculiar appearance explains its common names. Sometimes reaching almost 10 in. (25.4 cm) in length, the Pacific bananaslug is one of the largest species of slugs in the world. Most individuals in Cold Canyon Reserve are somewhat smaller. It has been suggested that the metabolic cost of producing mucus (which slugs and snails need to glide on) makes slugs much larger than this species biologically improbable.

Credits: All pictures were obtained from Calphotos (http://galaxy.cs.berkeley.edu/photos/fauna/).

Last Updated 03/09/06