plankton and detritus
to 1 inch (2.5 cm)
cowry snails, conch snails; Phylum: Mollusca; Family: Calyptraeida
British Columbia to Baja California
These slipper snails have dark brown shells with hooked peaks that face backward. On the inside of the shells, white shelves curved forward at both ends protect the slipper snails' delicate soft body parts. Overturned, empty shells look like tiny slippers, hence the name "slipper snail." Unlike most snails—which use a rasping tongue, called a radula, to scrape algae from rocks—slipper snails use a mucous net to strain small particles of organic material from the water.
Creatures that live on rocky shores are vulnerable to polluted runoff from land. Unfortunately, people discard 350 million gallons of oil every year in storm drains, waterways and on soil. One quart of motor oil dumped down a storm drain can pollute 250,000 gallons of water. You can make a difference by properly disposing of motor oils and other pollutants.
Adult slipper snails lead a sedentary life, stacking themselves on the shells of other snails, with smaller ones sitting atop larger ones.
All slipper snails are born male. When they're two months old, they start changing into females. After several weeks, the change is complete—the males have become females.
To reproduce, male slipper snails deposit sperm under a female's shell. Her eggs hatch into larvae that stay put until they've developed into exact miniatures of adult snails. Periodically, females lift their shells and, with their heads, push the juveniles out into the cold marine world. Newly hatched young can't cling well, so they sink to the bottom, where they scrape algae from rocks. Eventually they're able to cling to host snails, like their parents, where most become immobile—even depending on the host snail to carry them away from predators.