Checkered Periwinkle (also known as the Tretorn or Zebra Periwinkle)
Phylum: Mollusca, Class: Gastropoda, Order: Littorinimorpha, Family: Littorinidae, Genus: Littorina, Species: Littorina scutulata · Littorinidae (Periwinkle family) · Gastropod, whole spiral shell
Species
Littorina scutulata
Shell Type
Gastropod, whole spiral shell
Family
Littorinidae (Periwinkle family)
Size
Approximately 0.5 to 0.75 inches, which is average for an adult specimen of this species. Adults typically range from 0.4 to 0.8 inches.
Color & Pattern
Mottled dark brown, black, and olive-green checkered or zig-zag pattern over a lighter background. The interior aperture is smooth with a glossy, dark brown or purplish sheen.
Rarity
Very Common
Habitat
Intertidal zone, typically found on rocky shores, intertidal rocks, and tide pools, clinging tightly to surfaces to withstand heavy wave action and desiccation during low tide. Marine species.
Geographic Range
Pacific coast of North America, ranging from the Aleutian Islands in Alaska down to Baja California, Mexico.
Description
A sturdy, compact spiral shell with a pointed spire and rounded body whorl. The surface features fine growth lines and a distinctive checkered pattern of dark markings on a greenish-brown base. The aperture is rounded-oval with a thickened outer lip and no siphonal canal.
Key Features
Small, solid, turbinate shape with a low to moderately high spire; distinctive dark checkering or reticulated pattern; smooth interior outer lip without teeth or folds.
Collector Value
Low to moderate commercial value as it is very common, but it remains a staple foundational piece for micro-mollusk and regional intertidal collections. Typically sold in bulk or minor tourist shops for nominal prices.
Condition Notes
Good condition. Intact overall structure with clear color patterns showing minimal wear or bleaching. Collectibility grade is Good to Fine.
Interesting Facts
Periwinkles are remarkably resilient marine snails capable of surviving extended periods completely out of water by sealing themselves against rocks using a mucous secretion. They feed primarily by grazing on microscopic algae scraped off rocks with their radula.
Ecological Role
Acts as a primary herbivorous grazer in rocky intertidal ecosystems, playing a vital role in controlling algal growth and serving as a key food source for shorebirds, crabs, and small fish.
Similar Species
Littorina plena (Plain Periwinkle), which is often smaller and typically features a distinct white spot or patch on the columella, and Littorina littorea (Common Periwinkle), which is larger and heavily introduced.
Beach Finding Tips
Look along rocky intertidal shorelines during extreme low tide. Check crevices, tide pools, and the sheltered sides of boulders where they aggregate in large numbers.