Littorina plena Gould, 1849
Phylum Mollusca, Cl. Gastropoda, Subcl. Orthogastropoda, Superorder Caenogastropoda, O.Sorbeoconcha, F. Littorinidae
Periwinkle; shell to 19 mm; black or w. fine marbling on background of brown, olive or black, usually w. fine incised spiral grooves; aperture less than half length of shell w. narrow stripe at base of aperture (arrow) but lacks flattened parietal area of L. keenae; columella narrow; cephalic tentacles black or with longitudinal black dark stripe.
Abundant throughout intertidal zone; exposed & protected outer coast, also salt marshes & estuaries.
Geo Range: Kodiak Is. Alaska to Baja
Synonyms: included in Littorina scutulata until 1979.
Similar species: Littorina scutulata has black bands on tentacles & lacks spiral grooves; L. keenae is larger, has smooth parietal area & a stripe on interior of aperture. Must examine reproductive structures to confirm identification.
Image: L. plena (center & left), probably L. scutulata at right