Land Snails and Slugs of the Pacific Northwest

Species Accounts

Species Accounts 66 LAND SNAILS AND SLUGS OF THE PACIFIC NORTHWEST Phylum: mollusca class: Gastropoda Subclass: Eugastropoda Gastropods that breathe through gills and have an operculum that closes the aperture when the animal is withdrawn into the shell. order: Neotaenioglossa Superfamily: LIttoRINoIdEA Family: LIttoRINIdAE Genus: Littorina Littorina subrotundata (carpenter, 1864) Newcomb’s Littorine Snail Synonyms: Algamorda subrotundata; Algamorda newcombiana (Hemphill, 1877) Description: A snail of intertidal salt marshes, the shell is higher than wide, turbinate, with a rather globose body whorl and a conical spire tapering to an acute apex. The aperture is teardrop-shaped, about half the height of the shell, and is closed by an operculum when the animal is withdrawn. The shell may attain a height to about 8 mm, but most are smaller. It is brown with narrow lighter or whitish spiral bands. The columellar lip margin is reflected to form a narrow groove under it. Similar Species: The habitat on which it is found separates this species from most other snails. A similar snail in some of the same areas, Littorina sp., has brighter-colored, more distinct and more evenly spaced, alternating yellow and dark brown bands. Its aperture is more bilaterally symmetrical than that of L. subrotundata, and it lacks the distinct twist in the columella and the angle at the columellar insertion. It appears to be more numerous than L. subrotundata in Coos Bay, Oregon, but much less common in the Washington salt marshes. Of the other salt marsh snails, Assiminea californica has a similarly shaped shell, but it is smaller and more narrowly conic than the Newcomb’s littorine snail, and it is uniformly brown, lacking the light-colored bands. Distribution: L. subrotundata inhabits the upper intertidal zone, which is inundated only occasionally. It can be found in the salt marshes on Salicornia (glasswort or pickleweed) or on the mud under these plants. It occurs in a few bays along the Pacific Coast, having been reported from Humboldt Bay, California, to Neah Bay, Washington. However, there has been some controversy over whether or not these reports are of a single species. L. sub­ rotundata occurs in Willapa Bay and Gray’s Harbor, Washington; Coos Bay, Oregon; and presumably in Humboldt Bay, California. Its occurrence is questionable and needs to be confirmed in other areas from which it has been reported. SPECIES ACCOUNTS: LITTORINIDAE 67 2 1 & 2: Littorina subrotundata: Bay Center, Willapa Bay, Pacific Co., WA; scale bar = 1 mm 3: Littorina subrotundata (operculum): Bay Center, Willapa Bay, Pacific Co., WA 4: Littorina sp. (L. subrotundata cf.): Coos Bay, Coos Co., OR; scale bar = 2 mm 4 1 3 68 LAND SNAILS AND SLUGS OF THE PACIFIC NORTHWEST Superfamily: RISSooIdEA Family: ASSImINEIdAE Genus: Assiminea Assiminea californica (tryon, 1865) california Assiminea Description: A small snail of intertidal salt marshes, the shell is higher than wide, turbinate , with a rather globose body whorl and a conical spire tapering to an acute apex. The aperture is teardrop-shaped, about half the height of the shell, and is closed by an operculum when the animal is withdrawn. The shell, with 5 to 5½ whorls, measures less than 5 mm high by about 3 mm wide. It is dark brown, smooth, with no specific markings. There is no distinct groove under the columellar lip margin. Similar Species: Within the salt marshes, Littorina subrotundata is the most similar species, but its shell is larger, relatively broader, and is marked with alternating brown and whitish bands. Distribution: A. californica can be found along the Pacific Coast and the shores of Puget Sound in intertidal salt marshes, in the upper intertidal zone, under Salicornia, and under other plants and debris. Its range extends from southern British Columbia to Baja California. Assiminea californica: South Bend, Willapa Bay, Pacific Co., WA; scale bar = 2 mm SPECIES ACCOUNTS: ASSIMINEIDAE, POMATIOPSIDAE 69 Family: PomAtIoPSIdAE Genus: Cecina Cecina manchurica A. Adams, 1861 manchurian cecina Description: This is a small snail of intertidal salt marshes with a somewhat cylindrical shell. The periphery of the whorls is only gently rounded, and the sides of the spire are slightly but evenly tapered toward the apex, which is normally truncated and healed to a rounded end at about three whorls. As such, the shell measures about 6 mm in length. The aperture is small, obliquely-ovate or teardrop-shaped, and it is closed by an operculum when the animal is withdrawn. Similar Species: No other snail of this...