Northern Range Extension for Assiminea translucens (Carpenter, 1864)
Robert G. Forsyth
[Reprinted from The Festivus 35(2): 17-18]
Figure 1. Assiminea californica. Larcom Island, Observatory Inlet, B.C., Canada. RBCM 002-175-004.
Assiminea translucens (Carpenter, 1864), better known by its junior synonym A. califomica (Tryon, 1865), is a minute semi-marine gastropod (Rissooidea: Assimineidae) previously recorded along the west coast of North America from Vancouver Island, British Columbia, Canada (Oldroyd, 1927; Keen, 1971; McLean, 1978) to Puerto Lobos, Cabo Tepoca, Mexico (Skoglund & Koch, 1995). Baxter (1987) did not record this species from Alaska, but included it his list as a species with potential to be found in Alaska. According to J.H. McLean (personal communication, 2002), there is a northern record of A. translucens in the Smithsonian Institution from “Granges Harbor, Vancouver Island” (USNM 150953), but this locality is likely Ganges Harbour, Saltspring Island, since there is no locality by the other name. (The California Academy of Sciences does not have any holdings of this species from British Columbia; E. Kools, personal communication, 2002).
A. translucens has been recorded from this and other localities (based on Royal British Columbia Museum and Forsyth collections) around the southern Strait of Georgia, including Vancouver Island, north to Union Bay, Vancouver Island, B.C. (49° 35' N, 124° 53' W; Forsyth collection). It is locally common in salt marshes at the heads of bays and inlets. In these situations, the dominant plant is American glasswort, Salicomia virginica. The gastropod usually associated with A. translucens is Myosotella myosotis (Draparnaud, 1801). but in some places, Littorina subrotundata (Carpenter. 1864) and Cecina manchurica A. Adams, 1861, also occur with it. On one occasion, I have encountered A. translucens on a rocky shore in Howe Sound, near Vancouver, British Columbia living among mussels (Mytilus trossulus Gould, 1850), and the acorn barnacle (Balanus glandula Darwin, 1854).
On 26 June 2002, Assiminea translucens was found on a cobble and gravel beach on the east side of Larcom Island, Observatory Inlet, British Columbia, Canada (55° 23.39' N, 129° 43.6' W) (Figures 1, 2). In Observatory Inlet, Assiminea translucens was living on the undersides of cobbles and small stones along with Littorina sitkana (Philippi, 1846), Tectura persona (Rathke in Eschscholtz, 1833), and acorn barnacles (Balanus glandula). Associated plants included seaside plantain (Plantago maritima juncoides), sea milk-wort (Glaux maritima obtusifolia), sedges, and several other brackish-water plants. Assiminea translucens extended down the gently sloping beach to the upper limit of the Mytilus trossulus and rockweed (Fucus sp.) zone. It was absent higher on the beach, where the dominant vegetation consisted of sedges (Carex sp.), grasses, and arrow grass (Triglochina maritimum).
Figure 2. Larcome Island, Observatory Inlet, B.C., Canada. Left foreground: cobble beach occupied by Assiminea californica.
This new record on the north coast of British Columbia, near the southern end of the Alaskan Panhandle and at about the same latitude as Ketchikan, Alaska, represents a range extension northward from the Strait of Georgia, B.C.
All specimens have been deposited in the invertebrate collection of the Royal British Columbia Museum (RBCM 002-175-004; 26 specimens, dry). The largest specimen (Figure 1) measures 2.9 mm high.
I thank Dr. James H. McLean (Natural History Museum of Los Angeles County) for advising me of the correct name to use for this species and for bringing the “Granges Harbor” record to my attention, and Elizabeth Kools (California Academy of Sciences) for checking the California Academy of Sciences collection.
LITERATURE CITED
BAXTER, RAE. 1987. Mollusks of Alaska. Shells and Sea Life, Bayside, Calif. 163 pp.
KEEN, A. MYRA. 1971. Sea Shells of Tropical West America; Marine Mollusks from Baja California to Peru, 2nd edition. Stanford University Press, Stanford, Calif.: xiv + 1064 pp.
McLEAN, JAMES H. 1978. Marine shells of southern California. Natural History Museum of Los Angeles County, Science Series 24 (revised): 104 pp.
OLDROYD, IDA S. 1927. The Marine Shells of the West Coast of North America. Stanford University Publications, University Series, Geological Sciences 2(3): 603-941, pls. 73-108.
SKOGLUND, CAROL & ROBERT KOCH. 1995. New distributional information for Panamic Province Rissoidea (Mollusca: Gastropoda). The Festivus 27(2): 23-28.