Acharax johnsoni, DALL, 1891

Charles L. Powell, Ii, Clites, Erica C. & Poust, Ashley W., 2019, Miocene marine macropaleontology of the fourth bore Caldecott Tunnel excavation, Berkeley Hills, Oakland, California, USA, PaleoBios 36, pp. 1-34 : 5

ACHARAX JOHNSONI DALL, 1891

FIG. 4

The single, double-valved specimen, UCMP 410421, compares well with Acharax johnsoni . This specimen has numerous, shallow, radial ribs and interspaces, which occur from the anterior end past the middle of the shell, characteristics shared by Ach. johnsoni . The poor preservation and single specimen make precise identification impossible. Fossil Ach. johnsoni are rare in the eastern Pacific occurring only in the Pliocene (Woodring 1938; Roth, 1979) from northern and southern California, while in the western Pacific it has been reported from the Eocene to Pliocene (O'Hara and Nemoto 1988, Nobuhara and Tanaka 1993, Kafanov and Ogasawara 2003, 2004). Coan et al. (2000) list the modern range of Ach. johnsoni as from Sitka, Alaska, south through to the Isla de Afuera, Peru in water depths from 400 to 4,100 m.

The family Solemyidae favors reduced oxygen and high organic content environments, and harbors chemoautotrophic bacteria in their gill filaments to obtain nutrition. In the northeastern Pacific they are typically found in basins on the continental shelf and nearshore where there is an accumulation of plant debris ( Coan et al. 2000). It is represented by two genera off the coast of California and the northeast Pacific, Acharax and Solemya , with three modern species and three fossil species. Modern species include Solemya (So.) reidi Bernard, 1980 which occurs from Vancouver Island, British Columbia, Canada, south to San Diego, California at water depths between 40 and 600 m ( Coan et al. 2000), So. (Petrasma) valvulus ( Carpenter,1864) which occurs from Monterey Bay, California south to Jalisco, Mexico, including the Golfo de California at water depths between the intertidal zone and 360 m, and Ach. johnsoni occurring from Sitka, Alaska through the Golfo de California south to off Lima , Peru at water depths between 100 and 5,379 m ( Coan and Valentich-Scott 2012). In addition to the modern species there are three fossil species in the Pacific northwest: Ach. dalli ( Clark, 1925) from the lower Miocene of Washington ( Addicott 1976), Ach. ventricosa ( Conrad 1849) from the middle Miocene to lower Pleistocene of Washington south to northern California (Moore 1963, Addicott 1976), and Ach. willapaensis (Weaver, 1942) that occurs from the upper Eocene to lower Miocene of Washington (Weaver 1942).