PIECING TOGETHER THE MARINE DEEP-WATER MUD-SHRIMP, CALLIANOPIS CLALLAMENSIS (WITHERS), LATE OLIGOCENE-EARLY MIOCENE OF NORTHWEST WASHINGTON STATE, USA

The fossil mud-shrimp Callianassa clallamensis (Thalassinidea) was first discovered in 1868 from Oligocene sedimentary rocks that crop out along Clallam Bay on the northern Olympic Peninsula, Washington State. It was first described as C. clallemensis by Withers (1924) based solely on small cheliped pieces. Rathbun (1926) further described C. clallemensis, and named a new species, C. twinensis, from cheliped pieces found in outcrops farther to the east of Clallam Bay. All these sedimentary rocks are now included in the Pysht Formation, the uppermost member of the Twin Rivers Group, that spans the Oligocene-Miocene boundary. Sedimentary and paleontological features indicate that the shrimp-bearing strata in the upper Pysht Formation were deposited in upper slope to bathyal depths.

In the last 20 years, an extensive collection of this fossil thallassinid has been assembled, most notably by Ross and Marion Berglund. Their generous donations of fossil decapods to the Burke Museum, University of Washington and other institutions has resulted in a comprehensive collection of almost all anatomical hard-parts of the both species of shrimp. The two described species from the Oligocene/Miocene of northwestern Washington have been reassigned from the genus Callianassa to Callianopsis, and in fact C. clallamensis is recognized as the male and C. twinensis as the female of the same species (Schweitzer Hopkins and Feldman, 1997). Abundant specimens of this taxon are preserved in calcite- cemented concretions, frequently as disassociated parts. Thus it is now possible to piece together separate body parts to render a more complete morphological reconstruction of both the male and female animals and compare these to Withers' and Rathbun’s holotype, photographs and original diagrams. This new composite reveals considerable sexual dimorphism and the close morphological similarity with the extant species Callianopsis goniophthalma (Rathbun, 1902) that lives at slope depths from the Gulf of Alaska to Baja California, Mexico.