Soft corals of the family Nephtheidae have received limited attention in recent literature. Since morphological characters of several genera have been shown to overlap, revisionary systematics of much of the family is necessary (L.P. van Ofwegen, pers. comm., and Ofwegen & Groenenberg, 2007). Three nephtheid genera have recently been described, Pacifiphyton Williams, 1997, Leptophyton Ofwegen & Schleyer, 1997, and Chromonephthea Ofwegen, 2005.
Species in the genus Gersemia are cold-temperate to polar taxa, ranging from 21 m to depths over 2000 m (present paper). The descriptions of G. antarctica and G. marenzelleri (Kükenthal 1906a and Kükenthal 1906b, respectively) are the most recent descriptions of species belonging to this genus, with the exception of the new and revised species described here. The remaining nine species were described between 1806 and 1900.
Throughout the past twenty years, the Monterey Bay Aquarium Research Institute (MBARI) has been using remotely operated vehicles (ROVs) to explore the deep in the Monterey Bay and other locations in the northeast Pacific Ocean. ROV surveys at nearby seamounts and dive sites within Monterey Canyon have yielded many new species descriptions recently, including several gorgonian corals (Cairns, 2007) and an unusual predatory sponge, Cladorhiza pteron (Reiswig & Lee, 2007).
The new species of Gersemia described in this paper was first discovered and collected at Rodriguez Seamount in 2004 and has since been observed and collected at other seamounts off the coast of California, in Monterey Canyon, and on the continental slope off northern California, central Oregon, and northern Washington (fig. 1).