Nebalia gerkenae, a new species of leptostracan (Crustacea: Malacostraca: Phyllocarida) from the Bennett Slough region of Monterey Bay, California

—A new species of leptostracan crustacean, Nebalia gerkenae, is described from Bennett Slough, Monterey County, California. The species is similar to N. hessleri from deeper waters off La Jolla, California. It differs from N. hessleri in the shape and color of the pigmented region of the eyes, armature of the antennule and antenna, the degree that the carapace covers the abdominal somites, dentition of the protopod of the fourth pleopod, and details of the pleonite border spination. Variation in this spination is discussed, and guidelines are suggested for future descriptions of leptostracan species. The Leptostraca are malacostracan crustaceans characterized in part by a hinged rostrum, bivalved carapace, phyllopodous thoracopods, and the presence of seven abdominal segments (Kaestner 1980, Schram 1986). In the marine environment, these animals are ubiquitous. They have been recorded from a wide range of habitats, including intertidal mudflats, mangrove lagoons, caves, submarine canyons, the bathypelagic zone, and hydrothermal vents. The order Leptostraca includes 32 nominal species in nine genera. However, the true diversity of the group far exceeds this number; the literature includes many references to collections of undescribed species (Dahl 1985, Vetter 1996b, Olesen 1999). Historically, the leptostracan Crustacea of the Pacific Coast of the United States have all been identified as Nebalia pugettensis (Clark, 1932). Although sometimes present in large numbers (Vetter 1994, Gerken 1995), the leptostracan fauna of California is poorly known. Ecological studies on Leptostraca of southern California (Vetter 1994, 1996a) led to the recognition of three taxa, two of which have been described. Nebalia daytoni Vetter, 1996a, was recorded from oligotrophic sands off the coast of San Diego. Nebalia hessleri Martin et al., 1996, was described from enriched sediments and detrital mats at the head of Scripps Canyon off La Jolla, California. Because Clark's (1932) description was inadequate and type material was not available, Martin et al. (1996) declared Nebalia pugettensis (Clark, 1932) a nomen nudum. Actually, the name Nebalia pugettensis is available, but a neotype must be established in order to avoid taxonomic confusion. Thus, in addition to N. pugettensis, two valid nominal taxa and one undescribed species have been reported from the coast of California. In addition, the identity of populations formerly referred to as N. pugettensis is uncertain. New collections of leptostracans from Monterey Bay represent a fourth species of Nebalia from the coast of California, described herein. VOLUME n 3 , NUMBER 4 997 Materials and Methods The leptostracans were collected from intertidal algal mats of Chaetomorpha sp. and Gracilaria sp. Salinity, recorded with a hand refractometer, was 33-34%c. Most specimens were placed directly into 75% ethyl alcohol, but five specimens were preserved frozen using dry ice and later transferred to a freezer held at ^80°C. Written descriptions and illustrations are of the mature females. Additionally, sexually dimorphic features are described. Illustrations were made with the aid of a camera lucida attached to a Wild M5APO dissecting microscope and a Nikon Labophot. Specimens were prepared for scanning electron microscopy according to the method of Martin et al. (1996) and examined with a Cambridge Stereoscan 360. Length measurements were made from the base of the rostrum to the center of the posterior emargination of the carapace (dorsal carapace length) or to the tip of the caudal ramus but excluding the setation (total length). The carapace also was measured in the lateral aspect from the anterior to posterior margin (lateral carapace length) and from the dorsal to ventral margin (carapace height). The female holotype, male allotype, and 60 paratype specimens were deposited in the Crustacea collections of the Natural History Museum of Los Angeles County (LACM). Additionally, 54 paratype specimens (34 of which are juveniles) have been deposited in the National Museum of Natural History, Washington, D.C. (USNM).