In August 1959 Pacific Marine Station (P.M.S.) located at Dillon Beach, began a program of oceanographic study as a member of the California Cooperative Oceanic Fisheries Investigations (C.C.O.F.I.). The program continued throughout the summer of 1963 and consisted of a monthly hydrographic station and sampling the plankton at the head of Bodega Submarine Canyon, located twenty-five miles west of Bodega Bay. Two plankton tows were taken on each ocean run. One of the samples, along with collection and hydrographic data, was sent to Scripps Institute of Oceanography. The other sample was retained at P.M.S. and constitutes the material for the present study. Pelagic gastropods were present in every tow in varying numbers and species. Two groups, pteropods and heteropods, were found in the samples. One species of pteropod, Limacina helicina, was the dominant member in all of the tows and occurred during the entire year. Little work has been done on the pelagic gastropods of the North Pacific. The information available has been mainly compiled by Tesch in the Dana Reports and McGowan (1960). Taxonomically the group has been extensively studied, but little is known about the life cycles, size ranges, growth rates, physiology, behavior, distribution and abundance. No previous study on the pelagic gastropods collected by P.M.S. has been made. This paper is a discussion of the pelagic gastropods collected over a period of four years. It is the purpose of this study to identify, examine, and present information of the local specimens collected by Pacific Marine Station.

Work on the copepoda parasitizing anoidiens has been relatively extensive in Europe, loss so on the East Coast of the United States and negligible on the West Coast. of this work, a major portion has been concerned with the solitary ascidians, while the colonial or compound forms have been largely neglected. The apparent lack of interest in copepods parasitizing compound be attributed to the manliness of the animals, their associations with both Zooids and the colonial matrix which makes dissection difficult and the chaotic condition of their taxonomy.

Two common limpets, Collis~ (Acmaea) digitalis and Collisella (Acmaea) scabra have overlapping distributions in the upper int.ertidal .spray zone. Haven (1971) found that Q. digitalis is more abundant on vertical surfaces while Q. scabra dominates horizontal surfaces. He assumed this preference to be due to differential abilities to withstand desiccation. In this study I report field work demonstrating a high correlation between the-ratio of abundance of Q. digitalis/ Q. scabra and angle of slope of substrate. Length (mm) of Q. scabra declines linearly with angle, but Q. digitalis shows no such trends. Results of laboratory measurements of angle of substrate and small and large members of the species do not alone explain the size distribution and abundance relationships found be·tween the two species in the field .• Although resistance to desiccation may play a part in determining distribution and abundance, especially in the upper intertidal, it is clear that other factors may be important, such as food resources. Fecal pellets were used as a technique to study food resource partioning. Limpet size and abundance is related to the availability of microalgae on a particular slope of substrate. Differences in the amount of movement between the two species may be. related to time and distance traveled in foraging for food. The ratio of abundances of these limpets and its relation to substrate angle needs to be studied from the point of view of competitive interactions with respect to food resource partioning, since these species seem to have tolerances to desiccation greatly exceeding environmental stress conditions.

Various studies indicate the acmaeid limpet species Collisella digitalis, Collisella pelta and Notoacmea scutum inhabit different vertical zones in the rocky-intertidal region. At Sunset Bay, Oregon, Shotwell (1950) found that C. digitalis was situated in the upper intertidal C. pelta inhabited the mid-intertidal and N. scutum was located in the mid to lower zone in the rocky-intertidal region. Frank (1965) observed the same distribution patterns at Coos Bay, Oregon as did the author in the rocky-intertidal region near Dillon Beach, California. Species distributions in the rocky-intertidal region are thought to be limited from above by physical stress and from below by predation or competition (Connell 1970; Dayton 1971; Vermeij 1972; Paine 1974; Bertness 1977). The purpose of the present study was to investigate effects of the predators Pisaster ochraceus, Cancer antennarius and Pachygrapsus crassipes on the distributions of the three acmaeid limpet species particularly with respect to their lower limits.

Studies on trematodes of marine organisms of the Pacific Coast have been of a scattered and fragmentary nature. J. Stafford (1904) collected and described a number of trematodes from fishes of the north Pacific, but, in his historical survey, Manter (1926) fails to mention specifically any studies covering the waters south of Canada. More recently, in the United States, several contributions to the field have been made by Dr. John E. Guberlet at the University of Washington and at the College of the Pacific by Dr. Alden Noble, under whose guidance this study was made. James Park (1937) revised the genus Podocotyle and added eight new species .from Dillon Beach, California. Descriptions of individual trematodes have been made by various other investigators. The investigation covered by this paper was begun during the summer or 1946 at the Pacific Marine Station.

In the present study, information concerning morphology, ecology, fertilization and larval development of three sympatric species of Eusonus is presented. Morphological similarities are reviewed in part I. These similarities correspond with significant lack of variation found in larval development (part IV). Despite these similarities, as well as the ability to cross fertilize their species, the ecological and reproductive isolating mechanisms presented in part II and II provide a positive indication of the existence of three biologically distinct species. A comparative discussion reviews the efficacy of morphological criteria in differentiating the three closely related Euzonus species.