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Polychaetes of the family Arenicoliclae, commonly called lugworms, are important members of the infauna of muddy-sand beaches throughout the world, both in estuaries and along the open coast where wave action is slight (Wells, 1963). On suitable beaches, lugworms may be so abundant that their burrowing and feeding activities markedly influence the composition and structure of the substrate (Clay, 1959;Klein, 1967), much as do certain other mudflat polychaetes studied quantitatively by Rhoads (1967). Lugworms are of great importance in processing organic detritus and debris in estuaries (

Volume regulation in marine and estuarine invertebrates is usually assessed by the extent of restoration of original weight following a salinity transfer. However, volume regulation also includes the limitation of osmotic water movements. Mechanisms of volume regulation include 1) reduction of permeability of the body wall to water, reducing the rate of osmotic water movement; euryhaline species are less permeable to water than stenohaline species, and may show further adaptive reduction when in low salinities; 2) expulsion of excess water following osmotic influx, primarily as bulk elimination in the urine; and 3) changes in the numbers of extracellular osmolytes, also reducing the osmotic gradient, the major route being loss of solutes to the medium across the body wall and through the urine. Two theoretical approaches to analysis of volume regulation are discussed (Machin, '75; Oglesby, '75) and it is concluded that while both are somewhat imprecise, the approach of Oglesby ('75) has more versatility and resolving power in dealing with both osmoregulators and osmoconformers.

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The Salton Sea is a large (200 square miles) closed salt lake in a below-sealevel depression in the Colorado Desert of southeastern California. The Sea was formed accidentally from 1905 to 1907 when flood waters of the Colorado River broke through poorly constructed headgates of an irrigation canal. Following repair of is little published information on high salinity adaptations in polychaetes (Bayly, 1972;Oglesby, 1978), and only one published study on the effects of higher salinities on N. snccinca in the Salton Sea. Hanson (1972) observed that pileworms survived 96-hr exposures to salinities as high as 67.5'vV, but speculated