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Antarctic Research Series, vol. 11. American GeophysicalUnion Pub., 1579: vii. 1968. (By WALDOL. SCHMITT& GERHARDPRETZMANN). Eine neue Trichodactylus-Art aus Kolumbien. Entomol. Nachrichtenblatt, 15 (2): 6. 1969. Colombian freshwater crab notes. Proc. biol. Soc. Washington, 82: 93-111, figs. 1-7. 1972. Response to "A tribute to Waldo LaSalle Schmitt" by George A. Llano. In MEREDITHL. JONES,ed., The Panamic biota: some observations prior to a sea-level canal. Bull. biol. Soc. Washington, 2: 5, 6. 1973. Mary J. Rathbun, 1860-1943. Crustaceana, 24 (3): 283-297, pl. 1. 1973. (By WALDO L. SCHMTT,JOHN C. MCCAIN & EDWARDS. DAVIDSON).Decapoda I. Brachyura I. Fam. Pinnotheridae. Crustaceorum Catalogus, 3: 1-160. SOME ASPECTS OF OSMOREGULATION IN MYSIS RELICTA LOVEN (MYSIDACEA) BY K. A. DORMAAR P.O. Box 1044, Department of Development, Charlottetown, Prince Edward Island, Canada and S. COREY Department of Zoology, University of Guelph, Guelph, Ontario, Canada - Introduction. My.ri.r rehcta Lov6n is a freshwater mysid that occurs in great numbers in deep lakes formed at the periphery of glaciers during the Pleistocene in North America and Eurasia (Ricker, 1959). It has also been found sporadically 91 in marine and brackish-waters (Ricker, 1959) especially in parts of the Baltic Sea, White Sea, around Spitzbergen, along the east coast of Greenland (Holmquist, 1949; Ricker, 1959; Segerstrale, 1962), and in a coastal lagoon in Alaska (Mohr, 1 95 3 ) . Most freshwater Crustacea are oligostenohaline, i.e., with hyperosmotic regula- tions over a narrow range of low salinities. Most truly marine Crustacea are polystenohaline, and show little if any osmoregulation. Coastal and estuarine Crus- tacea usually show greater osmoregulative capacities and are defined as euryhaline osmoregulators (Kinne, 1963). Osmoregulation of the haemolymph is here defined as regulation of the total dissolved particle concentration of the haemolymph, at a level different from that of the external medium. - Materials and methods. Specimens of M. relicta were collected from Fairy Lake (45°19'N 79°11'W), Lake Ontario (43°37'N 79°20'W) and Lake Canadai- gua (42°55'N 77°20'W). In Fairy Lake and Lake Canadaigua specimens were collected at night in the deepest areas of the lakes by horizontally towing a net (1 m in diameter, 11 mesh/cm) for 10-15 min., 2-3 m below the thermocline. In Lake Ontario vertical tows from the bottom during the daytime yielded the greater number of specimens. Experimental animals were kept in the laboratory in seven 40 litre aquaria at 4° C, and at 75-90% 02 saturation. Specimens were held at a maximum density of two per litre. Specimens were kept in total darkness except during handling. Food was provided by adding 500 ml of lake bottom mud to each tank. The water in each tank was slowly recirculated through a charcoal filter to maintain a low ammonia level ( < 1.2 ppm). Salt ("Instant Ocean" Aquarium systems, Inc.) was added to each tank at a rate of 50/00 over intervals of 4 days, until salinities of 5, 10, 15, 20, 25, and 300/0o were achieved. A control tank was also maintained. Salinities were determined daily with a hydrometer (range: 1.000-1.050) cali- brated with standard seawater and de-ionized water at 4° C. Daily haemolymph samples were taken from 5 specimens at each salinity and their freezing point depressions determined. The specimens were then discarded. Specimens were first sampled one day after the required salinity was obtained in each tank, and sampling continued until the freezing point depression remained constant. Only mature males and mature non-gravid females with food in their stomachs were used. To collect haemolymph, the dorsal carapace immediately posterior to the stomach was punctured with a fine pin. The tip (0.8 mm diameter) of a micropipette was then inserted into the dorsal blood sinus. The micropipette was connected by a polyethylene tube to a modified RGI micrometer syringe ( #S-l loo ) . This entire system was filled with Cargilles "A" immersion oil. The haemolymph was taken by slowly turning the micrometer until enough haemolymph was collected. The sample of haemolymph was then transferred into 6 small openings of a sample holding platfom of the freezing module of a cryostat osmometer (Clifton Tech- .