Reference: Biol. null.. 154 : 409-429. (June, 1978) OSMOTIC AND IONIC REGULATION IN SEVERAL WESTERN ATLANTIC CALLIANASSIDAE (CRUSTACEA, DECAPODA, THALASSINIDEA) 1 DARRYL L. FELDER 2 Department of Zoology and Physiology, Louisiana State University. Baton Rouge, Louisiana 70893 Thalassinid mud shrimps of the genera Callianassa and Upogebia are frequently characterized as capable of ionic and volume regulation but incapable of osmotic regulation (Gross, 1957; Brown and Stein, 1960; Lockwood, 1962; Kinne, 1963). Studies by Zenkevich (1938), L. Thompson and Pritcharcl (1969), and Hill (1971), however, document osmoregulatory ability among upogebids. The assumed ab-sence of this ability among callianassids is meanwhile supported by L. Thompson and Pritchard's (1969) studies of Callianassa californiensis and C. filholi. The recent report of strong ionic and osmotic regulation in C. kraiissi from southern Africa (Forbes, 1974) constitutes the first evidence of such ability within the genus. However, other Callianassa species are also in some way adapted to low or varying salinities (Monod, 1927; Hedgpeth, 1950; Wass, 1955; Phillips, 1971; Rodrigues, 1971; LeLoeuff and Intes, 1974). Generalizations at the generic level must, therefore, await further physiological studies or perhaps be altogether abandoned until the systematic fate of the genus Callianassa Leach has been resolved ; revisions proposed by de Saint Laurent (1973), for example, would partition Callianassa into six genera. The present study compares osmotic adaptations of three species of Callianas-sidae from Louisiana and correlates these adaptations to local distributions. Spe-cifically, salinity tolerance, osmotic regulation, and ionic regulation are reported. Despite the wide distribution of the species concerned, their trophic significance (Frankenberg, Coles, and Johannes, 1967), their potential as bait fisheries (Hail-stone and Stephenson, 1961 ; Bybee, 1969), and the value of mud shrimp burrows in interpreting ancient environments (Weimer and Hoyt, 1964; Dewindt, 1974), basic understanding of their salinity tolerances and regulatory capacities is lacking. Species concerned in the present study are Callianassa jainaiccnsc Schmitt, 1935, C. major Say, 1818, and C. islagrandc Schmitt, 1935. all of which fall within the subgenus Callichiriis Stimpson, 1866. In a study of western African thalas-sinids, LeLoeuff and Intes (1974) note that Callichinis is frequently euryhaline and typically restricted to littoral waters in tropical latitudes. Habitats of Callia-nassa on the Louisiana coast are poorly documented, except in observations made on several coastal islands by Willis (1942) ; he notes predominance of C. islagrandc on front beaches, interspersion of C. islagrandc and C. major on ends of islands, 1 Adapted from part of a doctoral dissertation submitted to the Department of Zoology and Physiology, Louisiana State University, Baton Rouge. 2 Present address : Department of Biology, University of Southwestern Louisiana, Lafayette, 70504. 409
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