. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. LARVAL CRUSTACEAN OSMOREGULATION 517 motic or hypo-osmotic at this salinity. The gradient sustained between blood and medium at Wc/cc is less than that for S. rcticulatiim. During the seventh zoeal stage, the ability to osmoregulate is apparently lost, and the larvae become isos- motic at all salinities (Kalber, 1970). Larvae of the land crab, Cardisoma guan- humi, are usually hypo-osmotic at 4Q(/C. During the third zoeal stage they become hypo-osmotic in salinities as low as 20%c as well. The gradient maintained between blo
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. LARVAL CRUSTACEAN OSMOREGULATION 517 motic or hypo-osmotic at this salinity. The gradient sustained between blood and medium at Wc/cc is less than that for S. rcticulatiim. During the seventh zoeal stage, the ability to osmoregulate is apparently lost, and the larvae become isos- motic at all salinities (Kalber, 1970). Larvae of the land crab, Cardisoma guan- humi, are usually hypo-osmotic at 4Q(/C. During the third zoeal stage they become hypo-osmotic in salinities as low as 20%c as well. The gradient maintained between blood and medium at I0c/f,0 by larvae in the first two zoeal stages is similar to the response by 6\ rcticulafnin larvae. In later stages, the sustained gradient is con- siderably diminished (Kalber and Costlow, 1968). Osmoregulation in larvae of two polystenohaline crabs, Hcpatns cpliditicits and Libinia cmarginat-a, resembles that of typical estuarine species. To the first day of the third zoeal stage, larvae of H. cphditiciis remain hyper-osmotic in salinities up to approximately 35%e and hypo-osmotic in 40r/cc sea water. As in S. reticiilatitin, the osmotic response varies little throughout development. Larvae of Libinia cinarginata, on the other hand, begin zoeal life isosmotic to the medium in all salinities, gradually develop hyper- regulation in salinities less than 27 to 30/£r during the middle of larval life, and again become isosmotic in the third day of megalops development (Kalber, 1970). Kalber and Costlow (1966, 1968) and Kalber (1970) allowed a 1 hr period of adjustment for larvae of R. harrisii and 2 hr for larvae of C. guanhumi, C. sapidus, and L. cinarginata following exposure to test salinities before sampling the body fluids. However, no data showing the time-course of osmotic equilibrium were presented to confirm that equilibrium had, indeed, been attained within those time periods. The change in blood concentration after a change in the salinity of the medi
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