. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. OSMOREGULATION IX CALLIANASSIDAE 419 this salinity in part explains more frequent occurrence of C. major inside the isohaline and its predominance on ends of coastal islands where salinities occasion- ally fluctuate. Preliminary evidence of low-salinity tolerance and slight hyperosmotic regulation in juveniles of C. islagrande suggests an ontogenic loss of tolerance and regulatory ability, although the two juveniles studied furnish an insufficient sample for firm conclusions. Juveniles of the hermit crab, Pagnrus bemhardus,
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. OSMOREGULATION IX CALLIANASSIDAE 419 this salinity in part explains more frequent occurrence of C. major inside the isohaline and its predominance on ends of coastal islands where salinities occasion- ally fluctuate. Preliminary evidence of low-salinity tolerance and slight hyperosmotic regulation in juveniles of C. islagrande suggests an ontogenic loss of tolerance and regulatory ability, although the two juveniles studied furnish an insufficient sample for firm conclusions. Juveniles of the hermit crab, Pagnrus bemhardus, regulate volume in lower salinities than adults, and Davenport (1972a) suggests that the aperture of the nephropores in relation to body size limits this capacity in adults. Tolerance of dilute media by Callianassa major and C. islagrande may prove of only short-term benefit for survival of populations. Hill (1971) notes that while Upogebia africana can tolerate a salinity of '/,, it can only survive through a molt in a salinity > 3A(/l(. Although C. major and adult C. islagrande do not appear to osmoregulate (Fig. 1), their tolerance of dilute media may in part relate to accommodation of short-term increases in blood volume. The anterior portion of the abdomen is soft, and its elasticity may minimize mechanical effects of turgor. Davenport (1972b) suggests such an adaptation in Pagnrus bernhardns and shows that with increased blood volume in low salinity, a larger proportion of the blood shifts from the thorax to the abdomen. The degree of hypoionicity in blood chloride of Callianassa major and adult 80 Q 70 O o m 60 rr LL) t 50 E 40 ID c/> 30 LU 20 10. 10 20 30 40 50 60 70 MAGNESIUM mM/LITER MEDIUM 80 FIGURE 6. Blood magnesium concentration in acclimated C. jamaicense (solid circles) and C. major (open circles) as a function of media magnesium concentrations. Each large solid or open circle is mean of 6 to 10 determinations; vertical lines indicate standard errors wh
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
