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Effect of eyestalk removal on linear growth and water uptake during the molt cycle of the crab, Hemigrapsus nudus (DANA) Baldwin, Mary Frances

Abstract

When eyestalks are removed from Hemigrapsus nudus at least 10 days before ecdysis, linear growth of the destalked animals, measured as an increase in carapace width after ecdysis, is significantly higher than the linear growth of the unoperated control animals. The amount of water that control and destalked H. nudus absorb during ecdysis (stage E) is not significantly different; however, during early postecdysis the destalked animals show a significantly greater increase in wet weight than the controls. The greater linear growth calculated for destalked animals must be realized during early postecdysis. To investigate one possible mechanism to account for the large increase in wet weight characteristic of destalked animals during postecdysis, total osmotic pressure of the blood was measured throughout the molt cycle for control and destalked animals. The osmotic pressure measured from destalked animals is not significantly different from the measurements of osmotic pressure from control animals during the short period of ecdysis, however determinations of osmotic pressure from destalked animals during pro- and postecdysis are significantly lower than those from control animals. There is postulated a water balance-regulating principle located in the eyestalk which regulates the early postecdysial absorption of water. The absorbent surface of the destalked crab may become more permeable to water just after ecdysis, thus causing an increase in wet weight and an increase in size.

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