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Observations on Egg Hatching in the Estuarine Crab Sesarma haematocheir

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Title: Observations on Egg Hatching in the Estuarine Crab Sesarma haematocheir
Authors: Saigusa, Masayuki
Issue Date: Oct 1992
Publisher: University of Hawai'i Press
Citation: Saigusa M. 1992. Observations on egg hatching in the estuarine crab Sesarma haematocheir. Pac Sci 46(4): 484-494.
Abstract: A female of the terrestrial crab Sesarma haematoeheir incubates
30,000-50,000 eggs on her abdomen. After 1 month of embryonic development,
zoeae larvae are released into estuarine waters within 3-5 sec by means of vigorous
fanning motions of the abdomen. Hatching (breakage of the outer egg membrane)
occurs on land just before larval release. The release behavior itself does
not cause rupture of the egg case, nor has the presence of a "hatching enzyme"
been obviously demonstrated. Hatching seems to be induced by mechanical
rupture of the egg case. The pressure responsible for hatching may be produced
either by the larva itself, or by osmotic swelling of thin inner membranes encasing
the larva, although neither of these hypotheses is sufficient at present to explain
the complete hatching mechanism. If hatching is explained by such mechanisms,
then there remains the question of how hatching is synchronized among the large
number of embryos attached to the female. Hatching of detached embryos is
synchronized to some extent, but the degree of synchronization is less than that
occurring in the larvae carried by the female. This observation suggests that
stimuli from the female are important in establishing highly synchronized
hatching. The ecological significance of the hatching system is also discussed.
ISSN: 0030-8870
Appears in Collections:Pacific Science Volume 46, Number 4, 1992

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