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Subitaneous eggs of the neritic calanoid copepod Acartia tonsa (Dana) are capable of entering a resting state called quiescence to overcome adverse environmental conditions. Although physiological changes associated with this transition have been described, the molecular mechanisms are thus far not studied in any calanoid copepod. Two stress-related proteins, hsp70 and ferritin, were cloned from A. tonsa and their expression determined in embryos of A. tonsa during transition between subitaneous and quiescence eggs. Expression of hsp70 remained low during quiescence despite environmental stress. However, ferritin expression exhibited a strong increase from days 3 to 5 of quiescence followed by a declined. After 2 weeks of quiescence, development of the embryos recovered by the addition of oxygen and increased temperature. The expression of both genes increased 222-fold for hsp70 and 52-fold for ferritin during the recovery phase toward hatching. This suggests that ferritin is a protein needed when embryos of A. tonsa enter quiescence. Both hsp70 and ferritin are required during recovery from quiescent to subitaneous state when embryogenesis continues toward egg hatching.