THE INTERMOLT CYCLE OF CIRRIPEDS: CRITERIA FOR ITS STAGES AND ITS DURATION IN BALANUS AMPHITRITE

¹ Duke University Marine Laboratory, Beaufort, North Carolina 28516 U. S. A.

The intermolt cycle of the barnacle Balanus amphitrite is divided into three postecdysial, one interecdysial, and four proecdysial stages based on integumental changes in the cirri. Stage A is characterized by a seemingly single-layered exoskeleton and tortuous cirri. Stages B₁, B₂, and C are characterized by the increasing thickness of the endocuticle. Stage D₀, D₁, D₂, and D₃ are characterized by the progression of setogenesis, formation of the new exoskeleton, and resorption of the old endocuticle. The durations of the intermolt stages have a wide variability. The integumental changes both within and between the rami of an animal progress synchronously. The criteria allows the use of live, intact animals taken at random from laboratory or field populations. The method is assumed to be applicable to all thoracic cirripeds as long as the exoskeleton is transparent enough to allow microscopic examination.

The duration of the intermolt cycles of adult specimens of B. amphitrite varied from 1.5 to 23.5 days under constant conditions (23° C, 30, LD 12:12). The distributions of the cycles are significantly (P < 0.001) leptokurtic and positively skewed. There is no correlation between the durations of successive intermolt cycles of individual animals.

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