Reference: Biol. Bull., 145: 310-322. (October, 1973) THE INTERMOLT CYCLE OF CIRRIPEDS : CRITERIA FOR ITS STAGES AND ITS DURATION IN BALANUS AMPHITRITE C. WILLIAM DAVIS *, UNNI E. H. FYHN, AND H. J. FYHN -Duke University Marine Laboratory, Bcaujort, North Carolina 28516 U. S. A. Many physiological and behavioral responses in crustaceans change markedly during the course of an intermolt cycle. To take such variations into account it is necessary to identify the stages of the intermolt cycle. Drach (1939, 1944) success-fully divided the intermolt cycle of brachyurans and natantians into four main stages, A, B, C, and D, and, using structural changes in the integument, developed criteria by which these stages could be identified. Orach's method has found wide application within the Malacostraca (see Yamaoka and Scheer, 1970). In the Cirripedia, however, an intermolt staging method for live animals chosen at ran-dom has not been available. Studies which have related to the intermolt cycle in cirripeds have generally used animals at timed intervals after ecdysis (Patel and Crisp, 1961; Barnes and Barnes, 1963; Costlow, 1963; Shimony and Nigrelli, 1972). A requisite for the successful application of the timed interval method is intermolt cycles of uniform duration. This condition, however, may not be met in the cirripeds. Costlow and Bookhout (1953, 1956) found wide variations in the durations of the intermolt cycles of juvenile specimens of Balanits improvisus and B. amphitrite; there is no information in this regard for adult barnacles. Intermolt stages in cirripeds have been morphologically identified in only a few studies. Using the criteria of Drach. Bocquet (1956) identified Stages D! and D 2 in Chthamalus stcllatus by microscopically examining the cirri. Bocquet-Vedrine (1965) developed a method for histologically identifying intermolt stages of Elmin'ms modestus in thin sections of whole animals. The present study had two major objectives: (1) to develop an intermolt staging method for barnacles which can utilize live, intact specimens taken at random, and (2) to statistically analyze the intermolt cycle of adult specimens of B. amphitrite. MATERIALS AND METHODS Specimens of the intertidal barnacle Balanus amphitrite amphitrite Darwin (Harding, 1962) were collected from the noncreosoted portions of the laboratory dock in Beaufort, North Carolina, from February to November. 1972. The rostro-carinal diameter of the animals ranged from 5 to 10 mm. The animals were main-tained in aquaria containing continuously aerated seawater at a salinity of 30%o and fed Artemia nauplii (Metaframe San Francisco Bay Brand) for one month prior to experimentation. During the experiments the animals were maintained individually in compartmentalized plastic boxes in 40 to 50 ml of seawater at a 1 Address after September 1, 1^73 : Department of Zoology, University of North Carolina. Chapel Hill, North Carolina 27514. 2 Permanent address : Institute of Zoophysiology, University of Oslo, Oslo, Norway. 310
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