THE CYPRID MOLT CYCLE AND ITS HORMONAL CONTROL IN THE BARNACLE BALANUS AMPHITRITE

ABSTRACT The cyprid molt cycle was examined in Balanus amphitrite. The duration of the cyprid instar was variable. While some cyprids settled and metamorphosed within several days, others did not settle at all during the I 2-day observation period. The premolt period (stage D) began at different times in different regions of the integument. Anterior, posterior, and ventral regions of the carapace valves underwent apolysis within 10-12 h following ecdysis to the cyprid, while the dorsal carapace epidermis did not undergo apolysis until attachment to the substratum, which occurred at various times during the 12-day period. 20-Hydroxyecdysone, at concentrations of 1–10 µg/ml seawater, did not accelerate early premolt apolysis in the anterior, posterior, or ventral carapace valves. However, the integumental activities associated with postattachment metamorphosis (dorsal carapace apolysis, epidermal morphogenesis, thoracic adductor muscle degeneration) were stimulated by 20-HE in a dosedependent manner. Some 20-HE exposed cyprids underwent metamorphosis without prior attachment to the substratum.