Marsupial developmental stages in Americamysis bahia (Mysida: Mysidae)

The marsupial development of a population of Americamysis (= Mysidopsis bahia from the Gulf of Mexico was examined at 16 degree C, 20 degree C, and 29 degree C from oviposition to the juvenile stage. Three phases of development, divided into five stages, occurred during in vitro culture of larvae. The embryonic phase (Stage 1) is spherical and surrounded by the egg membrane. The nauplioid phase begins with hatching from the egg membrane and consists of an early (Stage 2) and late (Stage 3) stage. The early nauplioid stage, which is divided into three substages, elongates into a commashaped larva and ends with the appearance of thoracic chromatophores. Stage 3 begins with the formation of eye pigment and ends with the shedding of the naupliar cuticle. The subsequent post-nauplioid phase has two stages. Stage 4 is characterized by the formation of a yolk protuberance anterodorsal to the carapace. Stage 5 begins with enclosure of the yolk in the carapace and ends with release of the larvae from the marsupium and a molt to the juvenile stage. Following liberation of young at night, the female molts, and usually mates and extrudes another brood of eggs. Survival rates of A. bahia larvae in vitro increased with age and with decreasing temperature. Average brood durations of larvae were 15.5 days at 16 degree C, 10.4 days at 20 degree C, and 4.6 days at 29 degree C. Observations of brood release, spatial organization within the marsupium, and adoption of larvae are discussed.