LARVAL EVOLUTION IN THE CRUSTACEA

Earlier publications include the suggestion that larval transfer (the transfer from one phylogenetic lineage to another of genes coded for l arval features) provides the best explanation of anomalies between adu lt and larval morphologies in the Dromioidea and in the crab Dorhynchu s thomsoni. It is now suggested that most crustacean larvae, other tha n postlarvae and megalopas, evolved from transferred larvae. Examples include zoeas (except those of the Polychelidae), phyllosomas, mysid l arvae, protozoeas, and nauplii. The 2nd and 3rd appendages of nauplii are similar and postoral. The 2nd appendages are preoral in most extan t non-naupliar crustaceans, but they remain postoral in the Ostracoda and Mystacocarida and in the Cambrian Martinssonia. The evolution of t hese groups is briefly discussed, and it is postulated that nauplii an d similar forms were originally transferred from non-crustacean arthro pods. The Sergestoidea and the Amphionidacea provide striking examples of the problems faced by those who would dismiss the concept of larva l transfer in crustacean evolution. The taxonomic value of the charact ers of transferred larvae is discussed.