A Free-swimming Nauplioid Stage in Palinurus.

Abstract

THE larva of Palinurus, Scyllarus, and the Loricata generally has hitherto been supposed to hatch out from the egg in the form of a " phyllosoma,' characterised by a flattened transparent body and the presence of swimmingorgans, in the form of the exopodites of some of the thoracic appendages.A number of observations, which I have made on the early stages of Palinurus (JSasus) lalandi, seems to indicate that this is not so in the case of this South African Crawfish.The observations were made on a number of specimens of this crustacean kept alive in tanks at the Marine Laboratory at St. James, near Cape Town.They are hardy animals, and can be kept in good condition for a considerable length of time without much trouble.On hatching, the larve are given off in large numbers, and are readily seen by the naked eye in the typical phyllosoma stage.Among these slowly-moving larve was observed a number of nauplius-like forms, with large biramose antenne, by means of which they rose to the surface in a series of rapid dancing movements.These larvee on closer examination proved to be, not nauplii, but the earliest free stage, differing considerably from a phyllosoma.The duration of this stage is very brief (4-6 hours), and is readily overlooked, especially if iiching takes place during the night.