On the feeding mechanism of the nauplius of Balanus perforatus Bruguière.

Abstract

The rearing of Balanus nauplii in the laboratory and the stage at which hatching occurs are discussed. The external morphology of the second stage nauplius of Balanus per-foratus is described. The setae on the limbs I divide into two types—swimming setae and feeding setae. The limbs beat in a metachronal rhythm. During the back-stroke particles are swept backwards and inwards, converging from each side just behind the body. From here they are sucked forward along the ventral surface during the fore-stroke of the mandibles and antennae. They are retained in the region behind the labrum by the feeding setae and their setules, by spinules on the ventral surface of the body, and by setules on the tip of the labrum. As the limbs beat back the feeding setae push the particles towards the mouth. A groove under the labrum leads to the mouth itself, into which the particles are pushed by prongs on the antennal jaw processes. Feeding is rapid and not selective. But particles over 6μ in diameter cannot be swallowed, though diatoms 25μ long are freely taken. It appears that single cells may be torn from filamentous algae and then swallowed. But there is never any true mastication, and larger bodies do not form part of the food. The first stage nauplius does not feed. The mouth is apparently open, but the feeding structures are very radimentary, and particles can thus reach the mouth only by accident.