SCANNING ELECTRON-MICROSCOPY OF CYPRIS LARVAE OF BALANUS AMPHITRITE (CIRRIPEDIA, THORACICA, BALANOMORPHA)

We describe the external morphology of the cypris larvae of Balanus amphitrite Darwin using scanning electron microscopy. The cyprid of B. amphitrite generally resembles that of Semibalanus balanoides, but differs in a number of morphological details. Cyprids of B. amphitrite carry fewer pores and setae on the carapace than Semibalanus balanoides. We found minor but consistent differences in morphology of the antennules and the caudal rami. The latter are 2-segmented and carry 6 setae. The thoracopods exhibit the most significant differences. The endopods and exopods are both 2-segmented, but with indications of an ancestral division into three segments in the endopod. The endopod carries a single plumose seta on the proximal segment and 3 plumose setae on the distal segment. In thoracopod 1, the exopod carries a short, sickle-shaped seta laterally on the proximal segment anti on the distal segment 3 plumose setae and a single biserrate seta. Thoracopods 2-6 have an additional plumose seta on the distal segment. We emphasize the insufficiency of most existing descriptions and that only scanning electron microscopy allows the level of morphological detail needed for future comparative studies on cyprid morphology.