OBSERVATIONS ON THE FUNCTION OF THE FRONTOLATERAL HORNS AND HORN GLANDS OF BARNACLE NAUPLII (CIRRIPEDIA)

¹ Department of Oceanography, University of Washington, Seattle, Washington 98105

1. Barnacle nauplii characteristically have frontolateral horns and horn glands, but the function of these is unknown. To examine the hypothesis that they are venomous organs that serve in defense against predation, observations were made on living specimens in the presence of potential predators.

2. Laboratory observations of two general types were made on Balanus spp. nauplii. One was to observe directly the behavioral interactions between the nauplii and potential predators. The other involved survival trials, in which barnacle nauplii were introduced into vessels with potential predators; the losses due to predation were recorded at intervals.

3. The results of these observations strongly suggest that barnacle nauplii lack a generalized defense against predation, and there was no indication that the frontolateral horns and horn glands are used as venomous organs. The observed indifference of certain hydromedusae to most contacts with barnacle nauplii suggests, however, that there might be a specialized defense mechanism.

4. Other possible functions of the frontolateral horns are discussed in view of the results.