Prospectus on larval cirriped setation formulae, revisited

Abstract

Setation sequences of the appendages, as well as other characters of cirriped nauplii reared in the laboratory, are invaluable in identification of nauplii taken from the plankton, and in the past few decades those of numerous coastal and a few oceanic species have been described. In addition, larval characters have provided insights into the relationships between various taxa, and it is now apparent certain clades exhibit unique patterns. However, setation sequence patterns of the sixth or last naupliar stage have not been used in phylogenetic studies. Therefore, we have compiled and attempted to standardize them for a preliminary cladistic analysis. Setal characteristics of 31 taxa are compared cladistically with a previously published matrix of largely other naupliar characters. While the results fell short of expectations, rank-order comparisons with a generally accepted classification demonstrates a moderately strong positive correlation between them, that between larval characters and setation sequencing being stronger than either set of larval characteristics was with the classification. Analyses of certain species groups run to test various hypotheses were eminently more satisfactory. Although the present database is limited by the reliability of the original data and our manipulations of them, the results indicate there is sufficient phylogenetic information in larval characters and setation sequences to allow comparisons with generally accepted phylogenies based on adult characters. Refinements of setation sequencing appearing in several recent studies, including recognition of additional setal types and more rigorous comparative approaches in establishing homologies, hold great promise for the future.