A reexamination of Waikalasma (Cirripedia: Thoracica) and its significance in balanomorph phylogeny

Abstract

When waikalasma was first recorded from early Miocene strata in New Zealand (Buckeridge, 1983) it was described as possessing eight compartmental plates but lacking basal whorls of imbricating plates. However, subsequent study and comparison of the holotype with extant Chionelasmus has shown that the remnants of several small plates remaining at the base of the rostrum represent the remains of two or three basal whorls (Figure 1). Furthermore, new evidence concerning the structure of the wall of the Chionelasmatinae has indicated not only that the true or median latus has been replaced by the carinolatus in balanomorphs, but that an additional or secondary carinolatus has been added in higher balanomorphs (Yamaguchi and Newman, 1990). The structure of the wall in Waikalasma can now be reinterpreted in light of these findings (Figure 2). It turns out, in terms of current phylogeny, that Waikalasma should be placed amongst the most primitive of the balanomorph barnacles, representing an important step in balanomorph evolution rather than simply an evolutionary offshoot as envisaged by Buckeridge (1983) and Foster and Buckeridge (1987) (Figure 3).