GENERIC CHARACTERIZATION OF ACTINOCYCLUS: CONSIDERATION IN LIGHT OF THREE NEW SPECIES

Abstract

Three new species of Actinocyclus are described: A. circellus, from the Gulf of Mexico and North Atlantic (in Gulf Stream warm core rings); A. vestigulus, also from warm core rings; and A. spiritus, from antarctic waters. The morphology of these species provides insights into the generic characterization and evolution of Actinocyclus. The taxononomic preeminence of the pseudonodulus is challenged; a morphological continuum supports the suggestion that the pseudonodulus formed from a fusion of several marginal areolae. A possible rudimentary labiate process is shown near the centre of a forming valve of A. vestigulus, suggesting that Actinocyclus at least shares a common ancestor with Azpeitia. Segmented bands were seen on the largest of the three species, A. circellus.