Tunic Cuticular Protrusions in Ascidians (Chordata, Tunicata): A Perspective of Their Character-State Distribution

Abstract

Fine structure of the ascidian tunic cuticle was surveyed for minute protrusions in 30 species of the suborder Aplousobranchia, 10 species of Phlebobranchia and 23 species of Stolidobranchia (Ascidiacea, Chordata). The present results, combined with previously published data, describe the fine structure of the tunic cuticle in 116 species of ascidians covering all the families and subfamilies of the class Ascidiacea except for the phlebobranch families Octacnemidae and Plurellidae. These data confirm the general stability of the character-state distribution (presence or absence) of the tunic cuticular protrusions within families or subfamilies. Cuticular protrusions occur only in Polyclininae and Clavelininae of the order Enterogona (Aplousobranchia and Phlebobranchia) and in all families of the order Pleurogona (Stolidobranchia and Aspiraculata). A few exceptions were the occurrence of cuticular protrusions in Polycitor proliferus (Polycitorinae), Distaplia dubia (Holozoinae), Pterygascidia longa (Cionidae) and Adagnesia vesiculiphora (Agneziidae), and the absence in some styelids and pyurids that have hard tunics. Possible character-state changes in the ascidian phytogenies are discussed briefly.