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The family Catophragmidae is one of the lower balanomorphs from traditional and recent multiple mitochondrial and nuclear markers molecular analysis. Here, we characterized the first mitogenome of the catophragmid barnacle Catomerus polymerus, which was 15,446 bp in length with a 68.3% AT content. The mitogenome had the typical pancrustacean gene arrangement, which was identical to the mitogenome configurations of the chthamalid Octomeris sp. and pachylasmatoid Eochionelasmus ohtai. On the mitogenomic tree, the catophragmid Catomerus polymerus formed an independent branch that was basal to the members of the superfamilies Tetraclitoidea and Balanoidea, which was inconsistent with previous findings.

The evolutionary history of the lower balanomorphan barnacle has remained controversial because of the complexities in shell wall ontogeny and the prevalence of plesiomorphic characteristics. Catophragmus Sowerby, 1826, Eochionelasmus Yamaguchi, 1990, Pachylasma Darwin, 1854 and Waikalasma Buckeridge, 1983 have been proposed as potentially the most primitive extant balanomorphans. In this study, we present the first molecular phylogenetic hypothesis on the evolution of lower Balanomorpha Pilsbry, 1916, based on 89 species and six molecular markers (mitochondrial 12S and 16S, nuclear 18S rRNA, histone 3, elongation factor 1a subunit and RNA polymerase subunit II). Chionelasmatoidea Buckeridge, 1983, Chthamaloidea Darwin, 1854 and Pachylasmatoidea Utinomi, 1968 intermingled, thus forming the earliest diverged lineage within the monophyletic Balanomorpha in the inferred phylogeny. Five major lineages (corresponding closely to Catophragmidae Utinomi, 1968, Chionelasmatidae Buckeridge, 1983, Chthamalidae Darwin, 1854, Pachylasmatidae Utinomi, 1968 and Waikalasmatidae Ross & Newman, 2001) were identified from this lower clade; however, the phylogenetic relationships amongst the five lineages could not be resolved in the present study. Pseudoctomeris Poltarukha, 1996 was previously considered Chthamalidae because it is a shallow-water inhabitant. However, it is nested within Pachylasmatidae in the phylogenetic analysis of the present study, and its opercular plates and rostrum are highly similar to those of Pachylasma. Bathylasmatidae Newman & Ross, 1971 and Tetraclitidae Gruvel, 1903 are sister families, whereas Austrobalanus Pilsbry, 1916 is highly diverged from the Bathylasmatidae and Tetraclitidae, supporting Buckeridge & Newman's (2010, in A review of the subfamily Elminiinae (Cirripedia: Thoracica: Austrobalanidae) including a new genus, Protelminius nov., from the Oligecene of New Zealand. Zootaxa 2349: 39-54.) proposal of full family ranking for Austrobalanidae Newman & Ross, 1976. However, Austrominius Buckeridge, 1983 and Epopella Ross, 1970 inclusions in Austrobalanidae are not supported because they are more closely related to Balanoidea and Tetraclitidae, respectively. On the basis of the molecular phylogenetic analyses in the present study and morphological evidence from previous analyses, a revised family-level classification in Pachylasmatoidea and Tetraclitoidea is proposed. [ABSTRACT FROM AUTHOR]

Abstract: The Chthamaloidea (Balanomorpha) present the most plesiomorphic characters in shell plates and cirri, mouthparts, and oral cone within the acorn barnacles (Thoracica: Sessilia). Due to their importance in understanding both the origin and diversification of the Balanomorpha, the evolution of the Chthamaloidea has been debated since Darwin’s seminal monographs. Theories of morphological and ontogenetic evolution suggest that the group could have evolved multiple times from pedunculated relatives and that shell plate number diminished gradually (8→6→4) from an ancestral state with eight wall plates surrounded by whorls of small imbricating plates; but this hypothesis has never been subjected to a rigorous phylogenetic test. Here we used multilocus sequence data and extensive taxon sampling to build a comprehensive phylogeny of the Chthamaloidea as a basis for understanding their morphological evolution. Our maximum likelihood and Bayesian analyses separate the Catophragmidae (eight shell plates and imbricating plates) from the Chthamalidae (8–4 shell plates and no imbricating plates), but do no support a gradual reduction in shell plates (8→6→4). This suggests that evolution at the base of the Balanomorpha involved a considerable amount of homoplasy. [Copyright &y& Elsevier]

The family Catophragmidae is one of the lower balanomorphs from traditional and recent multiple mitochondrial and nuclear markers molecular analysis. Here, we characterized the first mitogenome of the catophragmid barnacle Catomerus polymerus, which was 15,446 bp in length with a 68.3% AT content. The mitogenome had the typical pancrustacean gene arrangement, which was identical to the mitogenome configurations of the chthamalid Octomeris sp. and pachylasmatoid Eochionelasmus ohtai. On the mitogenomic tree, the catophragmid Catomerus polymerus formed an independent branch that was basal to the members of the superfamilies Tetraclitoidea and Balanoidea, which was inconsistent with previous findings. [ABSTRACT FROM AUTHOR]