Four times boring: investigating spathiporid bryozoans reveals multiple convergent evolution of an endolithic lifestyle

Context

Boring bryozoans drill into calcium carbonate substrates by chemical means leaving unique traces which are diagnostic for genera. Previously, species were primarily described based on colony and external autozooidal morphology. Consequently, their phylogenetic placement remained ambiguous.

Aims

To examine type material and newly collected specimens to investigate soft-body characters, use molecular techniques to generate sequence data and refine the characterization of the monotypic Spathiporidae and its species.

Taxon

Species assigned to Spathipora (Bryozoa: Gymnolaemata: Ctenostomata) were analysed.

Methods

Morphological characters were assessed by immunocytochemical staining and confocal laser scans, histology, resin casts and 3D reconstructions. Molecular phylogenetic analyses were based on a concatenated dataset of twelve protein coding genes, two ribosomal rRNA genes (16S and 12S) and two nuclear ribosomal genes (18S and 28S).

Key results

Morphological and molecular analyses support the classification of Spathiporidae and a distinct new clade Sileniellidae fam. nov. as vesicularioideans, thus resolving their phylogenetic placement. Additionally, we describe Sileniella gen. nov. with three species characterized by pedunculate, nearly vertical autozooids with gizzards and kenozooidal stolons. All new species are from the Pacific Ocean, Sileniella chilensis sp. nov. (Chile), Sileniella sagamica sp. nov. (Japan) and Sileniella sp. nov. (New Zealand). Our findings suggest that the boring lifestyle evolved independently in vesicularioideans and independently four times in ctenostomes.

Conclusions

This study, which integrates sequence data of representatives from all extant endolithic bryozoan families, underpins the multiplicity of convergent evolution of this lifestyle. Additionally, we provide a framework for traits to consider when delineating boring species.

ZooBank: urn:lsid:zoobank.org:pub:0E7E622E-A8A5-4440-99AD-E9DA54D8D56B.