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

Boring bryozoans are a fascinating group of bryozoans that drill into calcium carbonate substrates using chemical means. Spathiporidae constitutes one of the four extant boring bryozoan families. Spathipora are pedunculated stolonate ctenostomes with autozooids positioned horizontal, or nearly so, to the substrate surface. The genus was erected in 1866, but partial autozooidal characters only described in 1938. Two species with histology were then described in 1950 and 1975. Concurrently, additional species were described based primarily on the colony and external autozooidal morphology. We re-examined type material and collected additional samples to investigate the soft-body morphology using histology, confocal laser scanning microscopy, 3D-reconstructions and molecular techniques. Although the emphasis was on extant species, relevant fossil taxa were included. For the first time we report the presence of spathiporids from Roscoff, France, the three species are Spathipora sertum, S. cf. comma, S. occidentalis and the tracemaker of the latter. We describe a new endolithic bryozoan family and genus with three species, characterized by pedunculated, nearly vertical autozooids with gizzards and kenozooidal stolons. All species, Silenia chilensis gen et sp. nov. (Chile), Silenia sagamica sp. nov. (Japan), Silenia sp. nov. (New Zealand), are from the Pacific Ocean. Sequences of Spathipora and Silenia gen. nov., were generated for the first time and incorporated into existing ctenostome mitogenomes, to reconstruct the phylogeny. The soft-body morphology and mitogenome analyses support the characterization of Spathipora and Silenia fam. nov. as vesicularidioideans. The boring lifestyle evolved two times independently in vesicularidioideans and overall, four times independently in ctenostomes.