Microporella uncovered: past and present diversity of a successful cheilostome bryozoan in Aotearoa New Zealand, with new species descriptions and distribution maps

The genus Microporella is highly diverse worldwide, with its greatest diversity documented to date in New Zealand, where it appears in the Early Miocene, the earliest known record of the genus, and persists to the present day. Owing to its successful evolutionary history, Microporella has become a model system for addressing macroevolutionary questions, which in turn require a robust understanding of its true taxonomic diversity. This study provides the first comprehensive revision of all available Recent and fossil material of Microporella from New Zealand. We redefine the encrusting species M. agonistes, M. discors, M. intermedia and M. speculum, which appeared widely distributed through time and across New Zealand; a neotype is designated for M. agonistes. In several cases, we identify and describe cryptic taxa that had long been referred to one of these species. We further describe 16 new Recent species, namely M. anomopora sp. nov., M. bairdi sp. nov., M. bifora sp. nov., M. diadematoides sp. nov., M. diaphora sp. nov., M. maerloides sp. nov., M. mucronata sp. nov., M. murdochi sp. nov., M. perissospinosa sp. nov., M. plentyensis sp. nov., M. polaris sp. nov., M. pseudolineata sp. nov., M. puncticulata sp. nov., M. speculoides sp. nov., M. taylori sp. nov., M. tenuidistans sp. nov., some also including Pliocene or Pleistocene records, most of which are associated with poorly investigated deep-water environments. A detailed morphological comparison among all species is presented, and we summarise diagnostic characters, including size-related traits, for all remaining species described in recent studies, which are mostly erect bifoliate forms or encrusting forms known only from the fossil record. We recognize a total of 29 Microporella species, five of which are known exclusively from the fossil record. Distributional maps are compiled to provide a clear regional overview of Microporella diversity. The observed pattern is consistent with New Zealand’s long-recognized status as a centre of marine endemism and diversification, shaped by its prolonged geographic isolation, complex tectonic history, and wide range of environmental settings.