This short account is an invited contribution to the Zootaxa special volume ‘Twenty years of Zootaxa.’ Zootaxa was first published on 28 May 2001. Between this date and December 2020, 116 papers were published in Zootaxa that mention Bryozoa, comprising mostly descriptions of new species and higher taxa, but also including molecular sequencing (e.g. Fehlauer-Ale et al. 2011; Taylor et al. 2011; Franjevic et al. 2015), invasive-species research (e.g. Ryland et al. 2014; Vieira et al. 2014), checklists (e.g. Vieira et al. 2008), classification (e.g. Bock & Gordon 2013), bryozoans as associates of other organisms (e.g. Rudman 2007; Chatterjee & Dovgal 2020; Chatterjee et al. 2020), metazoan phylogeny (e.g. Giribet et al. 2013), biographies of historical figures who worked on bryozoans (e.g. Calder & Brinkmann-Voss 2011; Calder 2015) and a catalogue of the fossil invertebrate taxa described by William Gabb (including 67 bryozoan species) (Groves & Squires 2018). Of the 116 papers, 15 (13%) were open-access.

The number of species that exist on Earth has been an intriguing question in ecology and evolution. For marine species, previous works have analysed trends in the discovery of extant species, without comparison to the fossil record. Here, we compared the rate of description between extant and fossil species of the same group of marine invertebrates, Bryozoa. There are nearly 3 times as many described fossil species as there are extant species. This indicates that current biodiversity represents only a small proportion of Earth's past biodiversity, at least for Bryozoa. Despite these differences, our results showed similar trends in the description of new species between extant and fossil groups. There has been an increase in taxonomic effort during the past century, characterized by an increase in the number of taxonomists, but no change in their relative productivity (i.e. similar proportions of authors described most species). The 20th century had the most species described per author, reflecting increased effort in exploration and technological developments. Despite this progress, future projections in the discovery of bryozoan species predict that around 10 and 20% more fossil and extant species than named species, respectively, will be discovered by 2100, representing 2430 and 1350 more fossil and extant species, respectively. This highlights the continued need for both new species descriptions and taxonomic revisions, as well as ecological and biogeographical research, to better understand the biodiversity of Bryozoa.

BACKGROUND:Understanding the phylogenetic relationships among species is one of the main goals of systematic biology. Simultaneously, credible phylogenetic hypotheses are often the first requirement for unveiling the evolutionary history of traits and for modelling macroevolutionary processes. However, many non-model taxa have not yet been sequenced to an extent such that statistically well-supported molecular phylogenies can be constructed for these purposes. Here, we use a genome-skimming approach to extract sequence information for 15 mitochondrial and 2 ribosomal operon genes from the cheilostome bryozoan family, Adeonidae, Busk, 1884, whose current systematics is based purely on morphological traits. The members of the Adeonidae are, like all cheilostome bryozoans, benthic, colonial, marine organisms. Adeonids are also geographically widely-distributed, often locally common, and are sometimes important habitat-builders.RESULTS:We successfully genome-skimmed 35 adeonid colonies representing 6 genera (Adeona, Adeonellopsis, Bracebridgia, Adeonella, Laminopora and Cucullipora). We also contributed 16 new, circularised mitochondrial genomes to the eight previously published for cheilostome bryozoans. Using the aforementioned mitochondrial and ribosomal genes, we inferred the relationships among these 35 samples. Contrary to some previous suggestions, the Adeonidae is a robustly supported monophyletic clade. However, the genera Adeonella and Laminopora are in need of revision: Adeonella is polyphyletic and Laminopora paraphyletically forms a clade with some Adeonella species. Additionally, we assign a sequence clustering identity using cox1 barcoding region of 99% at the species and 83% at the genus level.CONCLUSIONS:We provide sequence data, obtained via genome-skimming, that greatly increases the resolution of the phylogenetic relationships within the adeonids. We present a highly-supported topology based on 17 genes and substantially increase availability of circularised cheilostome mitochondrial genomes, and highlight how we can extend our pipeline to other bryozoans.

This paper is an invited contribution to the Zootaxa series ‘Animal biodiversity: An outline of higher-level classification and survey of taxonomic richness.’ (Zhang 2011). This series pertains to living biodiversity and the species numbers given here are more or less derived from the World Register of Marine Species (WoRMS), for which the two authors of this paper are listed as editors (PEB hands-on editor; DPG advisory editor). Thus circumscribed, Bryozoa includes 3 classes, 4 orders, 187 families, 808 genera and 5869 species [Phylactolaemata 86 species, Stenolaemata 543 species, Gymnolaemata 5240 species (Ctenostomata 319 species, Cheilostomata 4921 species)]. Although all Phylactolaemata and several species of Ctenostomata are freshwater organisms, the full list of bryozoan species is accessible on WoRMS. The WoRMS list must be understood to be provisional, owing to the need for taxonomic revisions of many genera. Nevertheless, even if not all species in the list are accurately attributed to genera, the names represent operational taxonomic units (OTUs) that are indicative of living species diversity as known to date.

Two new genera of the bryozoan family Calloporidae are described from New Zealand. The first, Leptinatella, is introduced for L. gordoni n. sp., specimens of which have been referred in the past to Watersia militaris(Waters) but are distinct from this species, which is a phase of the cribrimorph Corbulipora tubulifera (Hincks). The second genus, Bryocalyx, is introduced for B. cinnameus n. sp., which has small, conical colonies anchored by rhizoids. Another species of Bryocalyx is known from a few fragments only: and has also been referred in the past to Watersia sp. It is briefly discussed, but left unnamed here.

Quadriscutella gen. nov. is introduced for Q. papillata sp. nov., an erect, branching, nodal Recent species from South Australia, belonging to a complex of forms which is otherwise known only from Tertiary localities in Victoria and South Australia. The species complex, members of which have usually been known as 'Hippoporina burlingtoniensis', has been analysed and found to comprise five taxa: Q. papillata sp. nov., the Recent form, together with Q. burlingtoniensis (Waters) sensu stricto, Q. costata (Maplestone), Q. clavata (Maplestone), and Q. punctata sp. nov., all of which are known only as Tertiary fossils. The morphology of Quadriscutella has similarities with that of both Tropidozoum Harmer (1957) and Neoeuthryis Bretnall (1921), and the genus is therefore assigned with them to the family Euthyrisellidae Bassler.

Pachystomaria parvipuncta MacGillivray is redescribed for the first time since its original introduction, from additional material from the Victorian Tertiary. Colonies are inferred to have been attached by rhizoids. The probable systematic relationships of Pachystomaria are briefly discussed.

The family Conescharellinidae Levinsen is defined and is regarded as comprising seven cheilostome genera (Conescharellina, Bipora, Trochosodon, Flabellopora, Zeuglopora, Crucescharellina and Ptoboroa). The astogeny of colonies, that consists of frontally budded zooids with reversed orientation, is briefly described and compared between genera. The morphology of zooids and heterozooids is defined and keys to genera and Australian species are provided. Taxa that were first described from Australia or from reliable subsequent records are redescribed and illustrated where possible. Australian specimens that have been identified as non-Australian species, have generally been found to be distinct and are here redescribed as new species. Some non-Australian records of specimens previously assigned to Australian species have also been re-examined. These are described and sometimes referred to other taxa. Altogether, eight previously described species that have not been found in the present material are discussed and 27 taxa are described from collections, principally from the eastern and southern coasts of Australia and from the Tertiary of Victoria. Eighteen of these are considered to be new species. Where possible, type or at least topotype material of previously described species has been examined. Colonies from the collections of Museum Victoria (NMV) and the Natural History Museum, London (BMNH), have been examined. New species from Australia described here are: Conescharellina cognata, C. ecstasis, C. diffusa, C. obscura, C. stellata, C. plana, C. perculta, C. pustulosa, C. ocellata, C. macgillivrayi, C. humerus; Trochosodon fecundus, T. asymmetricus, T. diommatus, T. aster, T. anomalus, T. praecox and Crucescharellina australis. In addition, the New Zealand bryozoan Trochosodon multiarmatus (Gordon, 1989) (not Bipora multiarmata Maplestone, 1909) is described as Trochosodon gordoni sp. nov.

Examination of samples of bryozoans from the south- eastern slope sediments of Australia (Franklin SLOPE Stations 6, 7), has revealed the presence of many specimens of several genera with species which have minute, rooted colony forms. Among these are new species of the genera Batopora Reuss (B. problematica) and Lacrimula Cook (L. affinis). The structure of colonies is briefly described. The family Batoporidae is considered to contain only these two genera, although they have relationships with the discoidal genus Orbitulipora, and similarities in colony form to the genera assigned to the Conescharellinidae.

Dimorphic brooding zooids in the genus Adeona Lamouroux from Australia (Bryozoa: Cheilostomata).Memoirs of Museum Victoria 61(

The broad-scale distribution of fossils within Victoria is controlled by general global patterns in the biological evolution of life on Earth, the local development and environmental evolution of habitats, and the occurrence of geological processes conducive to the preservation of fossil floras and faunas. Early Palaeozoic fossils are mostly marine in origin because of the predominance of marine sedimentary rocks in Victoria and because life on land was not significant during most of this time interval. Middle Palaeozoic sequences have both terrestrial and marine fossil records. Within Victoria, marine rocks are only very minor components of strata deposited during the late Palaeozoic, so that few marine fossils are known from this time period. A similar situation existed during most of the Mesozoic except towards the end of this era when marine conditions began to prevail in the Bass Strait region. During long intervals in the Cainozoic, large areas of Victoria were flooded by shallow-marine seas, particularly in the southern basins of Bass Strait, as well as in the northwest of the State (Murray Basin). Cainozoic sediments contain an extraordinary range of animal and plant fossils. During the Quaternary, the landscape of Victoria became, and continues to be, dominated by continental environments including, at times, extensive freshwater lake systems. Fossil floras and faunas from sediments deposited in these lake systems and from other continental sediments, as well as from Quaternary sediments deposited in marginal marine environments, collectively record a history of rapid fluctuations in climate and sea level.

Recent sediment samples recovered from the mid-latitude South West Shelf (SWS) of Western Australia (23 degrees - 32 degreesS) by a scientific tram aboard the RV Franklin have produced large numbers of free-living, lunulitiform bryozoans. Among these ale three undescribed species, Otionellina boneae sp. nov., Selenaria kayae sp. nov., and Selenaria meganae sp. nov. The Australasian lunulite fauna is both diverse and abundant and the new species bring the total of described taxa to sixty (P. Cook unpub.). Twelve lunulite species have been recorded from thr SWS. These findings have extended the known geographical range of several lunulite species.

Until recently, species of the deep-water ascophoran genus Siphonicytara have been recorded from only two areas, nearly 10,000 km apart. Three species were known from the East Indies and one from the southwest Indian Ocean. A hitherto unrecognized species is now known from the southern-most Philippine region, and six new species have recently been described from New Caledonia. A further new species from relatively shallow water, S. occidentalis, is described here from Western Australia. Examination of fossil specimens from the Tertiary of Victoria and South Australia has shown that specimens attributed to Parina clypeata Waters have a close relationship with Siphonicytara, and the species is referred here to this genus, as is Mucronella airensis Maplestone. Another Tertiary species with a similar distribution, 'Eschara elevata' Waters not Tenison Woods, is assigned to Siphonicytara irregularis (Maplestone). The stratigraphic range for the family extends from the Late Eocene to Recent. Eschara elevata Tenison Woods sensu stricto is the type species of the genus Tubitrabecularia Bassler, and a discussion of the nature and status of this genus is included. A key to the species described is given.

Bryozoans are an important part of the benthic marine fauna in a wide variety of modern environments and are found in rock forming abundance in a number of settings throughout much of the Phanerozoic. Bryozoologists and nonspecialists have grouped taxa into colonial growth forms (e.g., erect fenestrates or encrusting sheets), both to simplify analyses and because correlations exist between some colony growth forms and the environmental conditions in which the organism lived. These correlations allow for the possibility of paleoenvironmental analyses based on skeletons alone. Existing bryozoan colonial growth form classifications do not, however, fully exploit the ecological information present in colony form. A new scheme is proposed here (Analytical Bryozoan Growth Habit Classification), which provides a list of colony-level morphological characteristics for bryozoan growth habits. This differs from previous approaches to bryozoan growth form analysis in that it is a classification of growth habit characteristics rather than a classification of morphological groups as such. The classification is based on eleven character classes, which describe the orientation of the colony and its occupation of, and placement in space. The overall colony shape is described based on the arrangement of modules in colonial growth. This classification provides a common ground for systematic comparison of character states among varied bryozoan growth habits. This approach allows for the evaluation of correlations among observed morphological character states and specific environmental conditions in which they develop. In addition, these growth habit characters can be used to recognize, characterize, evaluate, and apply more traditional growth form groups in broader studies.