The Bryozoa collection of the Italian National Antarctic Museum, with an updated checklist from Terra Nova Bay, Ross Sea

Abstract This study provides taxonomic and distributional data of bryozoan species from the Ross Sea area, mainly around Terra Nova Bay, based on specimens curated at the Italian National Antarctic Museum (MNA, Section of Genoa). Bryozoan specimens were collected at 75 different sampling stations in the Ross Sea and in the Magellan Strait, in a bathymetric range of 18–711 meters, during 13 expeditions of the Italian National Antarctic Research Program (PNRA) conducted between 1988 and 2014. A total of 282 MNA vouchers corresponding to 311 specimens and 127 morphospecies have been identified and included in the present dataset. 62% of the species were already reported for the Terra Nova Bay area, where most of the Italian samples come from, with a 35% of samples representing new records classified at the specific level, and 3% classified at the genus level. These new additions increase to 124 the total number of species known to occur in Terra Nova Bay. Four 3D-models of Antarctic bryozoans from the Ross Sea are also presented and will be released for research and educational purposes on the Museum website.


Introduction
In the last 30 years, several Italian expeditions have been conducted in the Ross Sea leading to the publication of contributions on different taxonomic groups. Among the different phyla, Bryozoa was extensively studied until 2000 with papers reporting data on bryozoan species obtained during the first Italian Antarctic campaigns in Terra Nova Bay (i.e., 1988Bay (i.e., -1995 (Di Geronimo and Rosso 1990;Rosso 1990Rosso , 1991Rosso , 1992aRosso , 1994Rosso and Sanfilippo 2000).
From 2000 onwards, new Antarctic campaigns were annually conducted and the number of new samples acquired by the Italian National Antarctic Museum (MNA, section of Genoa) progressively increased. However, no new taxonomic characterization was carried out on this material until now. Few samples from the Magellan Strait, collected during the VI Italian National Antarctic Program (PNRA) expedition in 1991, are also included here. The present study provides distributional data and taxonomic identification, at the lowest possible level, of bryozoans collected during 13 scientific expeditions of the PNRA in the Ross Sea and the Magellan Strait. These data are combined with previous literature checklists for the area with the aim of providing an updated checklist for Terra Nova Bay and distributional data for all the available vouchers. All bryozoan specimens reported in this paper are stored at the MNA and at the museum of the IPOP in Catania (Figure 1). This dataset is the sixth MNA contribution to the Antarctic Biodiversity Portal, the thematic Antarctic node for both the Ocean Biogeographic Information System (AntOBIS) and the Global Biodiversity Information Facility (ANTABIF) (http://www.biodiversity.aq). Previous contributions on Mollusca, Tanaidacea, Fungi, Ophiuroidea and Porifera were respectively published in Ghiglione et al. (2013), Piazza et al. (2014), Selbmann et al. (2015), Cecchetto et al. (2017) and Ghiglione et al. (2018).   Design: Data were assembled by revising all the distributional records of the specimens stored in the MNA collections (section of Genoa, Italy) and in the museum of the IPOP in Catania.

Sampling
The distributional data of Bryozoa, here illustrated, came from different research expeditions, conducted between 1988 and 2014, and include 75 sampling stations, located between 18 and 711 metres of depth (Figs 2-5). Sampling was performed by using a variety of methods and gears such as dredges (Charcot dredge, Naturalist dredge, Triangular dredge, and Picard dredge), Van Veen grabs of different volumes and, for opportunistic sampling, fishing long lines, mid-water trawls (that accidentally touched the bottom due to a failure of the winches providing additional material), trammel nets and other fishing nets. In addition, during the XXV PNRA expedition, some samples were hand-collected by SCUBA diving by one of the authors (SS) (Figs 6, 7). Images of bryozoan colonies were also obtained through ROV video transects performed during the XXIX expedition, and subsequently identified at least to the genus level ( Figure 7). Station coordinates and sampling events were recorded during sampling activities based on various GPS systems. The data flowchart ( Figure 1) illustrates the sampling, sorting and storing procedures for specimens as well as data and image availability.

Quality control
Once at the MNA, all specimens were classified at the lowest possible taxonomic level; only those that were classified at least to genus level were included in the present dataset. Several researchers contributed in classifying the specimens, and the last taxonomic revision of the MNA bryozoan collection was conducted in the past two years by Chiara Lombardi, Silvia Cocito, and Piotr Kuklinski. During all phases of sorting, classification and storage of samples at the MNA, quality control and data cleaning have been undertaken at various stages in order to produce high quality data, and make consistent cross-references between the database and samples' labels. The MNA (www.mna.it)     (1), a detail of the yellow tips of the colony in the field (2), and the whole fresh colony after the collection (3); the last two corresponding to the same voucher (MNA 2872) collected by SCUBA diving; colony of the cyclostome Hornera enclosing a sponge (4); fan-shaped colony of the cyclostome Hornera sp. growing on a boulder (5); colony of the cheilostome Reteporella sp. living in association with other bryozoans, hydroids, polychaetes (6); rounded greyish colony of the cyclostome Fasciculipora ramosa D'Orbigny 1839 growing on the sea bottom (7).
uses the R-Shiny web application (https://steu.shinyapps.io/MNA-generale/) to manage and show its collections, and a Microsoft SQL database (Specify 6) to link all the data (photos, glass slides, etc.) to the physical samples in the collection. Of a total of 282 MNA vouchers, 29 samples were collected and studied before the MNA was established in 1999, and they were stored at the museum of the Istituto Policattedra di Oceanologia e Paleoecologia (IPOP) in Catania. All other samples are permanently curated at the MNA and available for study to the scientific community.

Taxonomic coverage
The present dataset reports distributional data on bryozoan specimens belonging to the classes Stenolaemata and Gymnolaemata collected in the Ross Sea and in Magellan Strait. It includes a total of 311 specimens corresponding to 282 MNA vouchers and belonging to 127 morphospecies. Out of these, 100 were classified to species level and 27 to genus level, representing three orders and 34 families (Figs 8,9). Considering only the records collected in the Terra Nova Bay area, 41 species (62.12%) were already known for the area, whereas 25 are new records, out of which 23 (34.85%) are classified at species level and two (3.03%) at the genus level. These new records are annotated by 'NR' immediately after the species name in the Checklist. By merging previously published records (i.e., Di Geronimo and Rosso 1990, Rosso 1990, Rosso 1991, Rosso 1992a, Rosso 1994, Rosso and Sanfilippo 2000 with the new ones, the number of bryozoan morphospecies occurring in the Terra Nova Bay area increases to 124 ( Fig. 10 and Suppl. material 1: Table 1). From this regional checklist we have excluded identifications of specimens lacking key morphological characters, so as to avoid future misidentifications (e.g., Larvapora cf. mawsoni, Fenestrulina sp.). Therefore, the total number of species reported in the area may increase in the future.
The MNA collection includes one bryozoan holotype: Melicerita digeronimoi (voucher: MNA 1054). This species, deposited at the museum of the IPOP in Catania (catalogue number IPOP. B1.8.8.1991) in 1991, was published by Rosso in 1992(Rosso 1992b, i.e., eight years before the establishment of the MNA. To keep track of this voucher, an MNA catalogue number (MNA 1054) has also been assigned, although the sample is curated by the IPOP.

Taxonomic update for Cyclostomatida species previously reported in literature
Defrancia sarsi (Borg, 1944), reported for Terra Nova Bay in 2000 (Rosso and Sanfilippo 2000), is here classified as Apsendesia sarsi following Bock and Gordon (2013); Idmidronea magna Androsova, 1968(as reported by Rosso 1990) is synonym of Idmidronea obtecta Borg, 1944. Tubulipora tubigera Busk, 1866 (reported by Rosso 1991, Rosso andSanfilippo 2000) is classified as Supercytis tubigera as stated in Bock and Gordon (2013). Lastly, although the record Bearta sp. has been reported in the literature (Rosso 1990), it is certainly a misspelling and should be referred to Beania sp. Specimen preservation method: Part of the old collection was initially fixed in 4% formalin and then transferred in 70% ethanol. Samples collected from 2002 onwards were directly fixed in ethanol (99%) for molecular studies or air-dried. Bryozoan MNA vouchers are now preserved in 90% ethanol (~38% of the entire collection) or dried (~62%).
Database virtual collection of vouchers and 3D-models: 3D-models of four Antarctic bryozoans  were obtained from four specimens through micro-CT imaging performed at the Department of Geosciences (University of Padua) by CM. Acquisitions were performed using a bench-top Skyscan 1172 micro-CT system (Bruker), equipped with a Hamamatsu 100/250 microfocus X-ray source and a Hamamatsu C9300 11 megapixel camera (with a pixel size of 8.68 μm) filtered by a 0.5 mm Aluminium foil. Projection images were acquired with 70 kV source voltage, 141 μA current, 540 ms exposure time, 2×2 binning mode, 0.25° rotation step over 360°, averaged over 12 frames and in vertical random movement mode to minimise noise, providing an image pixel size of about 9 μm. Two connected scans were necessary to comprise the whole sample height. The run time for each sample was about 400 minutes. Post-acquisition reconstruction was performed using the NRecon (Bruker mi-croCT) software package, starting from raw projection images, and applying thermal correction, misalignment compensation, ring artefact reduction and beam hardening correction. Segmentation was then performed with CT Analyser (Bruker microCT) software package, using a 3D-adaptive thresholding procedure (mean of minimum and maximum value) within spherical kernels of radius 8 pixels, starting from a predetermined pre-thresholding value. Resulting images were saved as monochrome (1 bit) bitmaps and imported in the CTVox (Bruker microCT) software package to perform 3D-rendering and animations. The model will be available on the MNA web site (www.mna.it) and on Sketchfab (https://sketchfab.com/MNA).
Hastingsia irregularis Borg, 1944 (MNA 10490, Figure 11) belongs to the Cyclostomatida, the only extant order of the class Stenolaemata, whose species are widely spread from all over the world, including the Antarctic Region. The scarce knowledge of cyclostome species for the Ross Sea, compared to cheilostomes, is attributable to the complex taxonomy of the group, which has been studied partly by Borg (1944) and Androsova (1968) but not for the Ross Sea or continent as a whole. The scan shows the structure of an H. irregularis colony, which develops well-calcified 3D-architectures, offering a space-resource to other species. H. irregularis forms erect colonies composed of 'fascicles' of long narrow zooids (ridge-like structures) becoming autozooids at their distal ends. The long and narrow zooids have small-scattered pseudopores and their skeletal walls are characterized by grooves between adjacent zooids and distinct growth ridges. Gonozooids (i.e., reproductive zooids) develops between colony branches (see the median branch developing a gonozooid on the top, Figure 11).
This model clearly provides an example of how the cyclostome colony acts as a resource for another bryozoan genus, Arachnopusia (Cheilostomatida, shown in detail in Figure 12). The genus Arachnopusia includes encrusting species, usually occurring in shallow shelf seas and only growing on biogenic carbonates (Hayward 1995). The species illustrated in the model (MNA 10491) grows on the reverse (dorsal) side of H. irregularis branches, where the surface is smoother compared to the rough substrate created by the tubular processes on the other side. Thus, this encruster might take advantage of the erect habit of the cyclostome (i.e., accessing the food on the water column) without interfering with its activities such as feeding and growing, which mainly occur on the other side.
Idmidronea cf. obtecta Borg, 1944 (MNA 9890, Figure 13) is a cyclostome forming large, erect, well-calcified colonies, with cylindrical branches. These branches are dichotomous, not very regularly spaced, with an oval transverse section, subcircular or rounded trapezoidal. Although bifurcations are not very regular on I. obtecta colonies, the whole zoarial shape is 3D-structured. The species represents another example of bioconstructional bryozoan, thus offering substrate and space for other organisms to live and settle. Interestingly, the model shows on reverse sides of branches the presence of arcuate growth lines. The presence of "growth check lines", especially among Antarctic erect cheilostomes, is very common, indicating a transitional phase between growth and stop in the colony, usually during the winter period (Winston, 1983). These bryozoans represent good bioindicators and key-species for experimental studies thanks to their "growth lines", which can be easily measured, allowing the quantification of the growth of the entire colony, often related to variations in environmental conditions detectable via stable isotope analyses (i.e., food availability, salinity, temperature and pCO 2 variations) (Barnes 2015).  Eminoecia carsonae (Rogick, 1957) (NR) (MNA 8408, Figure 14) is an erect calcitic cheilostome bryozoan, originating from an encrusting base. This species develops erect branches, bifurcating dichotomously and shaping 3D colonies. Different characteristic morphological features of the autozooids, such as thick crenulated edges, tuberculate and coarse frontal walls, two pairs of pores at the proximal and distal end of the zooid and Figure 13. Video of the 3D-model of Idmidronea cf. obtecta Borg, 1944 (MNA 9890). Height and width of the colony are respectively ~20.4 mm and ~17.5 mm. frontal suboral avicularia, organized in bands on the colony branches, are illustrated in Figure 14. Being a bioconstructional bryozoan, this species offers space and advantages to other species to live and settle, thus it has a key role in promoting the biodiversity. Described as an endemic Antarctic species, E. carsonae is widespread in the Ross Sea (Hayward 1995; Moyano 2005) but it is here recorded for the first time for Terra Nova Bay. Smittina directa (Waters, 1904) (MNA 9883, Figure 15), an endemic Antarctic species, represents another example of an erect calcitic cheilostome, developing slender, cylindrical colonies originating from an encrusting base. Its autozooids, budding simultaneously, are organized in whorls of four or five, with frontal orifices opening around the whole branch ( Figure 15). The primary orifice has an anvil-shaped lyrula (e.g., median tooth) with a straight edge projecting corners and a peristome, and its distal third is in a continuum with the calcification of the next autozooid (Hayward 1995). Smittina directa is subject to marked secondary calcification processes, which lead, in later ontogeny, to the thickening of the frontal walls, thus some of its morphological features are hardly recognizable. In addition to the autozooids, the branch represented in Figure 15 bears kenozooids (e.g., zooids without muscles and primary orifice), whose main function is to provide structural strength to the colony.

Dataset metadata:
This dataset contains data on the phylum Bryozoa, represented by two classes and three orders in the Ross Sea, with focus on Terra Nova Bay, and the Magellan Strait. The present dataset has been formatted in order to fulfil the Darwin Core standard protocol required by the OBIS scheme (http://www.iobis.org/manual/lifewatchqc/) and according to the SCAR-MarBIN Data Toolkit (available at http://www.scarmarbin.be/documents/SM-FATv1.zip). The dataset was uploaded and integrated with the ANTOBIS database (the geospatial component of SCAR-MarBIN). Two studies have been based on this dataset: Rosso and Sanfilippo 1991;Rosso 1992b.
The Darwin Core elements included in the dataset are: ID, Institution code (i.e., the name of the institution where the samples are curated), basis of record, occurrence ID, catalogue number (i.e., MNA catalogue number), individual count, preparation (preservation method and more info about the sample, e.g., ETOH, dry, glass slides, etc.), event ID (i.e., original sampling station code), sampling protocol (sampling gear), event date, year, month, day, verbatim event date, field number (sampling station code as showed in the maps), event remarks (i.e., expedition), maximum depth meters, decimal latitude, decimal longitude, locality, taxon ID, scientific name ID, scientific name, kingdom, phylum, class, order, family, genus, subgenus, specific epithet, infraspecific epithet, scientific name authorship, taxon remarks. Some of the sampling stations are dredge stations, which have two sets of coordinates: the starting and ending points. In such cases, the coordinates reported in the dataset refer to the starting point of the dredge station.