Checklist of the marine Bryozoa from Uruguay (Southwest Atlantic)

: Knowledge of the marine bryozoan fauna of Uruguay is mostly based on scattered records found in local faunistic surveys and the taxonomic results of two oceanographic cruises to the Southwest Atlantic, but a comprehensive study has not yet been published for this area. This paper aims to compile an updated checklist, bringing together all the published information about the Uruguayan bryozoan fauna. Of the 73 recorded taxa, 30 (41%) are known only from deep waters off the Río de la Plata. Even considering undetermined species, these re- sults show the high degree of endemism as it was already shown for several other benthic groups such as Bivalvia, Ascidiacea and Pycnogonida. The absence of local taxonomists on bryozoans has resulted in the unprecedented situation that the deep-sea bryozoan fauna of Uruguay is better known than the coastal and shelf representatives of the phylum. The main conclusion of this faunal compilation is that efforts should be made to coordinate the gathering and taxonomic study of shallow and shelf bryozoan collections to bridge the present knowledge gap about the biodiversity of this important group of marine benthic invertebrates.

The aim of this study is to compile an updated checklist, bringing together all the published information on the Uruguayan marine fauna of bryozoans.

Study area
The area considered is the Uruguayan coastline influenced by marine waters (Fig. 1), the adjacent territorial waters in the Río de la Plata and inner continental shelf, as well as the Uruguayan Economic Exclusive Zone (URY EEZ), which extends 200 nautical miles off the Uruguayan coastline. Only one sampling site (station 242 of the cruise 60 of the RV Atlantis II) falling some miles off this zone is here included considering the forthcoming definitive enlargement of the URY EEZ.

Criteria for the construction of this checklist
The included species have been recorded from the area specified above. Scientific papers and book chapters taken into account are indicated as "References for the area". Full data of the stations of the HMS Challenger and RV Atlantis II cruises are provided in Appendix 1.
The synonymy includes the original description and, when it existed: a) references which re-describe the type material from Uruguay (e.g. Turritigera stellata Busk, 1884), and b) species described from Uruguay that have been later synonymized to other species (e.g. Formosocellaria abyssicola d . For species having a long or relatively complex taxonomic history (which we do not fully detail here) we also list at least one reference detailing its synonymy.
References to the geographic distribution of littoral species include: a) general/major revisions containing comprehensive treatment of these, or b) works extending considerably (i.e. thousands of kilometers) the range of a given species. In the case of deep-sea species we have considered all available references.
It must be noted that the station 320 of the HMS Challenger falls exactly on the maritime limit between Argentina and Uruguay and therefore the species recorded there are considered as part of the faunistic inventory of both countries.
Remarks: This species was initially listed by Obenat et al., 2001 on the basis of material collected alive on tubes of the polychaete Phyllochaetopterus socialis and identified by one of us (JLG). Frequently found in brackish environments, in the lower intertidal zone, and up to shallow subtidal waters; its most common substrates are oyster valves, stones, and other hard substrates (Hayward & Ryland, 1998). Orensanz et al. (2002) and Schwindt et al. (2020) considered this species as cryptogenic, but its presence in the area since the mid-Holocene has been recently confirmed . Recent observations made by us indicate that the references made by Barattini & Ureta (1961) (as Membranipora tehuelcha, partim), Riestra et al. (1992) and Giménez et al. (2005) (all as Membranipora sp.) belong to this species, which is very abundant and widely distributed in the Uruguayan coast. Since we have found another yet unidentified species of Membraniporidae in Uruguayan ports, it is not possible to assign with certainty the record by Calvo (1984) as Membranipora sp. to C. reticulum. Geographic distribution: Australia, New Zealand, Southern Chile (Moyano, 1974;Gordon, 1986;Figuerola et al., 2014). Atlantic: Uruguay and Argentina (Busk, 1884;López-Gappa, 2000;Figuerola et al., 2014).

Bathymetric distribution in Uruguayan waters: 1097 m.
References for the area: Busk (1884); López-Gappa (2000). Remarks: Collected by the HMS Challenger at Bass Strait (Australia) and the continental slope off Argentina and Uruguay (stn. 320) (Busk, 1884). This genus is recorded only for the Southern Hemisphere (South America to New Zealand) (Winston, 2005). Busk (1884) identified these specimens (from Australia and the Argentine basin) as belonging to the same species, without designating a holotype. The present identification therefore depends on the confirmation that all specimens examined by Busk (1884) belong to the same taxon. A lectotype was not designated by subsequent authors who studied or mentioned this species (Canu, 1900;Gordon, 1986).
Geographic distribution: Argentine Basin off Uruguay (d . Bathymetric distribution in Uruguayan waters: 2707 m. References for the area: d' . Remarks: Lower bathyal species, collected during the RV Atlantis II cruise 60 at stn. 245, off Uruguay, which is its type-locality (d .
Geographic distribution: Argentine Basin (off Uruguay) (d . Bathymetric distribution in Uruguayan waters: 2707 m. References for the area: d' . Remarks: Collected during the RV Atlantis II cruise 60 at stn. 245, which is its type-locality (d .

Bathymetric distribution in Uruguayan waters: Shallow subtidal.
References for the area: Calvo (1984) as Cryptosula sp.; Scarabino (2006). Remarks: This species is a frequent member of the fouling community (Orensanz et al., 2002). It is typically and commonly found in intertidal habitats, but it can also be found in the sublittoral, growing on stones, shells, and other hard or soft substrates such as polychaete tubes, algae and hydroids. It can be found from the upper littoral down to 200 m depth (Marcus, 1942), and it is considered as introduced in Uruguay-Argentina (Schwindt et al., 2020).

Bathymetric distribution in Uruguayan waters: 2707 m.
References for the area: d' ; López-Gappa (2000). Remarks: Flexible and delicate colonies of this species were collected off Uruguay by the RV Atlantis II cruise 60 at stn. 245 (type-locality).

Bathymetric distribution in Uruguayan waters: 1097 m.
References for the area: Busk (1884); López-Gappa (2000). Remarks: Collected during the HMS Challenger expedition at stn. 320, which is its type and unique known locality for this species.

Geographic distribution:
Only known from the lower slope of Argentine Basin (Uruguay) (d López-Gappa, 2000;Figuerola et al., 2014). Bathymetric distribution in Uruguayan waters: 2707 m. References for the area: d' ; López-Gappa (2000). Remarks: Colonies erect, dichotomously branched, collected by the RV Atlantis II cruise 60 at stn. 245, which is its type-locality and the unique site in which this species has been recorded (d .

Bathymetric distribution in Uruguayan waters: 1097 m.
References for the area: Cook & Hayward (1983). Remarks: Colony erect, branching, arising from encrusting bases. Colonies were collected during the HMS Challenger expedition at stn. 320, which is the type-locality (Cook & Hayward, 1983).
Geographic distribution: Southeast Pacific (Chile), Cape Horn, Magellanic region, Argentine Basin (Busk, 1884;Moyano, 1974;Cook & Hayward, 1983;López-Gappa & Lichtschein, 1988;López-Gappa, 2000;Ramalho et al., 2011;Figuerola et al., 2014). Bathymetric distribution in Uruguayan waters: 1097 m. Turritigera spectabilis was collected at 1661−4402 m (see Remarks below). References for the area: Busk (1884); López-Gappa (2000). Remarks: Erect and well calcified colonies were collected by the HMS Challenger expedition at stn. 320 (Busk, 1884). The original description was also based on material from South Africa. A colony from stn. 320 was selected by Hayward & Winston (2011) as the lectotype, that stn. thus becoming its type locality. Turritigera spectabilis d  was described from material obtained at similar depths at very close (stns. 239, 242 and 245 of the RV Atlantis II cruise 60) to the type locality of T. stellata. As a formal revision of type materials is needed to conclude that T. spectabilis is a junior synonym of T. stellata, in this compilation we have preferred to cite T. spectabilis as a separate species.

DISCUSSION AND CONCLUSION
This study compiled 73 taxa recorded in Uruguayan waters, from all three orders of extant marine bryozoans (Cheilostomatida, Ctenostomatida and Cyclostomatida). The most diverse order was Cheilostomatida with 63 taxa, followed by Cyclostomatida (7 taxa) and Ctenostomatida (3 taxa).
With an estimated diversity of more than 4,900 species in 2013 (Bock & Gordon, 2013), the Cheilostomatida is the most successful group among the Recent bryozoans. Its high species-diversity seems to be related to their variability in the use of substrates and the acquisition of special features such as zooidal polymorphism and complex reproductive patterns (Ryland, 1970).
On the other hand, the Cyclostomatida usually show modest levels of biodiversity when compared with the Cheilostomatida, accounting globally for up to 11% of the species in modern bryozoan faunas (Rosso, 2003;Ramalho et al., 2009). Three out of the seven taxa of Cyclostomatida herein mentioned were found at between 200 and 1500 m depth, while another four between 1500 and 3000 m. Hayward & Ryland (1985) mentioned that Cyclostomatida species are usually found to occur in shallow waters less than 1000 m depth, but this statement is undergoing changes from the new studies that are being carried out in deep waters. Grischenko et al. (2018) studying the bryozoan fauna associated with nodules, collected in the Russian deep sea (4510 and 5280 m), showed that cyclostomes are much more diverse than previously thought, comprising 34% of the total bryozoan fauna identified.
The Ctenostomatida commonly exhibit low biodiversity levels, but usually are very common and abundant in shallow waters. Three ctenostomes were recorded in the present study, two of them from depths up to 200 m and one at deeper waters.
Thirty out of the 73 taxa (41%) are known only from deep waters off the Río de la Plata, with an additional species also known from a station in Patagonian deep waters. Even considering there are some undetermined species, this result shows a high degree of endemism, as it was already shown for several benthic groups such as Bivalvia, Ascidiacea and Pycnogonida (Scarabino et al., 2016(Scarabino et al., , 2018(Scarabino et al., , 2019, and references therein). Furthermore, also molecular analysis could identify even more endemic species amongst some of the more seemingly widely distributed species. The remaining recorded species could be classified in three groups: 1) deep-sea species widely distributed over other basins (15), 2) shelf and deep-sea species of Antarctic and Subantarctic distribution (17), and 3) shelf species, including shallow water cryptogenic or introduced taxa (10). A similar pattern exists concerning the proportion of species for Ascidiacea and Pycnogonida from Uruguayan waters (Scarabino et al., 2018(Scarabino et al., , 2019 and it represents a bias. In fact, most of the species compiled in this study were gathered during two oceanographic cruises that surveyed the continental slope and abyssal plain off Uruguay. This fact, together with the absence of local bryozoan taxonomists, has resulted in the unprecedented situation that the deep-sea bryozoan fauna of Uruguay is better known than the coastal and shelf representatives of the phylum. Therefore, future efforts should be directed to coordinate the sampling and taxonomic study of shallow and shelf specimens in order to bridge the present gap in the knowledge of the Uruguayan bryozoan fauna. The present study is designed to kick-start more detailed empirical taxonomic studies to fill the gap in the knowledge of bryozoan distribution patterns along the Atlantic coast of South America.