Neorotalia leeuwinensis n. sp. is morphologically and genetically distinct from other calcarinids that are present in very shallow waters along the western margin of Australia and has not been recognised amongst known species elsewhere. The distributions of calcarinids along the margin has been surveyed from 22 sites. Four distinct latitudinally-based regions are defined related to temperature. Neorotalia leeuwinensis n. sp. has a known latitudinal range of 30°S to 34°S (>19°C, 30-year average winter minimum sea temperature in the north and >18°C in the south). The main microhabitat observed for the species is the articulate coralline algae Amphiroa gracilis, which usually lives among a diversity of macrophytes in very shallow high-energy environments on the rock platforms. Test shape, robust peripheral spines, and pore tubes are related to the high-energy epibiont lifestyle on the algal branches. Significant marine and terrestrial climatic gradients along the west coastline of Australia from the tropics to the south apparently control calcarinid species distributions, but the reasons for endemism require much more study of environmental parameters and molecular analyses of species.

Shallow-water rock platforms and tidal pools, including coral-algal reefs in the tropics and rock platforms dominated by macrophyte algae at higher latitudes, and their immediate marine surroundings are homes for a diversity of foraminifers in many different living microhabitats (e.g., Hohenegger, 1996; Fujita, 2008; Debenay & Payri, 2010; Weinmann & Langer, 2017; Manda, 2020; Narayan et al., 2022; Bérgamo et al., 2024). Over 400 benthic foraminiferal species are known from the inner neritic zone in Western Australia (open shelf; less than 30 m water depth) south of Exmouth on North West Cape (Parr 1950 in Fairbridge 1950; Betjeman, 1969; Haig, 1997; Orpin et al., 1999; Semeniuk, 2000, 2001; Parker, 2009; Buosi et al., 2020). Of these, over 300 species are present on submerged rock platforms and surrounding areas, with sandy, algal, seagrass and rare coral microhabitats, in southwest Western Australia.

The calcarinids (Family Calcarinidae) include the genera Calcarina d’Orbigny, Baculogypsina Sacco, Neorotalia Bermúdez, Pararotalia Le Calvez, and Schlumbergerella Hanzawa that are very common around the tropical coast of the Australian continent (Fig. 1), including New Guinea, Seram, and Timor (Cushman, 1942; Jell et al., 1965; Baccaert, 1986; Loeblich & Tappan, 1994; Langer & Hottinger, 2000; Lobegeier, 2002; Langer & Lipps, 2003; Glenn & Collins, 2005; Schueth & Frank, 2008; Uthicke & Nobes, 2008; Renema et al., 2013). Calcarinids decrease in diversity from North to South along the western margin of the Australian continent (Fig. 2). Neorotalia and Pararotalia extend further south than tropical Calcarina, Baculogypsina, and Schlumbergella (e.g., Parr in Fairbridge, 1951; Betjeman, 1969; Haig, 1997; Semeniuk, 2001; Parker, 2009). In previous studies on the biogeography of larger benthic foraminifera (Langer & Hottinger, 2000), the southern geographical limit of “Neorotalia calcar” along the Western Australia coast was suggested to be near the Houtman Abrolhos Islands at about 28.5°S (Fig. 1). Our recent survey of coastal rock platforms south of this latitude found abundant live populations of N. sp. cf. calcar further south—as far as 32.3°S. Near this southern limit of the biogeographical range of calcarinids, an undescribed species of Neorotalia, which is morphologically distinct from N. calcar, also is present with a known living range extending from 30°S to 34°S. Live populations of Pararotalia also extend at least as far south as 34°S. On the east Australian mainland shelf, the modern calcarinid Pararotalia can be found as far south as Moreton Bay (at about 27.4°S by Narayan & Pandolfi, 2010), and Baculogypsina and Neorotalia (recorded as Pararotalia) can be found offshore Lord Howe and adjacent islands (parts of Zealandia submerged continent) at about 31.5°S (Yassini & Jones, 2023). On the shelf seas of other southern continents, Pararotalia is recorded as far south as the uMlalazi Estuary, east coast of South Africa (at about 29.3°S; Schmitz et al., 2024), and on the east coast of Brazil, the endemic Pararotalia cananeiaensis Debenay, Duleba, Bonetti De Melo e Souza & Eichler was reported as far south 27.6°S (Debenay et al., 2001).

The aims of this study are to (i) document the known distributions of calcarinids along the western margin of the Australian continent through a latitudinal gradient from tropical to cool-temperate environments; (ii) describe a new endemic calcarinid species from the southern west coast of Australia, Neorotalia leeuwinensis, based on morphological and molecular analyses; (iii) record the living habitats of the new species and its lifestyle; (iv) suggest functional morphological reasons for some of the unusual aspects of test construction; and (v) investigate possible reasons for its endemism and narrow geographic range at the southernmost known extent of calcarinids.

Molecular studies are currently underway on many of the calcarinid species found along the western margin of the Australian continent, and these will add more precision to taxonomic determinations and the relationships between species. Until the molecular studies are completed, Calcarina, Baculogypsina, and Schlumbergerella are treated here as broad generic groups and Neorotalia spp. cf. calcar (d’Orbigny) and Pararotalia spp. cf. calcariformata McCulloch as broad species categories which show considerable morphological variability (see discussion in Morphological and Molecular Relationships).

Coastal Setting

Shallow rock platforms situated at the boundary between the low hinterland and open ocean are frequently exposed to various daily and seasonal disturbances. These encompass tidal fluctuations, strong wave activity, episodic events such as storms with high winds and heavy rainfall, and the accumulation and erosion of surrounding coastal dunes. Along the Western margin from North to South, the tidal range shifts from (i) macrotidal (>4 m north of 20°S; usually 8–9 m, in places up to 11 m tidal height range) to (ii) mesotidal (2–4 m from 20°S to about 28°S) and (iii) microtidal (<2 m) for all the southwest region (Fig. 3; Neill et al., 2021; Bureau of Meteorology, 2024). Alongside tidal change, rainfall patterns are marked by a gradient from north to south (Fig. 3), driven by climatic differences and the influence of the monsoon from the subequatorial belt (Rix et al., 2015). To the north, the climate is tropical with the wet season occurring between November and April, mainly driven by the Australian monsoon. During this period, warm, moist air masses from the Indian Ocean bring intense and often sporadic rainfall, resulting in high annual precipitation (averaging >800 mm). Furthermore, episodic cyclonic activity contributes significantly to rainfall, causing localized flooding and extreme weather events. The macrotidal conditions, the extreme summer freshwater outflow from rivers, and the remote coastline have resulted in very few published records of foraminifers along the mainland shoreline north of 20°S, and none of calcarinids. Moving southward into the central and southern parts of Western Australia, the climate transitions to arid/semi-arid and Mediterranean-like. Rainfall becomes more erratic, with lower annual totals and less pronounced seasonal variation (<300 mm annual rainfall). In the southwest, the climate is characterised by cool, wet winters and hot, dry summers. Here, rainfall primarily occurs between May and September, influenced by the passage of cold fronts and low-pressure systems. The influence of the monsoon is strongest in the north and diminishes gradually towards the south. During relatively short intervals, rocky shore habitats may experience great salinity variation with freshwater inputs from precipitation (mostly pronounced and more emphasized at low tide) or from groundwater discharge in areas with active springs on permeable rock platforms, such as coastal limestone (Silva, 2024).

Oceanographic Setting

Eastern ocean basins are characterised by cold equatorward boundary currents (Wang et al., 2023). In the southern hemisphere, the Benguela Current system along the south-west African coast and the Humboldt (or Peru) Current along the western South American coast, both support rich coastal fisheries due to highly productive ecosystems because of seasonal wind-driven upwelling of cold and nutrient-rich subsurface water (Pearce & Pattiaratchi, 1999). Along the eastern boundary of the Indian Ocean, off the coast of Western Australia (WA), although the wind regime is like along other eastern ocean margins, there is the poleward Leeuwin Current (LC). The LC is a shallow (<300-m deep), narrow (<100-km wide) band of warm, low salinity (<35 psu), nutrient-depleted water of tropical origin, which flows poleward against the prevailing winds (Fig. 2; Woo & Pattiaratchi, 2008).

The LC circulation pattern flows from the north to south coast of Western Australia (Fig. 2) thereby crossing through seven marine ecoregions from Seram–Timor to Cape Leeuwin (Hadiyanto et al., 2021). Its dynamics are primarily driven by the geopotential gradient from North to South due to the influx of warm, low salinity waters originating from the Pacific Ocean, traversing the Indonesian Archipelago into the Indian Ocean. Consequently, there is a noticeable difference in the density of water between Australia and Indonesia. The water in this area is less dense compared to the cooler, saltier waters near the southwestern coast of Australia. The resulting density difference, which sets up a sea-level gradient of about 0.5 m along the Western Australian coastline, is the LC’s driving force. The earth’s rotation causes water from the Indian Ocean to be entrained into the LC as the LC flows south; thus, the LC strengthens as it flows south (Pattiaratchi & Woo, 2009). The presence of the LC at the continental shelf edge can influence the water mass distribution, as the LC can induce downwelling of surface-water masses (Woo & Pattiaratchi, 2008). Observational studies have shown that the LC has a strong seasonal cycle with a maximum strength of about 0.5 m/s during the austral winter when the alongshore equatorward winds are weakest and minimal during the austral summer (Feng et al., 2013; Kataoka et al., 2014; Ridgway & Godfrey, 2015).

The LC is part of the broad Leeuwin current system, which consists of three major currents: the LC, the Leeuwin undercurrent (LU), and shelf current systems consisting of the Capes and Ningaloo currents. At the continental shelf edge, the LU can lead to upwelling of colder sub-surface water masses higher in the water column (Woo & Pattiaratchi, 2008). Compared to the farther offshore LC along the shelf edge, the continental shelf currents (the Capes and Ningaloo currents) transport cooler water northward. The Capes Current is a cool, inner shelf current that originated from the region between Capes Leeuwin and Naturaliste (i.e., 34°S) and moves equatorward along the south-west Australian coast during the austral summer (January–March) and can extend as far north as the Houtman Abrolhos Islands (28.7°S). The Capes current is sourced from water upwelled from the bottom of the LC, which usually occurs between Cape Leeuwin and Cape Naturaliste. There, the southerly wind stress overcomes the alongshore pressure gradient, which pushes the surface waters and the LC farther offshore and leads to upwelling of cold water onto the continental shelf (Pattiaratchi & Woo, 2009). The Ningaloo current flows northward along the Ningaloo reef inshore of the 50-m isobath, extending from Shark Bay (Fig. 2) to Northwest Cape and beyond, driven by a strong, southerly wind stress. Field data shows the Ningaloo current consists of colder (<23°C), more saline (34.92 psu) water than the offshore waters and has high nutrient concentrations, high phytoplankton biomass, and maximum regional primary production rates (Pattiaratchi & Woo, 2009).

General Distribution Pattern

Calcarinids are known from 22 sites along the western margin of the Australian continent (Table 1). They are distributed in four distinct regions related to the temperature ranges of the species (Fig. 2). From the equatorial zone to at least 18°S, on reef platforms on the outer continental shelf (>25°C, 30-year average winter minimum temperature), Calcarina, Baculogypsina, Schlumbergerella, Neorotalia spp. cf. calcar, and Pararotalia spp. cf. calcariformata are present in the calcarinid assemblages. From 20°S to about 29.5°S (>20°C, 30-year average winter minimum temperature), a low diversity assemblage of N. spp. cf. calcar and P. spp. cf. calcariformata is present. From about 30°S to at least 32.3°S (>19°C, 30-year average winter minimum temperature), a new species (N. leeuwinensis n. sp.) is added to the calcarinid assemblages. Between 32.3°S and 33.3°S, N. sp. cf. calcar disappears, and the calcarinid assemblages consist of N. leeuwinensis n. sp. and P. sp. cf. calcariformata until about 34°S (>18°C, 30-year average winter minimum temperature).

South of Site 22 (Fig. 1, Table 1), calcarinids were not observed during the present study. Quilty (1977, figs. 4, 52,53) recorded rare P. sp. cf. calcariformata (as “Calcarina calcar”) from Dead Water arm of the Hardy River, near the river’s mouth (Fig. 1). This occurrence at 34.3°S (>16°C, 30-year average winter minimum temperature) must be reconfirmed, because the specimens here may have been reworked from deposits of the Holocene sea-level high-stand or Pleistocene marine sediments.

Within the geographic range of the new species, N. leeuwinensis n. sp., two sites (18, Point Peron; 20, Bunker Bay; Table 1) have been found with abundant living populations of N. leeuwinensis n. sp., N. sp. cf. calcar and P. sp. cf. calcariformata (Site 18) and N. leeuwinensis n. sp. and P. sp. cf. calcariformata (Site 20). These sites and living microhabitats (Figs. 4, 5) are described below.

Point Peron

Point Peron (32.2711°S, 115.6875°E) is a narrow peninsula between Mangles Bay and Shoalwater Bay about 40 km southwest of Perth, Western Australia (Fig. 4). The region is home to a wide range of marine biota inhabiting shared microhabitats such as seagrass meadows, sandy seafloor, subtidal reefs, and intertidal limestone platforms (Fairbridge, 1950; Gordon, 1986). The peninsula is composed of Pleistocene Tamala limestone, which is overlain by early Holocene dune sand of the Quindalup Dune System (Fig. 4A; Gozzard, 2007). The dune system includes large-scale attenuated parabolic dunes that can extend up to 4 km inland (Fairbridge, 1950; Gozzard, 2007). The dunes are primarily composed of calcareous sediments, reflecting the marine origin of the sand (Fairbridge, 1950; Semeniuk, 1986). The modern coast is largely a result of rapid sea level rise during the mid-Holocene (Fairbridge, 1961; Semeniuk, 1986; Baker, et al., 2005). Point Peron has a low-energy shoreline with a microtidal range (Fig. 3), varying between 0.7 to 0.9 m (Gordon, 1986). Shallow wave-cut limestone platforms are present along the extension of the beach where samples were collected (Figs. 4A, B) as well as in coves along the coast. At low tide, the platforms are entirely exposed (Morgan, 2000).

The underwater flora of Point Peron consists of a large phytocenose that developed depending on suitable habitats on the reef platform (Gordon, 1986). The outer rims of these platforms on the seaward edge are dominated by brown algae such as Ecklonia radiata and Sargassum sp. (Gordon, 1986). These algal macrophytes overlie an understory of red algal species (Rhodophyta), including Amphiroa cryptarthrodia, Asparagopsis sp., and Plocamium sp. (Gordon, 1986). Amphiroa sp. is the dominant branching coralline algae (bright pink-colored) that was found in the study area to be growing in clusters on the intertidal reef flats (Figs. 4C, 4D). On the intertidal rock platforms from 31°S to 32.8°S including Point Peron, known invertebrates were listed by Kendrick & Rule (2014). Most invertebrate species (79% of a total 71 species) have temperate biogeographic ranges extending around the southern Australian innermost neritic shelf. A few species (7%) are tropical representatives, and 17% are endemic to Western Australia (some ranging into the tropics). The studied live calcarinids (Neorotalia sp. cf. calcar and Neorotalia leeuwinensis n. sp.) have been found in large proportion often in the upper part of the intricate branching structures of Amphiroa (Fig. 5D). These were mainly found in very shallow microhabitats, less than 1 m deep at high tide, that are aerially exposed under low-tide conditions.

Bunker Bay

Bunker Bay (Figs. 2, 5) lies in the northern part of the Ngari Capes Marine Park (Department of Environment and Conservation, D.E.C., 2013). The intertidal zone of Ngari Capes Marine Park hosts a diverse array of invertebrate communities inhabiting many microhabitats whose distributions are largely influenced by the Capes Current (Phillips, 2001; Westera et al., 2009). The coexistence of both tropical and temperate species makes this region a recognized diversity hotspot for invertebrate and other species (Phillips, 2001; D.E.C., 2013). Ngari Park houses approximately 100 species of echinoderms, including three species endemic to southwest Australia, and 115 species of crabs, prawns, and shrimps, with 43% endemic to southern Australia and 6% unique to the southwest of Western Australia. Many of the southwest invertebrates are temperate in origin, with only 2% showing tropical affinities (D.E.C., 2013). This multitude of marine taxa live mainly in seagrass meadows and algal beds that provide critical habitats and food sources. Bunker Bay (Fig. 5), located 5 km east of Cape Naturaliste (Janssen et al., 2003), is shaped by a major unconformity between coastal limestone above and Proterozoic metamorphic rocks below which form the present-day wave-cut platform (Freeman & Donaldson, 2006; Short & Short, 2020). Bunker Bay has a low-energy shoreline with microtidal fluctuation (0.7 m; Fig. 3) and sea temperature varying from 21°C at the height of the Western Australian summer to 16°C in winter (Bureau of Meteorology, 2024). The shallows are zoned by predominantly (i) sandy substrates between high-relief granite or gneiss rocks (covered by branching coralline algae including Amphiroa), (ii) small seagrass patches (Halophila sp., Heterozostera sp.), to (iii) dense persistent seagrass meadows (Amphibolis antartica and A. griffithii) on the deeper parts (personal observation). Like at Point Peron, Neorotalia leeuwinensis n. sp. shows a preference for the thin articulate branching Amphiroa sp. (Figs. 5C, D) despite the larger algal diversity in the bay.

Field Sampling Methods and Data Processing

Sediments and associated algal fragments were randomly sampled in small quantities on the rock platforms and surrounding intertidal zones. Samples were stored in collecting vials filled with seawater and stored in insulated containers. Immediately after collecting, the samples were examined, and a portion of the living specimens was cultured in the lab to examine the living behaviour and functions of morphological features. These were cultured in cell flasks with seawater changed every day over a week and maintained alive for observations of pseudopodia under an inverted optical microscope. Sand residues were subsequently dried at room temperature for a couple of days before being picked. About 100 specimens of N. leeuwinensis n. sp. from Point Peron and Bunker Bay were measured using Adobe Photoshop (Adobe Software) to capture the morphological variability among the two geographically distinct populations. Test maximum and minimum diameters, numbers of chambers in last whorl, average lengths of spines, and coiling directions were recorded.

From non-sieved samples, calcarinids and other benthic foraminifera were carefully picked with a silver sable-hair brush 3/0 to avoid damaging or crushing the specimens and mounted on micropaleontological cardboard slides. Successive reflected light micrographs were taken at different heights of focus planes under a biological compound microscope and repeated for each required orientation. The resulting images were stacked and rendered using Helicon Focus software (Helicon Soft). Detailed images of the wall and internal structures, apertural and foraminal shape and structure, chamber shape, pore arrangement, spines, and umbilical features were taken of coated specimens (20 nm Pt) under high vacuum, using an environmental scanning electron microscope (JEOL Neoscope benchtop SEM). Scanning electron micrographs were taken under 15 kV at lower magnification and 10 kV at higher magnification. Before imaging, specimens were dried at room temperature and mounted in required orientations using carbon tape on standard metal stubs.

DNA Extraction, PCR Amplification, and Sequencing

We extracted DNA from ten specimens of the undescribed Neorotalia using guanidine lysis buffer (Holzmann, 2024). Each extraction is characterized by a unique isolate number. Semi-nested PCR amplification was carried out for a part of the 18S barcoding fragment of foraminifera (Pawlowski & Holzmann, 2014) using forward primer s14F3 (ACGCAMGTGTGAAACTTG) and reverse primer s17 (CGGTCACGTTCGTTGC) for the first and forward primer s14F1 (AAGGGCACCACAAGAACGC) for the second amplification. Thirty-five and 25 cycles were performed for the first and the second PCR, with an annealing temperature of 50°C and 52°C, respectively.

Nine positive amplification products were obtained and purified using the Roti ®Prep PCR Purification Kit (Roth). Sequencing reactions were performed using the BigDye Terminator v3.1 Cycle Sequencing Kit (Applied Biosystems) and analysed on a 3130XL Genetic Analyzer (Applied Biosystems). Three sequences could be obtained that were deposited in the NCBI/GenBank database. Isolate and Accession numbers are specified in Table 2.

Phylogenetic Analysis

The obtained sequences were added to 15 sequences belonging to rotaliid foraminifera that are part of the publicly available NCBI/GenBank database (https://www.ncbi.nlm.nih.gov). All sequences were aligned using the default parameters of the Muscle automatic alignment option, as implemented in SeaView vs. 4.3.3. (Gouy et al., 2010). The alignment contains eighteen sequences with 1,075 sites used for analysis.

The phylogenetic tree was constructed using maximum likelihood phylogeny (PhyML 3.0) as implemented in ATGC: PhyML (Guindon et al., 2010). An automatic model selection by SMS (Lefort et al., 2017) based on Akaike Information Criterion (AIC) was used, resulting in an HKY85 substitution model being selected for the analysis. The initial tree is based on BioNJ. Bootstrap values (BV’s) are based on 100 replicates.

DESCRIPTION OF NEOROTALIA LEEUWINENSIS N. SP.

Neorotalia leeuwinensis, unnamed and undescribed until now, is significant because it appears to be endemic at the southern-most geographic range of calcarinids along the Western Australian coast, between present-day latitudes of 30°S and 34°S. This is the southern-most living record for the family anywhere. The species shows complex morphology that seems closest to Neorotalia spp. cf. calcar, which ranges from the main equatorial centre of tropical calcarinid diversity in the Indo-Pacific region to just south of 32°S where it overlaps with the range of N. leeuwinensis. A major question is why such a complex species as N. leeuwinensis, apparently unknown elsewhere, would appear so far south in the geographic range of the family. The following systematic description and morphological comparisons with other relevant calcarinids lead to a discussion that explores reasons that may have influenced the geographic ranges and the potential endemism of N. leeuwinensis.

  • Superfamily CALCARINOIDEA Schwager, 1876

  • Family CALCARINIDAE d’Orbigny, 1826 

  • Genus NEOROTALIA Bermúdez, 1952

Type species: Rotalia mexicana Nutall, 1928 (lectotype designated by Loeblich and Tappan 1964, see USNM CC 12559A illustrated at https://collections.nmnh.si.edu/search/paleo/).

Discussion

The differentiation by Hottinger et al. (1991) of Neorotalia from Calcarina d’Orbigny (type species, Nautilus spengleri Gmelin, following Renema & Hohenegger, 2005, and International Commission on Zoological Nomenclature, 2006), and from Pararotalia Le Calvez (type species Rotalina inermis Terquem, following Le Calvez, 1949) is recognised here. Neorotalia is separated from Pararotalia by the presence of an enveloping canal system that is lacking in the latter species. From Calcarina, Neorotalia is separated by the aperture, a single extraumbilical to interiomarginal opening, and the presence of a foramenal plate.

Neorotalia leeuwinensis Tremblin, Holzmann, Parker, & Haig n. sp.
Figs. 6, 7, 917 

    Neorotalia leeuwinensis Tremblin, Holzmann, Parker, & Haig n. sp.
    Figs. 6, 7, 917 

Type material

Holotype UWA183807 (Fig. 6.1); topotypes UWA183808–UWA183811 (Figs. 6.2–6.5); paratypes UWA183812–UWA183819 (Figs. 7.1–7.9).

Type level, type locality, known distribution.

Holocene (modern living population), Bunker Bay on the north-east side of Cape Naturaliste near Dunsborough, southwest Western Australia (33.53901°S; 115.03226°E; Fig. 5) between 0.2 m to 2 m water depth. Known distribution is in the inner-most neritic zone, especially on or adjacent to rock platforms along the Western Australian coast from 30.07°S to 33.99°S, see Table 1.

Etymology

The species is named after the major eastern boundary oceanographic current in the Indian Ocean, the Leeuwin Current, that brings warmer water south along the western Australian margin from the tropics to Cape Leeuwin where it turns east and continues along the southern coast of Australia (Fig. 2).

Examined material

Over 300 living specimens were picked and observed across studied sites. Measurements were taken from 100 specimens (50 specimens each) from Point Peron and Bunker Bay. Specimens examined from other localities along the Western Australian coast are from historical collections.

Other material

Type locality, three sequenced specimens (isolates 22309, 22311, 22313).

Diagnosis

A species of Neorotalia with test of glassy appearance; without strong ornament (e.g., feathering of ridges) on external chamber walls on the spiral or umbilical sides; without imperforate inflational ridges (radial shoulders) along the entire lengths of chambers on the umbilical side; with patches of imperforate thickened secondary lamination that limit openings of the pore tubes to discrete areas on both the external spiral and umbilical surfaces of chambers; with long robust canaliculate spines in alignment with the radial intercameral sutures and including continuations and branching of the canal system; with intraseptal spaces on umbilical side much reduced or absent.

Molecular features

The partial SSU rDNA sequences contain 361 nucleotides, the GC content is 42%. The obtained sequences are identical.

Description

Test trochospiral compressed, unequally biconvex to slightly concavo-convex (Figs. 6, 7) with average test diameter of measured specimens not including spines, 582.0 µm in maximum diameter and 455.8 µm in minimum diameter (Fig. 8A), and maximum equatorial diameter to axial height ratio ca. 3. Coiling in adult tests forms 1.5 to 2 whorls, in either a sinistral or dextral direction, with no preferred arrangement observed. The last whorl consists of 6–10 chambers, typically 7 (Fig. 8A). Specimens with less than six chambers in the last whorl are smaller and may be juveniles. Sutures radial, straight to very slightly curved and thickened by successive layers of secondary lamination. On the spiral side, radial intercameral and spiral sutures between chambers and whorls are flush between early chambers and variably depressed between final chambers. The spiral-side radial sutures are covered by secondary lamination that appears hyaline and smooth compared to adjacent chamber walls (Figs. 9.1a, 10.1). This layer may have irregular pores and a covering of microgranules that become more abundant and fuse in an elongate radial direction toward the periphery (Fig. 10.1a). Intercameral sutures on the umbilical side become deeply incised toward the umbilicus (Figs. 9.2c, 9.3). The umbilicus is broad, occupying about one-third of the test diameter (Figs. 6, 7, 9.2c), and is bordered by imperforate narrowly raised umbilical shoulders that terminate with a slight ventral projection (Figs. 9.2b, c, 9.3). The umbilicus is partly infilled with imperforate long narrow erect pillars, some of which have fused with adjacent pillars (Fig. 9.2c). Granules cover the floor of the spaces between pillars and the umbilical spiral canal and the umbilical shoulders. Except for an opening under the edge of the final chamber, there is no communication between the chamber lumen of earlier chambers and the umbilicus (Fig. 9.2c). The pillars have prominent discontinuous rugate ornament formed by the fusion and elongation of granules on the surface of the pillars (Fig. 9.2c). The equatorial periphery is roundly angled and smooth in axial view (Fig. 9.1b) with radially projecting robust long canaliculate spines projecting from the anterior of each chamber and appear continuous with intercameral sutures, giving a stellate outline to the test (Figs. 6, 7, 9.1a–c). Spines are narrowly elongate to spindle-shaped in exterior view (up to about 50 µm long; Fig. 9.1a) and “anchored” internally to underlying shell layers (Fig. 10C). They are ornamented by granules or composite granules. The granules are tightly packed with very narrow distinctly dendritic surface canals between them (Fig. 10.3) and are arranged in an irregularly twisted spiral along the spine (Fig. 9.3); internally each spine has a solid glassy structure penetrated by few branching internal canals of minute diameter (ca. 3 µm), several of which seem to open at the tip of each spine (Figs. 10.1, 10.2, 10.3, 10B). Pseudopodia radiate from the spines (Fig. 10A). At low magnification, the chamber wall externally appears smooth, but at high magnification it is shown to have (i) patchy distribution of pores either open or closed giving a slightly uneven topography at the surface of the wall (Figs. 11A, 11B, 11C), (ii) microgranular clusters at the base of the projecting spines and along and irregularly positioned on the intraseptal walls (Figs. 9, 10), (iii) a radial pattern of minute elongate granules on the terminal face of the last chamber above the bilobate aperture (Figs. 9.1c, 9.2b). In cross section, the wall is composed of four main layered units, from interior to exterior: (1) thin dark-brown organic lining (Fig. 12); (2) an inner amorphous very thin mineralised lining (not organic as it is unaffected by bleach;? inner lamella; <2 µm thick; Figs. 13.1c, 13.1d, 13.1f, 14.1b, 14.2b–d); (3) main mineralized wall (<30 µm thick) which appears multilaminated (Figs. 13.1c, 13.1e, 13.1f, 14.2b); and (4) an outer discontinuous thin amorphous mineralized layer of irregular thickness (<5 µm thick; Figs. 13.1e, 13.1f, 14.2c, 14.2d). The organic lining, which mirrors the chamber shapes (Fig. 11), is imperforate with a dimpled texture that corresponds with the undulations on the inner surface of the mineralised inner lining. The amorphous mineralized lining is extremely thin (<2 µm thick) and in some places becomes very slightly disconnected from the main wall (e.g., Figs. 14.2c, d). The main wall of each chamber is densely perforated with cylindrical non-branching pore tubes (average diameter ca. 2.5 µm) that are perpendicular to the surfaces of the test. Most of the pore tubes do not penetrate the inner mineralised lining and thus do not connect with the chamber lumen (Figs. 1315), except in the final chamber where most of the pore-tubes remain open. The average thickness of the main wall between pore tubes is about 3 µm, and the pore tubes average about 3 µm diameter. The wall becomes more solid at the base of the spine and at the spiral side sutures, with few perforations (Figs. 13.1d, 14.1b). The wall is microgranular. Within the main wall of each chamber, laminations are continuous and relatively uniform in thickness. There are 3–4 apparent laminae in the wall of the last chamber (Fig. 13.1c); up to 22 in earlier chambers of last whorl (Fig. 14.2b). The rate of newly added layers seems to be independent of the addition of a new chamber. The same laminations are seen within pore cavities in planar view of the wall surface (Figs. 11E, F). The outer amorphous layer is irregular in thickness, composed of indistinct laminae, and covers pores in irregular patches (Figs. 11B, C). The openings of the pores through this layer are variable and in some cases several pores open into a broader depression in the surface of the outer amorphous layer (Fig. 11F). The aperture is an extraumbilical opening with a narrow slit-shaped lobe that extends up the apertural face a short way and is obliquely oriented towards the spiral side (Figs. 9.1c, 9.2b, 13.1a). The slit is bordered by a thick pustular lip on both sides (Figs. 9.1b, 9.1c, 9.2a, b, 13.1a, 13.1b) and by sulci, infolds of the terminal face. At the aperture, the wall of the terminal face folds inward for just over 0.1 mm and then tightly folds backward to form the thick pustular lip (Fig. 15.2). Chambers are interconnected by basal, small internal foramina that reflect past positions of the aperture (Figs. 16.1c, 16.1d, 16.1e). A low smooth, arched, imperforate internal (foraminal) plate protrudes from the ventral side of the foramen and remains attached to the inner side of the chamber wall by a folded coverplate that connects to the plate of the earlier foramen (Figs. 15.1, 16.1c, 16.1e). The plate decreases in height across the inner chamber wall toward the foramen where it expands in width and curves above the opening (Fig. 16.1c).

Comparative Morphology

Test Outline

The test in Neorotalia leeuwinensis is more compressed than in the type species of Neorotalia, N. mexicana, and in the lectotype of modern N. calcar (ratio of maximum equatorial diameter to axial height in N. leeuwinensis is ca. 3, compared to 2.3 in the lectotype of N. mexicana). In axial view, N. leeuwinensis is more unequally biconvex than in the lectotype of N. mexicana. The spiral side is very gently elevated with a slightly more elevated inner spire as in the lectotype of N. calcar (illustrated in Le Calvez, 1977).

The equatorial outline in N. leeuwinensis is more stellate than in the lectotypes of N. mexicana and N. calcar. Neorotalia leeuwinensis has radially projecting long robust canaliculate cylindrical spines aligned with chamber sutures that are very different from the short canaliculate spines at the apex of pointed chambers in the type specimens of N. calcar illustrated by Le Calvez (1977). In contrast N. mexicana has very weak spine development at the apex of roundly angled chambers in equatorial outline. Pararotalia inermis, type species of Pararotalia, also has rare short spines (Loeblich & Tappan, 1957). In N. leeuwinensis, there is usually one spine developed per chamber in the last whorl as in typical N. calcar. In rare gerontic specimens of N. leeuwinensis, two very short spines are sometimes present on the final chamber (e.g., in holotype Fig. 6.1a, and topotype Fig. 9.1a). The number of spines on the equatorial periphery in N. leeuwinensis varies from 3 to 10, perhaps related to growth stage. There are differences between the two populations of N. leeuwinensis measured (Fig. 8, Point Peron and Bunker Bay) including the length of spines (Figs. 68), with spine length as long as 296 µm. This contrasts with a maximum length of about 170 µm for the conical spines of N. calcar at the Point Peron studied site. Poag (1966) considered that specimens of the type species of Neorotalia, N. mexicana from the Miocene of Mississippi and Alabama displayed large morphological variation (their pl. 9, figs. 1119), and that the spines varied from only one or two in a test to one on the periphery of every chamber. Hottinger et al. (1991) based their description of N. mexicana on specimens from the Miocene of Victoria that may represent a different species. Some of their specimens (e.g., Hottinger et al., 1991, fig. 2.3) have very short canaliculate spines aligned with the radial intercameral sutures, as in N. leeuwinensis, but not in N. calcar. Among other trochospiral hyaline foraminifers with prominent spinose peripheries, Asterorotalia pulchella (d’Orbigny, 1839), type species of Asterorotalia Hofker 1950, differs in having three robust smooth spines arising from an imperforate peripheral keel [see figured specimens of Loeblich & Tappan, 1987, either in the first whorl (megalospheric generation) or from the third whorl (microspheric generation)]. Asterorotalia trispinosa (Thalmann) of Billman et al. (1980, pls. 16, 17, text-fig. 20) shows a similar spine arrangement to A. pulchella. Rotalia beccarii (Linné) var. dentataParker and Jones (1865), which has been placed in Ammonia by Rao & Hussain (2017) and in Asterorotalia by Hayward et al. (2021), has smooth spines arising from an imperforate peripheral keel with a spine projecting from the apex of at least some of the chambers of the final whorl (see specimens figured by Billman et al., 1980, pl. 18, and by Rao & Hussain, 2017, fig. 1).

As in typical N. mexicana and N. calcar, a broad umbilicus is present in Neorotalia leeuwinensis. The umbilicus in these species is partly infilled by pillars that may coalesce. The prominent radial shoulders (imperforate inflational ridges with feathering of Hottinger, 2006) that Hottinger et al. (1991) illustrated for Lower Miocene specimens from Victoria, Australia, which they attributed to N. mexicana, are not distinct in the lectotype of N. mexicana (USNM CC 12259A - see https://collections.nmnh.si.edu/search/paleo/). Such radial shoulders are present in the lectotype of N. calcar (see Le Calvez, 1977) and in specimens described by Hottinger et al. (1991) from the Gulf of Aqaba, Red Sea. Morphotypes of N. calcar from Western Australia also include specimens with prominent radial shoulders. In N. leeuwinensis, prominent radial shoulders are not present along the full length of each chamber on the umbilical side. The umbilical end of chambers becomes elevated close to the umbilicus, and the tips of chambers stand as imperforate pillar-like elevations around the umbilical edge. This is a feature of Pararotalia inermis (Terquem, 1882), type species of PararotaliaLe Calvez, 1949, as described by Loeblich & Tappan (1957).

Sutures, Chamber and Spine Ornament, Canal System

As in the lectotypes of N. mexicana and N. calcar, the sutures on the spiral side of N. leeuwinensis are flush to slightly depressed between the early chambers of the last whorl and depressed between final chambers. Sutures on the umbilical sides of all these types are depressed, particularly toward the umbilicus. The lectotype of N. mexicana shows larger more densely packed granules along its very narrow incised sutures on the umbilical side. At the umbilicus, the sutures of all three species pass into open spaces within the umbilical bowl around the umbilical margin and between pillars. Pillars in the umbilical bowl of the lectotype of N. mexicana seem more numerous and more fused than in the N. calcar or N. leeuwinensis. However, fusion of the pillars may be partly a feature of burial diagenesis that has obviously affected the N. mexicana lectotype.

The apertural face of the N. mexicana lectotype is not preserved. The Victorian Miocene specimens, attributed to this species by Hottinger et al. (1991), show an indistinct radial pattern of small elongate granules from the aperture up the apertural face toward the periphery (Hottinger et al., 1991, fig. 2.5). The short peripheral spine at the top of the apertural face has elongate straight rugae (probably formed by coalesence of granules) along the spine. A view of the lectotype of N. calcar perpendicular to the terminal face was not provided by Le Calvez (1977), but an oblique view of the face from the umbilical side (Le Calvez, 1977, pl. 2, fig. 2) shows little ornament on a smooth terminal face. Specimens attributed to Neorotalia calcar from the Gulf of Aqaba and illustrated by Hottinger et al. (1991, figs. 4.3, 4.6) show a radial pattern of granules on the terminal face and the spines very similar to that found in N. leeuwinensis (see our Fig. 9). This is confirmed in specimens of N. sp. cf. calcar that are present with N. leeuwinensis at Point Peron (compare Figs. 17.1a, b and 17.2a, b). This pattern is unlike the smooth but coarsely perforate terminal face illustrated for Paratoralia inermis, type species of Pararotalia, from the Middle Eocene of France by Loeblich & Tappan (1957). Specimens of P. sp. cf. calcariformata occurring with N. leeuwinensis at Bunker Bay do not show a radial pattern of granules on the terminal face, but the granules are scattered on the face, coalescing along the spiral periphery of the face to form a “muricocarina” type “keel” (Fig. 17.3a).

Hottinger & Leutenegger (1980) and Hottinger et al. (1991, 1993) described the canal system of modern “Neorotalia calcar” from the Red Sea. Based on araldite casts, they noted that their specimens have “rudimentary enveloping canals” and a “spirally twisted network of umbilical canals.” In the present study, such araldite casts were not made, so that a detailed comparison of some aspects of the canal system between N. leeuwinensis and “N. calcar” (as interpreted by Hottinger & Leutenegger, 1980) cannot be made at this time. Light images of the umbilical sides of the holotype of N. leeuwinensis and other specimens of the species figured here (Figs. 6, 7) clearly show a continuation of fine canals in the intercameral sutures leading to greater branching of the canals in the spines. Intraseptal spaces on the umbilical side seem to be absent or very slightly developed in N. leeuwinensis (Figs. 15.3a, b) compared to the broad intraseptal spaces in N. calcar illustrated by Parker (2009, fig. 473h).

Laminations, Pore Distributions and Other External Features

Whether the multiple apparent laminations in the outer chamber walls of N. leeuwinensis may be secondary (outer) laminations that have been folded in a manner described by Hottinger & Leutenegger (1980) is uncertain. As indicated by Hottinger & Leutenegger (1980, p. 121) for other calcarinids, the pore tubes do not connect to the chamber cavities in N. leeuwinensis. The pattern of pore tubes opening to the outer surface in N. leeuwinensis is distinct from that in the more ornamented species of Neorotalia, including the specimens attributed to N. mexicana and to N. calcar by Hottinger et al. (1991). In the latter, pore tubes open to the outer chamber wall between thickened imperforate ornament elements (e.g., granules) and the imperforate feathered inflational ridges (radial shoulders) on the umbilical side. In N. leeuwinensis, the pore-tube openings on the external surface of chambers are arranged between thickened “patches” of secondary lamination (Fig. 11). In some areas on the umbilical side (e.g., Fig. 9.3), the pore tubes open at the centre of small, elevated mounds.

Aperture and Bordering Ornament, Internal Plate Structures

The aperture of N. leeuwinensis (Figs. 17.1a, 17.1b) is compared with that in some other calcarinids found along the western Australian margin. It is most like that in our specimens of N. sp. cf. calcar from Point Peron (Figs. 17.2) and to illustrations of “N. calcar” from the Red Sea (Hottinger et al., 1991, fig. 3). It differs markedly from the apertural arrangement and related ornament in Pararotalia species (e.g., Loeblich & Tappan, 1957, fig. 2c; our Fig. 17.3) and in Calcarina (Fig. 17.4). Internal plates were not described for the lectotypes of N. mexicana or N. calcar. It is unclear from figures provided by Hottinger et al. (1991, 1993) how the plate is positioned internally within each chamber of specimens attributed to N. calcar. Illustrations by Parker (2009, fig. 473h) of an obliquely sectioned specimen attributed to N. calcar shows a smooth plate structure like that in N. leeuwinensis but apparently broader (viewed from umbilical side, rather than from spiral side as in our illustrations of N. leeuwinensis, Fig. 16).

Taxonomic Implications from Morphological Comparisons

Hottinger & Leutenegger (1980) noted that for calcarinids, the pore tubes do not connect to the chamber cavities. From evidence shown in araldite casts cavities within the test, including pores and canals within the wall, they concluded that the inner pore mouth was sealed by an organic lining as well as an organic “poreplate”. However, our findings suggest the chamber lumen is separated from the pore tube by a thin almost continuous amorphous mineralized inner lamella that would have been dissolved out in Hottinger & Leutenegger’s (1980) preparations. Despite this, they were correct when they supposed that the pore tubes do not connect to the chamber lumen. This is demonstrated here for Neorotalia leeuwinensis. Among modern “simple” trochospiral species of the Family Calcarinidae, N. leeuwinensis is closest to N. calcar in apertural type, ornament on terminal face and spines, and in the nature of the canal system. Although N. calcar has been previously placed in (i) Calcarina from which it and N. leeuwinensis differ substantially in apertural details and ornament around the aperture; and (ii) Pararotalia from which these species differ in the aperture and in ornament on the peripheral margin (i.e., lacking the muricocarina of Pararotalia). In specimens of P. sp. cf. calcariformata (Fig. 2Be) living with N. leeuwinensis, the spines are much shorter (as in the type of P. calcariformata) and they lack the fine canals of N. leeuwinensis. In spine structure and development, both our N. sp. cf. calcar (Fig. 2Bd) and N. leeuwinensis are closer to N. mexicana the type species of Neorotalia than to the other species compared above.

The phylogenetic tree reveals that the sequenced Calcarinidae cluster in three groups (Fig. 18; Table 2). One group contains Neorotalia leeuwinensis (98% BV) branching as sister to a morphotype from Japan attributed to “Calcarina defrancii” and to a morphotype designated N. calcar also from Japan. Japanese morphotypes labelled Baculogypsinoides spinosus and Calcarina hispida are at the base of this cluster. The second group consists of Japanese morphotypes of P. nipponica and eastern Mediterranean P. calcariformata that are strongly supported (91% BV) with Japanese C. gaudichaudii branching at the base. A third group includes Indonesian Schlumbergerella neotetraeda and S. floresiana (100% BV) with Japanese Baculogypsina sphaerulata branching at the base. The latter group is moderately sustained (72% BV). Glabratellidae (Glabratella patelliformis, Planoglabratella opercularis) branch as sister group to Calcarinidae.

Morphological and Molecular Relationships

Recent studies of Ammonia species (Hayward et al., 2021), Amphisorus morphotypes (Macher et al., 2021), and Trochammina species (Tremblin et al., 2021) demonstrated that combined analyses of molecular and morphological features provide perhaps the best means for discriminating taxonomic diversity among Western Australian foraminiferal assemblages. Molecular analyses associated with detailed morphological studies of calcarinids have just commenced for these assemblages. However, a major problem exists because (1) many type specimens of species, particularly those designated before modern advances in microscopy (e.g., rendering of light images, and use of scanning electron microscopes), have not been defined with enough precision to make confident morphological comparisons; (2) some type specimens are lost; (3) precise type localities are uncertain; and (4) molecular analyses have not been performed on live individuals from many “type” populations.

Among the calcarinids associated with Neorotalia leeuwinensis in south-west Australia, Neorotalia sp. cf. calcar (Fig. 2Bd) and Pararotalia sp. cf. calcariformata (Fig. 2Be) are compared to taxa where the type locality is obscure although a lectotype has been designated (viz. N. calcar; lectotype selected by Le Calvez, 1977) or where no molecular studies have been performed on specimens from the type locality and the type specimen is known only from drawings and a brief description (viz. P. calcariformata McCulloch). We use the modern species P. calcariformata as a comparison for the Pararotalia morphotypes that Haig (1997) and Parker (2009) previously assigned to the Neogene P. nipponica (Asano). The preliminary results of continuing molecular analyses indicate that N. leeuwinensis is distinct from P. sp. cf. calcariformata and N. sp. cf. calcar, and that the latter species are distinct from morphotypes bearing their names that have been sequenced elsewhere (e.g., from Japan and the eastern Mediterranean Sea).

Neorotalia leeuwinensis is molecularly separated from its sister taxon N. calcar as identified for Japanese specimens LN87383 (NCBI/GenBank database accession number; see Fig. 18 and Table 2). It is also separated from the other sister taxon represented by “Calcarina defrancii” from Japan (AJ504680). The latter species was defined by d’Orbigny (1826, p. 276; pl. 13, figs. 57b) from the Red Sea. The most prominent features of the type illustrations are the ten long smooth spines that are continuous with prominent radial shoulders on the umbilical side that extend to a narrow umbilicus. These features differ from Neorotalia leeuwinensis. From other areas, a great variety of morphotypes has been categorized under the names of “C. defrancii” or “C. defrancei”. The morphotypes figured, for example, by Cushman (1919, pl. 44, fig. 2) from the Philippines, Hohenegger et al. (1999, fig. 23) from Japan, and Renema (2018, fig. 17) from Indonesia, all look different from the type of C. defrancii represented in the drawings of d’Orbigny (1826).

Aspects of the taxonomic problems with d’Orbigny’s (1826) Calcarina calcar were discussed by Hansen (1981) who figured a specimen from Mauritius, one of three areas where d’Orbigny’s (1826) found the species. Hansen’s (1981, pl. 2, figs. 12) specimen seems morphologically very close to the morphotypes occurring with N. leeuwinensis that we have recorded as N. sp. cf. calcar, and is distinct from Indonesian forms placed in N. calcar by Renema (2018, figs. 26A–D) and a Japanese specimen considered representative of the species by Hohenegger et al. (1999, fig. 21) and by Hohenegger (2006, fig. 2C). In test outline, the specimens figured by Renema (2018) from Palau and Sulawesi seem closer to Le Calvez’s lectotype of N. calcar (supposedly from Cuba) than to N. sp. cf. calcar.

Morphology Related to Lifestyle

The main microhabitat observed for Neorotalia leeuwinensis is the articulate coralline algae Amphiroa (probably A. gracilis Harvey). This calcified algal species lives among a diversity of macrophytes in the very shallow high-energy environments particularly on the edge of the rock platforms (Figs. 5C, D). The thallus is a small shrub-like structure, about 10 cm high, with articulate cylindrical calcified segments which form numerous branches (Fig. 5C). Janot & Martone (2018) showed that the thallus has considerable flexibility in bending. Neorotalia leeuwinensis lives on the upper branches where they cling using the pseudopodia emanating mainly from their spines (Figs. 10A, 19A). The compressed shape of N. leeuwinensis, with a more convex spiral side and an often flat to slightly concave umbilical side, suggests that they live closely attached to the branch segments of the algae, with the convex spiral side facing away from the branch (Fig. 19B). The flexibility of the algae and the attachment strategy of N. leeuwinensis seem to be adaptions for living in the very shallow high-energy environments on the rock platforms. These adaptions also suit the photosynthetic activity required for the coralline algae and for the possible unicellular algae that we have observed within the endoplasm of living N. leeuwinensis. The latter have not been studied here, and their symbiotic relationship has not been established.

One of the extraordinary morphological features of the test of Neorotalia leeuwinensis is the presence of pore tubes that are densely packed and open on the external walls of the chambers but mostly do not connect with the interior chamber spaces (Figs 9.1a, 10.1, 11, 14.2b, 16.1c). The purpose of these is not for the extrusion of pseudopodia. Their function may be related to (i) thermal regulation of the endoplasm within the chambers, (ii) buoyancy of the test and (iii) as light conductors for possible algal symbionts. The species lives in a microhabitat with constant water flow surrounding the test. This may create a pressure differential between the flowing outside water and the water within the pore tubes. The differences in pressure could result in frequent exchange of the tube water, thereby regulating the internal temperature. This scenario needs to be confirmed by fluid and thermal modelling such as suggested for other organisms and biofilms by Wheeler et al. (2019), Arzt et al. (2021), and Ahmerkamp et al. (2022). The pore tube distribution considerably decreases the density of the wall (Figs. 11, 13, 14). Therefore, the pore tubes may control the overall density of the test, creating more buoyancy to live high on the branches of Amphiroa gracilis.

Potential Endemism

As recognised above in “known calcarinid sites along Australian western margin”, four latitudinally based regions reflect changes in diversity and distributions of genera and species within the family. The appearance of apparently endemic Neorotalia leeuwinensis from 30°S to 34°S, at the southernmost part of the distributional range of the family, conforms to an increase in endemism in marine algal macrophytes and in invertebrates (Phillips, 2001; Richards et al., 2016). Although this endemism has been attributed to a long period of isolation and great stability of this region (Phillips, 2001), significant marine and terrestrial climatic gradients are present along the Western Australian coastline (Figs. 2, 3). These include the warm Leeuwin Current coming from the north and the subsidiary Capes and Ningaloo coastal currents branching from the Leeuwin Current and moving locally north. The coastal hinterland throughout Western Australia has very low relief and few major rivers. Coastal tides range from macrotidal in the north through mesotidal to microtidal in the south (Fig. 3). The terrestrial rainfall gradients form distinct belts with a monsoonal northern sector, a central arid sector, and a seasonally wet southwestern sector (Fig. 3). Rainfall affects freshwater outflow to coastal waters both via rivers and via permeability pathways in the rock units forming the coastal platforms. Neorotalia leeuwinensis is confined to the southwestern sector. Further study on the biota, including N. leeuwinensis and its algal host, is required to determine the effects of rapid changes in salinity associated with rainfall and in salinity and other chemical changes in groundwaters emanating from the rock platforms. Experimental thermal tolerance studies on the algae and N. leeuwinensis also should be undertaken (e.g., following the methodology of Titelboim et al., 2019, and Deldicq et al., 2021). Much more needs to be known about environmental parameters controlling the distribution of N. leeuwinensis and its molecular makeup in order to explain the apparent endemism of the species. The southernmost limit of the range of N. leeuwinensis at about 34°S may at present be controlled by the formation in this region of the cool north-flowing coastal Capes current that branches from the offshore Leeuwin Current.

Calcarinids are distributed in very shallow waters along the western margin of the Australian continent in four distinct regions related to temperature ranges. From the equatorial zone to at least 18°S, on reef platforms on the outer continental shelf (>25°C, 30-year average winter minimum temperature), Calcarina, Baculogypsina, Schlumbergerella, Neorotalia sp. cf. calcar, and Pararotalia sp. cf. calcariformata are present. From 20°S to about 29.5°S (>20°C, 30-year average winter minimum temperature), a low diversity assemblage of N. sp. cf. calcar and P. sp. cf. calcariformata occurs. From about 30°S to at least 32.3°S (>19°C, 30-year average winter minimum temperature), a new species (N. leeuwinensis n. sp.) is added to the calcarinid assemblages. Between 32.3°S and 33.3°S, N. sp. cf. calcar disappears, and the calcarine assemblages consist of N. leeuwinensis n. sp. and P. sp. cf. calcariformata until about 34°S (>18°C, 30-year average winter minimum temperature).

Neorotalia leeuwinensis is compared and differentiated from the type species of Neorotalia (N. mexicana) as well as from the extant N. calcar, and the type species of Pararotalia (P. inermis) and the extant P. calcariformata. Among the modern “simple” trochospiral species of the Family Calcarinidae, N. leeuwinensis is closest to N. calcar in apertural type, ornament on terminal face and spines, and in the nature of the canal system. It however lacks the large intraseptal spaces in the umbilical sutures. Neorotalia calcar has been previously placed in (i) Calcarina from which it and N. leeuwinensis differ substantially in apertural details and ornament around the aperture; and (ii) Pararotalia from which these species differ in ornament on the peripheral margin (i.e., lacking the muricocarina of Pararotalia). In spine structure and development, both N. calcar and N. leeuwinensis are closer to N. mexicana the type species of Neorotalia to species of Pararotalia, which lack a canal system in the umbilical sutures and spines. The species has a restricted geographic range in Western Australia and has not been recognised elsewhere.

The main microhabitat observed for Neorotalia leeuwinensis is the articulate coralline algae Amphiroa (probably A. gracilis Harvey) that usually lives among a diversity of macrophytes in very shallow high-energy environments particularly on the edge of rock platforms. The shape of the test and the spines are apparently designed for living high on the branches of the Amphiroa thallus. The presence of pore tubes that are densely packed and open on the external walls of the chambers of N. leeuwinensis but do not connect with the interior chamber spaces may be related to (i) thermal regulation of the endoplasm within the chambers or (ii) buoyancy of the test.

The appearance of apparently endemic Neorotalia leeuwinensis from 30°S to 34°S, at the southernmost part of the distributional range of the family, conforms to an increase in endemism in marine algal macrophytes and in invertebrates in southwest Australia. Significant marine and terrestrial climatic gradients are present along the west coastline of Australia from the tropics to the south. These apparently control the species distributions, but the reasons for endemism require much more study of environmental parameters and molecular analyses of species.

Clément M. Tremblin is grateful for a Joseph A. Cushman Award for Student Research 2024 given by the Cushman Foundation to pursue the ongoing study on the biogeography of calcarinids along the Western Australian margin. Dr. Alexandra Suvorova from the Centre for Microscopy, Characterisation & Analysis is thanked for her assistance and advice with the scanning electromicroscopy. Dr. Siri Kellner of The University of Western Australia is thanked for her curatorial assistance. Dr. Michele Trevisson gave valuable advice on the possible significance of the pore tubes and the fluid dynamics around living tests. Two anonymous reviewers are thanked for their detailed and constructive advice, which improved our manuscript. We thank the Oceans Institute at The University of Western Australia for facilitating the ongoing voluntary research of Clément M. Tremblin and the Honorary Senior Research Fellowship of David Haig. We thank the Western Australian Department of Biodiversity, Conservation and Attractions for Lawful Authority to collect at Bunker Bay and Point Peron, and the Department of Primary Industries and Regional Development for fisheries exemption. The authors acknowledge the facilities, and the scientific and technical assistance of Microscopy Australia at the Centre for Microscopy, Characterisation & Analysis, The University of Western Australia, a facility funded by the University, and State and Commonwealth Governments. The isolated specimens mounted on cardboard slides are curated in the Earth Science Museum at the University of Western Australia. The authors declare that they have no conflicts of interest.