A new reef-dwelling coral, Pavona giannii sp. nov. (Scleractinia, Agariciidae), with an overview of the skeletal morphology of the type specimens of the genus Pavona

123 A new reef-dwelling coral, Pavona giannii sp. nov. (Scleractinia, Agariciidae), with an overview of the skeletal morphology of the type specimens of the genus Pavona Francesca Benzoni1 1 Biological and Environmental Science and Engineering Division, Marine Science Program, HaBB Lab, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia Corresponding author: Francesca Benzoni (francesca.benz[email protected]) Copyright: © Francesca Benzoni. This is an open access article distributed under terms of the Creative Commons Attribution License (Attribution 4.0 International – CC BY 4.0). Research Article Abstract Hard coral species in the agariciid genus Pavona are common in shallow and mesophotic coral reef communities across the Indo-Pacific, but their taxonomy has long been overlooked. Pavona giannii sp. nov. is here described based on newly collected material across the Indian Ocean, and historical museum specimens. In vivo and skeletal morphological features are described, diagnostic characters measured, and comparison with congeners performed. The new species forms an encrusting corallum devoid of raised ridges on its surface. Its corallites are flush with the surface, not inclined, and less than half a corallite diameter apart. Corallites arrangement is thamnasteroid and series can form locally. Where they occur, the radial elements run over the shared walls to the adjacent series’ corallites creating a ladder-like arrangement similar to that observed over the ridges in congeners like Pavona varians and Pavona chiriquiensis. Despite the lack of ridges, P. giannii sp. nov. has morphological affinities with these two species. However, based on previously published morphometrics and meristics, P. giannii sp. nov. corallites are larger and more crowded, and the primary septa are longer and more numerous. In vivo, the new species is distinguished by fully extended white to beige tentacles during the daytime, giving it a white-bearded appearance. Despite the ecological relevance of Pavona corals, a taxonomic revision of the genus is overdue, and the existing molecular studies indicate that it is polyphyletic. Here, the proposed placement of P. giannii sp. nov. in the genus is based on morphological evidence alone and phylogenomic analyses are currently in progress. Key words: Morphometrics, museum collections, reef-building coral, skeletal morphology, taxonomy Introduction The colonial scleractinian genus Pavona Lamarck, 1801 is a common component of the shallow-water coral reef communities across the Indo-Pacific from the Red Sea and the Southwestern Indian Ocean to the East Pacific, spanning tropical and sub-tropical latitudes (Durham and Barnard 1952; Veron and Pichon 1980; Wijsman-Best et al. 1980; Pichon and Benzoni 2007; Glynn et al. 2017; Berumen et al. 2019). Pavona corals are zooxanthellate reef-builders Academic editor: Kaveh Samimi-Namin Received: 30 July 2025 Accepted: 1 October 2025 Published: 19 November 2025 ZooBank: https://zoobank. org/0072E066-E864-4B37-8D675EDE6D5F81A2 Citation: Benzoni F (2025) A new reef-dwelling coral, Pavona giannii sp. nov. (Scleractinia, Agariciidae), with an overview of the skeletal morphology of the type specimens of the genus Pavona. ZooKeys 1260: 123–147. https://doi.org/10.3897/ zookeys.1260.167263 ZooKeys 1260: 123–147 (2025) DOI: 10.3897/zookeys.1260.167263 124 ZooKeys 1260: 123–147 (2025), DOI: 10.3897/zookeys.1260.167263 Francesca Benzoni: A new Pavona coral from Indian Ocean reefs actively contributing to the structure and functioning of coral reef ecosystems (Tortolero-Langarica et al. 2022). Some frondose or columnar species can form giant colonies (Mezaki et al. 2014; Siena et al. 2025) and/or monospecific stands locally reaching metric size (Veron 1986; Montagne et al. 2013). Pavona species support a diverse and often specialized associated fauna and microbiomes (Hoeksema and van der Meij 2013; Montano and Maggioni 2018; Hu et al. 2020; Mehrotra et al. 2020; Yu et al. 2020; Cheng et al. 2023; Delgadillo Ordonez et al. 2022; van der Schoot and Hoeksema 2024; Bäher et al. 2025). Moreover, some species are depth generalists and thrive below 30 m depth as components of mesophotic coral ecosystems (Luck et al. 2013; Kramer et al. 2019; Longenecker et al. 2019). Pavona corals are considered stress-tolerant (Gleason 1993; Huntington et al. 2022) and have been studied for their acclimatory ability in marginal environments and resilience to changes in environmental conditions due to ocean warming (McClanahan, 2000; Solandt et al. 2003; Guzman and Cortés 2007; Tortolero-Langarica et al. 2022; Zhang et al. 2022, 2025; Khen et al. 2024). Despite its ecological relevance and being the target of fundamental and experimental research efforts, species boundaries within the genus Pavona and phylogenetic relationships are still only partially explored through a genetic approach. Available molecular data on a subset of species suggest that the genus is polyphyletic and requires formal taxonomic revision (Maté 2003; Moothien Pillay et al. 2006; Kitahara et al. 2012; Luck et al. 2013; Waheed et al. 2015; Terraneo et al. 2017; Quek et al. 2023). Belonging to the family Agariciidae Gray, 1847, Pavona currently includes 20 valid extant species although 57 nominal extant species have been historically ascribed to it (Hoeksema and Cairns 2024). Morphologically, species currently in the genus display remarkable differences in corallum and corallite shape, corallite arrangement, and columellar structure (Veron and Pichon 1980; Latypov 2014). Typically for an agariciid, corallite arrangement in Pavona is thamnasteroid: the radial elements run over the corallum surface from a corallite center to the adjacent ones, passing over their walls, which are generally poorly developed and scarcely visible (Chevalier and Beauvais 1987). The formation of new polyps in a colony, and new corallites in its corallum, occurs through intratentacular budding and can continue without the actual loss of organic connection among the buds (Matthai 1948c). This process in some species can lead to the formation of series of polyps aligned in valleys. Adjacent series are separated by variably continuous shared corallite walls that can develop into raised longer ridges or shorter monticules (Matthai 1948a; Veron and Pichon 1980: figs 47–53). These indeed vary in height, length and orientation depending on the species, and on their position in a single colony (Matthai 1948b). The radial elements running above any shape of elongated ridge in Pavona are parallel among them and perpendicular to the ridge’s main axis giving a typical ladder-like arrangement (Veron and Pichon 1980: figs 21, 24). An undescribed species of reef-dwelling Pavona was collected at different localities in the Gulf of Tadjoura, Gulf of Aden, Arabian Sea, Strait of Oman, the SW Indian Ocean, and the NE Indian Ocean. It is recognized based on its encrusting growth form, a smooth corallum surface devoid of ridges or monticules, a crowded corallite arrangement, strongly alternating radial elements with the taller ones always flush with the corallum surface giving it an even appearance. In vivo, the species has fully extended polyp tentacles at daytime. Oral disks and/or tentacles 125 ZooKeys 1260: 123–147 (2025), DOI: 10.3897/zookeys.1260.167263 Francesca Benzoni: A new Pavona coral from Indian Ocean reefs are white and give the colonies a distinctive white bearded appearance. The new species skeletal macroand micromorphology are described and illustrated in detail. Measurements and counts of skeletal characters previously analyzed for two congeners with an encrusting growth form and corallite morphological affinities with it, Pavona chiriquiensis Glynn, Maté & Stemann, 2001 and Pavona varians (Verrill, 1864) (Maté 2003), were obtained from the undescribed Pavona thus allowing a direct quantitative comparison. In the discussion section, type material of nine congeners and reference material from two more is illustrated to show the morphological variation of Pavona species and the differences with the new species. Materials and methods Collection and processing Material was collected during SCUBA at 13 localities in the southwestern Indian Ocean (Fig. 1A) and the Gulfs of Tadjoura and Aden, the Arabian Sea, and the Gulf of Oman (Fig. 1B) during multiple expeditions between 2007 and 2022. Before collection, living coral colonies were imaged in situ with digital cameras to document colony growth form, appearance and coloration, and polypar features. Specimens, mostly colony fragments, were sampled by hammer and chisel. Once on land, each specimen was tagged and subsampled to preserve coral tissue in molecular grade ethanol for DNA extraction. Coralla were then left overnight in a sodium hypochlorite solution (household bleach) to remove organic matter, rinsed in freshwater, and dried. Imaging and morphological analysis For macro-morphological observations of corallum surface and corallite arrangement, specimens were photographed with a Nikon Coolpix digital camera with a reference scale and through a Leica M80 microscope equipped with Figure 1. Map showing the type (star) and other collection (circle) localities of Pavona giannii sp. nov. A. Collection localities in the SW Indian Ocean, and B. The seas around the Arabian Peninsula. 1 = Maskali Island, Djibouti; 2 = Aden, Yemen; 3 = Balhaf, Yemen; 4 = Hyllanyia Island, Bir Ali, Yemen; 5 = Burum, Yemen; 6 = Al Mukallah, Yemen; 7 = Hawlaf, Socotra Island, Yemen; 8 = Dhalkut, Oman; 9 = Mirbat, Oman; 10 = Qinqari Bay, Oman; 11 = Muscat, Oman; 12 = Mayotte Island; 13 = Mahé Island, Seychelles; 14 = Galle, Sri Lanka; 15 = Pulau Songsong, Malaysia. Scale bar: 200 km. 126 ZooKeys 1260: 123–147 (2025), DOI: 10.3897/zookeys.1260.167263 Francesca Benzoni: A new Pavona coral from Indian Ocean reefs a Leica IC80HD camera at known magnification. To investigate and describe the skeletal features micro-morphology and their variability, fragments were obtained from two distinct specimens displaying different degrees of calcification of the corallum, namely UNIMIB BAL253 (thinner) and UNIMIB AD016 (thicker). Fragments were grinded, mounted on stubs using silver glue, sputter-coated with conductive gold film and examined using a Vega Tescan Scanning Electron Microscope at University of Milano-Bicocca, Italy. For specimen size measurements, a caliper was used. Corallite and radial element measurements and counts were taken on digital images with visible reference scale using Image J v. 1.54p (Schneider et al. 2012) for 13 specimens. For each specimen, five corallites were selected for measurements and counts. Only fullgrown corallites, not adjacent and not undergoing budding were considered. Following Maté (2003: fig. 3), the following skeletal characters that provided statistically significant differences among Pavona species were measured and counted: maximum calicular diameter, minimum calicular diameter, maximum columellar diameter, minimum columellar diameter, main septa (S1, 2) length, number of septa, number of septa reaching the columella. Statistical analysis to evaluate if any of the characters were statistically significantly different in the new species compared to the encrusting species examined by Maté (2003) was not possible because the original dataset was not included in which only averages (± SE) were reported for each character. Therefore, comparison of characters is hereafter performed based on the available information. Repositories and institutional acronyms The specimens collected for this study are deposited in the following repositories: Muséum national d'Histoire naturelle (MNHN), Paris, France; Florida Museum of Natural History (UF), Gainesville, Florida, USA; King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia; University of Milano-Bicocca (UNIMIB), Milan, Italy; University of the Seychelles (UNISEY), Anse Royale, Mahé, Seychelles. In September 2004, a visit to the Natural History Museum (NHMUK), London, UK, allowed the discovery of historical specimens showing the same diagnostic macro and micro-morphological characters as the collected material for this study. In the accompanying labels, they had all been identified as Pavona explanulata (Lamarck, 1816). Collected in the last century by different scientists from the Seychelles, Sri Lanka, and Malaysia, these specimens extend the known geographic distribution of the new species to two additional localities in the NE Indian Ocean (Fig. 1A). Examined type and reference material For comparative purpose, type or representative specimens of Pavona species examined or collected by the author, respectively, were included in this study and are listed hereafter. The holotype of Pavona diminuta Veron, 1990 (QMT G32480) was examined and photographed at the Queensland Museum Tropics (QMT), Townsville, Queensland, Australia, in May 2009. The holotype of Pavona minuta Wells, 1954 (USNM 44786) was studied and photographed in June 2009 at the United States National Museum (USNM), Washington DC, 127 ZooKeys 1260: 123–147 (2025), DOI: 10.3897/zookeys.1260.167263 Francesca Benzoni: A new Pavona coral from Indian Ocean reefs USA. During a subsequent visit in March 2023, the type specimens of Pavona decussata Dana, 1846 (USNM 201) and Pavona chiriquiensis Glynn, Maté & Stemann, 2001 (USNM 100871) were also examined and imaged. Images of the holotypes of Pavona diffluens (Lamarck, 1816) (MNHN IK-210-587) and Pavona maldivensis (Gardiner, 1905) (NHMUK 1937.11.17.806) were taken at the MNHN in February 2014 and at the NHMUK in September 2024, respectively. In October 2024, the type series of Pavona varians Verrill, 1864, a paratype of P. chiriquiensis (YPM 24153), and syntypes of Pavona clavus (Dana, 1846) (YPM 6249) and Pavona gigantea (Verrill, 1869) (YPM 1679A) were studied and imaged at the Yale Peabody Museum (YPM). An image with scale of specimen YPM IZ.001806.CN (syntype) was kindly provided by E. Lazo-Wasem. The type specimens of Pavona cactus (Forskål, 1775), type locality Red Sea, and Pavona explanulata (Lamarck, 1816), type locality Indian Ocean, were not examined. Instead, specimens KAUST SA 205, matching the original description of P. cactus, and KAUST SA 231, P. explanulata, from the Farasan Banks, Saudi Arabian Red Sea, were imaged at the Red Sea Research Center (RSRC), KAUST after collection in 2013. Taxonomic account Family Agariciidae Gray, 1847 Genus Pavona Lamarck, 1801 Pavona giannii sp. nov. https://zoobank.org/8396733D-1C70-4F02-BD5C-655C050C3C98 Figs 2–7 Type locality. Yemen: Shabwa Province, Bir Ali, Hyllanyia Island, 13°59.183'N, 48°19.137'E; depth 5 m; 11 November 2008, F. Benzoni leg. Type material. Holotype • 1 colony fragment (10.5 x 5.1 cm, Fig. 2); Original label: “Bir Ali, Hyllanyia Island, Yemen; 13°59.183'N, 48°19.137'E; 11 Nov. 2008; F. Benzoni leg.; UNIMIB-Creocean-Total Yemen Coral Biodiversity exped.; collection code BA034; MNHN-IK-2012-14233”. Other material. Djibouti • 1 colony fragment (Fig. 7C, part of the colony in situ); Maskali Island; 11°42.38'N, 43°9.24'E; 29 Feb. 2020; F. Benzoni leg.; Dolphin Cruise exped.; KAUST DJ403. Yemen • 1 colony fragment (Figs 3A, H, 5A, D, F, H–L); Aden, Ras Antouk; 12°45.085'N, 45°1.659'E; 8 Mar. 2009; F. Benzoni and M. Pichon leg.; UNIMIB-Creocean-Total Yemen Coral Biodiversity exped.; UNIMIB AD016 • 1 colony fragment (Fig. 6A, whole colony in situ); Balhaf; 13°58.402'N, 48°11.549'E; 22 Mar. 2014; F. Benzoni leg.; Creocean-Total Balhaf LNG Plant monitoring program exped.; UNIMIB BAL252 • 1 colony fragment (Fig. 5B, C, E, G); Balhaf; 13°58.413'N, 48°10.532'E; 24 Mar. 2014; F. Benzoni leg.; Creocean-Total Balhaf LNG Plant monitoring program exped.; UNIMIB BAL253 • 1 colony fragment; Bir Ali; 13°59.116'N, 48°15.372'E; 16 Nov. 2008; F. Benzoni leg.; UNIMIB-Creocean-Total Yemen Coral Biodiversity exped.; UNIMIB BA010 • 1 colony fragment; Bir Ali; 13°59.094'N, 48°14.018'E; 16 Nov. 2008; F. Benzoni leg.; UNIMIB-Creocean-Total Yemen Coral Biodiversity exped.; UNIMIB BA017 • 2 colony fragments (Fig. 3C); Bir Ali; 13°59.180'N, 48°15.692'E; 19 Nov. 2008; F. Benzoni leg.; UNIMIB-Creocean-Total Yemen 128 ZooKeys 1260: 123–147 (2025), DOI: 10.3897/zookeys.1260.167263 Francesca Benzoni: A new Pavona coral from Indian Ocean reefs Coral Biodiversity exped.; UNIMIB BA066 • 2 colony fragments (Fig. 6G, colony in situ); Burum; 14°19.266'N, 48°59.641'E; 18 Mar. 2009; F. Benzoni and M. Pichon leg.; UNIMIB-Creocean-Total Yemen Coral Biodiversity exped.; UNIMIB BU049 • 2 colony fragments; Al Mukallah; 14°30.923'N, 49°9.254'E; 17 Mar. 2007; F. Benzoni and M. Pichon leg.; UNIMIB-Creocean-Total Yemen Coral Biodiversity exped.; UNIMIB MU085 • 1 colony (Fig. 3B); Al Mukallah; 14°30.696'N, 49°9.360'E; 18 Mar. 2007; F. Benzoni and M. Pichon leg.; UNIMIB-Creocean-Total Yemen Coral Biodiversity exped.; UNIMIB MU128 • 1 colony fragment (Figs 3D, 6C, colony in situ); Socotra Island, Hawlaf; 12°40.662'N, 54°4.497'E; 14 Mar. 2010; F. Benzoni and M. Pichon leg.; UNIMIB-Creocean-Total Yemen Coral Biodiversity exped.; UNIMIB SO078. Oman • 1 colony fragment (10 x 8 cm); Dhalkut; 16°41.235'N, 53°11.749'E; depth 9.4 m; 4 Dec. 2022; F. Benzoni leg.; Oman Bioblitz exped.; collection code OM0895; UF 17903 • 2 colony fragments (Fig. 6B, colony in situ); Mirbat, Eagles Bay; 16°56.377'N, 054°47.799'E; depth 5.4 m; 9 Jan. 2022; F. Benzoni leg.; Oman Bioblitz exped.; collection code OM0096; UF 17957 • 1 colony fragment (Fig. 3F); Mirbat, Qinqari Bay; 17°0.561'N, 55°1.240'E; depth 6 m; 12 Jan. 2022; F. Benzoni leg.; Oman Bioblitz exped.; collection code OM0226; UF 18088 • 1 colony fragment (Fig. 3G); Muscat, Jazirat Al Fahl; 23°40.953'N, 58°30.011'E; depth 5.9 m; 1 Feb. 2022; F. Benzoni leg.; Oman Bioblitz exped.; collection code OM0722; UF 18089 • 1 colFigure 2. Holotype of Pavona giannii sp. nov. MNHN-IK-2012-14233 A. the whole colony in situ at Hyllanyia Island, Bir Ali, Yemen, prior to sampling and B. corallum of the sampled fragment. C. Top view of the corallum showing corallite arrangement and the position of some of the corallite series boundaries (dashed pink lines) marked by the presence of parallel radial elements running over and across them, and D. side view showing its even surface given by equally high and flat top margins of S1 and S2 septa, and the deep-seated fossae. Scale bars: 1 cm (B); 5 mm (C, D). 129 ZooKeys 1260: 123–147 (2025), DOI: 10.3897/zookeys.1260.167263 Francesca Benzoni: A new Pavona coral from Indian Ocean reefs ony fragment; Mirbat, Marriott Wreck; 16°56.933'N, 054°43.686'E; depth 10.4 m; 7 Jan. 2022; F. Benzoni leg.; Oman Bioblitz exped.; collection code OM0017; UF 18090. Mayotte • 3 colony fragments (Figs 3E, 5E, part of the colony in situ); Îlot Mtsamboro; 12°38.031'S, 45°1.140'E; 1 Jun. 2010; F. Benzoni leg.; Tara Oceans exped.; UNIMIB MY069. Seychelles • 1 colony fragment; Mahé Island, Horse Shoe Reef; 24 Feb. 2019; F. Benzoni and R. Arrigoni leg.; University of Seychelles Outer Islands coral collection facility exped.; UNISEY SY079 • 1 colony fragment; same data as for preceding; UNISEY SY080 • 1 colony; Mahé Island, Le Cap; 12 Jan. 1966; B.R. Rosen leg.; NHMUK 1981.3.5.425 • 1 colony; Mahé Island, Baie Ternay; 28 Dec. 1965; B.R. Rosen leg.; NHMUK 1981.3.5.426 • 1 colony (Fig. 4A, B); Mahé Island, North East Point; 22 Dec. 1965; B.R. Rosen leg.; NHMUK 1981.3.5.427. Sri Lanka • 1 colony (Fig. 4C, D); Galle; W.C. Ondaatje leg.; NHMUK 1883.3.24.4 • 1 colony; W.C. Ondaatje leg.; NHMUK 1883.5.23.8. Malaysia • 1 colony (Fig. 4E, F); Pulau Songsong, West Coast, Peninsular Malaysia; C. Betterton leg.; NHMUK 1979.9.24.66. Description. Colonial, corallum encrusting with attached margins, growing on the underlying substrate and broadly following its surface relief (Figs 2–4, 6, 7); maximum observed thickness 1 cm. Corallum surface smooth and devoid of ridges, crests, monticules or hydnophorae (Figs 2B–D, 3, 4). Corallites crowded, less than a corallite diameter apart, and thamnasteroid in arrangement (Figs 2B–D, 3, 4, 5A–F). Budding intratentacular, locally leading to the formation of variably developed corallites series by repeated incomplete separation of walls after budding. Their outline is variable even within the same colony ranging from elliptical to kidney-shaped (Fig. 3H), polygonal (Fig. 3F) or irregular (Figs 2C, 3C). Corallites 2.4 mm (± 0.1 SE) in average maximum diameter and 1.7 mm (± 0.1 SE) in average minimum diameter. On average, 23 septa (± 1 SE) occur per corallite (Table 1), the 6 S1 reaching the columella, their inner margin fusing with it; their average length is 0.9 mm (Table 1). Septa arranged in three orders (Fig. 5G, K, L), those of the first and second (S1 and S2, respectively) sub-equal in thickness and length, all attaining the same height (Fig. 5J–L). S2 may reach the columella or remain slightly shorter either with free margin or occasionally fusing with the columella more deeply in the fossa. Third order septa (S3) are always present, almost complete. S3 septa are less than ½ of S1 and S2 in length (Fig. 5J, K), never reaching the columella, and are thinner and Table 1. Comparison of mean (±SE) corallite and radial elements dimensions (mm) and counts among Pavona giannii sp. nov., Pavona chiriquiensis, and Pavona varians. Character names, measurements and counts for P. chiriquiensis and P. varians are derived from Maté (2003: table 6) retaining the original number of decimal places used therein. P. giannii sp. nov. P. chiriquiensis P. varians Mean (±SE) Mean (±SE) Mean (±SE) Maximum calicular diameter 2.39 (±0.09) 1.85 (±0.05) 1.31 (±0.03) Minimum calicular diameter 1.66 (±0.10) 1.11 (±0.04) 1.50 (±0.02) Maximum columellar diameter 0.46 (±0.05) 0.34 (±0.03) 0.26 (±0.01) Minimum columellar diameter 0.20 (±0.02) 0.20 (±0.02) 0.16 (±0.01) Main septa length 0.90 (±0.06) 0.62 (±0.02) 0.47 (±0.01) Number of septa 23.35 (±0.74) 20.02 (±0.53) 19.86 (±0.62) Number of septa reaching the columella 6.34 (±0.31) 7.17 (±0.16) 7.88 (±0.15) 130 ZooKeys 1260: 123–147 (2025), DOI: 10.3897/zookeys.1260.167263 Francesca Benzoni: A new Pavona coral from Indian Ocean reefs Figure 3. Top views of the coralla showing corallite arrangement in the Pavona giannii sp. nov. specimens collected for this study: A. UNIMIB AD016, from Aden, Yemen; B. UNIMIB MU128, from Al Mukallah, Yemen; C. UNIMIB BA066, from Bir Ali, Yemen; D. UNIMIB SO078, from Socotra Island, Yemen; E. UNIMIB MY069, from Mayotte Island; F. UF 18088 (collection code OM226), from Mirbat, Oman; G. UF 18089 (collection code OM722), from Muscat, Oman; H. Same specimen as in A. Dashed pink lines indicate the position of some of the corallite series boundaries marked by the presence of parallel radial elements running over and across them. Scale bars: 1 cm (A, B); 5 mm (C–H). 131 ZooKeys 1260: 123–147 (2025), DOI: 10.3897/zookeys.1260.167263 Francesca Benzoni: A new Pavona coral from Indian Ocean reefs shorter in height than S1–2 (Fig. 5L). Septal sides of S1 and S2 ornamented with scattered blunt granules, S3 sides smooth (Fig. 5J–L). Synapticulae connecting radial element lateral sides horizontally can be visible in less densely calcified specimens (Fig. 5B, C, E). S1 and S2 upper margins flush, flattened and running parallel to corallum surface giving it an overall even appearance (Figs 2D, 5C, F). Where corallite series occur, radial elements run beyond the seFigure 4. Corallum and corallite macro-morphology of the Natural History Museum (UK) specimens originally identified as Pavona explanulata and here re-identified as Pavona giannii sp. nov. from localities 13–15 in Figure 1. A. View of the whole corallum of specimen NHMUK 1981.3.5.427 from Mahé Island, Seychelles, encrusting a large piece of coral rubble also colonized by other benthic organisms including crustose coralline algae (CCA) and benthic foraminifera; B. Detail of A showing corallite arrangement; C. Top view of specimen NHMUK 83.3.24.4 from Galle, Sri Lanka; D. Detail of the corallum surface of the specimen in C; E. Top view of specimen NHMUK 1979.9.24.66 from Pulau Songsong, Malaysia, encrusting a block of coral rubble also overgrown by CCA (bottom right); F. Closer view of the same specimen in E. Scale bars: 1 cm (A–E); 5 mm (F). 138 ZooKeys 1260: 123–147 (2025), DOI: 10.3897/zookeys.1260.167263 Francesca Benzoni: A new Pavona coral from Indian Ocean reefs early-development stage colonies of these species are distinct from P. giannii sp. nov., typically devoid of ridges. Moreover, corallites in P. cactus, P. danai, P. frondifera and P. minor are smaller than 2 mm in largest diameter (Table 2) while P. giannii sp. nov. forms corallites wider than 2 mm in diameter. Among the Pavona species forming predominantly encrusting coralla devoid of ridges, both Pavona minuta Wells, 1954 (Fig. 8G) and Pavona xarifae Scheer & Pillai, 1974 form corallites less than 2 mm in diameter, hence smaller than in the new species, while P. explanulata (Lamarck, 1816) (Fig. 8H) has corallites more than 4 mm in diameter, larger than in the new species. Furthermore, in these three species, corallites can be more than 1 corallite diameter apart while they are always less than one corallite apart in P. giannii sp. nov. Table 2. List of the corallum and corallite characters and their states for Pavona giannii sp. nov. and the currently valid Pavona species. Corallum growth form (CGF): massive (mv), submassive (sm), columnar (cl), frondose (fr), foliose (fl), encrusting (en); Corallite arrangement in series (CS): mostly present (yes), partially present, or only in some coralla but not in others (pars), mostly absent (no); Raised corallum ridges (CR) present (yes), absent (no); short (sh), long (lo); Corallite distance (CDIS): more than 1 corallite diameter apart (>), less than 1 corallite diameter apart (<); Corallite wall vertical development (CW): raised from the corallum surface (r), flush with the corallum surface (f); Corallite diameter (CD): CD < 2 mm (a); 2mm ≤ CD <4 mm (b), CD ≥4 mm (c); corallite outline (CO): circular (ci), elliptical (el), polygonal (po), irregular (ir), indistinct (in); Septal thickness (ST): equal or sub-equal (eq), unequal (un); Septal upper margin shape above the corallite wall (SUM): rounded (ro), flattened (fl); Columella vertical development in the fossa respective to the septal upper margin (CDE): high (hi), low (lo), indistinct (in). * = corallum margins free, not attached to the substrate. na = information not available from the original description and illustration, type not examined. ^ = from the subsequent description by Milne-Edwards (1860: 67). Pavona species CGF CS CR CDIS CW CD CO ST SUM CDE P. cactus fr yes yes >f a el-in eq fl lo P. danai fr yes yes >f a ci-el-in un ro hi P. frondifera^ fr yes yes na f a na un na hi P. decussata fr yes yes <fbel-po-in un ro-fl lo P. divaricata fr yes yes </> fbel-in eq ro-fl hi P. minor fr yes yes na f a po-in na ro in P. diminuta mv pars no <fbel-in un fl hi P. distincta mv* no no <f na in eq fl in P. gigantea mv pars no >f c ci-el un ro hi P. duerdeni mv pars no <f a ci-el eq ro lo P. diffluens sm-c-en* no no <r-f c ci-el un ro hi P. clavus sm-c pars no <fbci-el-ir un ro hi P. bipartita sm-en* pars no <fbci-el-ir un ro hi P. venosa m-sm-en pars yes <rbpo-ir eq ro lo P. maldivensis cl, fl, en* no no </> rbci-el eq ro hi P. explanulata fl, en* pars no >r c ci-el un ro hi P. minuta fl, en pars no >r-f a ci-el-in eq ro lo P. xarifae en* no no >f a ci-el-in un ro lo P. varians en* pars yes <f a ir-in un ro-fl lo P. chiriquiensis en pars yes <f a ir-in un fl lo P. giannii sp. nov. en pars no <fbpo-ir-in un fl lo 139 ZooKeys 1260: 123–147 (2025), DOI: 10.3897/zookeys.1260.167263 Francesca Benzoni: A new Pavona coral from Indian Ocean reefs Figure 9. Type specimens of Pavona chiriquiensis, Pavona decussata and Pavona varians showing the position, arrangement, and length of the corallum ridges, their upper margin marked by transparent dashed pink lines. A. Top view of specimen USNM 100871, holotype of P. chiriquiensis from Uva Island, Panama; the transparent dashed grey polygon indicates the position of the surface portion shown in B; B. Detail of A showing irregularly arranged and shaped ridges on the corallum, some more elongated and others reduced to conical structures defined by different authors as “hydnophorae” (Glynn et al. 2001), or “conical monticules” (Veron and Pichon 1980); C. Close up view of the corallites and ridges of P. chiriquiensis paratype (YPM 24153); D. Side view of the anastomosing fronds in specimen USNM 201, syntype of P. decussata from Fiji, the two white arrows on the sides of it show the original colony growth direction from the base of the corallum to the fronds top margin; the transparent dashed grey polygon indicates the position of the surface portion in B; E. Detail of C showing long and well-defined, ridges growing along the frond and separating adjacent corallite series, the ladder-like arrangement of the radial elements running over the ridges is visible; F. View of specimen YPM IZ.001806.CN, syntype of P. varians, with well-developed crest-like ridges separating corallite series. Scale bars: 1 cm (A, B, D–F); 5 mm (C). 140 ZooKeys 1260: 123–147 (2025), DOI: 10.3897/zookeys.1260.167263 Francesca Benzoni: A new Pavona coral from Indian Ocean reefs The two encrusting Pavona species that bear more similarity at the corallite level to the new species described here are Pavona chiriquiensis Glynn, Maté & Stemann, 2001 and Pavona varians (Verrill, 1864) (Table 2). However, both species have smaller corallite diameter (Table 1) based on the morphometric analyses performed by Maté (2003). Moreover, Pavona chiriquiensis has S1 = S2 > S3 and S3 are ornamented with same shape and size granules as S1–2 (Glynn et al. 2001: fig. 2B), while Pavona giannii sp. nov. has smooth S3 (Fig. 5G–L). While the new species and P. varians have a similar minimum corallite diameter, corallites in the latter are on average 1 mm smaller in maximum diameter than in P. giannii sp. nov. corallites. Consequently, P. varians has shorter S1 radial elements and has on average less septa per corallite, but more of them reach the columella (Table 1). Finally, both P. varians and P. chiriquiensis form variably long ridges that never develop into fronds (Fig. 9A–C, F). In P. varians, ridges can be straight or contorted, develop radially or perpendicularly to the colony margin (Lewis et al. 2025: fig. 2), and in larger colonies their distribution and development become more irregular (Matthai 1948b). Because of such variability, these structures in the genus Pavona have been referred to with different terms, namely “crests” (Verrill 1864), “vertical keels” (Gardiner 1898), “ridges” (Matthai 1948a, 1948b; Veron and Pichon 1980; Latypov 2014; Lewis et al. 2025), “collines” (Matthai 1948a, b; Veron and Pichon 1980; Sheppard and Sheppard 1991; Glynn et al. 2001; Maté 2003; Latypov 2014), for the more elongated variants, and “monticules” (Matthai 1948a), “conical monticules” (Veron and Pichon 1980), and “hydnophorae” (Glynn et al. 2001) for the shorter ones. Regardless of the length or orientation, radial elements run over the raised ridges in Pavona species perpendicularly to their main axis leading to a typical ladder-like arrangement (dashed pink lines in Fig. 9). This becomes less obvious when a ridge further develops in height into a crest or a frond. Although P. giannii sp. nov. is devoid of ridges on the corallum surface, more or less elongated walls enclosing series of corallites can form. Their position is detectable because the strongly alternating septa are neatly and regularly arranged perpendicular to their direction and form the same ladder-like arrangement (dashed pink lines in Figs 2, 3, 5) observed over ridges in species where these form. Historically, polyp features in scleractinian corals are seldom considered in taxonomic descriptions especially for taxa described before sampling and observations could take place during SCUBA diving or in aquarium facilities. Some notable exceptions are represented by genera like Euphyllia Dana, 1846 and Fimbriaphyllia Veron & Pichon, 1980 in which polyp shape and coloration bear more informative characters than the actual skeleton (Veron and Pichon 1980; Luzon et al. 2017; Arrigoni et al. 2023). In taxa like Blastomussa Wells, 1968, Alveopora Blainville, 1830, Goniopora de Blainville, 1830, Bernardpora Kitano & Fukami, 2014 and Porites Link, 1807 polyp characters have been shown to be informative or diagnostic (Benzoni et al. 2014; Kitano et al. 2014; Terraneo et al. 2016, 2019). In most Agariciidae animal features in vivo are barely visible due to the small size and transparent nature of the polyps (Veron and Pichon 1980). Nevertheless, polyp expansion in the daytime and pale coloration of the tentacles are typical and diagnostic features of P. giannii sp. nov. throughout its known geographic distribution range regardless of the local environmental conditions. Maté (2003: 431) remarked that in the Pacific coast of Panama in his study of P. frondifera, P. chiriquiensis and P. varians “none of the three 141 ZooKeys 1260: 123–147 (2025), DOI: 10.3897/zookeys.1260.167263 Francesca Benzoni: A new Pavona coral from Indian Ocean reefs Pavona species displays expanded polyps during the day except during periods of rapid water flow”. Glynn et al. (2001) and Maté (2003) indicate that tissue coloration in vivo is a diagnostic character to identify P. chiriquiensis in the field and to distinguish it from congeners. Maté (2003: 438) remarked that “dark polyps and coenosarc, and contrasting bright white to silvery oral discs and tentacles” characterized the P. chiriquiensis colonies in Panama. This character seems to be conserved also at other locations. In fact, the same coloration was consistently observed during the coral biodiversity surveys in the Marquises Archipelago, French Polynesia, where P. chiriquiensis was the most frequently encountered scleractinian coral found at 94% of the surveyed sites (Salvat et al. 2016: fig. 4A). Amongst congeners, P. gigantea and P. explanulata (Fig. 7C) usually have polyp tentacles variably extended during the daytime, however they are grey to white in the former and green to brown in the latter, and both species have different growth forms and polyp/corallite size (Table 1). Finally, the in vivo coloration of P. distincta is unknown (Latypov 2014). Conclusions Pavona giannii sp. nov., a new species of colonial hard coral in the genus Pavona, is described, highlighting the diagnostic value of both skeletal and polyp morphology. This species, with its distinctive encrusting growth form, smooth corallum surface, and characteristic daytime polyp expansion and coloration, stands apart from all currently recognized Pavona species. It inhabits shallow water coral reefs and hard grounds in the Indian Ocean. A detailed comparative analysis, including morphometric data and comparisons with type and reference material, underscored the morphological distinctiveness of P. giannii sp. nov. and provided an illustrated summary of the morphological variability within the genus. Future research on Pavona and other Agariciidae, should prioritize expanded species sampling from diverse geographic localities including type localities, coupled with phylogenomic analyses. Such efforts will be essential to resolve the complex phylogenetic relationships within Pavona and ultimately establish a robust and stable taxonomic framework for this ecologically important coral genus. Acknowledgements The author is grateful to B.W. Hoeksema, S.D. Cairns, K. Samimi-Namin, and an anonymous reviewer for their useful suggestions and revisions which have helped improve the manuscript and Natahlie Yonow for the final proofing. Fieldwork organization, logistics, and sampling permits from the relevant authorities in Yemen were possible thanks to the support of E. Dutrieux (Creocean), C.H. Chaineau (Total SA), R. Hirst, and M. Abdul Aziz (YLNG). I am grateful to S. Basheen (Professional Divers Yemen) for technical and logistical support. I am especially grateful to M. Pichon (Museum of Tropical Queensland) for inviting me to be part of the 2005-2014 biodiversity expedition and monitoring surveys in Yemen. Sampling in Mayotte was possible thanks to the Tara Oceans scientific expedition and the OCEANS Consortium. I am grateful in particular to E. Karsenti (EMBL) and E. Bougois (Tara Expeditions) for allowing reef research during the expedition, to S. Kandels-Lewis (EMBL), R. Trouble (Fonds Tara), R. Friederich (World Courier) for expedition organization and logistics, and to Captain 142 ZooKeys 1260: 123–147 (2025), DOI: 10.3897/zookeys.1260.167263 Francesca Benzoni: A new Pavona coral from Indian Ocean reefs H. Bourmaud and the Tara crew, and to M. Oriot and J.J. Kerdraon in particular. I am especially indebted to L. Bigot (ECOMAR) for his assistance and support for fieldwork in Mayotte. Tara Oceans. I thank the commitment of the following people and additional sponsors who made this singular expedition possible: CNRS, EMBL, Genoscope/CEA, VIB, Stazione Zoologica Anton Dohrn, UNIMIB, ANR (projects POSEIDON/ANR09-BLAN-0348, BIOMARKS/ANR-08-BDVA-003, PROMETHEUS/ ANR-09-GENM-031, and TARA-GIRUS/ANR-09-PCSGENM-218), EU FP7 (MicroB3/No.287589), FWO, BIO5, Biosphere 2, the Veolia Environment Foundation, Région Bretagne, World Courier, Illumina, Cap L’Orient, the EDF Foundation EDF Diversiterre, FRB, the Prince Albert II de Monaco Foundation, E. Bourgois, the Tara schooner, and its captain and crew. Tara Oceans would not exist without continuous support from 23 institutes (https://oceans.taraexpeditions. org). This is contribution number 162 based on material collected during the Tara Oceans Expedition 2009–2012. I am grateful to D. Barshish and M. Fine for the invitation to join the 2020 Djibouti Dolphin cruise which they fully organized and supported. The Ministry of the Environment and Sustainable Development (MEDD) and Ministère de l’Urbanisme, de l’Environnement et du Tourisme (MUET) are acknowledged for their critical assistance in supporting the research in Djibouti, particularly Mme Bilan Hassan Ismail, through coordination of the research, permits, and sample transport. Corals in Djibouti were collected under the permitting authority of the MUET and MEDD. Field work and sampling in the Seychelles was possible thanks to the University of the Seychelles and James Michel Blue Economy Research Institute. I am grateful to K. Hoareau and R. Walton for organizing and supporting the coral biodiversity workshop and reference collection establishment under the GoS/UNDP/GEF Outer Islands project, and M. Leotta for the guidance in the field. M.-M. Muzungaile (Ministry of Environment, Energy and Climate Change) is acknowledged for her support with the collection permits. Collection fieldwork in Oman was supported by NSF DEB-1457817 to G. Paulay (Florida Museum of Natural History). C. McFadden, M. and E. Claereboudt, N. Stauft, K. Samimi-Namin, S. Wilson, and other members of the Oman Bioblitz expeditions are acknowledged for facilitating fieldwork, and the Environment Authority of Oman for permits. I am deeply indebted to my colleagues R. Arrigoni (SZN), Tullia I. Terraneo (KAUST) for their support, collaboration and help with sampling and reference collection curation on multiple sampling expeditions over the years. For museum reference collection study visits I am sincerely grateful to A. Quattrini and T. Coffer (USNM), B.W. Hoeksema and J. Goud (RMNH), M. Lowe and N. Santodomingo (NHMUK), A. Andouche (MNHN), E. Lazo-Wasem and L. Rojas (YPM), A. Bemis and G. Paulay (UF), and F. Barreca (KAUST). Additional information Conflict of interest The author have declared that no competing interests exist. Ethical statement No ethical statement was reported. Use of AI No use of AI was reported. 143 ZooKeys 1260: 123–147 (2025), DOI: 10.3897/zookeys.1260.167263 Francesca Benzoni: A new Pavona coral from Indian Ocean reefs Funding This study was funded by the author’s baseline at KAUST and the Red Sea Research Center FCC/1/1973-49-01. Author contributions The author solely contributed to this work. Author ORCIDs Francesca Benzoni https://orcid.org/0000-0001-8906-1309 Data availability All of the data that support the findings of this study are available in the main text. 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