Ocean sunfishes, also known as molids (family Molidae, Order Tetradontiformes), are among the most distinctive marine teleost, characterized by their unique body shape, including the complete absence of a true caudal fin, and their huge size, reaching over 3 m in total length and more than 2,000 kg in body mass (Sawai et al., 2018). Although research on molid morphology and taxonomy dates back to the 16^th century, their systematics remain as a long-standing legacy of taxonomic confusion that continues to the present day (Fraser-Brunner, 1951; Sawai et al., 2018). This taxonomic confusion arises because all molid species undergo significant morphological transformation during early life stages, which are poorly documented, and continue to exhibit such morphological changes as they grow larger (Fraser-Brunner, 1951; Martin and Drewry, 1978; Hellenbrecht et al., 2019). Additionally, information on key life history traits, particularly size at maturity of most molids is either lacking or poorly understood. Establishing a key diagnostic characteristic for each species at different life stages is therefore vital for accurate species identification and effective fisheries and molid resource management (Sawai et al., 2020). Several morphological characteristics in Mola spp. develop with size and should be observed with utmost caution, including head bump, chin bump, wavy clavus, ossicles and body scale structure (see Nyegaard et al., 2018; Sawai et al., 2018).

Historically, Fraser-Brunner (1951) conducted the first comprehensive review of Molidae based on morphology, reexamining all nominal species documented in the literature. He accepted only three genera and five valid species (including two subspecies) within the family: Ranzania laevis laevis, R. laevis makua, Masturus lanceolatus, M. oxyuropterus, Mola mola, and M. ramsayi. Subsequently, Parenti (2003) provided the first checklist of Molidae, listing 19 nominal genera and 57 nominal species, though recognizing only 4 valid species across 2 or 3 genera (Masturus lanceolatus, Mola mola, M. ramsayi and Ranzania laevis) depending on the author. However, Fraser-Brunner’s classification remained widely accepted and endorsed by major taxonomic authorities until recent studies. More recently, Nyegaard et al. (2018) confirmed the presence of three distinct species within the genus Mola: M. tecta (a new species from New Zealand and Australia), M. ramsayi and M. mola, using an integrative taxonomic approach and provided a provisional key to distinguishing the adult forms of Mola species. This represented the first discovery of a new Mola species in 125 years. Subsequently, Sawai et al. (2018) found that M. ramsayi is no longer a valid species and resurrected M. alexandrini (Ranzani 1839) from synonymy with M. mola (Fraser-Brunner, 1951), treating it as the senior synonym of M. ramsayi. They redescribed M. alexandrini as a valid species based on the rediscovered dried holotype (MZUB, 190 cm total length) that was unnumbered, along with 21 additional fresh and preserved specimens. Due to the absence of a type specimen, a neotype was designated for M. mola to facilitate comparison with M. alexandrini, given the historical confusion between these species. However, Britz (2022) questioned the validity of M. alexandrini (Ranzani, 1839) following a meticulous analysis of morphometric data and images from Sawai et al. (2018), the purported holotype and Ranzani’s (1839) illustration of O. alexandrini. Britz identified discrepancies suggesting that Sawai et al. (2018) may have been misled, and the putative holotype of M. alexandrini cannot be a type specimen because of the mismatches between the reported length and the image/illustration. In light of this confusion and following an additional literature review, Sawai and Nyegaard (2023) again confirmed the valid species status of M. alexandrini (Ranzani, 1839) by addressing the issues raised by Britz (2022). At present, the genus Mola is therefore considered to include only three valid species: M. alexandrini (Ranzani 1839), M. mola (Linnaeus 1758), and M. tecta Nyegaard et al., 2017 (Nyegaard et al., 2018; Sawai et al., 2018; Sawai and Nyegaard, 2023).

The first molecular investigation of Molidae was undertaken by Streelman et al. (2003), who developed five nuclear DNA microsatellite markers specific to M. mola. Yamanoue et al. (2004) subsequently determined the first complete mitochondrial genomes and phylogeny of three molids: R. laevis, M. lanceolatus, and M. alexandrini (as M. mola). Sagara et al. (2005) identified two distinct clades of M. mola in Japanese waters through phylogenetic analysis of full nucleotide sequences of the mitochondrial D-loop region. In the same year, Bass et al. (2005) identified four genetically distinct clades based on analysis of D-loop and cytochrome b mitochondrial regions. Yoshita et al. (2009) validated the global classification of Mola species into three distinct groups (designated as Mola sp. A, Mola sp. B, and Mola sp. C) through a molecular phylogenetic analysis of the D-loop region based on the specimens collected from both inside and outside Japanese waters. Yamanoue et al. (2010) developed a multiplex PCR method for genotyping the mitochondrial DNA of Mola sp. A and Mola sp. B in Japan. Nyegaard et al. (2018) confirmed the presence of three distinct species within the genus Mola (Mola sp. A, Mola sp. B and Mola sp. C as M. ramsayi, M. mola, M. tecta, respectively), as first suggested by Yoshita et al. (2009), using morphological characteristics and mitochondrial DNA analysis (D-loop and COI). Recently, Sawai et al. (2018) clarified the nomenclatural status of the two remaining genetically identified species (Mola sp. A as M. alexandrini and Mola sp. B as M. mola) through an extensive morphological and molecular studies.

On the Indian coast, ocean sunfishes of the genus Mola have usually been reported as M. mola, and in certain instances as M. ramsayi and M. alexandrini (see Table 1). The first record dates back to 1975 in the name of M. mola from Satpati, Bombay coast (present name Mumbai) in the Arabian Sea (Khan, 1975). Afterwards, the species was reported from various parts of the country: Visakhapatnam (Ram Bhaskar et al., 1988), northwestern Indian EEZ (Somvanshi, 1996), Veraval (Monoj Kumar et al., 1998), Tuticorin (Chellappa et al., 2002), Kayalpatnam (Chellappa et al., 2006), Chennai (Mohan et al., 2006), Malpe (Thomas et al., 2006), Parangipettai (Murugan et al., 2007), Calicut (Monoj Kumar and Pavithran, 2007), Karwar (Praveen Dube et al., 2013), Munambam (Kishore et al., 2013), Digha (Ray et al., 2019), Panchupada (Fullonton et al., 2020), Kakinada (Chatla and Padmavathi, 2021), Vasai (Thakurdas et al., 2022) and recently from southwest coast of India (Devi et al., 2023). Most of these publications are distribution records based on surface morphology and photographic evidence and lack detailed meristic counts and supporting molecular data. Mola spp. are difficult to distinguish from each other, especially during the early life stages and smaller sizes, due to strong morphological similarities, resulting in frequent misidentifications and erroneous GenBank submissions (Nyegaard et al., 2018; Sawai et al., 2018; present study). Therefore, traditional taxonomic tools stand alone are not sufficient for reliable identifications of these contentious species.

Given the lack of detailed taxonomic studies and the limited availability of reference sequences for Indian Mola in public databases, this study tests whether Indian Mola records attributed to M. mola represent misidentifications of M. alexandrini using an integrative taxonomy approach that combines classical taxonomic tools (such as morphology and anatomical traits) with molecular data generated from two mitochondrial regions, D-loop and COI. The COI region serves as the standard DNA barcode for fishes, which enables reliable species discrimination, while the rapidly evolving mitochondrial control region (D-loop) provides additional resolution among closely related species. Together, these two mitochondrial regions are effective for taxonomic clarification within the genus Mola (Nyegaard et al., 2018).

In the present study, Mola alexandrini is documented based on seven fresh specimens and eight photographic records collected from both the east and west coasts of India. An integrative assessment combining literature review, morphological examination, and molecular characterization using two mitochondrial markers (COI and D-loop) indicates that M. alexandrini is widely distributed along the Indian coastline. In contrast, the occurrence of M. mola in Indian waters appears to be absent or remains doubtful. Sawai et al. (2018) confirmed that M. ramsayi is not a valid species, whereas M. alexandrini is a distinct species with a widespread distribution across the world’s oceans, including the Indian coast. Their findings based on morphological and genetic evidence, further pointed out that the distribution of M. mola is biased towards the Northern Hemisphere, with no verified records from the Indian Ocean. In contrast, M. tecta appear to be distributed predominantly in the temperate waters of the Southern Hemisphere (Nyegaard et al., 2018). Nevertheless, the distributional ranges of all Mola species warranted re-evaluation in future studies due to widespread species confusion and persistent taxonomic uncertainties, particularly concerning M. mola (Sawai et al., 2018).

Despite recent advances in species-level taxonomic resolution and improved clarity regarding the geographic distributions of Mola species, several recent studies continued to misidentify and report ocean sunfishes from Indian waters as M. mola (Ray et al., 2019; Fullonton et al., 2020; Kar et al., 2020; Thakurdas et al., 2022; Devi et al., 2023). Such misidentifications likely arise because many of these records involve large individuals, for which the collection of detailed morpho-meristic data in the field is particularly challenging. Counts of dorsal, anal, and clavus fin rays and associated ossicles are difficult to obtain accurately and are often under- or overestimated when assessed by tactile examination, as these structures are hidden by the thick subcutaneous gelatinous layer. Moreover, some clavus fin rays may be erroneously counted as dorsal or anal fin rays. Accurate enumeration of fin rays, ossicles, and vertebrae therefore requires dissections of medium to large specimens or X-radiography of smaller individuals; however, such approaches are often impractical for very large specimens due to difficulties associated with transport, preservation, and storage. Consequently, much of the published morpho-meristic information from Indian waters is likely biased toward the historically well-known species M. mola, even after recent taxonomic revisions (Nyegaard et al., 2018; Sawai et al., 2018). These limitations highlight that reliance on morphology alone is insufficient for reliable species identification in ocean sunfishes, and that an integrative approach combining morphological, anatomical and molecular evidence provides a more accurate and robust framework for resolving the taxonomy of enigmatic taxa (Roul et al., 2021; Jeena et al., 2022).

The fin ray and clavus ossicle counts observed in the present study are consistent with those reported for M. alexandrini by Sawai et al. (2018), including 11–12 pectoral fin rays, 16–19 dorsal fin rays, 15–17 anal fin rays, 14–25 clavus fin rays, 51–55 D+C+A fin rays, and 0–15 clavus ossicles (Table 2). In addition, diagnostic characters such as rounded clavus margin, and clavus with a smooth band lacking a back-fold were observed, in agreement with Sawai et al. (2018). However, head and chin bumps as well as lateral ridges above or below the eyes, were absent in the present specimens, likely because all individuals examined were juveniles (58.9–87.1 cm TL), as these features are known to develop with age (Sawai et al., 2018). Previous studies have shown that rectangular scale shape is a reliable diagnostic character for M. alexandrini in specimens exceeding 162.5 cm TL, whereas scale morphology remains uncertain in individuals smaller than 70.0 cm TL (Sawai et al., 2018). In contrast, the present study identified a conical scale shape with branching tips in specimens ranging from 58.9 to 87.1 cm TL, while scale morphology in individuals below this size range remains unresolved.

Public sequence databases such as GenBank may contain misidentified entries, particularly for morphologically conserved and taxonomically complex groups like Mola, with some sequences deposited prior to recent taxonomic revisions (Sawai et al., 2018). Therefore, molecular inferences based solely on public databases should be interpreted with caution, a limitation addressed here by integrating genetic data with detailed morphological and anatomical evidence. Comparative phylogenetic analyses of COI and D-loop sequences from this study and publicly available data confirm that the Indian specimens are M. alexandrini. While COI is effective for species-level identification in Mola (Nyegaard et al., 2018), the major mitochondrial noncoding region (D-loop) allows better intraspecific differentiation in closely related groups due to its relatively rapid rate of evolution (Stepien and Kocher, 1997). Phylograms of these two regions showed consistent results, supporting the taxonomic conclusions of Sawai et al. (2018). The D-loop phylogeny further revealed geographic structuring between eastern and western Pacific populations of Mola mola, a pattern not evident in the COI analysis and consistent with previous findings (Yoshita et al., 2009). Historically, M. alexandrini has been regarded as a Southern Hemisphere species by various authors (Fraser-Brunner, 1951; Heemstra, 1986; Bass et al., 2005) and has not been documented in any ocean other than the Indian Ocean. Overall, from the combined morphological and molecular evidence from this study, as well as prior research, it is clear that M. alexandrini is commonly distributed throughout the world’s oceans including Indian water (see Figure 1).

This study resolves the taxonomic ambiguity surrounding ocean sunfishes in Indian waters by applying an integrative approach that combines morphological, anatomical, and molecular data. The present findings support the identification of Indian Mola specimens as Mola alexandrini, thereby refining species-level understanding within the Indian Exclusive Economic Zone. This clarification contributes to a more accurate interpretation of regional Mola diversity and distribution. The findings highlight the limitations of morphology-based identifications in morphologically conserved taxa that undergo substantial ontogenetic change. Difficulties associated with large body size, incomplete meristic data, and inconsistent reference sequences in public databases can perpetuate misidentifications if not carefully addressed. By integrating classical taxonomy with molecular data, this study demonstrates a robust framework for resolving such challenges and improving taxonomic reliability. Beyond systematics, accurate species identification is essential for understanding ecological patterns, fisheries interactions, and life-history traits of ocean sunfishes. The reference material and genetic data generated here provide a foundation for re-evaluating historical records and for guiding future research across all life stages (pre-juvenile, juvenile, and adult) along the Indian coast. Improved taxonomic resolution will be critical for informing species-specific conservation assessments and management strategies for ocean sunfishes in Indian waters, particularly in the context of increasing fishing pressure and limited biological data.