27Accurate information of taxonomy and geographic range of seahorse species (genus 28 Hippocampus) is the first step in preparing threat assessments and designing effective 29 conservation measures. Here, we report the range expansion and first occurrence of the 30 Japanese seahorse, Hippocampus mohnikei (Bleeker, 1853) from the Mandovi estuarine 31 ecosystem of Goa, central west coast of India (CWCI) based on morpho-molecular analyses. 32 The morphometric and meristic traits particularly, short snout (29-35% head length), double 33 cheek spine, low coronet and long tail (51.2-57.9% of standard length), 11 trunk rings, 37-39 34 tail rings, 15-16 dorsal and 12-14 fin rays observed in four collected specimens matched 35 with the reported key diagnostic morphological criteria of vouchered specimens of H. 36 mohnikei. The seahorse mitochondrial cytochrome oxidase subunit I (COI) and cytochrome b 37 (Cyt b) genes were partially sequenced for conclusive genetic identification of the species 38 under study. Molecular analysis showed that all four individuals of seahorse species clustered 39 together suggesting a monophyletic lineage. Using the maximum similarity with GenBank 40 database, maximum likelihood network and subsequent morphological analysis, the identity 41 of the collected seahorse species was reconfirmed as H. mohnikei. With this new report, the 42 geographic range of H. mohnikei extended significantly to the westward side from its 43 previously known range. This new sighting of H. mohnikei could indicate a long-distance 44 dispersal facilitated by due to prevailing oceanic circulation in the Indo-Pacific region or 45 increased habitat suitability in bay-estuarine systems of Goa, CWCI. Comparison of the pair-46 wise genetic distances (Kimura 2-parameter) based on COI and Cyt b sequences revealed that 47 whether H. mohnikei are vagrants or previously unreported established population, long-term 50 inter-annual sampling and analyses are warranted. 51 52 53 Seahorses (Syngnathiformes; Syngnathidae) belonging to the single genus, Hippocampus 54 (Rafinesque, 1810) are a fascinating and remarkable group of fishes with their unusual body 55 shape and their biology, with males incubating the fertilized eggs in a brood pouch [1]. They 56 are small, cryptic, and sedentary marine fishes that occur worldwide in shallow temperate to 57 tropical waters in a wide variety of habitats, including seagrass beds, estuaries, coral and 58 rocky reefs and mangroves [2−4]. Their remarkable ability to camouflage with structurally 59 complex habitats further reduces the risk of predation [5], while providing stealth for prey 60 capture [6]. However, these biological traits often also make them unnoticeable from coastal 61 habitat. Due to their cryptic nature, their ability to camouflage and the sparse distribution, 62 seahorses become almost unnoticeable and thus restricting the biologists for their 63 identification in dense coastal marine habitats. 64The primary step in preparing threat assessments and designing effective conserva...