Morphology and phylogeny of two species of Bathypathes from the tropical western Pacific, with description of a new species

The black coral genus Bathypathes Brook, 1889 represents a relatively diverse and ecologically important assemblage comprising the deep-sea hard substrate communities. Recent phylogenetic investigations have revealed the polyphyletic nature of Bathypathes, urging further morphological analysis to understand its systematics. By combing morphological and molecular data, we describe Bathypathes multifurcata sp. nov. and report B. pseudoalternata Molodtsova, Opresko & Wagner, 2022 based on the specimens collected from the tropical western Pacific. The phylogenetic topology reconstructed using nuclear ITS1-5.8S-ITS2 and three mitochondrial fragments suggests the separation of Bathypathes into four groups. Our analysis of morphological characters, particularly the colony branch and pinnule patterns also roughly classify Bathypathes into four morphological groups A-D. Group A is characterized by the unbranched colony and the subopposite arrangement of pinnules. In contrast to Group A, Groups B-D have the alternately arranged pinnules. Among these, Group C exhibits a distinctly long unpinnulated stem compared to Groups B and D. Group B has unbranched colony, relatively short unpinnulated stem, and spines on pinnules have blunt apex. Within Group D, large colonies (higher than 40 cm) have one or a few branches, small colonies (less than 40 cm) are unbranched, and spines on pinnules have acute apex. Further data particularly those species without sequences are necessary to verify the classification of these groups.