Dimorphic life cycle through transverse division in burrowing hard coral Deltocyathoides orientalis

Abstract

Abstract The azooxanthellate solitary scleractinian Deltocyathoides orientalis (family Turbinoliidae), which has bowl-shaped costate corallites, exhibits burrowing behavior on soft substrates and can adapt to an infaunal mode of life. Here, we describe previously unknown aspects of their life history and asexual mode of reproduction based on morphological and molecular phylogenetic analyses. The findings reveal that (1) D. orientalis exhibits asexual reproduction by transverse division; (2) smaller bowl-shaped costate anthocyathus derived from cylindrical to tympanoid anthocaulus were attached to hard substrates, including shell fragments and gravels on soft substrates; and (3) anthocyathus only reproduce sexually after division, and anthocaulus was found to regrow and repeatedly produce anthocyathi through transverse division. The bowl-shaped corallum morphology of the anthocyathus just after division might reduce the time required for skeletal formation to enable infaunal adaption after transverse division. Immediately after division, D. orientalis can smoothly shift to a burrowing lifestyle that efficiently utilizes soft-substrate environments, thus increasing its survival rate. The morphological formation of prospective anthocyathus in the anthocaulus stage is consequently thought to involve an increase in clonal individuals as well as adaptations for a burrowing free-living mode of life in the anthocyathus stage.