Dimorphic life cycle through transverse division in burrowing hard corals

<jats:title>Abstract</jats:title> <jats:p>The azooxanthellate solitary scleractinian Deltocyathoides orientalis (Family Turbinoliidae), which has bowl-shaped costate corallites, exhibits burrowing behavior on soft substrates and adapts to an infaunal mode of life. Here, we describe the previously unknown aspects of their life history and asexual mode of reproduction based on morphological and molecular phylogenetic analyses. The findings revealed that (1) D. orientalis exhibits asexual reproduction by transverse division; (2) smaller bowl-shaped costate anthocyathus derived from cylindrical to tympanoid anthocaulus attached to hard substrates, including shell fragments and gravels on soft substrates; (3) the anthocyathus only reproduces sexually after division and the anthocaulus regrew and repeatedly produces anthocyathi through transverse division. The bowl-shaped corallum morphology of the anthocyathus just after division might reduce and time of skeletal formation for infaunal adaptation after transverse division. Immediately after division, D. orientalis is able to smoothly shift to a burrowing lifestyle that efficiently utilizes soft-substrate environments, increasing its survival rate. Thus, morphological formation of prospective anthocyathus in the anthocaulus stage is thought to involve not only increasing clonal individuals but also adaptation to the necessarily burrowing free-living mode of life in the anthocyathus stage.</jats:p>