Phymanthus crucifer is a sea anemone (family Phymanthidae, order Actiniaria) found in shallow Caribbean reef and rocky habitats, characterized by distinctive tentacles with branched, cross-like (cruciform) tips that give it its specific epithet. It typically inhabits crevices, rubble, and reef rock surfaces in shallow tropical Atlantic environments. The family Phymanthidae occupies an interesting phylogenetic position within Actiniaria and contributes to the diversity of Caribbean sea anemone fauna. Genomic data have been generated for this species and are available in public databases, enabling comparative studies of cnidarian evolution and ecology.