Plexauridae  Plexauridae is a family of marine colonial octocorals in the phylum Cnidaria. Members of this family are found in shallow tropical and subtropical seas. Many species contain symbiotic photosynthetic protists called zooxanthellae. The Plexauridae have a branching colony form and many are known as sea rods or sea fans. The axial core of the coral skeleton is horny and hollow, and contains no sclerites. This is covered by a layer of tissue called coenenchyme in which is embedded calcareous sclerites. The sclerites are very varied in form in the Plexauridae, and examination of their morphology is helpful in identifying the different species. The calyces in which the polyps sit are strengthened by further sclerites and have eight fine dividing walls called septa. The polyps each have eight pinnate tentacles. The World Register of Marine Species includes these genera in this family: