title: Descriptions of two azooxanthellate Palythoa species (Subclass Hexacorallia, Order Zoantharia) from the Ryukyu Archipelago, southern Japan.
abstract: Two new species of zoantharians (Hexacorallia, Zoantharia, Sphenopidae), Palythoamizigama sp. n. and Palythoaumbrosa sp. n., are described from the Ryukyu Archipelago, southern Japan. Unlike almost all other known Palythoa spp., both species are azooxanthellate and inhabit low-light environments such as floors or sides of caves, crevasses, or hollows of shallow coral reefs. The two species were initially considered to be the same species from their similar habitat environments and highly similar morphological features. However, phylogenetic analyses of nuclear internal transcribed spacer (ITS) ribosomal DNA, mitochondrial 16S ribosomal DNA, and cytochrome oxidase subunit I (COI) sequences revealed that these two species have a genetically distant relationship within the genus Palythoa. Morphological characteristics, including polyp size, tentacle number, external/internal coloration, and types and sizes of cnidae were examined in this study. As a result, only tentacle coloration was found to be useful for the morphological distinction between the two species. Palythoamizigama possesses white tentacles with black horizontal stripes while Palythoaumbrosa possesses white tentacles without any stripe patterns. Considering their distant phylogenetic relationship, it can be assumed that their unique yet similar morphological and ecological characteristics developed independently in each species as an example of parallel evolution.
authors: Molecular Invertebrate Systematics and Ecology Laboratory, Graduate School of Engineering and Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan.
authors: Yuka
authors: Y
authors: Irei
authors: Environmental Impact Assessment Research Group, R&D Center for Submarine Resources, Global Oceanographic Data Center, Japan Agency for Marine Science and Technology, 224-3 Toyohara, Nago, Okinawa 905-2172, Japan ; Sesoko Station, Tropical Biosphere Research Center, 3422 Sesoko, Motobu, Okinawa 905-0227, Japan.
authors: Frederic
authors: F
authors: Sinniger
authors: Molecular Invertebrate Systematics and Ecology Laboratory, Graduate School of Engineering and Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan.
authors: James Davis
authors: JD
authors: Reimer
keywords: Cave-dwelling; ITS-rDNA; Ryukyu Archipelago; cryptic species; zoantharian