A New Shallow-Water Species, Polycyathus chaishanensis sp. nov. (Scleractinia: Caryophylliidae), from Chaishan, Kaohsiung, Taiwan

A small population of a new species of zooxanthellate scleractinian coral, Polycyathus chaishanensis sp. nov., is described from shallow water (< 3 m) off Chiashan, Kaohsiung, an uplifted Pleistocene reef located on the southwest coast of Taiwan. Polycyathus chaishanensis sp. nov. is a zooxanthellate coral associated with Symbiodinium Cl and forms small encrusting colonies. Polycyathus chaishanensis sp. nov. differs from other Polycyathus by having (1) the smallest corallites (2.0-3.7 mm in calicular diameter) reported in the genus Polycyathus; (2) septa hexamerally arranged in 4 incomplete cycles displaying dentate or laciniate axial edges; (3) crispate and well-developed pali before the secondary septa; and (4) light brown pigmented pali/columellar elements. When expanded, vivid-red to brown polyps rise considerably above the calice, and long and slender tentacles are covered with white nematocyst batteries. Polycyathus chaishanensis is the only species of Polycyathus known from Taiwanese waters and appears to be endemic to a small region at Chaishan. The small population of this new species raises concerns as to its vulnerability to natural and anthropogenic threats.