Overview of the genus Sympodium Ehrenberg, 1834 (Octocorallia, Alcyonacea, Xeniidae), with the description of new species, revealing regional endemism Author Benayahu, Yehuda 0000-0002-6999-0239 School of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, 69978, Israel yehudab @ tauex. tau. ac. il; https: // orcid. org / 0000 - 0002 - 6999 - 0239 yehudab@tauex.tau.ac.il Author Ekins, Merrick Queensland Museum, South Brisbane BC, Queensland 4101, Australia. Author Mcfadden, Catherine S. Department of Biology, Harvey Mudd College, Claremont, CA 91711, USA. text Zootaxa 2021 2021-12-01 5072 4 324 350 journal article 3152 10.11646/zootaxa.5072.4.2 87c4739e-7fe1-41e7-a25f-aae7e837fb33 1175-5326 5748862 810459A8-AF47-47A9-B5B6-BE45659B3E7F Sympodium subtilis sp. n. Figs. 12 , 13 , 14A FIGURE 12. Sympodium subtilis sp. n. : morphology of type material colonies. (A) Syntypes (SMNHTAU_Co_38204) encrusting colonies with delicate membrane growing on a bivalve shell. (B) Higher magnification of portion of syntypes showing both expanded and retracted polyps on spreading membrane. Material. Japan . Syntypes : SMNHTAU_ Co _38204, Nagasaki , Danjo Islands , south of Arasesaki , Ojima, NW side ( 32.051168°N , 128.391857°E ), 23 September 2018 , 10– 20 m , coll. C. McFadden ; Paratypes : SMNHTAU_ Co _38092 Nagasaki , Danjo Islands , Ojima, SE side ( 32.038886°N , 128.387278°E ), 22 September 2018 , 10– 20 m , coll. C. McFadden (molecular sample only); SMNHTAU_Co_38103 Nagasaki , Danjo Islands , rocks west of Yorijima ( 32.024824°N , 128.364289°E ), 23 September 2018 , 10– 20 m , coll. C. McFadden (molecular sample only); SMNHTAU_ Co _38104, same details . Description . The syntypes comprise several irregular encrusting colonies with a delicate thin spreading membrane (< 0.5 mm ) attached to a bivalve shell ( Fig. 12A ). The largest colony has a surface area of ca. 15 mm 2 . In addition, there are a few small colonies measuring 3–5 mm 2 . It was not possible to separate a single colony as a holotype without compromising its integrity and therefore syntypes were assigned. The polyps emerge from the membrane 1–5 mm apart and exhibit various degrees of retraction ( Fig. 12B ). The few expanded polyps are up to 1.5 mm long and their tentacles are approximately 0.5 mm long. The pinnules are either totally or partially contracted, with a single row of 3–5 pinnules on either side of the tentacle. The sclerites of the syntypes are ellipsoid platelets, abundant throughout the colony and measuring 0.010 –0.012 x 0.013 –0.015 mm in diameter ( Fig.13A ). They are composed of densely packed calcite rods whose tips provide a uniform granular appearance to the sclerite surface ( Fig. 13B ). FIGURE 13 . Scanning electron micrographs of sclerites of Sympodium subtilis sp. n. Syntypes (SMNHTAU_Co_38204): (A) Ellipsoid platelets. (B) Tips of calcite rods provide a uniform granular appearance to the sclerite surface. Color. The ethanol-preserved syntypes are light gray, almost white. Etymology. The species’ name, subtilis from the Latin meaning delicate, refers to the delicate encrusting membrane of the species. Variation. The paratype SMNHTAU_Co_38104 is a small colony measuring only a few mm in size, but otherwise resembles the holotype . Living features . The live colonies feature polyps arranged in groups ( Fig. 14A ). Distribution . Japan . Remarks . The colonies are characterized by a remarkably thin and delicate spreading membrane which is suggested to be diagnostic for this species. The ethanol-preserved syntypes and paratypes were sequenced and subsequently assigned to MOTU68.