Spirobranchus is the second largest genus of tube-building annelid fanworms in the family Serpulidae. Members of Spirobranchus are known as Christmas tree worms.
The worms form a calcareous tube which becomes incorporated into their host coral. The prominent features visible externally are a pair of conical spiral radiole bundles ("trees"), and an operculum that closes when they retract into their tube.
The crown of radioles serves for both food-gathering and respiration. "Christmas tree" refers to the tiered, tapered shape, whilst "Spirobranchus" translates to "spiral gill".
Taxonomy and systematics The type species Spirobranchus giganteus was described by Peter Simon Pallas in 1766 as Serpula gigantea. In 1818, Henri de Blainville separated "S. gigantea de Linné" into a its own genus named in French as "Spirobranche".Blainville, Henri Marie Ducrotay de. (1818). Mémoire sur la classe des Sétipodes, partie des Vers à sang rouge de M. Cuvier, et des Annélides de M. de Lamarck. Bulletin des Sciences, par la Société Philomatique de Paris. 1818: 78-85., available online at https://biodiversitylibrary.org/page/4146409 (p. 79).
Species The species in the genus (World Register of Marine Species) include:
Spirobranchus aloni Perry, Bronstein, Simon-Blecher, Atkins, Kupriyanova, ten Hove, Levy & Fine, 2018 Spirobranchus corniculatus (Grube, 1862) Spirobranchus latiscapus Marenzeller, 1885 Spirobranchus americanus (Day, 1973) Spirobranchus arabicus Monro, 1937 Spirobranchus baileybrockae Pillai. 2009 Spirobranchus cariniferus (Gray, 1843) Spirobranchus coronatus Straughan, 1967 Spirobranchus corrugatus Straughan, 1967 Spirobranchus decoratus Imajima, 1982 Spirobranchus dendropoma Mörch, 1863 Spirobranchus eitzeni Augener, 1918 Spirobranchus gardineri Pixell, 1913 Spirobranchus giganteus (Pallas, 1766) Spirobranchus incrassatus Krøyer in Mörch, 1863 Spirobranchus kraussii (Baird, 1865) Spirobranchus lamarcki (Quatrefages, 1866) Spirobranchus latiscapus (Marenzeller, 1885) Spirobranchus lima (Grube, 1862) Spirobranchus maldivensis Pixell, 1913 Spirobranchus minutus (Rioja, 1941) Spirobranchus murrayi Pillai, 2009 Spirobranchus nigranucha (Fischli, 1903) Spirobranchus paumotanus (Chamberlin, 1919) Spirobranchus polycerus (Schmarda, 1861) Spirobranchus polytrema (Philippi, 1844) Spirobranchus pseudopolytremus Pillai, 2009 Spirobranchus richardsmithi Pillai, 2009 Spirobranchus spinosus Moore, 1923 Spirobranchus taeniatus (Lamarck, 1818) Spirobranchus tenhovei Pillai, 2009 Spirobranchus tetraceros (Schmarda, 1861) Spirobranchus triqueter (Linnaeus, 1758) Spirobranchus zelandicus Pillai, 2009 Spirobranchus zibrowii Pillai, 2009
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