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The flabellids are known from the Early Cretaceous (about 135 million years ago) to the Recent, and are widespread in today's oceans from the North Sea to continental Antarctica. They range from depths from 0 to 3200 meters and from temperatures of -1°C (continental Antarctica) to the tropics. They are exclusively azooxanthellate. Flabellids range in size from the small Falcatoflabellum, which is only 3 mm in greater diameter and 10 mm in height, to Flabellum impensum, which is one of the largest solitary Scleractinia, measuring up to 128 mm in greater calicular diameter and 80 mm in height. One hundred three Recent species are known in 11 genera, most of these (73) occurring in two speciose genera: Flabellum and Truncatoflabellum, and the rate of description of new species shows no decline (Cairns et al., 1999). The flabellids are better represented in the fossil record, there being almost twice as many fossil species as Recent (Cairns, 1989a).
Left (top): Truncatoflabellum candeanum: The neotype specimen, including both anthocaulus (basal) and anthocyathus (distal) stages, collected from the Philippines (depth 194 m). Greater calicular diameter 18 mm (from Cairns, 1989a). Middle: Flabellum apertum: Calicular view of a skeleton collected from the Macquarie Ridge (depth 1647 m), an example of a free-living flabellid. Greater calicular diameter 27 mm. Copyright © 2002 S. D. Cairns. Right (bottom): Rhizotrochus typus: Side view of a skeleton collected from the Philippines (depth 124 m). This genus is characterized by tubular hollow basal rootlets that help attach the coral to the substrate. Height of corallum 43 mm. Copyright © 2002 S. D. Cairns
Flabellids are exclusively solitary in growth form -- never forming colonies -- but certain genera reproduce asexually by transverse division (Cairns, 1989b) and budding from the thecal edge. The corallum of many flabellids is fan-shaped, as implied by the root of its name (flabellum, Latin for a small fan), having a calice elliptical in cross section. There are as many attached as free living forms, the former sometimes attached by contiguous or noncontiguous, hollow rootlets. The coralla of those genera characterized by transverse division usually bear several pairs of thecal edge spines that do not reach the substrate. Some genera are hosts for the galls of ascothoracidan Crustacea (Grygier and Zibrowius, 1985), and one genus, Javania, is the host of the burrows of acrothoracican cirripeds (Cairns and Zibrowius, 1997).
Some other publications that include significant information regarding flabellids are: Cairns (1994), Gardiner (1902), Squires (1962, 1963, 1964), and Yabe and Eguchi (1942).