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Members of the subclass Octocorallia, sometimes referred to as the subclass Alcyonaria, are sedentary, colonial, exclusively polypoid Anthozoa, each with feeding polyps bearing 8 unpaired, pinnate tentacles and 8 gastric mesenteries . All species have numerous, usually microscopic, calcareous (calcitic) skeletal elements called sclerites in their tissue; most arborescent species also have a calcified (aragonitic or calcitic) or collagenous skeleton that provides axial support for the colony. In the vernacular, octocorals are known as gorgonians, soft corals, sea fans, sea whips, sea feathers, sea pens, bamboo corals, and precious corals (Cairns et al. 2002). An illustrated synthesis of the classification, morphology , biology, and methods of study of this subclass was published by Bayer (1956) just 2 years after the first edition of the Gulf checklist, and remains the modern starting point for serious study of the group. Other seminal works on this subclass include an illustrated key to all genera (exclusive of the pennatulids; Bayer 1981b); a bibliography of over 1400 octocoral references (Bayer 1981a), which includes 110 references to octocorals of the western Atlantic; an illustrated trilingual glossary of morphological terms applied to octocorals (Bayer, Grasshoff, and Verseveldt 1983); and a key and descriptions of the higher taxa of the order Pennatulacea (Williams 1995). Bayer (1954: 279) prefaced his account of the Gulf of Mexico octocorals by saying: “The Alcyonaria of the Gulf of Mexico are little known.” Despite an addition of 71 species to that checklist herein, this statement is still true. There has never been a concerted effort to study and synthesize information on the octocorals of the Gulf, most of the new information since 1954 having resulted from incidental reports from studies of other regions (see checklist , references). Nonetheless, one of the richest sources of post-1954 records for the Gulf is Bayer (1958), who listed many species collected by the M/V Oregon from relatively deep water of the northern and eastern coasts of the Gulf. Bayer’s (1961) revision of the shallow-water octocorals of the West Indian region is also a rich source of additional records of most of the shallow-water spe321 13 Octocorallia (Cnidaria) of the Gulf of Mexico Stephen D. Cairns and Frederick M. Bayer  Octocorallia. After Wright and Studer 1889. 322 ~ Octocorallia (Cnidaria) well-documented account of the octocorals of the Gulf of Mexico. Octocorals are exclusively marine and are ubiquitous in that environment, occurring from the Arctic to the Antarctic and at depths from the intertidal to over 6000 m deep. They are a highly diverse group, estimated to consist of about 2900 species, 278 of which are known to occur in the western Atlantic. Of the 278 species, 162 (and an additional 2 subspecies or varieties) are reported herein from the Gulf of Mexico, an addition of 71 species from the 91 reported in 1954 (Bayer 1954), constituting 58% of the western Atlantic and 5.6% of the world fauna. Although octocorals are common in shallow reef environments, and dead colonies can occasionally be seen washed up on beaches, 77 of the Gulf taxa (48%) live in deep water, occurring below 200 m. Among the 4 quadrants or sectors of the Gulf (southeastern , northeastern, northwestern, and southwestern), octocorals are most diverse in the geographically smallest southeastern sector (115 species, 71%). This sector includes the Florida Keys, the northwestern coast of Cuba, and the eastern Campeche Bank, which together provide a variety of shallow- and deepwater habitats, as well as constituting a confluence of tropical elements from the Caribbean and warm temperate elements from the north. Thus, the octocoral species found here include tropical species as well as southern range extensions of usually more northern species. Eighty-two species are known from the northeastern quadrant, 58 from the northwestern quadrant, and only 15 from the southwestern quadrant. The small number from the western Gulf cies known to occur in the Gulf of Mexico. A field guide to the commoner shallow-water species of the Gulf and Caribbean was published by Cairns (1977), and a listing of the 121 shallow-water (less than 200 m) North American species was published by Cairns et al. (2002). Grimm and Hopkins (1977) listed 13 shallow-water species from the Florida Middle Grounds (northeastern quadrant), and Rezak, Bright, and McGrail (1985) listed 20 species from the outer continental shelf of the northwest quadrant, including 5 new records for the Gulf. Cairns (2001), Bayer (2001), and Cairns and Bayer (2002, 2003, 2004a, b) are now engaged in revising the deepwater western Atlantic octocorals, including records...

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