ANTIPATHARIA, Milne-Edwards & Haime, 1857

Brugler, Mercer R., Opresko, Dennis M. & France, Scott C., 2013, The evolutionary history of the order Antipatharia (Cnidaria: Anthozoa: Hexacorallia) as inferred from mitochondrial and nuclear DNA: implications for black coral taxonomy and systematics, Zoological Journal of the Linnean Society 169 (2), pp. 312-361 : 313-314

OF THE ANTIPATHARIA

Until a recent study by Balinski, Sun & Dzik (2012), only a single antipatharian genus, Leiopathes , had been identified from the fossil record, and only two specimens were known, dated from the Miocene and Holocene ( Wells & Hill, 1956). Balinski et al. (2012) located phosphatic remains of the putative antipatharian Sinopathes reptans from the early Ordovician Fenxiang Formation (470 Mya) in Hubei Province, southern China. Based on a number of observations that are not consistent with Recent black corals [antipatharian spines do not form distinct, continuous longitudinal ridges, are not tubular in structure, and do not have a central canal (only axial structures – stem and branches – have a central canal)], we hypothesize that the fossils described by Balinski et al. (2012) are more representative of a cnidarian closely related to the hydrozoan Hydractinia than to an antipatharian. Because the black coral skeleton is unmineralized and composed primarily of laminar chitin complexed with protein, it is not readily fossilized ( Hyman, 1956; Balinski et al., 2012).

Early black coral taxonomy was based solely on the naked axial skeleton, as the coenenchyme and delicate polyps rarely survived the harsh handling conditions of deep-water trawls and dredges. In the 10th edition of Systema Naturae, Linnaeus (1758) placed three species of black coral in the genus Gorgonia Linnaeus, 1758 ( G. abies , G. aenea , and G. spiralis ). However, Pallas (1766) established a new genus, Antipathes (Anti ‘against’; pathos, ‘disease’) for those species displaying a spiny axial skeleton and non-spiculated tissue. Marsigli (1725) was one of the first to publish an illustration of the axial spines along an antipatharian branch. However, it was not until Ellis & Solander (1786) that the first drawings of black coral polyps (or zooids) were published. Ehrenberg (1834) used the term ‘Antipathina’ to describe a family-level taxon within the order Scleropoda (class Bryozoa). Opresko & Baron-Szabo (2001a) noted that the usage of Antipathina as a family-level taxon takes priority over subsequent designations even though Ehrenberg used the term to describe a bryozoan that was encrusting a black coral skeleton. Milne-Edwards & Haime (1857) and Lacaze-Duthiers (1865) were the first to recognize the Antipatharia as a distinct order. Brook (1889), using material collected during the Challenger expedition, erected 11 genera and described 41 new species based on internal and external polyp morphology [i.e. the arrangement of polyps along/around the skeletal axis, size and position of tentacles around the oral cone (mouth) and the number of ‘septa’ (now referred to as mesenteries)]. Branched forms (Divisae) were separated from unbranched forms (Indivisae), and ‘monomorphic’ zooids (Antipathinae) from those considered as ‘dimorphic’ ( Schizopathinae ). Later work by Thomson (1905) and van Pesch (1914) discredited this ‘dimorphism’, showing that the modification simply represented specialization of the polyp, with reproductive tissues isolated in the lateral chambers of the elongated coelenterons. Schultze (1896) divided the Antipathidae solely on the number of ‘septa’ in the polyp, creating the Hexamerota (lacking secondary ‘septa’), Dekamerota (two pairs of secondary ‘septa’), and Dodekamerota (three pairs of secondary ‘septa’). In 1914, van Pesch published a report from the Siboga Expedition , splitting the Antipathidae into two subfamilies based on the presence (Heterotaeniales) or absence (Homoeotaeniales) of secondary ‘septa.’ For the next 58 years, the Antipatharia remained largely unrevised.

In the late 1960s, Opresko began re-evaluating taxonomic characters used by past workers, including Pallas (1766), Esper (1788), Milne-Edwards & Haime (1857), Verrill (1864), Gray (1868), de Pourtalès (1868, 1871, 1874, 1878, 1880), Duchassaing (1870), Brook (1889), Schultze (1896) and van Pesch (1914) ( Opresko, 1972, 1974; see also Opresko & Baron-Szabo, 2001a), leading to a modern reinterpretation of the group. A clear taxonomic hierarchy at the generic and familial levels was missing, in part because of the incorrect inclusion within the order of several non-antipatharians: the zoanthid Savalia Brito & Ócaña, 2004 , which has an antipatharian-like axis ( Carlgren, 1895), the octocoral Dendrobrachia fallax Brook, 1889 , which has axial spines ( Opresko & Bayer, 1991), and the hydroid Tropidopathes saliciformis Silberfeld, 1909 , where apophyses of the hydrocauli were mistakenly identified as antipatharian spines ( Opresko & Baron-Szabo, 2001b). Opresko followed Schultze (1896) in defining antipatharian families based on the number of mesenteries in the polyp ( Cladopathidae : 6; Aphanipathidae , Myriopathidae , Schizopathidae and Stylopathidae : 10; Leiopathidae : 12), but also considered the size and morphology of the polyps, and the morphology of the axial spines. Genera within families are differentiated by the gross morphology of the corallum, and species within genera by the size and morphology of the polyps and the size, shape, and ornamentation of the axial spines ( Opresko, 2003b; an illustrated key to the families is provided in Appendix 1). Only recently has the morphology of living polyps been used to infer taxonomic relationships (i.e. the size and dimension of the polyp along both the transverse and the sagittal axis, as well as the shape and relative length of the sagittal versus lateral tentacles, both of which are often obscured in preservation; e.g. Opresko, 2005a; Wagner et al., 2010a).

Opresko established three new families ( Aphanipathidae Opresko, 2004 , Myriopathidae Opresko, 2001b , and Stylopathidae Opresko, 2006 ) and revised two others ( Cladopathidae Kinoshita, 1910 and Schizopathidae Brook, 1889 ) (Opresko, 2001b, 2002, 2003b, 2004, 2006; Opresko & de Laia Loiola, 2008; see also Opresko, 2005b). The families Antipathidae Ehrenberg, 1834 , historically considered a taxonomic dumping ground, and Leiopathidae Haeckel, 1896 , a monogeneric family, are currently undergoing revision. Opresko (1998) suggested that the Leiopathidae , the only family characterized by a full complement of mesenteries (N = 12) and reduced or absent spines on the stem and larger branches of the corallum, might prove to be the most primitive family within the Antipatharia and merit higher taxonomic status.