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[[ Genus Squatina Dumeril ZBK ]]
Squatina Dumeril, 1806 ZBK is a monotypic genus within the family Squatinidae (Bonaparte, 1838). Although morphologically similar to batoids, squatinids are distinct from true batoids in that the squatinids have lateral gill openings, pectoral fin lobes that are free lateral to the gills, and possess a lower caudal fin lobe that is longer than the upper caudal lobe. Within the genus these sharks can be difficult to distinguish due to the lack of well defined characteristics. Adding to the confusion in the literature are the inadequate original descriptions of many species.
Sixteen valid species are recognized worldwide, with four reported to occur in the western North Pacific (WNP; Compagno et al., 2005). These four species include Squatina formosa Shen and Ting, 1972 ZBK , S. japonica Bleeker, 1858 ZBK , S. nebulosa Regan, 1906 ZBK , and S. tergocellatoides Chen, 1963 ZBK . Distinctions among these four WNP species hinge upon the nasal barbel shape, interorbital and interspiracle distances, ocellus patterns, number of dermal folds about the mouth, and the presence of midback thorns (Lindberg & Legeza, 1967; Shen & Ting, 1972; Nakabo, 2002). However, specific identification is hard to assign to individuals because many of these characters are difficult to distinguish, and many characters currently used are susceptible to damage during collection or from preservation. Additionally, inadequate original descriptions for some species and confusion within the subsequent literature have further obscured definitive characters among the WNP species. Because members of this genus are frequently targeted in fisheries in an area that has sparsely recorded catch information, and congeners are particularly sensitive to fishing pressure (Gaida, 1997; Stevens et al, 2000), it is imperative that adequate descriptions are available to identify individual species.
During two field expeditions to Taiwan, one of us (DAE) observed at least four species of Squatina ZBK that were frequently landed at fish markets around Taiwan. Attempts to identify the various species were often hampered by a lack of adequate fish keys and descriptive characters for the various Squatina ZBK species observed. Furthermore, we had the opportunity to examine the holotype and three paratypes of S. formosa ZBK as well as collect additional material.
Using this information, we provide a detailed redescription of three of the species, S. formosa ZBK , S. japonica ZBK , and S. nebulosa ZBK , with new material from Japanese and Taiwanese waters. In addition, we supply a list of important key characters for distinguishing all known WNP squatinids, especially to facilitate identification of the two most similar species, S. formosa ZBK and S. nebulosa ZBK .