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No place on earth can compete with the enormity of physical and biological constraints imposed on life in the deep oceanic midwaters. With temperatures near freezing, the absence of solar radiation, inconceivable pressures from the weight of water above, and biomass so low that meals are far and few between, it is almost inconceivable that animals could occupy this vast and forbidding habitat (Fig. 1). Yet fishes are there in surprising profusion, having adapted to these extreme limitations in a host of bizarre and unpredictable ways. Few groups, however, are as prolific and spectacular as the deep-sea ceratioid anglerfishes. Ceratioids are part of a much larger assemblage—an order of teleost fishes called the Lophiiformes—nearly all of which share a peculiar and unique mode of feeding characterized most strikingly by the structure of the first dorsal-fin spine (called the “illicium”), placed out on the tip of the snout and modified to serve as a luring apparatus to attract prey. The 18 families, 66 genera, and approximately 323 living species of the Lophiiformes are distributed among five suborders (Pietsch, 1984): the Lophioidei (Caruso, 1981, 1983, 1985, 1986; Caruso and Bullis, 1976; Caruso and Suttkus, 1979), Antennarioidei (Last et al., 1983, 2007; Pietsch and Grobecker, 1987), Chaunacoidei (Caruso, 1989a, 1989b), Ogcocephaloidei (Ochiai and Mitani, 1956; Bradbury, 1967, 1980, 1988, 1999; Endo and Shinohara, 1999), and deep-sea Ceratioidei (Fig. 2). The most phylogenetically derived of these suborders is the Ceratioidei, distributed throughout the world’s oceans below a depth of 300 m (Pietsch, 1984; Pietsch and Orr, 2007). With 160 species, it constitutes by far the most species-rich vertebrate taxon within the bathypelagic zone and below (Fig. 1), containing more than twice as many families and genera and more than three times the number of species as the whalefishes—suborder Cetomimoidei—the next most species-rich deep-sea vertebrate taxon (see Paxton, 1998; Herring, 2002). At the same time, new species are being added to the suborder at a steady if not increasing rate. Members of the group differ remarkably from their lessderived , bottom-living relatives by having an extreme sexual dimorphism (shared by all contained taxa) and a unique mode of reproduction in which the males are dwarfed—those of some linophrynids, adults at 6 to 10 mm standard length, competing for the title of world’s smallest mature vertebrates (see Winterbottom and Emery, 1981; Roberts, 1986; Weitzman and Vari, 1988; Kottelat and Vidthayanon, 1993; Watson and Walker, 2004; Pietsch, 2005b; Kottelat et al., 2006; Guinness World Records, 2007:41)—and attach themselves (either temporarily or permanently) to the bodies of relatively gigantic females (Figs. 3, 4). In Ceratias holboelli, the Northern Giant Seadevil, where the most extreme examples are found, females may be more than 60 times the length and about a half-amillion times as heavy as the males (Bertelsen, 1951; Pietsch, 1976, 1986b, 2005b). The males lack a luring apparatus, and those of most species are equipped with large well-developed eyes (Munk, 1964, 1966) and huge nostrils (Marshall, 1967a, 1967b), the latter apparently used for homing in on a femaleemitted , species-specific chemical attractant (Bertelsen, 1951; Pietsch, 1976, 2005b; Munk, 1992). Normal jaw teeth of males are lost during metamorphosis but are replaced by a set of pincerlike denticles at the anterior tips of the jaws for grasping and holding fast to a prospective mate (Figs. 5, 6). In some taxa, attachment is followed by fusion of epidermal and dermal tissues and, eventually, by an apparent connection of the circulatory systems so that the male becomes permanently dependent on the female for blood-transported nutrients, while the host female becomes a kind of self-fertilizing hermaphrodite (Regan, 1925a, 1925b, 1926; Parr, 1930b; Regan and Trewavas, 1932; Bertelsen, 1951; Pietsch, 1975a, 1976, 2005b; Munk and Bertelsen, 1983; Munk, 2000). Permanent attachment is usually accomplished by means of separate outgrowths from the snout and tip of the lower jaw of the male, both of which eventually fuse with the skin of the female . In some species, a papilla of female tissue protrudes into the mouth of the male, sometimes appearing to completely occlude the pharynx. The heads of some males become broadly fused to the skin of the female, extending from the tip of the O N E Introduction and Historical Perspective The medieval imagination, rioting in strange imps and hobgoblins , could hardly have invented anything more malevolent in appearance than the ceratioids or deep-sea anglerfishes, sometime called black devils. Naturally enough, these black...

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