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The Ceratioidei, containing all the deep-sea anglerfishes, is by far the most species-rich vertebrate taxon within the bathypelagic realm, a vast, largely empty body of cold, nutrient-poor water that constitutes the world’s oceans below 1000 m. When compared to other vertebrate groups that inhabit these waters, nothing comes close to anglerfishes for variety and number of forms. The present chapter is devoted to a demonstration of this surprisingly rich diversity, providing evidence for the recognition of 11 ceratioid families, 35 genera, and 160 species. It begins with a concise summary of the most significant distinguishing characters of the suborder (a “diagnosis,” to use the scientific term) to serve as evidence that all subtaxa of the group are united in monophyly, that is, that all the diverse lineages of deep-sea anglerfishes evolved from a single common ancestor . This is followed by a brief synopsis of the families—an illustrated key of sorts that serves as a means of identification of each major lineage, while at the same time providing a better understanding of the family and generic accounts that follow. Suborder Ceratioidei Gill DISTINGUISHING CHARACTERS Ceratioid fishes are recognized as one of five suborders of anglerfishes that together constitute the teleost order Lophiiformes . They are uniquely different and evolutionarily derived in a host of ways that clearly separate them from all other anglerfishes and, for that matter, from all other fishes. First and foremost, monophyly for the Ceratioidei is supported by extreme sexual dimorphism, an extraordinary difference between males and females of all included taxa that has no comparison in other organisms, at least not among vertebrate animals. This difference is much more than size. Along the evolutionary pathway toward male dwarfism, natural selective pressures have affected every organ system of the male body, resulting in an almost total structural reorganization. What can be most easily observed in the males, in addition to their small size, is the loss of the luring apparatus, the presence of denticular bones—found in no other fishes and used to grasp and hold fast to a prospective mate—and the greatly enlarged nostrils and eyes. But there are also the numerous unseen and poorly understood physiological and behavioral adaptations that allow for a unique mode of reproduction: the mechanisms that led to mate location and selection, male attachment to females, sexual parasitism, and the hormonal communication that in turn mediates simultaneous gamete maturation and subsequent spawning (see Reproduction and Early Life History, Chapter Eight). Monophyly for the Ceratioidei is also supported by the mutual loss of a number of bony parts that are well developed in other anglerfishes. In their transition from a benthic life-style to a pelagic midwater existence, ceratioids as a group have lost the pelvic fins and have undergone a drastic repositioning and reduction in size of the pectoral fins, all resulting in the loss of the benthic ambulatory function that is so highly developed in the shallow-water, bottom-living ancestors of ceratioids, the goosefishes, frogfishes, batfishes, and their allies (see Fig. 1). Finally, reflective of the nutrient-poor environment in which they live, ceratioid monophyly is supported by a general trend toward the reduction of body density through an overall decrease in skeletal ossification and the extent of muscle development, as well as the infusion of lipids throughout. In short, there is no reason to doubt that ceratioids have diverged and evolved together from a single common lophiiform ancestor. For more exhaustive diagnoses as well as descriptions of females, males, and larvae of the suborder, see Part Two: A Classification of Deep-Sea Anglerfishes. The suborder contains 11 families, differentiated as follows: SYNOPSIS OF CERATIOID FAMILIES The following key is provided to allow for the placement of ceratioids into the proper family. Each entry consists of a combination of features that together serve to differentiate each family. It works by progressively eliminating the most morphologically unique family; for that reason it should always be entered from the beginning. All character states listed for each family must correspond to the specimen being keyed; if not, the user should proceed to the next set of character states. The emphasis here, and throughout this chapter, is on the more common and much better known females, which are, with few exceptions, the defining entities for all ceratioid families, genera , and species. For a full overview of both genders, as well as larvae, including traditional dichotomous keys to the identification of all taxa, see Part Two: A Classification of...

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