Oceanic Anglerfishes: Extraordinary Diversity in the Deep Sea

Preface

My purpose in writing this book is to bring together a diverse and previously scattered array of facts and data surrounding an astonishing assemblage of deep-water oceanic fishes commonly referred to as the devilfishes or seadevils, and scientifically known as the deep-sea ceratioid anglerfishes. Although rarely seen by anyone but a small handful of specialists, these remarkable animals are surprisingly abundant and widespread geographically, contributing significantly to the biodiversity of the marine ecosystem. The 160 currently recognized species of ceratioids dwell primarily in the inky black oceanic midwaters below 1000 m, where their existence depends on their ability to lure prey with a uniquely modified dorsal-fin spine equipped with a bioluminescent bait. While females may attain a length of a meter or more, the males of all included taxa are dwarfed, reaching only a small fraction of the size of the females. Equipped with large, well-developed eyes, a highly developed sense of smell, and a specialized nipping device at the tips of its jaws, the male’s sole purpose in life is to find a female. Once found, by a combination of visual and chemical cues, the male bites onto her body and in some cases remains there, only to become permanently joined to her body, the blood circulatory systems of the pair fusing so that the male becomes a sexual parasite on the female, and she, with ovaries, and now with testes as well, becomes a functional hermaphrodite . These adaptations alone, unique among fishes, and for that matter, among all animals, make these creatures one of the most intriguing groups of organisms for the lay person as well as the professional ichthyologist. They never fail to amaze any audience. This monograph is the result of some 40 years of research and study, beginning in 1967 as a first-year graduate student at the University of Southern California, and greatly benefiting over the next three decades from a close collaboration with the famous Danish ichthyologist and world expert on ceratioids , the late Erik Bertelsen of the Zoological Museum of the University of Copenhagen. Working either jointly or apart, Bertel (as he always wanted to be called) and I embarked on a program of biological study of the various families, genera, and species that has finally reached culmination here in this book. It is the result of a critical review of the world literature on the Ceratioidei, as well as a detailed examination of approximately 7,095 specimens (including 6,310 females, 785 males, and all extant type material) made available by the curators and staffs of some 90 institutions located around the world. Following an introduction and a history of our knowledge of the Ceratioidei , from the earliest discoveries to the present, an analysis of the characters that best differentiate the taxa is provided. This is followed by an overview of the biological diversity found within the group, focusing primarily on the families and genera, within which most of the morphological variation is found. An analysis of evolutionary relationships is then presented , followed by a discussion of geographic and depth distributions in relation to environmental factors, including temperature, salinity, oxygen, light, currents, and food supply. The known facts concerning bioluminescence and the functional morphology of luring, a unique mode of energy capture so highly developed in these fishes, are then summarized, followed by what is known about ceratioid locomotion, food and feeding, and reproductive biology. Finally, in Part Two, a classification of the suborder is provided, along with definitions and a synopsis of the methods employed in this part of the study, followed by evidence for the recognition of the 160 species of ceratioids, including synonymies, diagnoses, descriptions , and keys to facilitate their identification. In some ways this is a biosystematic monograph, designed to satisfy the needs and interests of students and professionals in ichthyology ; but to a greater extent I hope that these fascinating creatures have been presented in such a way that this book will be enjoyed by all those who find excitement in the wonders of the natural world. PREFACE ix This page intentionally left blank ...