Sharks, Skates, and Rays: The Biology of Elasmobranch Fishes
SHARKS, SKATES, AND RAYS: THE BIOLOGY OF ELASMOBRANCH FISHES. William C. Hamlett, ed. 1999. Johns Hopkins University Press, 2715 North Charles Street, Baltimore, Maryland 21218-4363. ISBN 0-8018-6048-2. 515 p. $115.00 (hardcover).—The last decade of the millennium has witnessed a remarkable shift in the public perception of sharks and their batoid relatives. Because of an increased awareness that sharks may, in fact, be beneficial to the ocean ecosystem, the Hollywood image that sharks are lying in wait for unsuspecting beachgoers has undergone a dramatic metamorphosis. In addition to numerous television documentaries, much of the credit for the renewed awareness must be given to the dozen or so books published during the past 15 years providing vivid glimpses of the natural history of this incredible group of animals. With the exception of several nicely organized symposium proceedings focusing on specific aspects of elasmobranch biology, it has been some time since a technical offering encompassing virtually all of the functional anatomy found in sharks has been attempted. The volume reviewed here is such an undertaking.
In his Preface, William Hamlett implies that his book might serve as a successor to the 1922 Frank Daniel classic, The Elasmobranch Fishes, which reappeared as a second edition in 1928 and as a third, revised edition in 1934. In fact, on first glance, the Tables of Contents in the Hamlett volume and the Daniel editions are virtually identical, from the topics selected to the relative order of their presentation. In building on the Daniel legacy, Hamlett, by his own admission, has decided to focus on a systems approach, restricted to anatomy and physiology. For the most part, the contributors assembled have succeeded in restating and updating the knowledge of elasmobranch functional anatomy originally offered by Daniel. A refreshing variation on the theme is the concerted effort by the contributors to address the batoid literature whenever possible. Although attention to the batoid relatives is certainly welcomed, its inclusion undoubtedly led to the unfortunate choice of Sharks, Skates, and Rays as the book's title. This title may be a source of confusion to unknowing buyers who are familiar with the popular Gilbert, Mathewson, and Rall volume of the same name, also published, coincidentally, by the Johns Hopkins University Press.
The volume at hand is organized into 16 chapters plus an appendix containing a checklist of living elasmobranchs. The chapters do not conform to any one particular format, allowing each contributing author to cover the topic in a fashion of his or her choosing. The chapters are enhanced with a variety of drawings, graphs, or plots, and many contain black-and-white photographs to illustrate the anatomy, histology, or ultrastructure.
The first chapter, “Systematics and Body Form,” is tremendously expanded over Daniel's version. In tackling this complicated topic, Leonard Compagno admits “… that there are at least as many classifications … of cartilaginous fishes as authors who have published them.” Nevertheless, Compagno is an excellent choice to provide his version and does so in a clearly defined framework of recognized problem areas in neoselachian classification and phylogeny and appropriately includes references that provide alternative interpretations. The bulk of the chapter is a review of the extant neoselachian orders and families and includes the batoids. The illustrations are not intended as reproductions from his FAO Species Catalogue but are rather simplified, not-to-scale silhouettes that serve his purpose of stressing the variations in body form described in great detail in the accompanying text.
Chapter 2, “Integumentary System and Teeth,” is a nicely organized, well-documented, informative chapter, describing evolutionary, structural, and functional aspects of the skin, placoid scales, stomodaeal denticles and gillrakers, dermal fin rays, fin spines, and teeth. Authored by Norman Kemp, this chapter is highlighted with detailed line drawings and photographs, including histological sections, microradiographs, and electron micrographs, to illustrate his message. The section devoted to the teeth of elasmobranchs is especially noteworthy.
The third chapter, the second contributed by Leonard Compagno, provides a comprehensive account of the elasmobranch endoskeleton. In a descriptive style that is more detailed than is typically found in a comparative anatomy text, Compagno methodically depicts the numerous components of the axial skeleton, vertebral column, and appendicular skeleton for living sharks as well as living rays. As in his earlier chapter, Compagno's illustrations enhance the take-home message of the text. Through the use of idealized skeletal drawings, instead of the typical depiction of the spiny dogfish as a representative elasmobranch, concepts of endoskeletal variation among neoselachian sharks and rays are more easily conveyed.
Two chapters are devoted to the muscular system, chapter 4 concentrating on the gross anatomy and chapter 5 focusing on the microscopic anatomy and physiology. The first part of chapter 4, coauthored by Karel Liem and Adam Summers, assumes a rather classic approach to descriptive anatomy and includes crisp renderings of the usual somatic muscular perspectives. A refreshing addition is the inclusion of batoid somatic musculature illustrations. The highlight of this chapter is a thoroughly referenced section on functional morphology, documenting recent experimental efforts to relate muscular systems to their ultimate functions, including the mechanics of feeding, respiration, and locomotion.
In the second muscle chapter, Quentin Bone relates very nicely the information available on elasmobranch muscle fibers. The section on sharks is divided into well-documented and clearly illustrated discussions of microscopic anatomy, electrophysiology, and biochemistry, with obvious emphasis on the relationship of structure to function. A considerable portion of the chapter is devoted to batoid musculature, a topic that historically has received very little attention. In fact, the current knowledge is so sparse that much of this batoid section is unpublished material of the author, including informative comparisons between shark and batoid muscle fiber anatomy, innervation, and functional roles.
Chapter 6 is an extensively referenced account of the elasmobranch digestive system. Using photographs and detailed illustrations of gross anatomy, in combination with light and fluorescent micrographs, coauthors Susanne Holmgren and Stefan Nilsson have clearly summarized the organ arrangement, innervation, and endocrine control of the elasmobranch digestive process. The section devoted to the physiology of gut motility and blood flow is effectively presented, with x-ray photography and representative experimental data to illustrate various aspects of digestive tract physiology.
The seventh chapter, authored by Patrick Butler, describes the respiratory system as it relates to the morphology and blood circulation of the gills. With the exception of a 1992 reference to digital radiographic imaging of circulating blood, however, the information in this chapter appears to differ very little from that put forth in a 1988 review by the same author on the same topic, including essentially the same collection of drawings and photographs.
The next two chapters address the elasmobranch circulatory system. In chapter 8, Ramon Munoz-Chapuli provides a comparative discussion of the peripheral circulation across six elasmobranch taxa: three selachian and three batoid. The anatomical comparisons are elegantly presented through corrosion casts, many of which are included as photographs and provide a dramatic way to illustrate the differences. In chapter 9, Geoffrey Satchell addresses some of the “distinctive attributes” of elasmobranch circulation. Although discussions of the pseudobranch, cutaneous vessels, lateral abdominal veins, venous sinuses, hepatic vein sphincters, and various retial systems contributing to blood warming are appropriate for this chapter, the summary of the elasmobranch immune system is grossly outdated and, in many instances, inaccurate.
Among this book's finest chapters is chapter 10, simply titled, “Heart.” Not only has he contributed a thorough and clearly illustrated chapter, Bruno Tota has also compiled a comprehensive mix of the classic and contemporary (40 citations from the 1990s) literature pertaining to the elasmobranch heart and its function.
The 11th chapter, authored by Michael Hofmann, is a nicely presented, thoroughly documented anatomical description of the elasmobranch nervous system, with references to electrophysiology and function (behavior) whenever possible. The use of subdivided brain cross-sections, with a histologically stained half and an illustrated half showing locations of major nuclei, are particularly effective.
Chapter 12, coauthored by Horst Bleckman and Michael Hofmann, is a well-organized review of the anatomy, peripheral physiology, behavior, and neural connections for the handful of special senses, including chemical, visual, acoustic, hydrodynamic, tactile, electric, and magnetic reception, that have contributed greatly to the evolutionary success of the elasmobranch fishes. The extensive list of references is a nice blend of the classic and contemporary literature on the variety of these sensory topics.
A chapter on the rectal gland, contributed by Kenneth Olson, and a chapter on the urinary system, coauthored by Eric Lacy and Enrico Reale, focus on the strategies developed by elasmobranchs to maintain osmotic and ionic homeostasis. Both chapters are dominated by ultrastructure as the means to describe the physiological significance of the respective organs. Lacy and Reale, recognized experts on the functional morphology of the elasmobranch kidney, do a particularly nice job of sorting through the literature describing renal structure and function obtained from a variety of sharks, skates, and rays, from both marine and freshwater environments.
The final two chapters in the book address the female and male reproductive systems, respectively, and are contributed by volume editor William Hamlett, with Thomas Koob as coauthor on the female system. Both chapters are excellent summaries of the numerous reviews of elasmobranch reproduction that have appeared during the past few decades, with updated information from the current literature. References cited in both chapters are appropriately extensive.
In keeping with his stated intent to offer a resource of general introductory information with current technical citations, Hamlett has succeeded in compiling an extremely useful elasmobranch reference text for novices and experts alike. As a result, this volume can be recommended as a valuable addition to personal libraries, libraries at marine laboratories, and departmental libraries at teaching facilities offering courses in elasmobranch biology.