ABSTRACT
The extant holocephalans belong to the Subclass Euchondrocephali, a group of chondrichthyan shes dened by the presence of a primitive autodiastylic suspensorium with ethmoid region shifted forward. Closely related to the holocephalans, and also grouped within the Euchondrocephali, are the extinct iniopterygians as well as a group of enigmatic euchondrocephalan forms known collectively as the Paraselachii (Grogan and Lund, 2004; Grogan et al., 1999; Lund and Grogan, 1997). The holocephalans are characterized by a unique form of holostyly derived from the primitive
autodiastylic condition in which the upper jaw fuses to the neurocranium, the ethmoid region is extended anteriorly, and the branchial arches are shifted anteriorly to lie below the cranium (Didier, 1995; Grogan et al., 1999). In addition, the holocephalans exhibit a trend toward reduced number of tooth elements and the formation of nonreplaceable, hypermineralized tooth plates (Didier, 1995; Grogan and Lund, 2004; Lund and Grogan, 1997; Maisey, 1986). The living holocephalans and their closest fossil relatives belong to the Order Chimaeriformes, which includes three families-Callorhinchidae, Rhinochimaeridae, and Chimaeridae-each of which is distinguished by a unique snout morphology (Figure 4.1). The living holocephalans as a group are commonly
CONTENTS
4.1 Introduction ..................................................................................................................................................................... 97 4.2 General Morphological Features .................................................................................................................................. 99
4.2.1 External Features ................................................................................................................................................ 99 4.2.1.1 Lateral Line Canals .............................................................................................................................. 99 4.2.1.2 Fins and Fin Spines ............................................................................................................................ 102
4.2.2 Skeleton .............................................................................................................................................................. 103 4.2.3 Tooth Plates ........................................................................................................................................................ 103 4.2.4 Secondary Sexual Characteristics .................................................................................................................. 104
4.3 Classication and Zoogeography ............................................................................................................................... 105 4.3.1 Classication ...................................................................................................................................................... 105
4.3.1.1 Callorhinchidae .................................................................................................................................. 105 4.3.1.2 Rhinochimaeridae ............................................................................................................................. 106 4.3.1.3 Chimaeridae ....................................................................................................................................... 108
4.3.2 Zoogeography ................................................................................................................................................... 108 4.4 Life Histories ................................................................................................................................................................. 109
4.4.1 Reproduction and Development..................................................................................................................... 109 4.4.2 Age and Growth .................................................................................................................................................110 4.4.3 Diet and Feeding Ecology ................................................................................................................................111 4.4.4 Habitat Association .......................................................................................................................................... 112
4.5 Fisheries and Conservation ..........................................................................................................................................113 4.5.1 Fisheries ...............................................................................................................................................................113 4.5.2 Conservation.......................................................................................................................................................114
