ABSTRACT
The species that comprise class Chondrichthyes exhibit a wide diversity of reproductive strategies, but they all have internal fertilization and a relatively small number of large offspring. Although the Chondrichthyes are comprised of two sister taxa (Elasmobranchii and Holocephali), the number of extant elasmobranchs is considerably larger, and this chapter emphasizes the reproductive biology of this group. The diversity of reproductive modes found within the elasmobranchs is often reected in reproductive anatomy and tends to be related to how the embryo receives nourishment. Historically,
elasmobranch reproductive modes were divided into oviparity, aplacental viviparity, and placental viviparity; however, the aplacental viviparous group is problematic, as it includes a diversity of unrelated reproductive strategies and this classication will not be used. Reproductive modes in this chapter are distinguished based on the maternal contribution to development. Recent research that emphasizes the importance of maternal contributions via mucoid histotroph and the continuum in reproductive strategies from yolk-sac viviparity to oviparity and mucoid histotrophy to placentotrophy and oophagy will be discussed. This research suggests that dividing species into discrete modes of reproduction while convenient may not always be realistic.
