Overview
Chondrichthyan fishes have cartilaginous skeletons (which may become calcified in large species, but seldom ossified), a skull that lacks sutures, teeth that are not fused to jaws and are replaced serially, horny unsegmented soft fin rays epidermal in origin, no swim bladder, a spiral valve in the intestine, fertilisation that is internal in modern forms (males with claspers that are inserted into female cloaca and oviduct), and an embryo encapsulated in a leather-like case that may be laid externally (oviparous) or retained internally (viviparous, ovoviparous).
Two main evolutionary lines are recognised: the holocephalans (chimaeras or ghost sharks) and elasmobranchs (sharks and rays). Each is a monophyletic group, with holocephalans the most primitive. A good fossil record exists from the Devonian onwards, usually represented by teeth.
Currently, at least 106 species (in 59 genera) of cartilaginous fishes are recognised in New Zealand waters, with 29 (27.4%) being endemic. However, the known number of chondrichthyan fishes from the New Zealand EEZ increases annually, with better sampling of existing fisheries and as new areas and habitats are investigated. The most speciose families (as currently classified) are the kitefin sharks (Dalatiidae, 22 spp.), skates (Rajidae, 13 spp.) and catsharks (Scyliorhinidae, 11 spp.). The last two also have high levels of endemism. New Zealand chondrichthyan fishes have many taxonomic problems that in some cases require regional or global revisions to resolve. Incredibly, over 25% of New Zealand’s cartilaginous fishes are scientifically unnamed or not able to be accurately identified at present.