| Chondrichthyes | |
|---|---|
| |
| Photo of Tiger Shark (Galeocerdo cuvier) | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| clade: | Chondrichthyes |
| Members | |
| |
Chondrichthyes is a class of fishes, referred to as cartilaginous fish or chondrichthyians, that originated in the Silurian period and lives to this day. This includes all jawed fish that have cartilage for the skeletal system rather than true bones. Chondrichthyes includes all sharks, rays, skates, chimeras, and sawfish. Famous extant chondrichthyians include the Great White Shark (Carcharodon carcharias), the Whale Shark (Rhincodon typus), and the Common Stingray (Dasyatis pastinaca). Popular extinct chondrichthyians include Otodus megalodon, Helicoprion, and Hybodus.
Chondrichthyians are some of the oldest animals still found today, with some remaining unchanged much longer than the average animal. This clade is very diverse in body plan, diet, and phylogenetic attributes and have survived 5 mass extinctions.
Description[]
Chondrichthyians are quite unique from other fish clades and have attributes that make them easy to identify. Its most famous trait that earned the clade its place is the skeletal system being comprised mostly of cartilage excluding teeth. Since they lack bone marrow, chondrichthyians grow red blood cells in the spleen and epigonal organs (excluding holocephalans who don't have the latter).
Most members of this clade are extremely electroreceptive, sporting sensitive organs such as the Ampullae of Lorenzini along with a lateral line system like in other fish clades. Rather than a swim bladder like in bony fish, chondrichthyians use an oil-filled liver to control buoyancy. These fish have two-chambered hearts and all fins are paired excluding the caudal fin.
As for external visual distinction, chondrichthyians excluding chimeras have 5-7 open gill slits unlike a bony fish's operculum which covers the gills. Generally this clade features tooth-shaped scaly skin that protects and reduces drag for members of the clade; all scales face backwards, making them feel like sandpaper in one direction but smooth the other. Some species did lose this aspect such as most free-swimming rays and chimeras, but these are the exception rather than the rule.
Classification[]
Phylogenetic tree with placement of Chondrichthyes with other clades; division of Chondrichthyes into smaller clades
Chondrichthyes is a class of vertebrate fish classified under Gnathostomata (jawed fish). The closest clade to the class is the extinct paraphyletic clade Acanthodii (which includes all stem cartilaginous fish not included in the main class), but the closest living clade to Chondrichthyes is the superclass Osteichthyes (includes all bony fish and tetrapods).
There are currently 2 subclasses of the clade Chondrichthyes:
- Elasmobranchii: includes all sharks, rays, skates, and sawfish. Houses 3 superorders, being Galeomorphii (houses ground sharks, carpet sharks, and mackerel sharks), Squalomorphii (houses frilled sharks, sawsharks, and angel sharks), and Batoidea (houses all rays, sawfishes, and skates). Known fully extinct orders include Protospinaciformes, Synechodontiformes, Hybodontiformes, and Ctenacanthiformes. Famous extinct elasmobranchs include the popular Otodus megalodon, crow shark (Squalicorax), and Cretoxyrhina.
- Holocephali: Mostly extinct subclass with only one surviving order, housing ghost sharks and elephant fish. Contains 13 extinct orders. Famous extinct holocephalans include Helicoprion.