OCEA 2000X Lecture Notes - Lecture 4: Chondrichthyes, Osteichthyes, Osmoregulation
31 Aug 2016
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Document Summary
Vertebrates (phylum chordata) dominate the higher trophic levels. Vertebrates are not nearly as numerically diverse as invertebrates, comprising only 3-5% of the. The evolution of a backbone, however, permitted the evolution more complex and powerful modes of locomotion. The fish are the largest group of vertebrates, representing 30,000 of the 55,000 described species. Fish evolved early in the history of complex life. The most primitive fish are the jawless agnathans - 2 groups: hagfish and lampreys. The cartilaginous fishes (chondrichthyes) are a larger, more important group of fishes. Two major subgroups: the elasmobranchs includes the sharks, skates, and rays. Sharks come in a range of shapes and sizes. Share some familiar common features: heterocercal caudal fin, anal fin, pelvic fin, first and second dorsal fin, pectoral fin, denticles (scales), spiracle, mouth, 5-7 gill slits. Skates and rays have body forms and lifestyles that differ significantly from the sharks: the chondrichthyans have several distinguishing features:
