Cetacea Cetacea Cetacea () is a widely distributed and diverse clade of aquatic mammals that today consists of whales, dolphins, and porpoises. Cetaceans are carnivorous and finned. Most species live in the sea, some in rivers. The name is derived from the Latin "cetus" "whale", itself from the Greek κῆτος "kētos" "huge fish". There are around 89 extant species, which are divided into two groups or parvorders, the Odontoceti or toothed whales, a group of more than 70 species that includes the dolphins, porpoises, belugas, narwhals, sperm and beaked whales, and the Mysticeti or baleen whales, of which there are now
Toothed belt in their reinforcement. Toothed belts have two failure modes, one gradual and one catastrophic. There is an increased risk of either over the lifetime of the belt, so it is common for highly-stressed belts to be given a service lifetime and to be replaced before this failure can occur. One failure mode is gradual wear to the tooth shape, which may eventually lead to slippage over rounded teeth. The belt often continues to work, but the relative timing between shafts changes. The catastrophic failure mode is caused by delamination between the belt and its fabric reinforcement. Although this may be