Explain what type of animals each class represents.
Explain how each type of class of animal contributes to biodiversity on Earth.
- arthropoda, crustacea, chordata, platyhelminthes, mollusca, amphibia, aves, mammalia, reptilia
Arthropoda ("jointed foot") are the most diverse of all the animal phyla. They include animals such as crustaceans (crabs, lobster), insects (ants), and spiders. All are typified by having segmented legs, jointed bodies, and exoskeletons composed of the carbohydrate chitin. Arthropods have occupied a variety of levels of the food chain throughout the history of the earth; some of the earliest predators included arthropods, and arthropods were almost certainly the first animals to colonize land.
Crustaceans are a subdivision of arthropods. Most live in the ocean, and include animals such as shrimp and crabs. Particularly small shrimp, called krill, have enormous populations throughout the world and are a primary food source for a variety of other animals including whales.
Chordata are a separate phyla; they include vertebrates, such as ourselves. Chordata are unique in that they possess a variety of structures that favor internal support over external support such as exoskeletons; this eliminates the vulnerability incurred by moulting. Chordata are a relatively minor part of the overall biodiversity of the earth when considered in terms of variety of species, but are among the largest, most complex, and most relevant to our own sense of biodiversity.
Platyhelminthes are commonly called flatworms. This phyla includes a wide arrangement of relatively similar worm-like creatures who are predominately parasitic. Their significance to the food chain is largely restricted to the species that they directly interact with. Their importance to humans is largely concerned with their parasitic behaviors.
Molluscs are sometimes confused with crustaceans, but are actually an entirely separate phyla from the arthropods. Molluscs are characterized by a shell, though this is sometimes greatly reduced, and a variety of unique internal and external structures such as tentacles and a spiked tongue-like structure called a radula. They also have a significantly more developed nervous system. Molluscs include octopi, squid, and snails. They are the most diverse marine group, and snails are significant on land as both pests and food sources.
Amphibia, Aves, Mammalia and Reptilia are all part of the Vertebrate subphylum, and are closely related. Amphibians preceded amniotes, which diverged into mammals and reptiles, with birds evolving from reptiles. The group Reptilia is not considered a useful or "modern" grouping because it cannot resolve certain problems of relationships between ancestral reptiles and birds; it is commonly replaced by the groups Diapsid and Anapsid, or Sauropsida. Amphibia are relatively low in diversity, but are important to biodiversity for their sensitivity to environmental conditions, which can serve as a sort of marker for ecological health. Birds and reptiles have been very successful and, with mammals, include the largest animals ever to live. Mammals currently include the largest living animals and many of the most intelligent, including humans.