The phylum Mollusca contains over 100,000 species with a variety of body forms and lifestyles. In mollusks, the coelom is reduced and limited to the region around the heart. The Mollusk body first appeared during the Cambrian Period. All mollusks have: 1. A visceral mass containing internal organs, including the digestive tract, paired kidneys, and reproductive organs. 2. A mantle [...]
The phylum Arthropoda contains animals with segmented appendages on their body segments. Arthropods occupy every habitat, and are in many respects the most successful animal group on Earth. There are conservatively over 1 million species of living arthropods. Biologist E.O. Wilson estimates there are 10 million species, 9 million of which are arthropods. Certain groups of arthropds have extremely complete [...]
The phylum Annelida contains segmented worms (such as the earthworm). The development of segmented bodies allowed the formation of specialised functions in different segments. Annelids have an enlarged coelom to accommodate more complex internal organs. The well-developed, fluid-filled coelom and the tough integument act as a hydrostatic skeleton. There are about 12,000 marine, freshwater, and terrestrial species usually divided into [...]