BIOL 1002 Chapter : Biol 1002 Chapter 23
Document Summary
Animals possess all of the following characteristics. They obtain energy by consuming other organisms. They are motile at some point in the life cycle. They are able to respond rapidly to external stimuli. Most animals are invertebrates (lack a vertebral column) Less than 3% of all known animals are vertebrates (possess a vertebral column) Flatworms may be parasitic or free living. Flatworms are bilaterally symmetrical and belong to the phylum platyhelminthes. Many species are parasites, organisms that live in or on the body of another organism. Non-parasitic, free-living flatworms inhabit aquatic, marine, and moist terrestrial habitats. Flatworms can reproduce both sexually and asexually; most are hermaphroditic, having both male and female sexual organs. Flatworms have organs but lack respiratory and circulatory systems. They possess a distinct head, along with sensory organs. The eyespots of freshwater planarians detect light and dark. Their nervous system consist of clusters of nerve cells called ganglia (singular: ganglion) in the head, forming a simple brain.
