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Invertebrates (Lineages (Sponges, ctenophores, and cnidarians are the most…

- - - - Basal animals
      - Lack true tissues
        
        Has different types of cells, such as choanocytes or collar cells
      - Sessile (fixed in one place)
      - 7,000 species
      - Hermaphroditic
        
        Can be both male and female (not at same time)
        
        Comes in handy, since they are sessile
    - - Radially symmetric and diploblastic
      - Jellies, corals, sea anemones
      - Body plan
        
        A sac with a gastrovascular cavity (digestive component) and an orifice for the mouth/anus
        
        Two body variants include sessile polyp and motile medusa
        
        Some have both phases in their life cycle
      - Contractile tissues and nerves, detecting stimuli from all directions; no brain
- - - - Named after process they go through, called ecdysis (molting)
      - Contains the most species
      - Two main phyla
        
        Nematodes
        
        "Roundworms"
        
        No appendages, most less than 1 mm, and has a coelem
        
        Very abundant (90,000 in one rotting apple, and nine billion per acre of farmland)
        
        Caenorhabditis elegans is a model organism
        
        Arthropods
        
        Jointed limbs,segmented bodies (head, thorax, abdomen)
        
        Exoskeletons
        
        Made of chitin
        
        Protection and attachment sites for muscle
        
        Prevents desiccation (removal of moisture)
        
        They must molt, since the exoskeleton cannot grow; this leaves them vulnerable
        
        Well-developed sensory organs (including antennae)
        
        Open circulatory system
        
        With a fluid called hemolymph (essentially insect-blood)
        
        Cheliceriforms
        
        Arachnids
        
        Includes scorpians, spiders, ticks, and mites
        
        Spiders have an organ called the spinneret which makes webs; web-making is inherited, so spiders can make a perfect web on the first try
        
        Myriapods
        
        Millipedes and centipedes
        
        Insects
        
        70% for all animals are insects (and most are beetles)
        
        Has wings that are a part of the exoskeleton and not true appendages (separated from the arms)
        
        Metamorphosis
        
        Incomplete
        
        Juveniles are a smaller version of the adult, but are sexually immature
        
        Complete
        
        Goes through a larva (eating) stage and an adult (reproductive) stage (stages look different) (thought to reduce competition)
        
        Change in animal's structure after birth
        
        Crustaceans
        
        Lobsters and crayfish
    - - Echinoderms
        
        Includes sea stars and sea urchins
        
        Note that humans are more closely related to echinoderms than to arachnids and insects, because we are both deuterostomes
    - - Lophophore
        
        A crown of ciliated tentacles for feeding
      - Trochophore
        
        A type of larva (common to marine mollusks and annelids) that has a ring of cilia around it for swimming (and in some species, sweeping particles into mouth)
      - Some have neither of these features
      - Includes flatworms, annelids, rotifers, ectoprocts, brachiopods, and molluscs