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The Animal Kingdom

Lower Invertebrate Phyla
Representative Diagram
Body Plan
Transport within the Body
Gas Exchange
Method of Waste Disposal
Nervous System
Important Distinguishing Feature
No symmetry (asymmetrical) Consists of a perforated sac
Neither acoelomate, psuedocoelomate or coelomate.
  • Suspension-feeders (filter feeders) collect food particles from water passed through types of food-trapping equipment
  • insides are lined by flagellated choanaocytes (collar cells) which generate a water current while the collar cells trap food particles and ingest them by phagocytosis
Water is drawn through the pores into a central cavity (the spongocoel) and allows for substance transport internally via canals.
(See transport) Sponges respirate by obtaining oxygen from the water transported through their body by diffusion.
Water and wastes flow out of the sponge through an opening called the osculum and via diffusion from the cells.
Sponges have no nerves or muscles, but individual cells can sense and react to changes in the environment and cells around pores and osculum can contract to close the openings
  • Sponges are hermaphrodites and can function as both male and female in sex by producing sperms and eggs.
  • gametes arise from chaonocytes/amaobocytes
  • eggs reside in mesohyl, and sperm are released into the spongocoel and are carried out of the sponge by the water current, allowing for cross-fertilization as sperm is drawn into neighboring individuals
  • fertilization occurs in mesohyl and zygotes develop into larvae covered with flagella which exit through the osculum
  • sponges can asexually reproduce by regenerating fragments broken off the parent sponge.
Sponges have existed for 580 million years and yet are the most simple of all animals in that they have no organs or brain. Their cell layers are loose federations of cells that are unspecialized (and thus are not tissues.)
Neither acoelomate, psuedocoelomate or coelomate.
  • Central digestive compartment is the gastrovascular cavity.
  • After the animal ingests the food, the gastrodermis secrets digestive enzymes into the gastrovaascular cavity. The gastrodermal cells engulf small pieces of the partially digested food by phagocytosis and digestion is finished within the cells in food vacuoles.
Water is pumped in and out of the gastrovascular cavity; flagella on the gastrodermal cells help distribute nutrients.
Oxygen diffuses across the surface.
Undigested remains are egested through the mouth/anus.
  • Muscles move by cell layers contracting by contractile fibers
  • movements are coordinated by a nerve net associated with simple sensory receptors distributed radially around the body.
In most polyps (a type of cnidaria with tentacles), reproduction consists of asexual “budding”. Sexual formation of gametes is prevalent in medusas (cnidaria that moves by contractions of its bell-shaped body) and some polyps.
  • Some cnidarians are dimorphic, and can be a polyp at one stage in their life and medusa in another.
  • tentacles are armed with batteries of cnidocytes, cells that function in defense and aid in the capture of prey.
  • Digestive juices are spilled onto prey, the pharynx then sucks small pieces of food into the gastrovascular cavity
  • digestion is completed within the cells lining the cavity, each branched for increased amount of surface area and distribution throughout the organism.
(See gas exchange and waste disposal.)
Lacks organs specialized for gas exchange and circulation.
Nitrogenous waste as ammonia diffuses from cells into the water because the flat shape makes the cells near the surrounding water. Undigested waste is also egested through the mouth. These organisms also have an excretory apparatus to maintain osmotic balance between the animal and its surroundings by flame cells (ciliated cells that waft fluid through branched ducts opening to the outside.)
Planaria has eye spots that detect light and lateral flaps for smell. The main sensory apparatus is the ganglia near the end of the worm, which is a dense cluster of nerve cells. It can modify responses to stimuli it recieves. Two longitudinal nerve cords run the length of the flatworms body.
Is hermaphroditic and can reproduce asexually through regeneration or fragmentation or sexually reproduce by cross-fertilization.
Produces the embryonic mesoderm, a third germ layer that allows for complex organs and true muscle tissue.
Nematodes possess a complete digestive tract running as a tube from the mouth to the anus.
Pseudocoelom and its fluid serves as a blood vascular system and transports nutrients throughout the body.
Gases diffuse across the cuticle
In some nematodes there are specialized cells that excrete nitrogenous waste. In others there are canals designed for excretion. Some nematodes use both of these systems.
There is a ring of nerve tissue around pharynx and ventral nerve cords running the length of the body.
Male and female are separate (not hermaphroditic) and breed using internal fertilization. The zygotes of most species are resistant cells capable of surviving harsh conditions.
Some nematodes that are free-living play a role in decomposition and nutrient cycling, and other roundworms parasitize animals, one (Trichinella spiralis) causes trichinosis in humans by eating undercooked meat.