The 20Invertebrates by B1ogVx


									The Invertebrates
Phylum Porifera
             General Characteristics
   9,000 species (100 live in fresh water the rest are marine).
   Sessile, and asymmetrical.
   Resembles a sac perforated with holes.
   Porifera (poh-RIF-ur-uh) means “pore bearers.”
   Water is drawn through the pores into a central cavity
    spongocoel, then flows out of the sponge through a larger
    opening called the osculum. This is how the sponge carries
    out feeding, respiration, circulation, and excretion.
   Suspension-feeders- collect food particles from the water
    passed through some kind of food-trapping equipment.
   Sponges have a simple skeleton. In harder sponges, the
    skeleton is made up of spicules, (spike-shaped structures),
    made up of calcium carbonate or glasslike silica. Softer
    sponges have an internal skeleton of spongin. (bath sponges)
   Lining the inside of the body are flagellated
    choanocytes (collar cells). The flagella create a water
    current, collars trap food particles and ingest them by
    phagocytosis. Amoebocytes take nutrients to other
   Sponges can reproduce either sexually or asexually.
   Most sponges are hermaphroditic and produce both
    eggs and sperm by meiosis. The eggs are fertilized
    inside the body (internal fertilization). Sperm are
    released from one sponge and carried by water
    currents to another sponge. They form a zygote and
    later a larva which is motile and uses the water current
    to settle on the sea floor. This sponge is not
    genetically identical to its parents.
   Sponges can reproduce asexually by budding where
    part of the parent sponge breaks off, settles to the sea
    floor, and grows into a new sponge. This new sponge
    is genetically identical to its parent.
   Least complex of all animals, capable of extensive
    regeneration (replacement of lost parts).
   Lack organs, cell layers, no nerves or muscles.
   Individual cells can sense and react to changes in the
   Sponges provide habitats for marine animals such as
    snails, sea stars, and shrimp. Sponges also form
    partnerships with photosynthetic bacteria, algae, and
    plantlike protists. (Mutualism both partners benefit).
               General Characteristics
   Cnidarians (ny-DAYR-ee-ans) are soft-bodied, carnivorous
    animals that have stinging tentacles arranged in circles
    around their mouths. They are the simplest animals to have
    body symmetry and specialized tissues.
   Members of phylum Cnidaria include hydras, jellyfish, sea
    anemones and coral animals. Some live as individuals, while
    others live in colonies in freshwater and oceans.
   Cnidarians get their name from cnidocytes, or stinging cells,
    that are located along their tentacles. Cnidarians use these
    for defense and to capture prey. Within each cnidocyte is a
    nematocyst. A nematocyst is a poison-filled, stinging
    structure that contains a tightly coiled dart. When a shrimp
    or small fish brushes up against the tentacles, thousands of
    nematocysts explode into the animal, releasing enough
    poison to paralyze or kill the prey.
                 Form & Function
   Cnidarians are radially symmetrical. They have a
    central mouth surrounded by numerous tentacles that
    extend outward.
   Cnidarians have a life cycle that includes two
    different-looking stages: a polyp and a medusa.
          Polyp                          Medusa
   A polyp is a cylindrical body with arm-like tentacles.
    Polyps are sessile with their mouth pointing upward.
   A medusa has a motile, bell-shaped body with a
    mouth on the bottom.
   Cnidarians have a body wall that surrounds an internal
    space called a gastrovascular cavity. This is where
    digestion takes place. Nutrients are transported
    through the body by diffusion.
   Cnidarians respire and eliminate their waste by
    diffusion through their body walls.
   They are able to gather information from their
    environment using specialized sensory cells or a nerve
    net. They can detect stimuli such as light and touch.
Reproductive Cycle
   Cnidarians move in different ways. Sea anemones have a
    hydrostatic skeleton (layer of circular and longitudinal
    muscles) while medusas move by jet propulsion.
   Jellyfish (Class Scyphozoa) means “cup animals.” Jellyfish
    live their lives primarily as medusas. The polyp form is
    limited to the larval stage, and no colonies form. Jellyfish
    reproduce sexually and may grow up to 4 meters in diameter
    with tentacles more than 30 meters long.
   Hydras (Class Hydrozoa) contains hydras and other related
    animals. The polyps of most hydrozoans grow in branching
    colonies. Within the colony, polyps are specialized to perform
    different functions. (ex. Portugese man of war). Hydras are
    different from other cnidarians in their class as they lack a
    medusa stage. Instead they live as single polyps and
    reproduce asexually or sexually.
   Sea Anemones and Corals (Class Anthozoa) These
    flower animals include the sea anemones and corals,
    animals that have only the polyp stage in their life
    cycle. Many species are colonial, or composed of
    many individual polyps.
The Worms
                   The Flatworms
   The phylum Platyhelminthes (plat-ih-hel-MIN-theez)
    consists of the flatworms.
   Flatworms are soft, flattened worms that have tissues
    and internal organ systems. They are the simplest
    animals to have three embryonic germ layers, bilateral
    symmetry and cephalization.
   Flatworms are known as acoelomates meaning
    without coelom. A coelom is a fluid filled body cavity
    that is lined with tissue.
   Flatworms are thin therefore materials can pass easily
    into and out of their body cells. They rely on
    diffusion for respiration, excretion, and circulation.
   Flatworms are free-living or parasitic.
   Free-living flatworms can be carnivores, or scavengers.
    They have a digestive cavity with a single opening or a
    mouth, through which food and wastes pass.
   Parasitic worms feed on blood, tissue fluids, or pieces of
    cells within the host’s body. Many parasitic worms obtain
    nutrients from foods that have already been digested by
    their host. As a result they have a very simple digestive
    system. Tapeworms have no digestive system.
   In free-living flatworms a head encloses several ganglia, or
    groups of nerve cells, that control the nervous system.
    Parasitic worms have a less complex nervous system.
   Free-living flatworms typically move by using cilia on their
    epidermal cells and through muscle cells.
   There are three main groups of flatworms; the turbellarians,
    flukes and tapeworms. Most turbellarians are free-living while
    the other flatworm species are parasites.
   Turbellarians The free-living flatworms belong to the class
    Turbellaria. Most live in marine or fresh water. Most species
    live in the sand or mud under stones and shells. Planarians
    are the most familiar flatworms.
   Flukes Members of the class Trematoda are known as flukes.
    Flukes are parasitic flatworms. Most flukes infect the internal
    organs of their host. (ex. The blood fluke Schistosoma mansoni
    needs two hosts a human and a snail and causes
   Tapeworms Members of the class Cestoda are called
    tapeworms. Tapeworms are long, flat, parasitic
    worms that are adapted to life inside the intestines of
    their hosts. The head of an adult tapeworm contains a
    scolex with suckers or hooks allowing it to attach to
    the intestinal wall. Transmitted through intermediate
    hosts such as cows, fish which are improperly cooked
    and consumed by humans.
                  The Roundworms
   The phylum Nematoda, are among the most
    numerous of all animals. A single rotting apple can
    contain as many as 90,000 roundworms.
   Roundworms are slender, unsegmented worms with
    tapering ends. They range in size from microscopic to
    a meter in length.
   Most species are free-living inhabiting soil, salt flats,
    sediment and water. Many others are parasitic and
    live in the hosts of almost every kind of plant and
   Roundworms develop from three germ layers and
    have a pseudocoelom. It is a false coelom because
    the body cavity is lined partially with tissue.
   Unlike flatworms, roundworms have a digestive tract with two
    openings; a mouth and an anus.
   Roundworms reproduce sexually and most species have
    separate sexes.
   Their response and movement is similar to flatworms. They
    exchange gases and excrete waste through their body walls
    using diffusion.
   Parasitic roundworms include trichinosis-causing worms,
    filarial worms, ascarid worms, and hookworms.
   Humans get trichinosis by eating raw or incompletely cooked
    pork. Causes terrible pain in organs.
   Filarial worms lead to elephantiasis where the affected part
    of the body swells enormously. These threadlike worms affect
    the lymphatic vessels and are transmitted through biting
   Ascaris lumbricoides is a serious parasite of humans and
    other vertebrates which causes malnutrition in more
    than one billion people worldwide. It is spread
    through eating unwashed vegetables and food. This is
    why puppies are wormed when they are young.
   Hookworms affect as many as one-quarter of the
    population. They live in the soil and use sharp tooth-
    like plates and hooks to burrow into the skin of an
    unprotected foot. They enter the bloodstream and
    suck the host’s blood causing weakness and poor
              The Segmented Worms
   Phylum Annelida refers to the ring-like appearance of
    annelid’s body segments. Earthworms, seaworms and
    leeches are examples of annelids.
   Annelids are worms with segmented bodies. They
    have a true coelom that is lined with the tissue derived
    from mesoderm.
   Annelids range from filter feeders to predators.
   Annelids typically have a closed circulatory system, in
    which blood is contained within a network of blood
   Land-dwelling annelids breathe through their moist
    skin, while aquatic annelids breathe through their gills.
   Annelids produce two kinds of waste. Digestive waste
    passes out the anus. Nitrogenous waste passes out the
   Most annelids have a well developed nervous system
    consisting of a brain and several nerve cords.
   Annelids move using two groups of body muscles;
    longitudinal and circular. Earthworms have bristles
    called setae to prevent slipping. Marine annelids have
    paddle-like appendages called parapodia on each
    segment for swimming and crawling.
   Most annelids reproduce sexually. Some use external
    fertilization and have separate sexes. Others are
    hermaphrodites. They rarely fertilize their own eggs
   Annelids are divided into three classes- oligochaetes,
    hirudinea, and polychaetes.
   The class Oligochaeta (AHL-ih-goh-keets) contains
    earthworms and their relatives. Most live in soil or
    fresh water, have streamlined bodies and relatively few
   The class Hirudinea (hir-yoo-DIN-ee-uh) contains
    the leeches, most of which live in moist habitats in
    tropical countries. Leeches are external parasites that
    suck the blood and body fluids of their host.
   The class Polychaea (PAHL-ih-keets), contains
    sandworms, bloodworms and their relatives.
    Polychaetes are marine annelids, that have paired,
    paddle-like appendages tipped with setae.
Phylum Mollusca
    Phylum Mollusca “soft bodies”
   Snails and slugs, oysters and clams, and
    octopuses and squids are all mollusks.
   50,000 species mostly marine, some inhabit
    fresh water and snails / slugs live on land.
   Mollusks are soft-bodied animals, but most are
    protected by a hard shell made of calcium
   Squids and octopuses have reduced shells that
    have been internalized
   All mollusks have a similar body plan with 3
    main parts:
   a muscular foot, usually for movement, a
    visceral mass, containing most of the internal
    organs, and a mantle, a heavy fold of tissue that
    may secrete a shell.
              Class Gastropoda
   The largest of the molluscan classes (40,000 sp)
   Most gastropods are marine, but there are also
    many freshwater species and garden snails and
    slugs that have adapted to land.
   Protected by single, spiraled shells into which
    the animals can retreat when threatened.
   Shell is often conical, sometimes flattened
   Slugs and sea slugs have lost their shells during
    their evolution
   Many have distinct heads with eyes at the tips of
   Gastropods inch along by a rippling motion of
    the elongated foot.
   Most gastropods graze on algae or plant
    material. Several other groups, however, are
   Aquatic gastropods respire using gills, terrestrial
    gastropods have a lung.
   Among the few invertebrate groups to have
    successfully populated the land.
Gastropod Pics
                 Class Bivalvia
   Include clams, oysters, mussels and scallops.
   Bivalves have shells divided into two halves.
   Two parts of the shell are hinged at the mid-
    dorsal line and powerful adductor muscles draw
    the two halves tightly together to protect the
    soft-bodied animal.
   Bivalves contain gills that are used for feeding as
    well as gas exchange.
   Most are suspension feeders, they trap fine food
    particles in mucus that coats the gills.
   Water flows into the mantle cavity through the
    incurrent siphon, passes over the gills and then
    exits the mantle cavity through an excurrent
   No distinct head; lead rather sedentary lives
   Sessile mussels secrete strong threads that cling
    to rocks
   Clams pull themselves into the sand or mud
    using the muscular foot
   Scallops dig and skitter along the seafloor by
    flapping their shells
Bilvalve Pics
    Class Cephalopoda “head foot”
   Unlike sluggish gastropods and the sedentary
    bivalves, cephalopods are built for speed, an
    adaptation that fits their carnivorous diet.
   Squids and octopuses use beaklike jaws to bite
    their prey; they then inject poison to immobilize
    the victim.
   The mouth is at the center of several long
   The shell is usually either reduced and internal
    (squids) or missing altogether (octopuses).
   A squid darts, usually backward by drawing
    water in and then firing a jet stream of water
    through the excurrent siphon that points
   Steers by pointing in different directions.
   Octopuses live on the seafloor where they creep
    and scurry about in search of crabs and food.
   Only mollusks with a closed circulatory system.
   Have a well developed nervous system with a
    complex brain. Why?
   Ability to learn and behave in a complex manner
    is more critical to fast moving predators.
Cephalopod Pics
Phylum Arthropoda
      General Characteristics
   Arthropoda means “jointed feet.”
   Nearly one million arthropod species have been
    described, mostly insects.
   Most successful phylum of animals, in all
    habitats. Their success is related to their
    segmentation, hard exoskeleton, and jointed
   All arthropods have the same basic body plan or
    some variation of it. The body is made up of
    three segments: the head, thorax, and abdomen.
   The body of an arthropod is completely covered by a
    cuticle, an exoskeleton made up of protein and chitin.
    Exoskeleton can be modified into thick hard armor or
    paper thin and flexible.
   One Problem. In order to grow an arthropod must
    shed its old exoskeleton and secrete a larger one. This
    process is called molting and it takes a lot of energy
    and leaves the animal temporarily vulnerable to its
   The first arthropods appeared in the sea 600 million
    years ago. Since arthropods have moved to all
    habitats. They have evolved specialized appendages
    for feeding, movement and other functions.
   Arthropods tune into their environment with
    well developed sensory organs including eyes
    (simple and compound), olfactory receptors for
    smell, and antennae for touch and smell.
    Cephalization is extensive.
   Arthropods have an open circulatory system
    where fluid called hemolymph is pumped by the
    heart through short arteries and then into spaces
    surrounding organs and tissues.
   Terrestrial arthropods have a tracheal system
    which consist of open tubes that connect to the
    outside by spiracles (pores in the cuticle).
    Arthropods are classified based on the number and
     structure of their body segments and appendages-
     particularly their mouthparts.
    Arthropods are divided into four subphyla
1.   Trilobitomorpha- trilobites (extinct).
2.   Chelicerata- spiders, mites & ticks, scorpions.
3.   Uniramia- insects, centipedes, millipedes.
4.   Crustacea- crabs, lobsters, shrimps, barnacles,
     crayfish etc.
                            Review Questions
1. What is the term for an organism which can produce both sperm and eggs?
2. Why are sponges classified as part of the animal kingdom?
3. Why is it helpful for an organism to be able to reproduce both sexually and asexually?
4. How does a jellyfish obtain food?
5. How has the digestive system of planaria been improved over that of the jellyfish?
6. How does an animal in the phylum Platyhelminthes obtain oxygen? Why is this sufficient for these
7. A tapeworm is a parasite that lives in the intestines of its host. What system would you expect to
    be missing from the tapeworm that would be found in other flatworms? By not having this
    system, the tapeworm has created extra space in its body. How do you think the worm has used
    this space?
8. How have the digestive systems of the roundworm and segmented worm been improved
    compared to that of flatworms?
9. What is meant by segmentation? How is segmentation an evolutionary advantage?
10. Some organisms have a circulatory system with blood but the blood has no hemoglobin. What is
    the function of the blood in these organisms? Why is it an advantage to have hemoglobin in the
11. How is the annelid coelom different from the body cavity of the roundworm.
12. Why is a simple circulatory system important for the earthworm?
13. In a parasitic worm, why would it be useful to be hermaphroditic?
14. Give a possible reason why bivalves have not tended toward cephalization.
15. Why have more complex organisms such as molluscs had to develop gills?
33. How is the circulatory system of most molluscs different from the annelids? Is this unexpected?
34. Describe feeding in the gastropods, bivalves, and cephalopods.
35. How are cephalopods different from other mollusks?
36. Explain how the gills of bivalves perform two separate functions?
37. How is the closed circulatory system an advantage to cephalopods?
38. List some characteristics of arthropods.
39. Why does the presence of an exoskeleton require the presence of jointed appendages?
40. Why is molting necessary?
41. What are the advantages and disadvantages of an exoskeleton?
42. What factors limit the size of the insects?

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