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Chapter 29: Echinoderms and Invertebrate Chordates

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Title: Chapter 29: Echinoderms and Invertebrate Chordates


1
Chapter 29Echinoderms and Invertebrate Chordates
  • Section 1 Echinoderms

2
Echinoderms
  • Includes starfish, sea urchins, sand dollars,
    etc.
  • Belong to the phylum Echinodermata
  • Stretches back to the beginning of the Cambrian
    Period, more than 580 million years ago

3
What Is an Echinoderm?
  • Echinoderms are spiny skinned animals
  • In addition to having a spiny skin, echinoderms
    are characterized by five-part radial symmetry,
    an internal skeleton, a water vascular system,
    and suction-cuplike structures called tube feet
  • The internal skeleton, or endoskeleton, is made
    up of hardened plates of calcium carbonate, which
    are often bumpy or spiny
  • The water vascular system consists of an internal
    network of fluid-filled canals connected to
    external appendages called tube feet
  • Water vascular system is involved in many
    essential life functions in echinoderms

4
Form and Function in Echinoderms
  • Adult echinoderms have a body plan with five
    parts organized symmetrically around a center
  • Typically have neither an anterior nor a
    posterior end and no brain
  • The side where the mouth is located is called the
    oral surface, and the opposite side is called the
    aboral surface

5
Form and Function in Echinoderms
  • The water vascular system opens to the outside
    through a sieve like structure called the
    madreporite
  • The entire water vascular system operates like a
    series of living hydraulic pumps that can propel
    water in or out of the tube feet
  • The tube feet act like living suction cups
  • All echinoderms walk with their tube feet, and
    some use their tube feet for feeding

6
Feeding
  • Carnivores
  • Use their tube feet to pry open the shells of
    bivalve mollusks such as clams and scallops
  • Once opened, the carnivores flips its stomach out
    of its mouth, pours out enzymes, and digests its
    prey in the preys own shell
  • Herbivores
  • Scrape algae from rocks by using their five-part
    jaw
  • Filter feeders
  • Use tube feet on flexible arms to capture
    plankton that float by on ocean currents
  • Detritus feeders
  • Move like a bulldozer across the ocean floor,
    taking in a mixture of sand and detritus

7
Respiration
  • Echinoderms need to exchange carbon dioxide for
    oxygen
  • In most species the thin walled tissue of the
    tube feet forms the main respiratory surface
  • In some species small outgrowths called skin
    gills also function in gas exchange

8
Internal Transport
  • The functions of transporting oxygen, food, and
    wastes are shared by different systems in
    echinoderms
  • The distribution of nutrients is performed
    primarily by the digestive glands and the fluid
    within the body cavity

9
Excretion
  • Solid wastes are released through the anus in the
    form of feces
  • Excrete nitrogen-containing wastes primarily in
    the form of ammonia
  • Wastes seem to be excreted in many of the same
    places around the body in which gas exchange
    takes place the tube feet and the skin gills

10
Response
  • Have primitive nervous systems
  • Have a nerve ring that surrounds the mouth and
    radial nerves that connect the ring with the body
    sections
  • Also have light sensitive cells to help them tell
    whether it is night or day
  • Many echinoderms hide under rocks and in crevices
    by day, coming out to feed at night, when most
    predators are asleep

11
Movement
  • Most echinoderms use tube feet and thin layers of
    muscle fibers attached to the plates of the
    endoskeleton to move
  • Mobility is determined by the structure of the
    endoskeleton
  • Some plates are fused
  • Some have flexible joints

12
Reproduction
  • Most are either male or female
  • Some are hermaphrodites
  • In starfish, the sperm and egg are produced in
    testes or ovaries which fill the arms during the
    reproductive season
  • Shed their sperm and eggs into the water
  • Larvae swim around for some time
  • Eventually, they will swim to the ocean bottom,
    where they mature and metamorphose into adults
    that have radial symmetry

13
The Echinoderm Classes
  • Almost 6000 species of living echinoderms
  • Found in almost every ocean in the world
  • No echinoderms have ever entered fresh water, and
    they cannot survive for long on land
  • Echinoderms are remarkably diverse in appearance

14
Starfish
  • Contains the common starfish, which are also
    known as sea stars
  • Occur in many colors
  • Many species have more than 5 arms
  • Starfish creep slowly along the ocean bottom
  • Most are carnivores, preying upon the bivalves
    they encounter as they move
  • Some species are important predators in rocky
    areas along the coast

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Brittle Stars
  • Live in tropical seas, especially on coral reefs
  • Look much like a common starfish, but they have
    longer, more flexible arms and are able to move
    much more rapidly
  • Brittle stars protect themselves by shedding one
    or more of their arms when attacked
  • The detached parts keep wriggling violently,
    distracting predators, while the rest of the
    animal escapes
  • Are filter and detritus feeders that hide by day
    and wander around in search of food at night

17
The brittle star gets its name from the fact that
it can shed its arms when it is threatened. This
distracts predators so that the brittle star can
escape. In time, it will regrow the missing arm.
Some starfish, such as the sun star, have more
than five arms.
18
Sea Urchins and Sand Dollars
  • Includes disk-shaped sand dollars, oval heart
    urchins, and round sea urchins
  • Most are grazers that eat large quantities of
    algae
  • Others are detritus feeders
  • Heart urchins and sand dollars live hidden in
    burrows
  • Most sea urchins wedge themselves in crevices in
    rock during the day and only come out at night
  • Many sea urchins have long, sharp spines

19
The slate urchin has thick, strong spines that
were once harvested for use as implements for
writing on slateboards. Sea urchins have a
lanternlike set of bony plates inside their body
that power their jaws. The sand dollar gets its
name from its flattened, coin-shaped appearance.
20
Sea Cucumbers
  • Look like warty moving pickles with a mouth at
    one end and an anus at the other
  • Most are detritus feeders
  • Not numerous in shallow water
  • Herds containing hundreds of thousands of them
    often cover areas of the sea floor at great
    depths
  • A few species expel sticky substances that attach
    to a predator
  • The predator is immobilized as it is glued into a
    helpless ball

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22
Sea Lilies and Feather Stars
  • These filter feeders, which have 50 or more long,
    feathery arms, comprise the most ancient class of
    echinoderms
  • Not common today
  • Sea lilies are sessile animals that are attached
    to the ocean bottom by a long, stem like stalk
  • Many feather stars live on coral reefs, where
    they perch on top of rocks at night and use their
    tube feet to catch floating plankton

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How Echinoderms Fit into the World
  • Numerous in most marine habitats
  • Control the populations of other animals
  • Control the distribution of algae
  • Considered delicacies by some people
  • Useful as research subjects and as possible
    sources of medicine

25
Chapter 29Echinoderms and Invertebrate Chordates
  • Section 2
  • Invertebrate Chordates

26
Invertebrate Chordates
  • Phylum Chordata
  • Fish, frogs, birds, snakes, dogs, cows, and
    humans
  • Most of the chordates are vertebrates, which
    means they have backbones, so they are placed in
    the subphylum Vertebrata
  • The invertebrate chordates are divided into two
    subphyla tunicates and lancelets

27
What Is a Chordate?
  • Belong to phylum Chordata
  • Chordates are animals that are characterized by a
    notochord, a hollow dorsal nerve cord, and
    pharyngeal (throat) slits
  • All chordates display these three characteristics
    at come stage in their life

28
1st Characteristic
  • The notochord, is a long, flexible supporting rod
    that runs through at least part of the body,
    usually along the dorsal surface just beneath the
    nerve cord
  • In most vertebrates, the notochord is quickly
    replaced by the backbone

29
2nd Characteristic
  • The hollow dorsal nerve cord, runs along the
    dorsal surface just above the notochord
  • In most chordates, the front end of this nerve
    cord develops into a large brain
  • Nerves leave this cord at regular intervals along
    the length of the animal and connect to internal
    organs, muscles, and sense organs

30
3rd Characteristic
  • Pharyngeal slits, are paired structures in the
    pharyngeal, or throat, region of the body
  • In aquatic chordates the pharyngeal slits are
    gill slits that connect the pharyngeal cavity
    with the outside
  • Many invertebrates have gills of some sort in
    various places, but only chordates have
    pharyngeal gills

31
3rd Characteristic
  • In terrestrial chordates that use lungs for
    respiration, pharyngeal slits are present only
    for a brief time during development
  • These slits soon close up as the embryo develops
  • In chordates such as humans, pouches form in the
    pharyngeal region but never open up to form slits
  • For this reason, some scientists regard
    pharyngeal pouches, not slits, as the true
    chordate characteristic

32
Tunicates
  • Small marine chordates that eat plankton they
    filter from the water
  • Get their name from a special body covering
    called the tunic
  • Only the tadpole-shaped larvae of tunicates have
    a notochord and a dorsal nerve cord
  • When tunicate larvae mature, they undergo
    metamorphosis and become sessile adults that grow
    into colonies attached to a solid surface
  • Both larval tunicates and adults filter feed and
    breathe at the same time through a pharyngeal
    basket pierced by gill slits

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34
Lancelets
  • Small fishlike creatures that live in the sandy
    bottom of shallow tropical oceans
  • Have a definite head
  • Have a mouth that opens into a long pharyngeal
    region with up to 100 pairs of gill slits
  • Feed by passing water through their pharynx,
    where food particles are caught in a sticky mucus
  • This mucus is swallowed into a digestive tract
    that starts at one end of the pharynx and
    continues straight through the animal to the
    anus, near the tail

35
Lancelets
  • Have a simple, primitive heart that pumps blood
    through vessels in a closed circulatory system
  • They show evidence of segmentation in the
    arrangement of their nerves and muscles
  • Muscles are organized into V-shaped units that
    are paired on either side of the body
  • Each muscle unit receives a branch from the main
    nerve cord
  • Lancelets have no jaw
  • Their mouth is composed entirely of soft tissues
  • Also lack appendages and can move only by bending
    their bodies back and forth

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How Invertebrate Chordates Fit into the World
  • It is important to remember that living
    vertebrates did not evolve from living lancelets
    or tunicates
  • Both these subphyla have evolved over time
  • However, similarities in structure and
    embryological development indicate that
    vertebrates and invertebrate chordates evolved
    from common ancestors many millions years ago

38
Homework
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