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

15
(No Transcript)
16
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

21
(No Transcript)
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

23
(No Transcript)
24
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

33
(No Transcript)
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

36
(No Transcript)
37
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

• Page 646 1 3