Download Echinoderms

Chapter 29 Echinoderms
and Invertebrate Chordates
Section 29-1
Echinoderms
OBJECTIVES:
– Relate
the structure of the
echinoderms to essential life
functions.
– Describe the characteristics of
the classes of echinoderms.
Section 29-1
Echinoderms
Phylum
Echinodermata- starfish,
sea urchins, sand dollars, etc.
– echino- means spiny; dermis
means skin
– these are spiny-skinned
animals
– Cambrian period; 580 million yr.
Section 29-1
Echinoderms
In
addition to having spiny skin,
they are characterized by:
– 5-part radial symmetry
– internal skeleton
– water vascular system
– suction-cuplike structures called
tube feet
Section 29-1
Echinoderms
 The
internal skeleton (or
endoskeleton) is made up of
hardened plates of calcium
carbonate; often bumpy or spiny.
 The water vascular system consists
of an internal network of fluid-filled
canals connected to the external
appendages called tube feet.
Section 29-1
Echinoderms
 The
water vascular system is
essential for:
– feeding; respiration; internal
transport; elimination of wastes;
and movement.
 Echinoderms have an internal
skeleton like Chordates, and some
similar development.
Section 29-1
Echinoderms
Thus,
some biologists feel that
among invertebrates,
echinoderms are most closely
related to humans!
Echinoderms are very well
adapted to life in the sea; some
have changed very little in
millions of years of evolution.
Section 29-1
Echinoderms
Adult
echinoderms have a body
plan with five parts organized
symmetrically around a center.
– neither anterior nor posterior
end; no brain
– but, they are two-sided
– mouth side is the oral surface
Section 29-1
Echinoderms
 Side
opposite the mouth is the aboral
surface.
 They have a unique system of
internal tubes called a water vascular
system.
– Opens to the outside through a
sieve-like structure called the
madreporite.
Section 29-1
Echinoderms
 In
starfish, the madreporite connects
to a tube called the ring canal that
forms a circle around the animal’s
digestive system.
– Figure 29-3, page 639
– From the ring canal, five radial
canals extend into each body
segment.
Section 29-1
Echinoderms
 Attached
to each radial canal are
hundreds of movable tube feet.
– This entire system acts like a
series of living hydraulic pumps
that can propel water in or out of
the tube feet.
– Can create a partial vacuum to
hold on to whatever it is touching
Section 29-1
Echinoderms
Feeding
in carnivores, such as
starfish, use their tube feet to pry
open the shells of bivalve
mollusks.
• Then the starfish flips the stomach
out of its mouth, pours out enzymes,
and digests its prey in its own shell;
then pulls the stomach back, leaving
an empty shell.
Section 29-1
Echinoderms
Herbivores,
such as sea urchins,
scrape algae from rocks by using
their 5-part jaw.
Filter feeders, such as sea lilies,
basket stars, and some brittle
stars, use tube feet on flexible
arms to capture plankton that
float by on ocean currents.
Section 29-1
Echinoderms
Detritus
feeders, such as sea
cucumbers, move much like a
bulldozer, taking in a mixture of
sand and detritus.
– Similar to earthworms, they
digest the organic material and
pass the sand grains out in their
feces.
Section 29-1
Echinoderms
Respiration
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.
Section 29-1
Echinoderms
Internal
transport (transporting
oxygen, food, and wastes which
is normally done by a circulatory
system) is shared by different
systems in echinoderms.
– They don’t really need a system
for gases, because of gills and
skin.
Section 29-1
Echinoderms
The
distribution of nutrients is
performed primarily by the
digestive glands and the fluid
within the body cavity
Excretion in almost all
echinoderms, solid wastes are
released through the anus (on
the aboral surface) as feces.
Section 29-1
Echinoderms
The
nitrogen-containing cellular
wastes are excreted primarily as
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.
Section 29-1
Echinoderms
 Response
since they have no head,
they have primitive nervous systems.
– They do have scattered sensory
cells to detect food.
– Starfish also have up to 200 lightsensitive cells clustered in
eyespots at the tip of each arm.
Section 29-1
Echinoderms
 However,
they can do little more than
tell whether it is light or dark.
– Also may have statocysts for
balance, to tell them whether
they’re right side up.
 The spiny surface is not really very
good protection; good only in a few
such as the crown-of-thorns starfish.
Section 29-1
Echinoderms
 Many
predators have learned that if
they turn these animals over, they
can attack them through their
unprotected underside.
– Thus, many echinoderms hide
during the day and are active at
night when most predators are
asleep.
Section 29-1
Echinoderms
Movement
= use tube feet and
thin layers of muscle fibers
attached to the plates of the
endoskeleton to move.
– In sand dollars and sea urchins,
the plates are fused together to
form a rigid box that encloses
the animal’s internal organs.
Section 29-1
Echinoderms
– In
sea cucumbers, the plates
are reduced to tiny vestiges
inside a soft, muscular body
wall. The loss of the plates
makes the body of sea
cucumbers very flexible.
Section 29-1
Echinoderms
 Reproduction
= most echinoderms
are either male or female, although
some are hermaphrodites.
– Egg and sperm are released and
fertilization takes place in the
water.
– The larvae have bilateral symmetry
= very advanced.
Section 29-1
Echinoderms
 When
the larvae mature and
metamorphose into adults, they
develop radial symmetry.
 Many starfish have incredible powers
of regeneration.
– Each piece can grow into a new
animal as long as it contains a
portion of the central part.
Section 29-1
Echinoderms
Almost
6,000 species found in
almost every ocean (salt water) in
the world.
– No echinoderms have ever
entered fresh water, and they
cannot survive for long on land.
Section 29-1
Echinoderms
Echinoderm
Classes
– Starfish
– Brittle
Stars
– Sea Urchins and Sand Dollars
– Sea Cucumbers
– Sea Lilies and Feather Stars
Section 29-1
Echinoderms
1.
Starfish = this class contains
the common starfish, which are
also known as sea stars.
– Some have more than 5 arms
– Figure 29-7, page 642
– Carnivorous, preying upon the
bivalves they encounter
Section 29-1
Echinoderms
 2.
Brittle Stars = live in tropical seas,
especially on coral reefs
– Look like common starfish, but
have longer, more flexible arms,
thus able to move much more
rapidly
– Protection by shedding one or
more arms when attacked; are filter
and detritus feeders
Section 29-1
Echinoderms
 3.
Sea Urchins and Sand Dollars =
includes disk-shaped sand dollars,
oval heart urchins, and round sea
urchins. Fig. 29-8, p. 643
– Are grazers that eat large quantities
of algae; may burrow into the sand
or mud; may protect themselves by
long sharp spines.
Section 29-1
Echinoderms
4.
Sea Cucumbers = look like
warty moving pickles, with a
mouth at one end and an anus at
the other.
– Figure 29-9, page 644 top
– Most are detritus feeders
– Some produce a sticky material
to “glue” a predator helpless
Section 29-1
Echinoderms
 5.
Sea Lilies and Feather Stars =
filter feeders, have 50 or more long
feathery arms.
– The most ancient class of
echinoderms; not common today,
but once were widely distributed.
– Sea lilies; sessile animals, p.644
Section 29-1
Echinoderms
How
Echinoderms Fit Into the
World:
– Starfish are important
carnivores, controlling other
animal populations; a rise or fall
in numbers affects other
populations.
Section 29-1
Echinoderms
For
example, several years ago
the coral-eating crown-of-thorns
starfish suddenly appeared in
great numbers in the Pacific
Ocean.
– Within a short period of time,
they caused extensive damage
to many coral reefs.
Section 29-1
Echinoderms
In
many coastal areas, sea
urchins are important because
they control distribution of algae.
In various parts of the world, sea
urchin eggs and sea cucumbers
are considered delicacies by
some people.
Section 29-1
Echinoderms
Several
chemicals from starfish
and sea cucumbers are currently
being studied as potential anticancer and anti-viral drugs.
Sea urchins have been helpful in
embryology studies, since they
produce large eggs; fertilize
externally; develop in sea water.
Section 29-2
Invertebrate Chordates
OBJECTIVES:
– Name
and discuss the three
distinguishing characteristics of
chordates.
– Describe the two subphyla of
invertebrate chordates.
Section 29-2
Invertebrate Chordates
The
phylum Chordata, to which
fishes, frogs, birds, snakes, dogs,
cows, and humans belong, will be
discussed in future chapters.
– Most chordates are vertebrates,
which means they have
backbones, and are placed in
the subphylum Vertebrata.
Section 29-2
Invertebrate Chordates
 But,
there are also invertebrate
chordates; these are divided into two
subphyla:
– 1. The tunicates
– 2. The lancelets
 Due to similar structures, the
chordate vertebrates and
invertebrates may have evolved from
a common ancestor.
Section 29-2
Invertebrate Chordates
 Chordates
are animals that are
characterized by a notochord, a
hollow dorsal nerve cord, and
pharyngeal (throat) slits.
– Some chordates posses these
characteristics as adults; others as
only embryos; but all have them at
some stage of development.
Section 29-2
Invertebrate Chordates
Notochord
= a long, flexible
supporting rod that runs through
at least part of the body, usually
along the dorsal surface just
beneath the nerve cord.
– Most chordates only have this
during the early part of
embryonic life.
Section 29-2
Invertebrate Chordates
Vertebrates
will replace the
notochord quickly with the
backbone.
The second chordate
characteristic, the hollow dorsal
nerve cord, runs along the dorsal
surface just above the notochord.
Section 29-2
Invertebrate Chordates
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 its internal organs,
muscles, and sense organs.
Section 29-2
Invertebrate Chordates
 The
third chordate characteristic, the
pharyngeal slits, are paired
structures in the pharyngeal (or
throat) region of the body.
– In aquatic chordates, such as
lancelets and fishes, the
pharyngeal slits are gill slits that
connect the pharyngeal cavity with
the outside.
Section 29-2
Invertebrate Chordates
In
terrestrial chordates that use
lungs for respiration, pharyngeal
slits are present for only a brief
time during the development of
the embryo.
– They soon close up as the
embryo develops. Page 283.
Section 29-2
Invertebrate Chordates
In
humans, pouches form in the
pharyngeal region, but never
open up to form slits.
– Thus, some scientists consider
the pharyngeal pouches, not
slits, as the “true” chordate
characteristic.
Section 29-2
Invertebrate Chordates
 Tunicates
= small marine chordates
that eat plankton they filter from the
water.
– Name from a special body covering
called the tunic.
– Only the tadpole-shaped larvae
have the notochord and dorsal
nerve cord.
Section 29-2
Invertebrate Chordates
Examples
of tunicates are the
sea squirts. Figure 29-11, page
646.
– Adults are sessile, living as
colonies attached to a solid
surface; larvae are free
swimming.
Section 29-2
Invertebrate Chordates
Lancelets
= small fishlike
creatures; live in sandy bottoms
of shallow tropical oceans.
– Unlike tunicates, the adult
lancelets have a definite head;
a mouth that opens into a long
pharyngeal region with up to
100 pairs of gills.
Section 29-2
Invertebrate Chordates
 Figure
29-12, page 646
– They feed by passing water
through their pharynx, where food
particles are caught in a sticky
mucus; lack any jaws.
– They have a primitive heart
pumping blood through closed
circulation.
Section 29-2
Invertebrate Chordates
 Lancelet’s
muscles are organized
into V-shaped units on either side of
the body.
– Each muscle unit receives a
branch from the main nerve cord;
lack any appendages.
– Similar system found in all living
vertebrates.
Section 29-2
Invertebrate Chordates
How
Invertebrate Chordates Fit
Into the World:
– By studying the invertebrate
chordates, it is like using a time
machine to study the ancestors
of our own subphylum.