Phylum:Echinodermata
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Transcript Phylum:Echinodermata
Phylum
Echinodermata
Chapter 16
Phylum:Echinodermata
Means
“spiny-skinned”
Approximately 7,000 species
All are found in marine habitats – all depths
Echinoderm Characteristics
Calcareous
endoskeleton in the form of ossicles
Adults with pentaradial symmetry and larvae with
bilateral symmetry
Water-vascular system used in locomotion,
attachment, and/or feeding
Complete digestive tract
Hemal system derived from coelomic cavities
Nervous system: nerve net, nerve ring, radial
nerves ( no “brain” )
Echinoderm Evolution
Thought
to share a
common ancestor with
hemichordates and
chordates.
Evidence:
Deuterostome
development
Bilaterally symmetrical
larval stages
Extinct forms were not
radially symmetric
Pentaradial Symmetry
Body
parts are
arranged in fives, or
multiples of fives,
around an oral-aboral
axis
No distinct head region
Adaptive for sedentary
or slow moving animals
(allows a uniform
distribution of sensory,
feeding, and other
structures)
Echinoderm Endoskeleton
Pentaradial
symmetry may be a result of the
evolution of the echinoderm endoskeleton
Consists of a series of ossicles – calcium
carbonate plates
Frequently modified into spines that project
from body surface
X-Ray of endoskeleton
Water-Vascular System
Unique
to echinoderms
Series of water-filled canals with extensions
called tube feet
Originates as a modification of the coelom
Ring canal surrounds the mouth, opens to the
outside through a stone canal and an
opening called the madreporite
5 (or multiples of) radial canals branch from
the ring canal; one in each arm of sea stars
Water-Vascular System
Water-Vascular System
Tube
feet are extensions of the canal
system and emerge through skeletal
ossicles
Internally: tube feet end in a bulblike,
muscular ampulla
Ampulla contracts and forces water
into the tube foot which then
extends
Suction cup at opposite ends of tube
feet contract and create a vacuum
Water- Vascular System
Used
in locomotion
but has additional
functions:
Original purpose:
feeding
Soft membranes of
tube feet allow for gas
exchange and
diffusion of
nitrogenous wastes
across the body wall
Hemal System
Consists
of strands of tissue that encircle an
echinoderm near the ring canal of the watervascular system and run into the radial canals
of the arms
Derived from the coelom
Circulates fluid using cilia that line channels
Function largely unknown but may aid in
transport of large molecules, hormones, or
coelomocytes (engulf and transport waste)
Class Asteroidea
Includes
Sea Stars
~ 1500 species
Most live on hard
substrates
Most brightly
colored
Class Asteroidea Characteristics
Usually
have five arms that radiate from
center
Has movable and fixed spines
Oral and aboral surface
Class Asteroidea Characteristics
Dermal
branchiae or
papulae: thin folds of the
body wall which function
in gas exchange
Ambulacral groove: series
of ossicles in arm which
run the length of the oral
surface
Houses the radial canal
Paired rows of tube feet
on either side
Class Asteroidea Movement
Sea
Star tube feet move in a
stepping motion coordinated by
the nervous system
Alternate extension, attachment
and contraction.
All tube feet move in the same
direction, but not in unison.
Provide attachment during wave
action
Class Asteroidea Feeding
Feed
on snails, bivalves,
crustaceans, corals, detritus, etc.
Mouth opens to a short
esophagus and then to stomach
area.
Two stomachs:
Cardiac
stomach – large oral
stomach which receives ingested
food
Pyloric stomach – smaller aboral
stomach absorbs digested food
Class Asteroidea Feeding
How
sea stars feed on bivalves:
Wraps around bivalve’s opening
Tube feet attach to outside of shell and forces
valves apart
Cardiac stomach lowered into bivalve
Digestive enzymes released into shell for partial
digestion
Continued digestion occurs in pyloric stomach
Stomach retracts into sea stars
Sea Star Eating Squid
Class Asteroidea Regeneration
Capable
of regeneration
In some cases, an entire sea
Click here for star can regenerate from a
piece of broken arm
regeneration
video
Broken
part must contain portion
of central disk
Complete
regeneration may
take up to a year
Class Asteroidea Reproduction
Most
are dioecious
Two gonads present in each arm
External fertilization
Spawning coordinated by
environmental factors
Length of light/dark
Water temperature
Bipinnaria
symmetric
larvae bilaterally
Class Ophiuroidea
“Snake
Tail”
Over 2,000 species
Most diverse group
Includes brittle stars and
basket stars
Arms are long and sharply set
off from central disk
Central disk has pentagonal
shape
Class Ophiuroidea
Water
vascular system is NOT used for
locomotion
Ossicles (calcium carbonate plates of
skeleton) are modified to permit a unique
form of grasping and movement
Result is snake-like locomotion
Tube feet do not have suction disks (unlike
sea stars)
Brittle Star "Crawling"
Class Ophiuroidea
Feeding
Predators
and
scavengers
Use arms and tube
feet to sweep in food
and trap plankton
Maintenance
Capable
of
regeneration
(autonomy for
defense)
Dioecious, males are
smaller and often
carried by females
Class Echinoidea
~1,000
species
“Spiny”
Includes sea urchins, sand dollars and heart urchins
Attach to hard substrates or burrow in sand
Class Echinoidea
Skeleton
is called a “test”
Made of 10 sets of closely fitting plates
Move
by using spines for pushing against substrate
and tube feet for pulling
Some sea urchins have sharp spines and venom
Class Echinoidea
Feeding
Feed
on algae, coral
polyps and dead
animal remains
Specialized chewing
apparatus:
“Aristotle’s Lantern”
Reproduction &
Development
Dioecious
Gametes
shed into
water
External fertilization
Larva undergoes
metamorphosis
Class Holothuroidea
“Sea
Cucumber”
~1,500 species
Includes the sea cucumbers
Lack arms
Have elongate bodies
Class Holothuroidea
Tube
feet enlarged and highly modified
Surround mouth and are called “tentacles”
Mostly
sluggish burrowers and creepers
Locomotion using tube feet is inefficient
Contraction of body-wall muscles produce
wormlike movements
Class Holothuroidea Feeding
Ingest
particles using
tentacles
Food is trapped by mucus
on tentacles
Thrust tentacles into mouth
and “wipe off” trapped
food
Stomach, long, looped
intestine, a rectum, and an
anus
Class Holothuroidea Respiration
“Respiratory
Trees”
Pair of tubes which attach at
rectum and branch
throughout body
Pumping action of rectum
circulates water into tubes
Gases and nitrogenous
wastes exchanged between
water and coelom through
respiratory trees
Class Holothuroidea Defense
Defenseless
against predators? No!
Many produce toxins in body walls
Some evert tubules of respiratory
trees through anus (turn inside out)
Tubules have toxins and are sticky
Can entangle and immobilize
predators
Evisceration
of respiratory trees
and/or gonads a result of chemical
and physical stress
Regeneration of lost parts
Class Holothuroidea
Reproduction
Most
are dioecious
Have a single gonad
External fertilization
Tentacles may trap eggs and bring to body
surface for brooding
Embryos
develop into planktonic larvae
Can also reproduce by transverse fission
followed by regeneration
Class Crinoidea
Only
~630 living species
Includes Sea Lilies and
Feather Stars
Most primitive of all
living echinoderms
Extensive fossil records
indicates high numbers
during Paleozoic era
(200 to 600 mya)
Class Crinoidea
Very
different from other
echinoderms
Sea Lilies attach
permanently to substrate by
a stalk (sessile)
Feather Stars swim by raising
and lowering the arms and
crawl by pulling with the tips
of their arms.
Class Crinoidea
Feeding
Suspension
feeding:
Outstretched arms
to trap plankton
Cilia carries to
mouth
Water-vascular
system used mostly
for feeding (not
locomotion)
Response
Lack
a nerve ring but
do have a “nerve
mass” and radial
nerves that extend
through each arm
Controls tube feet
Class Crinoidea
Reproduction
Most
dioecious
In monoecious
species, male
gametes develop
first to allow for
cross-fertilization
Regeneration