Phylum:Echinodermata

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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

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