Download echinoderms

KINGDOM ANIMALIA
Phylum Echinodermata
Members of the
Phylum Echinodermata
Date back 570
million years ago
13,000 fossil species
Only 7,000 species
today
Most are marine and
benthic (90%)
Range in size (<1cm
to 2 m)
5 Classes
Common Body Plan
Adults are
pentaradially
symmetrical
5 sets of
body parts
around an
oral-aboral
axis
Common Body Plan
However, larvae are bilaterally symmetrical
Settle near adults of their species and attach to
substrate
Metamorphosis: left side becomes oral surface of the
adult and right side becomes aboral
Larval mouth/anus disappear, gut migrates to adult
position, and new mouth/anus open
Endoskeleton
Unique system of calcareous
plates (ossicles)
Reduced in sea cucumbers
Fused to form a solid test in
sea urchins/sand dollars
Endoskeleton
Skeletal elements
bear pincer-like
structures called
pedicellariae
Use to rid body of
debris, defense,
grasp objects to
hide, or
capture/hold prey
Water-vascular system
Hydraulic system of canals and
reservoirs controls the
movement of tube feet (podia)
Critical to locomotion, gas
exchange, feeding, and sensory
reception
Water-vascular system
Water enters sieve
plate (madreporite)
Flows from stone
canal to radial canals
in each arm
Lateral canals
perpendicular to the
radial canal terminate
in muscular bulb
(ampulla) connected
to a tube foot
Water-vascular system
Water enters bulb, it
contracts and water
forced into foot
Extends foot, pressing
terminal sucker onto
substrate
Foot contracts, forcing
water back into bulb
and raises center of
sucker
Creates a vacuum seal;
only broken when bulb
contracts water into
foot again
Classification
There are 6
classes of
echinoderms
5 classes are
described on
the following
slides
Class Crinoidea
Most ancient/primitive
625 species
Base of 5 or 10 arms that can branch
up to 200 arms
Suspension feeders
Each arm bears suckerless podia that
produce mucus to capture detritus and
transport it to mouth
Class Crinoidea
Sessile sea lily
Cup-like body
attached to stalk
Attached to
substrate
Can bend stalk
and flex/extend
arms
Class Crinoidea
Free-moving
feather star
Stalk lost during
larval
development
Can crawl/swim
Jointed
appendages (cirri)
help it regain
balance
Class Asteroidea
1500 species of sea stars
5 or more broad arms
surround a central disk
Crawl on rocks or live on
sea bottom
Most are scavengers or
predators
Each arm bears podia
with suckers
Evert stomach into prey
and digest it
Class Ophiuroidea
2000 species of
brittle stars
Usually concealed in
sand or under objects
Some live in sponges
or other colonial
organisms
Only 5 arms that are
usually highly
branched
Class Ophiuroidea
Arms are distinct
from central disk
Can crawl/cling
Predators,
scavengers, or
suspension feeders
Flexible arms bear
suckerless podia that
secrete mucus to
entrap food and
transport it to mouth
Class Echinoidea
1000 species of sea urchins/sand dollars
Movable spines and podia surround body;
used for locomotion
Herbivorous, detrivorous, suspension
feed, a few predators
Class Echinoidea
Unique feeding
apparatus called
Aristotle’s lantern
Hard plates and
muscles just inside
mouth
Possesses 5
calcareous teeth
Teeth protract to
scrape algae off rocks
or tear chunks of kelp
Class Holothuroidea
1150 species of sea
cucumbers
Mucus-covered oral
tentacles trap on
plankton or ingest sand
organic matter
Gut modified to produce
respiratory trees used for
gas exchange
Expel portions of these
trees as defense
mechanism; regenerate