PHYLUM
ECHINODERMATA
DIVERSITY
 Over

7,000 species worldwide
Live in aquatic, marine environments
 Name
“Echinodermata” comes from their external
spines
 Notable characteristics:






1) Spiny endoskeleton of plates
2) Water-vascular system
3) Special outer layer (pedicellariae)
4) Respiratory system: dermal branchiae
5) Radial symmetry (in adults)
6) VERY bizarre and unique animals
DIVERSITY
 Examples

include:
starfish/sea star, brittle star, sea cucumber, sea lilies, sea
daisies, sea urchins
 Fill
a wide range of ecological roles and have
enormous variation

Food, bioindicators, decoration, etc
 Called
Echinoderms
 Echinoderm means “prickly skin”
CHARACTERISTICS OF ECHINODERMS
BODY TYPE AND SYMMETRY
Body is unsegmented
 Radial symmetry

Arranged around a central point
 Pentaradial - Most have five parts (called ambulacra)
that radiate outward
 Adult form radial/larva bilateral


Body shape


Round, cylindrical or star-shaped
Body contains spines

Can be external or internal
CHARACTERISTICS OF ECHINODERMS
EXTERNAL FEATURES
 Endoskeleton
Made of calcium (dermal calcareous
ossicles)
First endoskeleton we’ve seen (besides one
exception in Mollusks)

Pedicellariae which
keep debris off body,
protect animal and food
capture
CHARACTERISTICS OF ECHINODERMS
REPRODUCTION
Asexually (regeneration)
Separate sexes (except a few hermaphrodites)
Fertilization usually external
Free swimming, bilateral larval stages

Characteristics of Echinoderms
Water vascular system
Allow them to move, obtain food, exchange
gases and excretion
Parts:
1) Sieve plate – water enters and leaves
2) Ring canal – water flows into this from the
sieve plate

CHARACTERISTICS OF ECHINODERMS
 Water Vascular system, cont.

Parts, cont.:
3) Radial canal – each arm has one of
these, connected to ring canal
4) Ampulla – muscular sac that helps
force water into a tube foot
5) Tube foot – hollow tube with suctioncups on the end, helps with attachment,
detachment
Tube feet w/
moving sea star
CHARACTERISTICS OF ECHINODERMS
Complete digestive system
 Circulatory system (Blood-vascular or hemal) is
reduced in size
 Respiration

Dermal branchiae
 Tube feet
 Respiratory trees or bursae


NO Excretory organs
CHARACTERISTICS OF ECHINODERMS

Nervous system
No head or brain
 Few specialized sensory organs
 Do contain a few sense receptors, photoreceptors
(light), and chemoreceptors
 Ocelli at tips of arms
 Senses include touch, temperature, chemicals and light

CLASSIFICATION

Class Asteroidea
1500 living species
 Found on shorelines near rocks or near sandy/muddy bottoms
among coral reefs
 Brightly colored
 Range in size from centimeter across to almost 3 feet across
 Many are carnivorous (eat other animals – like mollusks, other
echinoderms, small fish)
 Ex: sea stars, starfish, pea star, leather star

CLASSIFICATION

Class Ophiuroidea




2000 living species
Found in ocean bottoms (benthic), marine areas
Very secretive animals where little to no light penetrates
Ex: brittle stars
CLASSIFICATION

Class Echinoidea




950 living species
Found in all sea areas (intertidal regions to deep ocean bottoms)
Lack arms, very brightly colored, some contain toxins
Ex: sea urchins, sand dollars, heart urchins
CLASSIFICATION

Class Holothuroidea
1150 living species
 Found in all sea areas (intertidal regions to deep ocean bottoms)
 Some crawl, others found beneath rocks, other burrow
 Elongated bodies, bodies are soft
 Ex: sea cucumbers

CLASSIFICATION

Class Crinoidea
625 living species
 Found in all sea areas (intertidal regions to deep ocean bottoms)
 Stay attached to ocean bottoms/rocks/coral most of their lives
 Stiff, hardened bodies
 Ex: sea lilies, feather stars

STARFISH CHARACTERISTICS
 General Characteristics
Radial symmetry
 Contain five arms/rays

Each arm radiates out from a central disc
If an arm is lost/damaged, it can usually
be regenerated.

STARFISH CHARACTERISTICS
Contain a coelom
Water vascular system:

Use this to move, gather food, respiration
and excrete wastes
Use tube feet (tiny podia that expel
water)


Excretion:
Contain anus
Also use water vascular system

STARFISH CHARACTERISTICS
 General Characteristics, cont.

Digestion:
Contain mouth (on underside/ventral side
of sea star)
Each arm is full of digestive glands (which
digest food that enters mouth)
Contain a pyloric stomach (digests food)
Also contain cardiac stomach (which they
can push OUT of body to engulf prey)
Intestines is SHORT (connects stomach to
anus)

STARFISH CHARACTERISTICS
 Diet:

Clams, oysters, small fish, other arthropods,
dead/decaying matter, coral, sponges, plankton
 Reproduction:



Capable of both sexual and asexual reproduction
Separate sexes
External fertilization
 Ecological


importance:
Decoration
Bio-indicators (help us to determine how polluted
water environments are)
DISSECTION STARFISH
Video Dissection External and Internal