Download Phylum Echinodermata: Echinoderms

Phylum Echinodermata:
Echinoderms
A. General Characteristics
1. Echin- Spiny
Dermis- Skin
2. Pentaradial: 5 part radial symmetry
3. Water Vascular System: System of internal
tubesinternal network of fluid filled canals connected to
tube-feet. Involved in many processes:





feeding
respiration
internal transport
elimination of wastes
movement
4. Tube-Feet: suction cup-like structures.
Structure
B. Structure
1. No anterior, posterior, or brain
2. Two sides:
a. aboral- top of the body
b. oral- side where the mouth is located
(hint to remember: orajel, oralB floss)
3. Spiny skinned
Movement
C. Water Vascular System
1. Sieve Plate (madreporite): located on the aboral surface
water enters into the starfish
2. Ring Canal: Surrounds the mouth
Surrounds the mouth
3. Stone canal: carries water into the ring canal.
4. Five Radial Canals: These extend from the ring canal to each
body segment. Water moves from the ring canal into these radial
canals. This is how water reaches the rest of the body.
5. Tube-Feet: Suction cup like structures
When water is pushed in- tube feet expands
When water is pulled out- The ampulla shrinks creating a vacuum
suctioning to what it is touching.
6. Ampulla: Muscular sac at the base of each tube foot that
contains fluid.

Hint: This is how a dropper works.
Feeding/Excretion
 Feeds on mollusks, worms, and other slow moving animals
D. Feeding Process:
1. use tube feet to pry open shells of mollusks
2. Once the shells are open, it flips its stomach out of
its mouth it pours out enzymes to digest the meat of
the mollusk in its own shell
3. when partially digested, the starfish pulls its
stomach back into its mouth to finish its meal
E. Excretion Process;
1. diffusion through the thin walls of the tube feet
2. diffusion through the skin gills.
Respiration/Nervous Systems
F. Respiration
1. Exchange of oxygen(O2) and carbon dioxide (CO2)
occurs through diffusion of skin gills and tube feet.
G. Nervous System
1. Nerve Ring: surrounds the mouth
2. Radial Nerves: connects to the nerve ring. they
extend into each arm.
3. Eyespots: located at the end of each arm, detect light
4. Tube feet: sense touch
5. Scattered sensory cells: sense chemicals
Reproductive System
H. Reproduction
1. Separate Sexes:
a. produce egg or sperm which fill the arms during the
reproductive season.
b. eggs and sperm are released into open water
c. starfish detect gametes of their own species
d. respond by releasing their gametes (egg or sperm)
into the water.
e. fertilization occurs in the open water.
2. Regeneration
a. this can occur if part of the central disc is present

anatomy of a starfish



ring canal
Circular canal in which filtered water enters through the madreporite and branches out into the
radiated canals.


rectal cecum
Lateral duct of the terminal part of the digestive tract, where waste is stored before being expelled
through the anus.


anus
Terminal orifice of the digestive tract allowing waste to be ejected; most of the undigested food is
regurgitated rather than expelled through the anus.


stomach
Dilated section of the digestive tract preceding the intestine; it receives food to be digested.


gonad
Each of the two glands located in each arm, producing gametes (spermatozoids or ovules) depending
on the sex of the starfish.


pyloric cecum
Radiated duct of the digestive tract producing digestive enzymes and also allowing digested food to
be stored.


gonopore
Dorsal opening through which gametes (spermatozoids and ovules) are expelled into the water to be
fertilized.


intestine
Section of the digestive tract between the stomach and the anus where absorption of nutrients is
carried out and waste is transformed into fecal matter.


radial canal
Canal running the length of the arm; it receives water from the annular canal, which then passed into
the tube feet.


ampulla
Bulb that contracts to let water enter the tube foot, allowing it to extend; when it dilates, the foot
retracts.


esophagus
Muscular membranous channel of the anterior section of the digestive tract; it allows food to reach the
stomach.


mouth
Anterior cavity of the digestive tract located on the ventral surface that allows food to be ingested.