Sea stars belong to the Phylum
Echinoderms. That means they are
related to sand dollars. Sea urchins, and
sea cucumbers. All echinoderms have
five-point radial symmetry , which means
that their body plan has five sections
arranged around a central disk.
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Although sea stars live underwater and
are commonly called “Starfish“, they are
not fish. They do not have gills, scales, or
fins like fish do and they move quite
differently from fish. While fish propel
themselves with their tails, sea stars have
tiny tube feet to help them move along
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While the five-armed varieties of sea star
are the most well known, not all sea stars
have 5 arms. Some have many more.
Take the sun star for instance, which has
up to 40 arms!
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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.
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Internal anatomy of a starfish: marine animal with radiating
symmetry. They are equipped with numerous tube feet.
Sieve plate: entrance to the water-vascular system of a
starfish.
Anus: end of the digestive tract of a starfish.
Rectal cecum: cul-de-sac related to the rectum.
Ray: limb of a starfish.
Ring canal: tube that forms a ring of a starfish.
Tube feet: organ of locomotion of a starfish.
Digestive gland: organ of a starfish that secrets digestive
enzymes.
Cardiac portion of the stomach: part of the stomach of a
starfish used for pumping blood.
Pyloric portion of the stomach: part of the stomach of a
starfish connected to the duodenum.
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Starfish vary in size. They usually have five to ten inches in length
and weigh up to 11 pounds.
Common feature for all starfish is that their body is radially
symmetrical. That means that their body can be divided in five
equal pieces (even if they have more than five arms).
Another impressive characteristic of the starfish is their ability to
regenerate different (missing) parts of their body. If predator eats
part of the starfish, remaining part (one arm for example) will
develop missing arms and bring back previous look after some
time. This process is not always fast and it may last up to one
year.
Starfish is a carnivore who likes to eat clams, shells and mussels. It
has two stomachs, one of which can be pushed outside the
body during eating. This tactic allows them to eat large prey
(that cannot be swallowed with their small mouth).
Starfish mouth is located on the underside of its body. Anus is
located on the upper side of the body.
http://visual.merriamwebster.com/animal-kingdom/simpleorganismsechinoderms/echinoderms/anatomystarfish.php
 http://www.softschools.com/facts/anim
als/starfish_facts/85/
 http://marinelife.about.com/od/inverteb
rates/tp/seastarfacts.htm
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