Phylum Echinodermata
ECHINODERMS!
Class Crinoidea
• Special Characteristics: Mouth Faces
Upward and is surrounded by many arms
– 600 species
– Species include- Sea Lilies and Feather Stars
Florometra serratissima
Class Asteroidea
• Body usually has five arms and double
rows of tube feet on each arm
• Mouth faces downward
• 1,500 Species
Ex. Sea Star
Six-Rayed Starfish
Leptasterias hexactis
Class Ophiuroidea
• Usually has five slender and delicate arms
or rays
• 2,000 Species
• Ex. Brittle Stars and Basket Stars
Daisy Brittle Star-Ophiopholis aculeata
Class Echinoidea
• Body is Spherical, oval, or disck shaped
• Arms lacking but five part body plan is still
seen
• 900 Species
• Ex. Sea Urchins and Sand Dollars
Centrostephanus rodgersii
Class Holothuroidea
• Elongated, thickened
body
• Tentacles around
Mouth
• 1,500 Species
• Ex. Sea Cucumbers
Thelenota rubralineata
Evolution
• Echinoderms first evolved from a single-celled organism
• Popular Belief that Echinoderms evolved from ancestors
which lived in the Pre-Cambrian and Cambrian Periods
– Supported by a fossils paleontologists found that they
believe was a pre-echinoderm ancestor in the PreCambrian period
– Other echinoderms resemble fossils of the Cambrian
Period as well
• No Fossils found of direct Echinoderms due to the lack
of calcium carbonate in the Echinoderm’s exoskeleton
• Echinoderms are most closely related to the Phylum
Chordata
Symmetry/Structural Support of an
Echinoderm
• Symmetry- Echinoderms have Pentaradial symmetry
– What's Pentaradial Symmetry?
– Pentaradial Symmetry is a form of body symmetry
where the body parts extend from the center along
five spokes Ex. Star Fish
• Structural Support- Echinoderms have an endoskeleton
composed of Ossicles
– Ossicles are plates composed of calcium carbonate
Body Cavity of Echinoderms
• Body Cavity- Echinoderms have a
Deuterostome body cavity
– That means that in the embryos of
echinoderms, the blastopore develops
into the anus, and a second opening in
the embryo becomes the mouth
Nutrition/Digestion
• Class Crinoidea
– Sea lilies and Feather Stars-Feed by using their stick tube feet,
which suck small organisms from the water
– The organisms get filtered and get transported by cilia to the
Crinoids' mouth which, unlike most echinoderms, faces up
• Class Ophiuroidea
– Basket Stars and Brittle Stars-Use their long arms to rake food
in, such as small organisms from the bottom of the ocean or from
Coral reefs
– Also, trap food particles with their tube feet or with mucous
strands
• Class Echinoidea
– Sea Urchins-Use their five teeth surrounding their mouth to
scrape algae from surfaces
– Sand Dollars- use their tube feet to capture food that lands on
their body or swims over them
Nutrition/Digestion Cont…
• Class Holothuroidea
– Sea Cucumbers – extend their tentacles,
made up of miniature tube feet, out of their
mouths and sweeps up food around itself
– Then it brings its tentacles inside its mouth
and cleans the food off of them
Nutrition/Digestion Cont…
• Class Asteroidea
– Sea Stars are carnivorous and feed on mollusks,
worms, clams, and slow moving objects
– Sea Stars, once they capture their prey extract their
cardiac stomach which sucks the food into itself
– When finished the Cardiac Stomach goes back into
the mouth and transfers the food to the Pyloric
Stomach
– The Pyloric Stomach is connected to digestive glands
in each arm which digest the food completely and
absorb the nutrients
Transportation/Circulation
• Echinoderms use the Water-Vascular System for
Transportation
• The Water-Vascular System is a network of canals filled
with water that connect to the tube feet of echinoderms
and through water pressure the tube feet extend and
contract causing the organism to move
– Water enters the system through small pores in the
madreporite
– Then it heads to the stone canal, a tube that
connects the madreporite to the ring canal, which
goes around the mouth
– Then the Radial canal extends from the ring canal to
the end of each arm sending water to the tubes
• Confused? Here’s a Movie to show you the movement
of the tube feet
• Circulation- All Echinoderms lack a circulatory system
however fluid from the coelom distributes nutrients and
Gas Exchange/Respiration
• Echinoderms don’t posses a
system of Respiration except
the fluid from the coelem that
gives the organism oxygen
• Gas exchange takes place by
diffusion through the skin
gills, hollow tubes that protect
from the coelom lining to the
exterior
• Some echinoderms use their
tube feet to exchange oxygen
and carbon dioxide with the
Water Balance/Excretion
• Echinoderms lack any main excretory
systems, but do excrete their wastes
through the thin walls of the tube feet
• Echinoderms use their tube feet to extract
water and use their madreporite to take
water in, which are part of the WaterVascular System
Reproduction/Development
• Most species of echinoderms are separate sexes
• Each arm that is attached to the central region contains
a pair of ovaries or testes which produce eggs or sperm
• Each is released from a different echinoderm and
fertilization occurs externally
• Each fertilized egg develops into a bipinnaria, a
bilaterally symmetrical free-swimming larva
• After a certain amount of time, usually two months, the
larva settles to the bottom of the ocean or sea and
begins metamorphosis
• During Metamorphosis the larva changes from a
bilaterally symmetrical organism to a pentaradially
symmetrical adult
•
Unique Characteristics and
Echinoderms are ableFacts
to regenerate any one of
their five appendages so long as it is attached to
the central region
• Regeneration may take up to a year
• This can be used as a great defense mechanism
• Echinoderms have always been great souvenirs,
so long as they have been properly dried
• Echinoderms are beloved characters of movies
and television, most notably Patrick Star
From SpongeBob SquarePants