Echinodermata and
Invertebrate Chordates
Chapter 40
Phylum Echinodermata
Characteristics
• Age of echinoderms is estimated as more than
•
•
•
•
•
•
•
•
•
•
•
500 mil years
All marine
Known as spiny-skinned animals
Endoskeleton known as the test is made of
calcium plates or ossicles with protruding spines
Includes sea stars, brittle stars, sand dollars, sea
urchins, & sea cucumbers
Undergo metamorphosis from bilateral, freeswimming larva to sessile or sedentary adult
Larval stage known as dipleurula or bipinnaria
Adults have pentaradial ( 5 part) symmetry
Lack segmentation or metamerism
Coelomate
Breathe through skin gills as adults
Capable of extensive regeneration
Characteristics cont…
• Ventral (lower) surface called the oral surface &
•
•
•
•
•
•
•
•
•
where mouth is located
Dorsal (upper) surface known as aboral surface &
where anus is located
Have a nervous system but no head or brain in
adults
No circulatory, respiratory, or excretory systems
Have a network of water-filled canals called the
water vascular system to help move & feed
Tube feet on the underside of arms help in
moving & feeding
One-way digestive system consists of mouth with
oral spines, gut, & anus
Deuterostomes (blastopore becomes the anus)
Separate sexes
Reproduce sexually & asexually
Phylum Echinodermata
• Includes 5 classes:
* Crinoidea - sea lilies &
feather stars
* Asteriodea - starfish
* Ophiuroidea - basket stars &
brittle stars
* Echinoidea - sea urchins &
sand dollars
* Holothuroidea - sea
cucumbers
Class Crinoidea
Characteristics
• Sessile
• Sea lilies & feather stars
• Have a long stalk with branching arms
•
•
•
•
that attach them to rocks & the ocean
bottom
Can detach & move around
Mouth & anus on upper surface
May have 5 to 200 arms with sticky tube
feet to help capture food (filter feeders) &
take in oxygen
Common in areas with strong currents &
usually nocturnal feeders
Class Crinoidea
FEATHER STAR
SEA LILY
Class Asteroidea
Characteristics
•
•
•
•
•
•
•
Usually sedentary along shorelines
Starfish or sea stars
Come in a variety of colors
Prey on bivalve mollusks such as clams &
oysters
Have 5 arms that can be regenerated
Arms project from the central disk
Mouth on oral surface (underside)
Class Asteroidea
Starfish Feeding on Clam
Class Ophiuroidea
Characteristics
• Largest class of echinoderms
• Includes basket stars & brittle stars
• Live on the ocean bottom beneath stones,
•
•
•
•
in crevices, or in holes
Have long, narrow arms resembling a
tangle of snakes
Arms readily break off & regenerate
Move quicker than starfish
Feed by raking in food with arms or
trapping it with its tube feet
Class Ophiuroidea
BASKET STAR
BRITTLE STAR
Class Echinoidea
Characteristics
• Includes sea urchins & sand dollars
• Internal organs enclosed by endoskeleton
•
•
•
•
•
or test made of fused skeletal plates
Body shaped like a sphere (sea urchin) or
a flattened disk (sand dollar)
Lack arms
Bodies covered with movable spines
Have a jawlike, crushing structure called
Aristotle's lantern to grind food
Use tube feet to move
Class Echinoidea
Characteristics cont…
• Sea Urchins:
•
* Spherical shape
* Live on ocean bottom
* Scrape algae to feed
* Long, barbed spines make venom
for
protection
Sand Dollars:
* Flattened body
* Live in sand along coastlines
* Shallow burrowers
* Have short spines
Class Echinoidea
SEA URCHIN
SAND DOLLAR
Class Holothuroidea
Characteristics
• Includes sea cucumber
• Lack arms
• Shaped like a pickle or cucumber
• Live on ocean bottoms hiding in caves during the
•
•
•
•
•
•
day
Have a soft body with a tough, leathery outer skin
Five rows of tube feet run lengthwise on the
aboral (top) surface of the body
Have a fringe of tentacles (modified tube feet)
surrounding the mouth to sweep in food & water
Tentacles have sticky ends to collect plankton
Show bilateral symmetry
Can eject parts of their internal organs
(evisceration) to scare predators; regenerate
these structures in days
Class Holothuroidea
SEA CUCUMBER
Structure & Function of
Starfish
Body Plan
• Range in size from 1 centimeter to 1 meter
• Mouth located on oral surface (underside)
• Have an endoskeleton made of calcium
•
•
plates
Sharp, protective spines made of calcium
plates called ossicles found under the skin
on the aboral (top) surface
Have pedicellariae or tiny, forcep-like
structures surrounding their spines to help
clean the body surface
Structure & Function of
Starfish
Body Plan
ABORAL SURFACE
Structure & Function of
Starfish
Water Vascular System
• Network of canals creating hydrostatic pressure
•
•
•
•
to help the starfish move
Water enters through sieve plate or madreporite
on aboral surface into a short, straight stone
canal
Stone canal connects to a circular canal around
the mouth called the ring canal
Five radial canals extend down each arm & are
connected to the ring canal
Radial canals carry water to hundreds of paired
tube feet
WATER VASCULAR SYSTEM
Structure & Function of
Starfish
Water Vascular System
• Bulb-like sacs or ampulla on the
upper end of each tube foot contract
& create suction to help move,
attach, or open bivalves
• Rows of tube feet on oral surface
(underside) are found in ambulcaral
grooves under each arm
Structure & Function of
Starfish
Water Vascular System
TUBE FEET
Tube Feet in Ambulcaral Grooves
Feeding & Digestion
• Tube feet attach to bivalve mollusk shells
•
•
& create suction to pull valves apart
slightly
Starfish everts (turns inside out) its
stomach through its mouth & inserts it
into prey
Stomach secretes enzymes to partially
digest bivalve then stomach withdrawn &
digestion completed inside starfish
Other Body Systems
• No circulatory, excretory, or respiratory systems
• Coelomic fluid bathes organs & distributes food &
•
•
•
•
•
oxygen
Gas exchange occurs through skin gills &
diffusion into the tube feet
No head or brain
Have a nerve ring surrounding the mouth that
branch into nerve cords down each arm
Eyespots on the tips of each arm detect light
Tube feet respond to touch
Reproduction
• Separate sexes
• Two gonads (ovaries or testes) in each
•
•
•
•
arm produce eggs or sperm
Have external fertilization
Females produce up to 200,000,000 eggs
per season
Fertilized eggs hatch into bipinnaria larva
which settles to the bottom after 2 years &
changes into adult
Asexually reproduce by regenerating arms
Characteristics of Chordates
• All chordates have a notochord, dorsal nerve cord,
•
•
•
•
pharyngeal pouches, & postanal tail at some time
in their life
Notochord is a firm, flexible rod of tissue located
on the dorsal side of the body that becomes part
of the endoskeleton in vertebrates
Dorsal nerve cord is a hollow tube lying dorsal to
the notochord that becomes the brain & spinal
cord in vertebrates
Pharyngeal pouches are small outpockets of the
anterior part of the digestive tract that become
gills in aquatic chordates & jaws, inner ear, &
tonsils in terrestrial chordates
Postanal tail consists of muscle tissue & lies
behind the posterior opening of the digestive
tract
Characteristics of Chordates
Subphyla of Chordates
• The Phylum Chordata includes all of the
•
•
vertebrates, as well as two groups of marine
animals that lack backbones and are called
invertebrate chordates
The phylum is divided into three subphyla,
determined by the development of the notochord
Subphylum Cephalochordata contains about 24
species of blade-shaped animals known as
lancelates that retain the notochord, dorsal nerve
chord, pharyngeal pouches, and postanal tail
throughout their life
Subphyla of Chordates
cont…
• Subphylum Urochordata contains 2,000
species commonly called tunicates
because their bodies are covered by a
tough covering, or tunic
* Called sea squirts because they shoot
out a stream of water when touched
*Sessile, barrel-shaped, filter feeding
animals that live on the sea bottom
*Adults have a pouch-like pharynx with
slits
*Adults do not have a notochord, dorsal
nerve cord, or postanal tail
Subphyla of Chordates
cont…
• Subphylum Vertebrata is the largest
subphylum in which the notochord is
replaced with vertebrae
* Skeletons consist of bone &/or
cartilage
* Brain is protected by a cranium
* Well developed 4 chambered heart
with a closed circulatory system
* Includes fish, amphibians, reptiles,
birds, & mammals
Chordate Characteristics
Feature
Notochord
Dorsal
Nerve
cord
Pharyngeal
pouch
Postanal
tail
Vertebrata
Cephalochordata
Urochordata