1. 31.1 Echinoderms Chordates are most closely related to echinoderms
Both groups are deuterostomes
Characteristics of Echinoderms
Marine animals
Endoskeleton made of calcium-rich plates
Spines stick out of their skin
Adults exhibit radial symmetry
Larva are bilateral

2. Echinoderms include:
Sea lilies
Sea cucumbers
Brittle stars
Sea urchins
sand dollars
Sea stars

3. Echinoderm Diversity

7. 31.1 Echinoderms Sea Stars Found along shorelines on rocky surfaces
Five-rayed body with mouth on underside (oral) and anus on upper side (aboral)
On oral surface, each arm has a groove surrounded by tube feet
Structures project through skin
Spines for protection
Pedicelleriae: around base of each spine, keep body surface free of debris
Skin gills: extensions of skin for gas exchange

8. 31.1 Echinoderms Sea Stars Feeding Nervous system
Opens bivalve with its tube feet
Everts cardiac stomach through open shell and releases enzymes
Digested food taken in and digestion completed in pyloric stomach
Intestine is very short and terminates at anus on aboral (upper) surface
Nervous system
No central brain
Central nerve ring gives off branches to each arm
Eyespot at tip of each arm

9. 31.1 Echinoderms
Sea Stars
Locomotion depends on a water vascular system
Water enters through madreporite on aboral side
Madreporite leads into stone canals, and these lead into radial canals in each arm
Water is pumped into tube feet
Suction is created by each small foot
No respiratory, excretory, or circulatory systems
Reproduction is both sexual and asexual
A body fragment, if large enough, can regenerate an entire animal
Bilateral symmetry in larva

10. Sea Star Anatomy and Behavior
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
arm
aboral side
bivalve mollusc a.
© Randy Morse, GoldenStateImages.com

11. Sea Star Anatomy and Behavior
arm
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
central
disc
arm
pedicellaria
endoskeletal
plates
skin gill
digestive gland
eyespot
ampula
radial canal
coelomic cavity
tube feet
b. Aboral side showing ray cross-section

12. Sea Star Anatomy and Behavior
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
rectum
rectal cecum
madreporite
anus
stone canal
pyloric stomach
cardiac stomach
gonads
esophagus
ring canal
mouth
gonopore
lateral canal
central nerve ring
c. Aboral side showing internal cross-section

13. Sunflower star

14. Tube feet

15. Crown of Thorns Starfish

16. Table. 31.1

17. 31.2 Chordates Phylum Chordata characteristics Notochord
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Phylum Chordata characteristics
Notochord
Dorsal tubular nerve cord
Pharyngeal pouches
Postanal tail
postanal tail
notochord
dorsal tubular
nerve cord
pharyngeal pouches

19. 31.2 Chordates Evolutionary trends among the chordates
Invertebrate chordates: tunicates and lancelets
Vertebrate chordates: fishes, amphibians, reptiles, birds, mammals
Cartilaginous fish: first to develop jaws
Some early bony fish had lungs
Not all bony fish have lungs
Amphibians: first to have jointed appendages and invade land
Reptiles, birds, mammals: terrestrial adaptations for reproduction

20. Phylogenetic Tree of Chordates
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mammary gland
common ancestor
amniotic egg
Mammals
Amniotes
limbs
Reptiles*
Tetrapods
Lungs
lungs
Amphibians
bony
skeleton
Gnathostomes
Lobe-finned Fishes
Vertebrates
jaws
Ray-finned Fishes
Chordates
vertebrae
Cartilaginous Fishes
Jawless Fishes
ancestral
chordate
Tunicates
Lancelets
*includes birds

21. 31.2 Chordates Nonvertebrate Chordates
Tunicates (subphylum Urochordata)
Sea squirts squirt water when their siphons are disturbed
Live in ocean and are filter-feeders
Larva is bilaterally symmetrical and has four chordate characteristics
Adults are sessile, thick-walled, sac-like organisms
The only chordate characteristics in the adults are pharynx and gill slits

22. Tunicate Life History Larva undergoes metamorphosis to adult form
oral opening
atrial opening
pharynx with gill slits
Larva undergoes metamorphosis to adult form
Tunicate adult
pharynx
nerve cord
notochord
gut
Tunicate larva
Figure 26.3 Page 446

23. Tunicates

24. Tunicate (Sea Squirt)

25. Sea Squirt, Halocynthia
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excurrent siphon
incurrent siphon
gill slit
tunic
© Rick Harbo

26. 31.2 Chordates Nonvertebrate Chordates
Lancelets (Subphylum Cephalochordata)
Knife-shaped bodies a few centimeters long
Live in shallow coastal waters
Retain all four chordate characteristics as an adult
Segmentation is present
Muscles are segmentally arranged
Nerve cord has branches

27. Lancelet, Branchiostoma
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
rostrum
pharynx
notochord
oral hood
with tentacles
dorsal tubular nerve cord
dorsal fin
gill bars
and slits
caudal fin
atrium
atriopore
ventral fin
anus

28. Lancelet, Branchiostoma
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© Heather Angel/Natural Visions

29. Lancelet, Branchiostoma
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
rostrum
pharynx
notochord
oral hood
with tentacles
dorsal tubular nerve cord
dorsal fin
gill bars
and slits
caudal fin
atrium
atriopore
ventral fin
anus
© Heather Angel/Natural Visions