Echinoderms and Invertebrate
Chordates
Ch 29
Echinodermata
• Endoskeleton, radial symmetry, simple
nervous system, varied nutrition, water
vascular system
– Water vascular system—hydraulic system
that operates under water pressure, enables
animal to move, exchange gases, capture
food, excrete wastes
• Move along surfaces and pry open food with tube
feet http://youtu.be/Ss24TLqbCfU http://youtu.be/A100m5EpfFI
– Water enters and leaves through
madreporite, a sievelike, disk-shaped
opening on the upper surface of body
• Bilaterally symmetrical, ciliated larvae
• Deuterostomes (mouth forms 2nd)
Diversity of Echinoderms
• ~6000 species exist today, 6 classes
– Asteroidea: sea stars (25% of phylum)
• most species have 5 rays, but some can have more than 40!
– Ophiuroidea: brittle stars
• Extremely fragile, rays can break off (helps survive predator attacks), propel
themselves by slithering, tube feet for feeding
– Echinoidea: sea urchins and sand dollars
• Globe-/disk-shaped, covered with spines, no rays, tube feet for eating and
modified as gills for respiration
– Holothuroidea: sea cucumbers
• Vegetable-like appearance, moves along ocean floor, expels tangled sticky
mass of tubes through anus or ruptures and loses organs, which regenerate
in a few weeks (evasion of predators)
– Crinoidea: sea lilies and feather stars
• Resemble plants, sea lilies only sessile echinoderms, feather stars sessile in
larval form; use feathery arms to swim around
– Concentricycloidea: sea daisies
• Two species discovered in New Zealand, tube feet around edge of disk
Invertebrate Chordates
• All chordates have a notochord—a long,
semirigid, rodlike structure between digestive
system and dorsal hollow nerve cord
– Made up of large, fluid-filled cells held within stiff
fibrous tissue
• Invertebrates: may retain notochord to adulthood
• Vertebrates: notochord replaced with backbone
• All chordates have dorsal hollow nerve cord
– Develops from a plate of ectoderm that rolls into a
hollow tube
• Composed of cells surrounding fluid-filled canal above the
notochord
Embryonic
invagination of the
notochord and
neural tube
Anterior region with
early central nervous
system
Commonalities in Chordates
• All chordates have a notochord
• All chordates have pharyngeal pouches
– Paired openings in pharynx behind mouth
• All chordates have a postanal tail
– At some point in development
• Development controlled by homeotic genes
Diversity of Invertebrate Chordates
• Tunicates (sea squirts): chordate features visible in
larval stages http://www.youtube.com/watch?v=s95rfGnclX0
• Lancelets (similar to fish): spend most of their time
buried in sand with only heads out to filter food
from water
Origins
• Fossil record is limited because of soft bodies
• Possibly arose from sessile animals that fed by
tentacles (larval stages may be similar)