1. Echinoderms
CHAPTER 14

3. Phylum Echinodermata: Diversity and Characteristics
All members have a calcareous skeleton
Spiny endoskeleton consists of plates
Unique water-vascular system
radial symmetry in adults

4. Phylum Echinodermata: Diversity and Characteristics
Likely descended from bilateral ancestors
Larvae are bilateral
Perhaps evolved radiality as an adaptation to sessile existence
Body plan is derived from crinoid-like ancestors transformed into free-moving descendants
Lack ability to osmoregulate
Restricts them to marine environments

6. Phylum Echinodermata: Diversity and Characteristics
None are parasitic
Asteroids or sea stars
Mostly predators
Ophiuroids or brittle stars
Move by bending their jointed muscular arms
May be scavengers, browsers, or commensal
Holothurians or sea cucumbers
Mostly suspension or deposit feeders

8. Phylum Echinodermata: Diversity and Characteristics
Echinoids or sea urchins
Found on hard bottoms while sand dollars prefer sand substrate
Feed on detritus
Crinoids
Sessile and flower-like as young and detach as adults
Suspension feeders

9. Phylum Echinodermata: Diversity and Characteristics
Ecology, Economics, and Research
Due to spiny structure, echinoderms are not often preyed upon
A few fish and otters are adapted to feed on sea urchins
Sea stars feed on molluscs, crustaceans, and other invertebrates
May damage oyster beds

10. Class Asteroidea Form and Function External Features
Have a central disc with tapering arms extending outward
Body is flattened and flexible, with a pigmented and ciliated epidermis
Mouth is on the underside or oral surface
Usually there are 5 arms but there may be more
rows of tube feet

13. Class Asteroidea Water-Vascular System
This system is another coelomic compartment and is unique to echinoderms
Functions in locomotion, food-gathering, respiration, and excretion
Opens to outside at madreporite on aboral side
Madreporite leads to stone canal, which joins ring (circular) canal that encircles the mouth
Radial canals diverge from ring canal and extend into each ray

15. Class Asteroidea Feeding and Digestive System
Mouth leads through a short esophagus to large central stomach
Lower part of stomach can be everted through the mouth during feeding
Anus is inconspicuous
Consume a wide range of food
Sea urchins
Molluscs
Sea stars pull valves apart and evert stomach through crack
Small particles carried by tube feet to mouth

16. Class Asteroidea Reproductive System, Regeneration, and Autonomy
Sexes separate in most sexes
Pair of gonads
Fertilization is external
Eggs and sperm are shed into the water in early summer
Regenerate lost parts
Cast off injured arms and regenerate new ones
An arm can regenerate a new sea star if at least one-fifth of central disc is present

17. Class Asteroidea Sea Daisies Diversity and Characteristics
Small, disc-shaped animals discovered in deep water off New Zealand
Described in 1986, only two species are known

19. Class Ophiuroidea Form and Function Largest in number of species
Over 2000 extant species
Arms of brittle stars are slender and distinct from the central disc
Tube feet lack suckers
Biology
Brittle stars are secretive and live on hard or sandy bottoms where little light penetrates
Often under rocks or in kelp holdfasts
Browse on food or suspension feed
Basket stars perch on corals and extend branched arms to capture plankton

22. Class Echinoidea Diversity Reproduction
Approximately 950 species of living echinoids
Sea urchins lack arms but their tests show five-part symmetry
Most sea urchins have radial symmetry and long spines
Sand dollars and heart urchins (irregular echinoids) have become bilateral with short spines
Echinoids occur from intertidal regions to deep ocean
Reproduction
Sexes separate
Gametes are shed into sea for external fertilization

25. Class Holothuroidea Diversity
Approximately 1150 species of holothuroids
As common name suggests, these animals resemble cucumbers
Greatly elongated in the oral-aboral axis
Ossicles are greatly reduced and body is soft
Some species crawl on the ocean bottom, others are found under rocks or burrow

27. Class Holothuroidea Reproduction Sexes are separate in most
Fertilization is external
A few brood their young inside the body or on the body surface
Biology
Sea cucumbers use ventral tube feet and muscular body waves to move
Some trap particles on the mucus of tentacles, ingesting food particles in pharynx
Others graze sea bottom with tentacles
Cast out part of viscera when irritated
Must regenerate these tissues
Organs of Cuvier are expelled in direction of an enemy
Sticky and have toxins
One small fish, Carapus, uses the cloaca and respiratory tree of a sea cucumber for shelter

29. Class Crinoidea Diversity
Crinoids include both sea lilies and feather stars
Far more numerous in fossil record
Unique in being attached for most of their life
Sea lilies have a flower-shaped body at tip of a stalk
Feather stars have long, many-branched arms
Adults are free-moving but may be sessile
Many crinoids are deep-water species
Feather stars are found in more shallow water