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Spiny-skinned animals
Section 31.1
Animal Development
 Echinoderms are related to vertebrates due
to their early development
 The gastrula is the early embryo – a
hollow ball of cells with an opening called a
 Other animals are protostomes – their
mouth develops first from or near the
 Echinoderms and chordates (vertebrates)
are deuterostomes – their anus develops
from the blastopore & their mouth develops
second from another part of the gastrula
Development, continued…
 First deuterostomes were marine
 Also the first animals to develop
 Chordates (including all vertebrates)
are deuterostomes
Features of Modern Echinoderms
1. Endoskeleton
Composed of plates called ossicles
In adults the plates may fuse and hold spines
that protrude through the skin
2. Five-part radial symmetry
Bilateral symmetry as larvae; develop radial
symmetry as adults
Have no head or brain, only a central ring of
nerves with branches into each arm
Features, continued…
3. Water-vascular system
Made of interconnected canals and hollow tube
The tube feet extend through the ossicles
They are used for locomotion and feeding, as
well as some gas exchange and waste excretion
4. Coelomic circulation & respiration
The body cavity acts as a simple circulatory and
respiratory system
Skin gills may grow along the spines to
increase surface area
Echinoderm Diversity
 Sea Stars
 Mostly carnivores
 Brittle Stars
 The largest class of echinoderms
 Have slender, branched arms
 Most are filter feeders
 Sea Lilies and Feather Stars
 Most primitive echinoderms
 Their mouth is located on their upper surface
 Usually sessile
Sea Stars
Brittle Stars
Sea Lilies
Feather Star
Diversity, continued…
 Sea Urchins and Sand Dollars
 Lack distinct arms
 Flattened bodies with protruding spines
that may have poison
 Sea Cucumbers
 Soft and slug-like
 Ossicles are not fused
 Sea Daisies
 Small group, discovered in deep water
Sea Urchin
Sand Dollar
Sea Cucumber
Sea Daisy