1) Particle feeding is believed to be the primitive mode in echinoderms; the ancestral use of podia was for feeding not locomotion!
a) crinoids capture suspended particles with simple, mucus-covered podia bordering the pinnules of long feather-like arms; ciliated grooves move food to the mouth
b) ophiuroids capture suspended or deposited particles with simple, mucus-covered podia or spines bordering the arms or mucus nets; a bolus of particles is moved toward the mouth by podia
c) holothuroids capture suspended or deposited particles with large, branched, mucus-covered tentacles (modified buccal podia); the entire tentacle is drawn through the mouth to ingest food
d) irregular echinoids (sand-dollars, heart urchins) live in sediment; small podia under spines move particles along grooves to mouth
2) Some groups feed on larger items
a) asteroids are mostly scavengers or carnivores; primitively, they swallow prey whole, but most can evert their stomach to feed
b) regular echinoids ('true' urchins) feed on algae and encrusting invertebrates with a remarkable scraping device: Aristotle's lantern
3) Primitive crinoids were sessile, with jointed cirri on a long stalk; remaining echinoderms move in a great variety of ways:
a) slender, jointed appendages (cirri in mobile crinoids)
b) coordinated tube feet (asteroids, regular echinoids, holothuroids)
c) rapid whip-like movement of arms (ophiuroids)
d) undulation of entire body (some holothuroids)
4) Respiration and excretion: all use skin and podia; some have other structures; a lack of excretory structures precludes life in fresh water
5) Sexes are separate and fertilization is typically external
a) cleavage is radial and early development is indeterminate
b) the early larva is bilaterally symmetrical and primitively exhibits a tri-partite coelom (axocoel, hydrocoel, somatocoel)
c) the water-vascular system arises from the fused axo-hydrocoel
d) perivisceral coelom (largest, for circulation) arises from somatocoel
e) many groups possess morphologically complex feeding larvae; some larvae pass through a dramatic metamorphosis