Purple urchins with flexible spines that periodically shiver
starfish topped by slender, writhing tentacles
starfish with spines that retract and extend - sometimes longer than half the star's width (how do they fit inside? Curl up? Slip past each other? Manufactured on the spot?)
urchins that look just like black clumps of grass (possibly photosynthetic)
starfish coated with what looks like copper tinsel
starfish covered with glitter that is left behind in their trails, making them easy to track (a disadvantage?)
starfish with saw-like edges that cut up small plants to eat.
urchins with no spines, but instead grainy, sandpaper-like surfaces
starfish with twenty arms usually held together in five groups of four
superficially urchin-like creatures with eyes, nose, and mouth on forward (based direction of motion) side of body, comes with complex, jointed, "tongue" (might be most like a sea cucumber)
possibly photosynthetic black starfish covered in "fern leaves" "maple leaves" or "pine branches"
Any of these might be aquatic, amphibious, or terrestrial. I'm not sure how to work all these into the second book just yet. Some of them might never be used. I also have an idea for a creature that maintains balance only by sensing the water level in a "bowl" in its back. I don't know if it should be echinoderm-like, vertebrate-like, or something else. I don't know yet how the characters figure this out, either. Tell me what you think.