asylum
bottom
brittle
brown
calcium
cavity
color
colorful
conceal
cuirass
deep
empty
fossil
half
hard
hide
hideout
hideyhole
hollow
invertebrate
isolated
leaf
limestone
marine
natural
nobody
object
ocean
orange
ossified
pearl
petrifaction
petrification
pink
protect
refuge
sea
seashell
shell
shellfish
shelter
skeleton
solid
studio
white background
yellow