- caecum
- calice
- calyx
- campanulate
- campanuliform
- capitate
- capitulum
- capstan
- capstan-like
- catkin
- cauline
- caulus
- circlet
- clavate
- clubs
- Cnidaria
- coenenchyme
- coenosarc
- coenosteum
- colonial
- colony
- columella
- column
- contractile
- coppinia
- corallite
- corallum
- corallum wall
- corbula
- costa
- crown
- crutches
- cryptomedusoid
- cusp
- cylinders