- cadophore
- Calamus
- calceolus
- Calcite crust
- Callus
- Calymma
- Cancellate
- capillary chaetae
- Capillary setae
- Capitate tentacle
- capitulum
- carapace
- carapace glands
- Carbonate compensation depth
- carina
- carinate
- cariniform
- Carpal cluster
- Carpal knobs
- Carpal suckers
- Carpus
- Cartilage
- Caruncle
- caudad
- caudal
- Caudal cilium
- caudal fin
- Caudal fold
- caudal furca
- Caudal joint
- caudal peduncle
- caudal process
- Caudal septum
- Caveola
- Ce
- Central capsule
- Central chamber
- Central depression
- Central dorsal rib
- central organ
- Centrifugal canal
- Centripetal canal
- Cephalic
- cephalic cage
- Cephalis
- Cephalon
- Cephalothorax
- cerebral ganglion
- Cervical apophyses
- Cervical pores
- Cervical stricture
- Chaeta
- Chaetiger
- Chamber
- Chambered rings
- chela
- chelate
- Cheliped
- chitin
- chitinophore
- chitinous
- Chordal tentacle
- chromatin
- Chromatophore
- Chromatophore extrategumental
- Chromatophore tegumental
- Chromophil gland
- chrysomitra
- cilia
- Ciliar band
- Ciliary row
- Ciliature
- cilium
- cillated tufts
- Circular canal
- Circular furrow
- Circular muscle
- circum-oesophageal ganglion
- Circumoral appendages
- circumpolar
- Cirri
- cirrophore
- Cirrus
- clade
- cladogram
- Clasp
- clasper
- Claviform
- cleaning leg
- Cleft
- cleithral symphysis
- cleithrum
- clinal variation
- Closing mechanism
- Closing membrane
- Club
- Club-like spines
- clypeus
- cnidoband
- Cnidocyst
- Cnidome
- Cnidophore
- Co
- coastal
- coelom
- coelomic fluid
- collar
- collar chaeta
- Collar plate
- Collar pores
- Collar stricture
- collarette
- Columella
- comb-chaetae
- commensalism
- companion chaetae
- competition
- compound chaetae
- compound eyes
- Compound seta
- conaria
- concave
- Cone
- Cone filaments
- conspecific
- Constriction
- Continental Shelf
- Continental Slope
- Contractile vacuole
- convex
- copulatory appendage
- coracoid
- Cordylus
- Corm
- cormidum
- Corneal membrane
- Cornet
- corona ciliata
- Coronal furrow
- Coronal groove
- Coronal muscle
- Coronal pores
- Coronatae
- Coronet
- Cortex
- Cortical granules
- Cortical shell
- cosmopolitan
- coxa
- coxal plate
- CR
- Craspedote
- Crenate
- Crenulate
- crest
- Crests
- Cristae
- crochets
- Crust
- Ctenidium
- Cubomedusae
- Cupola
- Cupolae
- cuticle
- cuttlebone
- cyathozooid
- Cylindrical spines
- Cymba
- Cyrtocyst
- cythozooid
- Cytoproct
- Cytostome