- sagittal
- salivary gland
- scaphocerite
- scaphognathite
- scutum
- scyphomedusa
- scyphozoan
- seminal pouch
- seminal vesicles
- septum
- serrated
- sessile
- seta
- setobranch
- setula
- seventh limb
- shell
- shoulder vault
- side angle
- side pockets
- sinistral
- sinus
- siphon
- siphonophore
- siphosome
- sixth limb
- somatocyst
- somite
- spatulate
- sperm
- spermatophore
- spermioduct
- spine
- spine mark
- spine surface
- spiniger
- spinules
- spiral
- spire
- spur canals
- stage
- statocyst
- stenotherm
- sternite
- stigmata
- stolon
- striae
- striation
- styliform
- stylocerite
- stylode
- sub-chordal cells
- subchela
- subchelate
- sucker
- sucker ring
- suckers
- sulcate
- sulcus
- supra-orbital spine
- suture
- swimming setae