- sagittal
- Sagittal plane
- Sagittal ring
- salivary gland
- Sc
- scaphocerite
- Scaphognathite
- scapula
- Scapulet
- Scopula
- Scutica
- Scyphistoma
- Scyphomedusa
- Scyphozoa
- Second lock
- Second shell
- Secondary aperture
- Secondary apophyses
- Secondary lateral spines
- Secondary spicule
- Secondary spines
- Segment
- Segmental glands
- Segmental organ
- Semaeostomae
- seminal pouch or receptacle
- Seminal receptacles
- seminal vesicles
- Septae
- Septum
- serrated
- sessile
- Seta
- Setiger
- Setigerous
- Setigerous lobe
- setobranch
- setose
- setula
- setule
- seventh limb
- Shaft
- shelf - continental shelf
- shell
- shoulder vault
- Side angle
- Side pockets
- Sieve-plate
- Silverline system
- sinistral
- sinus
- siphon
- siphosome
- sixth limb
- Skinny stage
- Skirt
- Snout
- Solid tentacle
- somatocyst
- Somite
- Spadix
- Spathilla
- Spathulate
- species
- sperm
- Spermatophore
- spermioduct
- sphenotic
- Spica
- Spicule
- Spindle-shaped
- Spine
- Spine mark
- spine surface
- Spines
- Spiniger
- Spinose
- Spinous process
- Spinulate
- spinules
- spiral
- Spiral side
- Spire
- Spongy meshwork
- spur canals
- Spur glands
- Stalk
- standard length
- Statocyst
- Stauromedusa
- stem
- stenotherm
- sternite
- stigmata
- stolon
- Stomach pouch
- Stomatogenesis
- Streptospiral
- Striae
- striation
- Strictures
- Strobilation
- Style
- styliform
- stylocerite
- stylode
- Stylus
- sub-chordal cells
- subchela
- subchelate
- Subhedral crystals
- Subpellicular platelet layer
- subspecies
- Subterminal teeth
- Subumbrella
- Subumbrellar cavity
- Subumbrellar surface
- Sucker
- Sucker ring
- Suckers
- Suckers primary
- Suckers secondary
- sulcate
- sulcus
- supra-orbital spine
- Suspensoria
- Sutural furrow
- Suture
- Swarmer
- Swimming membrane
- symphysis