- tactile
- tanaids
- taxon
- Taxonomy
- teleost
- telocentric
- temperate
- temperate waters
- temperature
- temporal region
- temporooccipital
- tentacle
- tenuate
- terminal
- terrestrial
- territorial
- territory
- tessellate
- testaceous
- testes
- testosterone
- tetraploid
- TFRI
- thermocline
- thermophile
- thoracic
- thorax
- thorn
- thread fin
- throat
- thyroxine
- tidal
- tide
- tinge
- tintinnids
- tongue
- tooth
- transition
- translucent
- transverse
- trefoil
- tricuspid
- tridentate
- trilinearis
- triploidy
- trochlear
- troglobitic
- trophic
- tropical
- truncate
- trunk
- tubercle
- tubicolous worms
- tubular
- turbidity
- type
- typical