- Tactile
- pertaining to the sense of touch
- Taxonomy
- science of classifying organisms in established categories according to their biological and evolutionary characteristics; nomenclature is usually Greek or Latin in derivation
- Temperate zone
- moderate temperature area located between the polar and tropical zones
- Tentacles
- long, cylindrical projections from an organism, specialized as sensory, grasping and food collecting structure
- Terrestrial
- pertaining to plant or animal life on land rather than in water
- Territory
- area with defined boundaries established and defended by an animal, usually for breeding and/or foraging
- Test
- shell or casing of an organism. Skeleton of a sea urchin.
- Tetrapod
- animals that are four-limbed (two pairs): includes amphibians, reptiles, birds, mammals
- Tetrodotoxin
- neurotoxin that acts specifically on nerve cells, commonly causing paralysis, especially tetrodotoxin, bactrachotoxin, and compounds found in the toxins of some bees, scorpions, and spiders
- Thermocline
- water layer in which temperature changes rapidly with increasing depth
- Thorax
- portion of the body between the head and abdomen; the chest region
- Tide
- periodic rise and fall of oceanic water levels (usually twice daily) along a shore caused by the unequal gravitational pull of the sun and moon on different parts of the rotating earth
- Tide pool
- pool of water left along the shore as the tide level falls
- Tidemark
- high water mark left by tidal water
- Toxin
- any substance harmful to living cells
- Trophic
- pertaining to growth or nutrition
- Tube feet
- extension of the water vascular system of echinoderms (sea stars, sea urchins, etc.) that aids in locomotion, grasping and feeding
- Turbid
- stirred up sediment; cloudy
- Turf
- thick mat of plants and animals on a substrate
