taiga The far northern (50 to 60 degrees north lati-
tude) open region of the boreal forest encompassing
parts of Siberia, Eurasia, Scandinavia, and North
America, just south of the tundra. Characterized by
open coniferous woodlands composed of tamarack,
black or white spruce, fir, pine and larch, and a floor of
lichens. The boreal forests represent the largest terres-
trial biome where seasons alternate between long, cold
winters and short, cool summers. These forests have
acidic, thin soils and a growing season of 130 days.
The average temperature is below freezing for half of
theyear.

tapeworms One of the cestode worms (Cestoda),
flatworms that are internal parasites.

tarantula A large hairy spider (arachnid) that lives in
warmareas such as South America, southern North
America, southern Europe, Africa, southern Asia, and
Australia, with the greatest concentration of tarantulas
in South America. There are about 300 species of
tarantulas. Aphonopelmaand Cyrtopholisare repre-
sentative genera. The female can live over 30 years, but
the life span of the male is considerably shorter.

tardigrade Amicroscopic animal that looks like a
miniature bear, hence the name water bear. They have
inflated round bodies with four pairs of stubby

clawed legs used for walking. If the environment dries

up, they have the ability to withstand hostile condi-

tions by undergoing a process called anhydrobiosis

(life without water), part of an adaptable technique of

cryptobiosis.

They are not affected by changes in salinity,

extreme vacuum, or lack of oxygen. They can survive

freezing or thawing in temperatures as cold as –328°F

or as hot as 304°F. When they turn into dried barrels

called tuns, they are able to survive for long periods of

time, and some have been brought back to life from

100-year-old mosses. Their typical environment is the

thin film of water that coats mosses and lichens, but

they have been found in a vast range of habitats. There

may be up to 1,000 species.

tautonym A biological term where the genus and

species are the same word, such as Amoracia armora-

cia,or Rattus rattus(the black rat). Triple tautonyms

are common in biological nomenclature.

taxis The behavior exhibited when an organism

reacts to an external stimulus by turning or moving

away from the stimulus.

taxon Agrouping of organisms by taxonomic rank,

such as order, family, genus, etc.; also a group of organ-

isms or other taxa sharing a single common ancestor.

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