CK12 Life Science

Table 12.4: (continued)

Subgroup of Arach-

nid

Representative Or-

ganisms

Approximate Num-

ber of Species

Description

Acarina Mites and ticks 30,000

Most are minute to

small (no more

than 1.0 mm

in length), but

some ticks and

one species

of mite may

reach lengths

of 10-20 mm

Live in nearly

every habi-

tat, including

aquatic and

terrestrial

Many are parasitic,

affecting both

invertebrates

and verte-

brates, and

may be vec-

tors of human

and other

mammalian

disease; those

that feed on

plants may

damage crops

Why Arthropods are Important

Many species of crustaceans, especially the familiar crabs, lobsters, shrimp, prawn, and
crayfish, are consumed by humans, and nearly 10,000,000 tons were produced in 2005. Over
70% by weight of all crustaceans caught for consumption are shrimp and prawns, and over
80% is produced in Asia, with China producing nearly half the world’s total.