24.1 Spiders and Their Relatives
The class Arachnida contains:
spiders, mites, ticks, scorpions
Most arachnids have 2 body segments:
1 cephalothorax
with 4 pairs of legs
2 abdomen
Chelicerae a spiders fangs;
used to inject poison
Pedipalps limbs used for grasping
prey
Spiders use silk to: trap food,
protect their young, line burrows, and as a safety line.
A scorpions pedipalps are in
the form of pincers.
Scorpions have a stinger to administer
poison.
Ticks & mites are parasitic
and often carry diseases.
Horseshoe crabs link ancient
arthropods and modern arthropods.
24.2 Insects, Millipedes, & Centipedes
Insects are the largest class
of Arthropods.
They have 3 main body parts:
head, thorax, abdomen.
They are classified by the number
of wings.
They develop by complete (egg>larva>pupae>adult)
or incomplete (egg>nymph>adult) metamorphosis.
Some (ants, bees, termites, wasps)
are very social and lived in organized societies.
Millipedes & centipedes,
while in a different class, share the same head structure as insects.
Millipedes have 2 pairs of legs
per body segment and eat decaying material.
Centipedes have 1 pair of legs
per body segment and are predators.
24.3 Crustaceans
Class Crustacea includes crabs,
crayfish, lobsters, shrimp, isopods.
Their bodies are usually divided
into 2 parts: the cephalothorax and abdomen.
Decapods (lobsters, shrimp, crabs,
crayfish) have 5 pairs of feet.
Isopods (roly-polys, doodlebugs)
have 7 pairs of walking legs and live on land.
Copepods (ex. daphnia) are the
smallest crustaceans. They are a vital link in the marine food web. |