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Chapter 13
Arthropods and
Echinoderms
Arthropods
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-contain the greatest number of species
-are our main competitors for food
-all have an exoskeleton (rigid outer covering)
- all have a segmented body like worms
- all have jointed appendages like legs, wings,
claws, and antennae
• -all have an open circulatory system
• -O2 is carried by gills, book lungs, or air tubes
• -reproduce sexually w/ internal fertilization
Crustaceans
• -have a hard exoskeleton, 2 pairs of
antennae, and mouthparts that crush/grind
• -body is divided into segments
• -appendages are attached to each segment
• -claws can be regenerated
• -get oxygen from gills
• -examples include barnacles, shrimp, crabs,
and lobsters
Centipedes & Millipedes
• -have many legs
• Millipedes have twice the number of legs that
centipedes do.
• -Millipedes are herbivorous. Centipedes are
carnivorous.
• -Centipedes have claws, shy millipedes do not
• -exoskeletons are not waterproof
• -usually found in moist, damp environments
Spiders & Relatives
• -include scorpions, ticks, mites, & spiders
• -body is divided into 2 segments: head/chest and
the abdomen
• -all have 8 legs
• -all spiders produce silk, but may NOT spin a web
• -venom can be injected by fangs by spiders
• -scorpions use claws & inject venom w/ stingers in
their tail
• -spiders can get O2 from book lungs & air tubes
• -ticks can be parasitic, sucking blood from animals
and thereby spreading disease like Lyme disease
Spider Anatomy
Insects
• -body is divided into 3 parts—head, chest, &
abdomen
• -have 6 legs attached to chest segment
• -simple eyes of insects can only detect amount of
light
• -compound eyes contain lenses that detect
movement
• -have 2 pairs of wings
• -does not have a well-developed respiratory
system, but has a system of air tubes or spiracles
Insect Development
• -insects grow quickly, so they must shed their
exoskeletons
• -insects pass through several stages of
development
• -metamorphosis can be complete or incomplete
• -complete metamorphosis has 4 stages: egg, larva,
pupa, and adult
• -incomplete metamorphosis has stages in which
the young look a lot like the adults (called the
nymph), often without wings or adult organs
Echinoderms
• -have spiny skin
• -have an internal skeleton made of bonylike plates made of
calcium that are bumpy
• -have a 5-part body
• -have a water vascular system made of tubes that carry food
and O2 & remove waste products
• -have suction-cuplike tube feet used for locomotion, to get
food, & to sense its environment
• -examples include sand dollars, sea urchins, sea cucumbers,
sea lilies, and starfishes
Starfishes
• -also called “sea stars”
• -have 5 or more arms that extend from a central body
• -their tube feet, found on the underside of the arms,
resemble tiny suction cups
• -tube feet can be used to grasp food by creating
tremendous force on the food
• -have the ability to regenerate