Chapter 28 Arthropods and Echinoderms

Introduction to Arthropods• “jointed feet”

• Most diverse and successful animals

• Over 750,000 species identified

• Segmented bodies

• Tough exoskeleton

• Jointed appendages

Body Terms• Exoskeleton- external skeleton that protects

and supports the body– Made of protein and a carbohydrate called chitin– Much variation on exoskeletons– Terrestrial arthropods (Ter. Arth.) have waxy

covering to prevent water loss

• Appendages- structures like legs and antennae that extend from the body wall

• Fewer body segments– The body segments fused together

• Highly specialized appendages – For feeding, movement, and more– Legs became: antennae, claws, wings,

flippers, tails, mouthparts and walking legs

Evolution has led to:

Form and Function• Feeding

• Varied eating habits- herbivores, carnivores, omnivores– Bloodsuckers, filter

feeders, detritivores, parasites

• Varied mouthparts- pincers, fangs, jaws

Respiration• Tracheal tubes- branching, air filled tubes that

are in many ter. arth.

• Spiracles- small openings alongside the body that allow air to enter and leave the tracheal tubes

• Book lungs- organs with layers of respiratory tissue stacked ex) spiders

• Gills- used by aquatic arthropods ex) crabs

• Book gills- used by horseshoe crab

Circulation

• Open circulatory system- well developed heart pumps blood arteries tissues sinus collects around the heart and re-enters to be pumped through again

Excretion• Malpighian tubules- saclike organs that

extract wastes from blood and add them to feces to move through the gut– Used in ter. Arth.

• Diffusion- moves cellular waste from the body to the water– Used in aquatic arth.

Response

• All have a brain

• Well developed nervous system

• Two nerves around the esophagus connect brain to the central nervous cord– Connects the ganglia which coordinate

movement of legs and wings

Movement

• Well developed muscles controlled by nervous system

• Individual muscles cells

• Muscles generate force (to fly, walk, swim) by contracting a muscle and pulling on the exoskeleton

Reproduction and Molting

• Terrestrial – Internal fertilization

• Aquatic– Internal and external

fertilization

• Molting– When an arthropod sheds its entire exoskeleton

and makes a larger one in its place– Controlled by the endocrine system with

hormones

Subphyla of Arthropods

• Crustacea – crabs, shrimp, crayfish

• Chelicerata – spiders, ticks, scorpions

• Uniramia – millipedes, centipedes

• Class Insecta (no subphylum)– 3 part body, 3 pairs of legs

28-4 Echinoderms• “spiny skin”

• Endoskeleton- hardened plates of calcium carbonate– Gives bumpy, irregular surface

• Only live in the sea

• No cephalization

• Two sided- oral (with mouth)/aboral

Echinoderm Characteristics

• Spiny skin

• Internal skeleton

• Water vascular system

• Suction cup structure called tube feet

• 5 part radial symmetry– Larvae- bilaterally symmetrical

• Deuterostomes

Water Vascular System• Carries out essential body functions like

respiration, circulation and movement

• Madreporite- opening to the outside through which water passes– Connects to ring canal which extend out into

radial canals along the 5 arms

• Tube feet- suction cups on the underside of the body that help with movement and feeding

Feeding• Urchins- scrape algae• Sea lilies- capture floating

plankton• Sea cucumbers- take in

sand and detritus off sea floor

• Sea stars- use tube feet to pull open bivalves, push stomach out, pour enzymes and digest mollusks, brings back stomach into body

Respiration and Circulation

• Water vascular system

• Thin walled tissues of tube feet for respiration

• Skin gills gas exchange

Excretion

• Digestive wastes- feces through anus

• Ammonia excreted through tube feet

Response and Movement

• Don’t have highly developed nervous system

• Nerve ring around the mouth

• Sensory organs that detect light

• Tube feet

• Endoskeleton structure/flexible joints

Reproduction

• External fertilization

• Separate sexes

Groups of Echinoderms

• Urchins

• Sand dollars

• Brittle stars

• Sea cucumbers

• Sea stars

• Sea lilies

• Feather stars

Ecology• Urchins control algae

• Sea stars control clams and corals

• Crown of Thorns– Feeds on corals– Rows of poisonous

spines on arms– Great Barrier Reef

damage