Transcript Arthropods
Arthropods
Phylum Arthropoda
Make up largest phylum of Animals, with
more than 1 million known species.
Of all animals on earth 3/4 are
arthropods.
Largest group insects. (on land)
Largest group in oceans (crustaceans).
Crustaceans (Subphylum
Crustacea)
Includes barnacles, shrimps, lobsters, and
crabs.
Bodies are segmented and bilaterally
symmetrical.
Body has jointed appendages, such as legs
and mouthparts moved by muscles.
Have exoskeleton made of chitin for
protection, support, flexibility, muscle
attachment.
Lobster (ventral view)
To grow arthropods molt.
Molt- shed their exoskeleton.
New shells develop under the old shell.
After old shell is molted the new shell
hardens.
This limits size of arthropods.
68,000 species of crustaceans, most
are marine.
Specialized for life in water by having
gills for obtaining oxygen, exoskeleton,
appendages for swimming, crawling,
and attachment for feeding and mating.
Have two antennae for sensing
surroundings.
Small Crustaceans
Copepods- abundant and important in
the plankton.
Use mouth parts to filter or capture
food.
Use elongated antennae to swim.
Many are parasitic.
Copepod
Barnacles
Filter feeders that live attached to
surfaces including on whales and crabs.
Are fouling organisms.
Look like molluscs because their bodies
are enclosed in calcareous plates.
Have feathery, filtering legs to sweep in
the water.
Amphipods
Have curved body that is flattened
sideways.
Head and tail curve downwards.
Beach hoppers are strong jumpers by
stretching their curved bodies.
Others crawl among seaweeds, or
burrow in skin of whales (whale lice).
Amphipod
Isopods
Main part of body has legs that are
similar to each other and are
dorsoventrally flattened.
Pill bugs are common on land.
Fish lice are parasites of fishes and
crustaceans.
Fish louse on fish eyeball.
Krill (Euphausiids)
Planktonic, shrimp-like.
Head is fused with body segments to
form a distinctive carapace that covers
the body like armor.
Most are filter feeders of diatoms and
plankton.
Exclusive source of food for whales,
penguins, and fishes.
Krill
Shrimps, Lobsters, and Crabs
10,000 species.
Decapods- ten legs.
Largest crustacean group.
Largest crustaceans in size.
Prized food source.
Body Structure
Have five pairs of legs (pereopods).
First pair of legs is usually heavier and has
claws for feeding and defense.
Three sets of maxillipeds close to mouth to
sort out food and push toward the mouth.
Have cephalothorax- fused head and thorax.
Rest of body is the abdomen.
Shrimps and lobsters have laterally
compressed bodies with elongated
abdomens “tails”..
Shrimps are scavengers feeding on
detritus.
Larry the Lobster
Hermit crabs- not true crabs are
scavengers.
Hide long, soft abdomens in empty
gastropod shells.
True Crabs
Abdomen is small and tucked under
broad cephalothorax.
V-shaped abdomen in males.
U-shaped abdomen in females for
carrying eggs.
Highly mobile move sideways “sidle”.
Most are scavengers or predators.
Mr. Krabs
Alaskan King Crab
Feeding and Digestion
Filter feeding common on copepods and
small crustaceans.
Stiff, hair-like bristles are used to catch
food particles in the water.
Appendages used to pierce and suck in
parasitic copepods and isopods.
Food passes to a stomach with
chitinous teeth for grinding and sifting.
Stomachs are connected to digestive glands
that secrete digestive enzymes and absorb
nutrients.
Intestine ends in an anus.
Nutrients absorbed by an open circulatory
system.
Gas exchange carried out by gills.
Crabs have gill chamber filled with air like our
lungs.
Nervous System and Behavior
Simple crustaceans have a ladder-like
nervous system.
Have a small,relatively simple brain but
well-developed sensory organs.
Most have compound eyes with 14,000
light sensors.
Decopods have eyes on the end of
movable stalks like periscopes.
Have keen sense of smell.
Many have statocysts for balance.
Behaviorally complex and use a variety
of signals to communicate.
Behaviors used to settle disputes, and
for courtship.
Reproduction and Life History
Most are separate sexes.
Males use specialized appendages to
transfer sperm directly to the female.
Hermaphrodites even transfer sperm
between each other.
Barnacles have a penis that can stretch
to reach others in the neighborhood.
Mating usually takes place after the
female molts while the exoskeleton in
soft.
Females store sperm to fertilize different
batches of eggs.
In decapods the eggs are carried in
Pleopods (swimmerets) beneath the
body.
Horseshoe Crabs
Class Merostomata
Not true crabs but “living fossils”
Live on soft bottoms in shallow water on
the Atlantic and Gulf Coasts of North
America and South East Asia.
Horseshoe-shaped carapace that
encloses body with five pairs of
appendages.
Horseshoe Crabs
Sea Spiders
Class Pycnogonida
Have four or more pairs of jointed legs
Large proboscis with the mouth at the
tip used to feed on soft invertebrates
such as anemones and hydrozoans.
Common in cold waters.
Sea Spider
Insects (Class Insecta)
Have only three pairs of legs as adults.
Most diverse on earth but rare in the
sea.
Most marine insects live at water’s edge
where they scavenge sea weeds,
barnacles, and rocks.
Marine Water Strider