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)
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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
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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