Transcript Arthropods Lecture

Arthropods
The Armored Achievers:
Numerically the largest Phyla and
literally means jointed foot.
Sub Phylum - Crustacea –
Crab, shrimp, barnacle, and lobster
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Segmented body and displays bilateral
symmetry.
Jointed appendages have a variety of
specialized functions
The body is covered by an exoskeleton
made of chiton
– Advantage: good protection,
muscles attach to it for strength
– Disadvantage: heavy, does not
grow: must molt becomes
vulnerable to prey
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Body has 2 segments – cephalothorax covered by the
carapace and the abdomen
Meroplanktonic larvae do not compete with adults for
food: metamorphosis provides a gradual change to adult
Open circulatory system contains a blue pigment called
hemocyanin to transport oxygen from gills to the body
– Blood carries copper instead of iron
– Excellent medium for long-term lab tests because it will not
support bacterial growth
Ventral nerve chord with a well-developed brain and
compound eyes.
– Neurosecretory cells control molting, color changes, food storage
and hormones.
The Small Crustaceans
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Copepods
Barnacles
Beach Hoppers
Isopods
Krill
Barnacles
Decapods – ten legged
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Five pairs of walking legs – first pair
usually heavier and has a claw
Shrimp, lobster and crabs
Horseshoe crab
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Only living member of Merostomata
Living fossil
Not a true crab
Molting
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Like many animals with hard shells, a horseshoe
crab must molt or shed its shell as it grows. Before
molting, a new shell begins to form. When this
new shell is ready, the horseshoe crab absorbs
water through its gills, making itself bigger.
The old, hard shell cannot expand and splits in the
front where the top and bottom join. The
horseshoe crab crawls out the front, leaving the
old shell behind. It takes about 24 hours for the
new soft shell to harden. With each molt, the
horseshoe crab increases in size by an estimated
25-30%.
Sea Spider
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Feeds on soft invertebrates
Common in cold waters
Hermit Crabs
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Not a true crab
Scavenger
Hide abdomen in
empty gastropod shells
– Sometimes cover shells
with sea anemones .
True Crabs
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Abdomen is small and tucked under
the compact cephalothorax
V shaped abdomen in males, U
shaped in females.
Most are scavengers and predators.
Biology of the Crustaceans
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Feeding and Digestion
– In general, digestion is extracellular and
absorbed nutrients are distributed in an open
circulatory system
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Nervous system
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Small simple brain
Most have compound eyes
Sensitive to chemicals
Pair of statocycst for balance
Behavior
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Complex
– Body postures and movements for
communication
– Disputes in territory and courtship
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Elaborate courtship behavior.
Reproduction
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Mostly separate sexes
Males use special appendages to transfer
sperm to females
Mating in decapods usually takes place
within a few a hours of the female molting.
Females in many species can save and store
sperm for different broods of eggs.
Decapods carry eggs using pleopods.
Marine Crustaceans Growth Chart
Weird but True?
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Do you know that horseshoe crabs are not really crabs at all?
They're actually the only four living species of a group, class
Merostomata, that are largely represented by fossils. Horseshoe
crabs are in fact living fossils, resembling creatures that went extinct
thousands of years ago!
Crabs don’t have ears. Still, they can detect sound which seems a
bit of a conundrum. Basically, the hollow hairs on the outside of the
crab’s body pick up vibrations created by sounds and vibrations in
the water. These hairs are also used for feeling, tasting and
smelling. How’s that for multi-tasking.
If a crab loses a claw, it grows back. Don’t you wish you had that
quality?
Crab legs and swimming. All crabs have legs. In fact, those are
generally the tastiest parts of the crab. Although they live in the
water, and have all of those legs, most can’t swim. The Blue and
Lady crabs have specialized legs for swimming. These swimming
legs are flattened out and act more like paddles. Other than that,
the legs are used for walking. These paddle legs move at 20 to 40
revolutions per minute.
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Crustaceans turn red when exposed to heat, so while you may see
the live ones with a nice blue color, the cooking process will change
the color. Similarly, a dead crab on a beach will turn red just because
of its exposure to the sun’s rays.
A male crab is called a Jimmy.
The female crab can only mate during the molting process. She
emits a powerful aroma to attract the male crab. The problem is, she
may not be in the molting process quite yet, so the male crab literally
stakes his claim by carrying the female crab around underneath his
own body until conditions are just right.
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The female blue crab lays her eggs from 2 to 9 months after mating,
depending upon when the mating took place.
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The oldest crab industry in the United States is the blue crab industry
of the Chesapeake Bay area, dating back almost to the early 1600s.
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The ghost crab is on record as having the fastest crawling speeds.
On firm sand, they have been clocked at 4 miles per hour, and 5
miles per hour on a solid, wooden deck.
A single Alaskan King Crab can yield over six pounds of meat. They
can measure up to a 6-foot leg span.