Download Lecture Crustacea

Lecture Crustacea
Ecdysis
 Molting animals grow in the intermolt phases, or instars.
 Soft tissue increases in size until there is no space
within the cuticle.
 When body fills the cuticle, animal is in the premolt
phase.
 Molting occurs often in young animals and may cease
in adults.
Arthropods
Chapter 20
 Chelicerata – Arachnids, horseshoe crabs, sea
spiders.
 Myriapoda – Centipedes, millipedes.
 Crustacea – Crabs, lobsters, shrimp, copepods,
ostracods, barnacles, pill bugs, brine shrimp, water
fleas, remipedes, ect.
 Hexapoda – Insects, silverfish, springtails.
 Chelicerata, unlike insects, have
only two body segments instead of
three: a fused head and thorax
(cephalothorax) and an abdomen
 Chelicerata species have eight legs
(four pairs) whereas insects have
six (three pairs).
 The Chelicerae are pointed
appendages to grasp food, and are
found in place of the chewing
mandibles most other arthropods
have.
Types of chelicerae: (A)
jackknife, (B) scissor, and
(C) 3-segmented chelate
HORSESHOE crab
• Use hemocyanin (protein) to carry
oxygen. The copper present in
hemocyanin make their blood blue.
• Blood contains amebocytes, which
play a role similar to white blood cells
of vertebrates in defending the
organism against pathogens.
• Amebocytes from the blood of L.
polyphemus are used to make
Limulus amebocyte lysate, which is
used for the detection of bacterial
endotoxins in medical applications.
Crustaceans
(Lobsters,Crabs, and Shrimp)
Just the Facts….
 Crustaceans belong to
the Phylum Arthropoda
(jointed feet).
 a segmented body that
is bilaterally
symmetrical
 All Arthropods have
jointed appendages.
 All Arthropods have an
exoskeleton (carapace).
• Their bodies are composed
of three body segments the head, the thorax and
the abdomen.
• In some species the head
and thorax are fused
together to form a
cephalothorax which is
covered by a single large
carapace.
• They also have eyes usually
on stalks
The Exoskeleton
 Is made of a tough fibrous
material called chitin.
 This gives the skeleton strength
and flexibility.
 There are several pairs (5 or
more) of jointed appendages
(movable arms and legs).
Subphylum Crustacea
 Crustaceans, subphylum
Crustacea typically have
biramous, branched,
appendages that are
extensively specialized for
feeding and locomotion.
Crustaceans
 On the segments of the head,
 two pairs of sensory antennae,
 one pair of mandibles (lower jaw for chewing food)
 two pairs of maxillae (to help the mandibles in
positioning the food).
 Two pairs of maxilliped: pair of appendages for holding
prey.
 The thorax has legs, which may be specialised for use in
walking or feeding.
 The abdomen has legs usually used for swimming
(swimmerets) and ends in a fan-shaped tail (telson).
 Crustaceans are the only arthropods that have two
pairs of antennae. They also have a pair of mandibles
(jaw-like appendages) and two pairs of maxillae on the
head.
Muscular System
• Extensor muscles extends the tail of the crayfish.
• Flexor muscle bends the tail of the crayfish.
Crustacea - Muscular System
 Most muscles arranged as antagonistic groups.
 Flexors draw a limb toward the body and extensors
straighten a limb out.
 Antagonistic pairs of muscles are muscle where one
move the bone in one direction and the other
moves it back the other way in transmission of
nerve impulses to the muscles. It is impossible to
fully stimulate the contraction of two antagonistic
muscles at the same time
• Encephalon: site of the mental functions of a crayfish.
• Digestive gland: glandular organ that produces digestive enzymes.
• Ganglion of ventral nerve cord: budge related to a collection of
nerves of the abdomen of a crayfish.
• Ventral nerve cord: collection of nerves in the abdomen of a
crayfish.
Crustacea - Respiratory System
 Smaller crustaceans may
exchange gases across
thinner areas of cuticle.
 Larger crustaceans use
featherlike gills for gas
exchange.
 2nd maxilla draws water
over gill filaments.
Haemolymph, is a
fluid, analogous to
the blood in higher
phyla, that
circulates in the
interior of the
arthropod body
remaining in direct
contact with the
animal's tissues.
The open circulatory system is a system in which a fluid in a cavity
called the hemocoel bathes the organs directly with oxygen and
nutrients and there is no distinction between blood and interstitial
fluid; this combined fluid is called hemolymph or haemolymph.
Circulatory system
• Hemolymph conducted to gills, if present, for oxygen and carbon
dioxide exchange.
• Hemolymph may be colorless, reddish, or bluish. Hemocyanin
(blue) and/or hemoglobin (red) are respiratory pigments.
• Hemolymph fills all of the interior hemocoel of the body and
surrounds all cells. Hemolymph is composed of water, inorganic
salts (mostly Na+, Cl−, K+, Mg2+, and Ca2+), and organic
compounds (mostly carbohydrates, proteins, and lipids). The
primary oxygen transporter molecule is hemocyanin.
• There are free-floating cells, the hemocytes, within the
hemolymph. They play a role in the arthropod immune system.
Ameboid cells may help prevent clotting.
Excretory System
 Antennal or maxillary glands are
called green glands in decapods.
 End sac of antennal gland has a
small vesicle and a spongy
labyrinth.
 Resorption of salts and amino
acids occurs as the filtrate passes
the excretory tubule and bladder.
 Mainly regulates the ionic and
osmotic composition of body
fluids.
Crustacea - Excretory System
 Nitrogenous wastes are excreted across thin
areas of cuticle in the gills.
 Freshwater crustaceans constantly threatened
by over-dilution with water.
 Gills must actively absorb Na+ and Cl-.
 Marine crustaceans have urine that is isosmotic
with blood.
Nervous System
 Pair of supra-esophageal ganglia connects to eyes and two pairs of
antennae.
 Neuron connectives join this brain to the subesophageal ganglion.
 Supplies nerves to mouth, appendages, esophagus, and antennal
glands.
 Double ventral nerve cord has a pair of ganglia for each somite to
control appendages.
Eye System
 Compound eyes are
made of many units
called ommatidia.
 Cornea focuses light
down the columnar
ommatidium.
Ommatidium of a krill.
Compound eye : Very good at detecting
movement (except Copepod)
reduces spatial resolution but
increases sensitivity to dim light.
Dark adaptation in the compound
eye of Aleochara bilineata.
the electroretinogram
(ERG) techniqueuses electrodes
to measure electrical activity in
the insect eye in response to
pulses of light.
Reproduction
• Most Crustaceans are either male or female and reproduce
sexually. A small number, including barnacles, are
hermaphrodites (monoecious), but they generally cross
fertilize. In other species, viable eggs are produced by a female
without needing to be fertilised by a male (Parthenogenesis,
Ostracods).
• In many decapods, the first one or two pairs of swimmerets are
specialised for sperm transfer by the males and the females
hold the eggs until they hatch into free-swimming larvae.
• In many species the fertilised eggs are just released into the
water or attached to objects in the water. The larvae
metamorphose through a number of stages before they
become adults.
Class Branchiopoda
 Water fleas produce females
parthenogenetically in
summer.
 Males are produced when
unfavorable conditions arise
 overwintering fertilized eggs
are produced that are
resistant to cold and
desiccation.
Diversity of Reproduction
 Most crustaceans
brood eggs in brood
chambers, in brood
sacs attached to the
abdomen, or attached
to abdominal
appendages.
 Crayfishes develop
directly without a larval
form.
Diversity of Reproduction
 Most crustaceans
have a larva
unlike the adult
in form, and
undergo
metamorphosis.
- Gulf shrimp
Diversity of Reproduction
 The nauplius is a common larval
form with uniramous first
antennae, and biramous second
antennae and mandibles that all
aid in swimming.
 Appendages and somites are added
in a series of molts.
 Metamorphosis of a barnacle
proceeds from a free-swimming
nauplius to a cypris larva with a
bivalve carapace and finally to a
sessile adult with plates.
Feeding Habits
 Same fundamental mouthparts in various
crustaceans are adapted to a wide array of
feeding habits.
 Suspension feeders generate water currents
in order to feed on plankton, detritus ,and
bacteria.
 Predators consume larvae, worms,
crustaceans, snails, and fishes.
 Scavengers eat dead animal and plant matter.
Feeding Habits
 Crayfishes have a two-part stomach.
 Gastric mill grinds up food in 1st compartment.
http://shapeoflife.org/video/marine-arthropodssuccessful-design