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Crustaceans
Chapter 20
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Subphylum Crustacea
Crustaceans,
subphylum
Crustacea typically
have biramous,branched,
appendages that are
extensively
specialized forfeeding and
locomotion.
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Subphylum Crustacea
Crustacea is
divided into 5
classes.
Currentmolecular
phylogenies do
not support the
monophyly of allclasses.
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Subphylum Crustacea - External
Features
Secreted cuticle is made of chitin, protein, and
calcareous material.
Heavy plates have more calcareous deposits -
joints are soft and thin, allowing flexibility.
Dorsal tergum and ventral sternum are plates
on each somite lacking a carapace.
Anterior end is a nonsegmented rostrum andthe posterior end is the unsegmented telson.
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Subphylum Crustacea
Crustaceans are the onlyarthropods that have two pairsof antennae.
They also have a pair ofmandibles (jaw-likeappendages) and two pairs ofmaxillae on the head.
Each body segment usually has
one pair of appendages. Ancestrally biramous except for the
first antennae.
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Subphylum Crustacea -
Appendages
Members of Malacostraca andRemipedia have appendages on eachsomite.
Other classes may not bear appendages onabdominal somites.
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Subphylum Crustacea -
Appendages
Appendages have become specialized by
evolving into a wide variety of walking legs,
mouthparts, swimmerets, etc. from
modification of the basic biramous appendage.
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Subphylum Crustacea
The ancestral condition in arthropods is
to have many body segments.
Fewer segments and increasedtagmatization is the derived condition.
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Subphylum Crustacea - Internal
Features
Muscular and nervous systems and
segmentation exhibit metamerism of
annelid-like ancestors.
Hemocoel - persistent blastocoel that
becomes filled with blood.
Coelomic compartments remain as end
sacs of excretory organs and gonads.
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Subphylum Crustacea - Muscular
System
Striated muscles make up a major
portion of crustacean body.
Most muscles arranged as antagonisticgroups.
Flexors draw a limb toward the body and
extensors straighten a limb out.
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Subphylum Crustacea - Muscular
System
Abdominal flexors of a crayfish allow it to
swim backward.
Strong muscles located on each side ofstomach control the mandibles.
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Subphylum Crustacea - Respiratory
System
Smaller crustaceansmay exchangegases across thinner
areas of cuticle. Larger crustaceans
use featherlike gillsfor gas exchange.
Bailer of 2ndmaxilla draws waterover gill filaments.
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Subphylum Crustacea - Circulatory
Open circulatory system Dorsal heart - single-chambered
sac of striated muscle.
Valves in the arteries preventbackflow of hemolymph.
Hemolymph conducted to gills, ifpresent, for oxygen and carbondioxide exchange.
Hemolymph may be colorless,reddish, or bluish.
Hemocyanin (blue) and/orhemoglobin (red) are respiratorypigments.
Contains ameboid cells thatmay help prevent clotting.
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Subphylum Crustacea - Excretory
System Antennal ormaxillary glands are
called green glands in decapods.
End sac of antennal gland has a
small vesicle and a spongy labyrinth.
Labyrinth connects by an excretorytubule to dorsal bladder that opens
to exterior pore.
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.
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Subphylum Crustacea - Excretory
System
Nitrogenous wastes are excreted across
thin areas of cuticle in the gills.
Freshwater crustaceans constantlythreatened by over-dilution with water.
Gills must actively absorb Na+ and Cl-.
Marine crustaceans have urine that is
isosmotic with blood.
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Subphylum Crustacea - Nervous
System
Pair ofsupra-esophageal ganglia connects to eyes and twopairs of antennae.
Neuron connectives join this brain to the subesophagealganglion.
Supplies nerves to mouth, appendages, esophagus, and
antennal glands. Double ventral nerve cord has a pair of ganglia for each somite
to control appendages
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Subphylum Crustacea - Sensory
System
Eyes and statocysts are the largest sensoryorgans.
Tactile hairs occur on the body, especially on
chelae, mouthparts and telson. Chemical sensing of taste and smell occurs in
hairs on antennae and mouth.
Statocyst opens at base of first antenna in
crayfish. Statocyst lined with sensory hairs that detect
position of grains of sand.
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Subphylum Crustacea - Sensory
System Compound eyes are made of
many units called ommatidia.
Cornea focuses light down thecolumnar ommatidium.
Distal retinal, proximal retinal,and reflecting pigment cellsform a sleeve around eachommatidium.
Each ommatidium detects arestricted area of objects, a
mosaic, in bright light. In dim light, the distal and
proximal pigments separateand produce a continuousimage.
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Subphylum Crustacea - Diversity of
Reproduction
Barnacles are monoecious but generally
cross-fertilize.
In some ostracods, males are scarce and
reproduction is by parthenogenesis.
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Subphylum Crustacea - 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.
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Subphylum Crustacea - Diversity of
Reproduction
Most
crustaceans
have a larva
unlike the adult
in form, and
undergo
metamorphosis.
Gulf shrimp
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Subphylum Crustacea - Diversity of
Reproduction The nauplius is a common
larval form with uniramousfirst antennae, and biramoussecond antennae andmandibles that all aid in
swimming. Appendages and somites are
added in a series of molts.
Metamorphosis of a barnacleproceeds from a free-
swimming nauplius to acypris larva with a bivalvecarapace and finally to asessile adult with plates.
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Subphylum Crustacea - Ecdysis
Ecdysis is necessary for a
crustacean to increase in size
the exoskeleton does not
grow. Physiology of molting affects
reproduction, behavior, and
many metabolic processes.
Underlying epidermis
secretes cuticle.
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Subphylum Crustacea - Ecdysis
Molting animals grow in the intermolt phases, orinstars.
Soft tissue increases in size until there is no spacewithin the cuticle.
When body fills the cuticle, animal is in the premoltphase.
Molting occurs often in young animals and may ceasein adults.
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Subphylum Crustacea - Ecdysis
Hormonal Control of Ecdysis:
Temperature, day length, or other stimuli
trigger central nervous system to begin
ecdysis.
Central nervous system decreases
production of molt-inhibiting hormone by the
X-organ. Promotes release of molting hormone from
the Y-organs which promotes ecdysis.
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Subphylum Crustacea - Endocrine
Functions
Removing eyestalks accelerates molting
and prevents color changes to match
background.
Hormones from neurosecretory cells in
eyestalk control dispersal of cell pigment.
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Subphylum Crustacea - Feeding
Habits
Same fundamental mouthparts in variouscrustaceans are adapted to a wide arrayof feeding habits.
Suspension feeders generate watercurrents in order to feed on plankton,detritus ,and bacteria.
Predators consume larvae, worms,
crustaceans, snails, and fishes. Scavengers eat dead animal and plant
matter.
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Subphylum Crustacea - Feeding
Habits
Crayfishes have a two-part stomach.
Gastric mill grinds up food in 1st
compartment.
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Class Remipedia
Only 10 described species inClass Remipedia.
All found in caves connected tothe sea.
Primitive features include 2538
segments with similar, paired,biramous, swimmingappendages.
Antennules also biramous.
Maxillae and maxillipeds areprehensile and specialized for
feeding. Swimming legs are directed
laterally rather than ventrally as isfound in copepods andcephalocarids.
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Class Cephalocarida
Only 9 species described inClass Cephalocarida.
Live in coastal bottomsediments from intertidal
zones to 300 meters depth. Thoracic limbs and 2nd
maxillae are very similar.
Lack eyes, a carapace, andabdominal appendages.
True hermaphrodites andunique in discharging eggsand sperm through sameduct.
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Class Branchiopoda
Includes three orders:
Anostraca fairy
shrimp and brine shrimp,
no carapace. Notostraca tadpole
shrimp, carapace forms
a large dorsal shield.
Diplostraca waterfleas carapace
encloses body but not
head.
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Class Branchiopoda
Phyllopodia legs that serve as
respiratory organs.
Legs may be used for filter feeding and
locomotion as well.
Mostly freshwater forms.
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Class Branchiopoda
Water fleas (like Daphnia) produce
females parthenogenetically in summer.
Males are produced when unfavorable
conditions arise and overwintering
fertilized eggs are produced that are
resistant to cold and desiccation.
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Class Ostracoda
Ostracods are enclosed in a two part
carapace and look a bit like a clam.
Marine or freshwater. Mostly benthic.
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Class Maxillopoda
axillopods generally
have 5 cephalic, 6
thoracic, and 4
abdominal segmentsplus a telson.
Reductions common.
The nauplius of
maxillopods has a
maxillopodan eye
unique to this group.
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Class Maxillopoda Subclass
Copepoda
Planktonic crustaceansinclude many species ofcopepods (subclass
Copepoda) which are amongthe most numerous of allanimals.
They lack a carapace.
Retain the simplemaxillopodan eye in adults.
Antennules used in swimming.
Very diverse.
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Class Maxillopoda Subclass
Copepoda
Parasitic forms highly modified and reduced -often unrecognizable as arthropods.
Free-living copepods may be the dominantconsumer.
Marine copepod Calanus is most abundantorganism in zooplankton by biomass.
Cyclops and Diaptomus important elements offreshwater plankton.
Some free-living copepods are intermediatehosts of human parasitic tapeworms andnematodes.
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Class Maxillopoda Subclass
Tantulocarida
Subclass Tantulocarida
- only recently
described.
Approximately 12species.
Tiny copepod-like
ectoparasites of deep-
sea benthic
crustaceans.
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Class Maxillopoda Subclass
Branchiura
Members of thesubclass Branchiuralack gills.
Most areectoparasites ofmarine andfreshwater fish.
510 mm long. Development is
direct.
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Class Maxillopoda Subclass
Pentastomida
Subclass Pentastomida -tongue worms.
Consist of about 90species of parasites of
vertebrate respiratorysystems.
Most infect reptile lungs,a few infect air sacs ofbirds or mammals.
Range from 1 to 13 cm inlength.
Chitinous cuticle regularlymolted.
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Class Maxillopoda Subclass
Cirripedia
Barnacles subclass cirripedia are a
group of mostly sessile crustaceans whose
cuticle is hardened into a shell.
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Class Maxillopoda Subclass
Cirripedia
Their legs are long,
many jointed cirri that
extend out through the
calcareous plates tofilter feed.
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Class Maxillopoda Subclass
Cirripedia
Barnacles are
hermaphroditic.
Most hatch as a nauplius
larva then become a cypridlarva (resembles the
ostracod Cypris).
Cyprids attach to the
substrates and beginsecreting calcareous plates.
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Class Maxillopoda Subclass
Cirripedia
Parasitic forms may have a kentrogon
stage that injects cells into the hemocoel
of host.
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Class Malacostraca
alacostracans
usually have a
head with 5 fused
segments, athorax with 8
segments and an
abdomen with 6.
Anteriorrostrum
Posteriortelson
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Class Malacostraca Order Isopoda
Order Isopoda including pill bugs. Only truly terrestrial crustaceans.
Also have marine and freshwater forms.
Dorsoventrally flattened, lack a carapace, and
have sessile compound eyes.
Compressed dorsoventrally.
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Class Malacostraca Order
Amphipoda
OrderAmphipoda many marine, terrestrial& freshwater forms.
Amphipods resemble isopods: Lack a carapace, have sessile compound eyes,
and one pair of maxillipeds. However, they are compressed laterally.
Development is direct.
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Class Malacostraca Order
Euphausiacea
OrderEuphausiacea contains approximately 90species.
Includes important ocean plankton called krill.
Most are bioluminescent with a light-producing organ
called a photophore. Form a major component of the diet of baleen whales
and of many fishes.
Eggs hatch as nauplii.
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Class Malacostraca
Harder, heavy plates in larger crustaceans
due to calcareous deposits in addition to
chitin.
The carapace covers much or all of thecephalothorax.
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Phylogeny
Remipedia appear to be the most
primitive of Crustacea.
Two pairs of uniramous limbs on each
segment.
One theory is that each modern somite
represents two ancestral somites that
fused together, forming the biramousappendage.
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Adaptive Diversification
Crustaceans are unquestionably the dominant
arthropod in marine environments.
They also share dominance in freshwater
environments with the insects. The class Malacostraca is most diverse and
members of Copepoda are most abundant.
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Classification
Class Remipedia
Class Cephalocarida
Class Branchiopoda Order Anostraca
Order Notostraca
Order Cladocera
Ph l d Ad ti
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Phylogeny and Adaptive
Diversification
Class Ostracoda
Class Maxillopoda
Subclass Copepoda Subclass Tantulocarida
Subclass Branchiura
Subclass Pentastomida
Subclass Cirripedia
Ph l d Ad ti
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Phylogeny and Adaptive
Diversification
Class Malacostraca
Order Isopoda
Order Amphipoda
Order Euphausiacea
Order Decapoda
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