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CHAPTER 20
Crustaceans
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Sally Lightfoot Crab,
from the Galapagos
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Subphylum Crustacea
General Nature of a Crustacean Main distinguishing characteristic of
crustaceans Two pairs of antennae
Head also has a pair of mandibles and 2 pairs of maxillae
One pair of appendages on each of the additional segments Some segments may lack appendages
All appendages, except perhaps first antennae, are biramous
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Tagmata (segments) are usually head, thorax,
and abdomen
In most one or more thoracic segments are
fused with the head as a cephalothorax
Arrangement of tagmata in Malacostraca is the
ancestral plan
Head has 5 fused somites
Thorax has 8
Abdomen has 6
Subphylum Crustacea
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Anterior end is a non-segmented rostrum
(covers eyes in some)
Telson, with the last abdominal somite and
uropods, forms a tail
Dorsal covering is the carapace
May cover most of body or just cephalothorax
Subphylum Crustacea
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Form and Function 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
Telson is not a somite Bears anus
Subphylum Crustacea
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Appendages Most have appendages on each somite
Appendages represent homology Have evolved a wide variety of walking legs, mouthparts,
swimmerets, etc. from modification of the basic biramous appendage
Subphylum Crustacea
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Appendages of crayfish: 3 main parts to each appendage
Protopod = brown Endopod = blue Exopod = yellow
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Appendage Function # of pairs
Antenna Touch, taste, equilibrium 2
Mandible Crushing food 1
Maxilla Handling food, drawing water
currents to gills
2
Maxilliped Touch, taste, handling food 3
Walking legs Offense, Defense, walking (cheliped
is 1st, with pincer)
5
Swimmeret Transfer sperm, create water
currents, carrying eggs and young
5
Uropod Swimming, egg protection in
females
1
Crawyfish Appendage and Function
(Number if pairs)
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Internal Features
Coelomates - reduced Persistent blastocoel that becomes filled with
blood Hemocoel
Protostomes (mouth first)
Complete Gut
Subphylum Crustacea
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Muscular System
Striated muscles
Make up a major portion of crustacean body
Most muscles arranged as antagonistic groups
Flexors draw a limb toward the body and extensors straighten a limb out
Abdominal flexors of a crayfish allow it to swim backward
Subphylum Crustacea
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Internal Anatomy of the crayfish. Green Gland = Kidney
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Respiratory System
Smaller crustaceans may exchange gases across thinner areas of cuticle
Larger crustaceans use featherlike gills for gas exchange
Circulatory Open circulatory system
No system of veins to separate blood from interstitial fluid
Hemolymph exits heart through arteries
Passes to hemocoel to return to the heart via sinuses
Dorsal heart
Single-chambered sac of striated muscle
Valves in the arteries prevent backflow
Hemolymph conducted to gills, if present, for oxygen and carbon dioxide exchange
Hemocyanin and/or hemoglobin are respiratory pigments
Subphylum Crustacea
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Hemolymph travel: Heart, Body, Sinus, Gills, Heart via Ostium (opening)
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Excretory System Antennal or maxillary glands
Called “green glands”
End sac of green gland has a small vesicle and a spongy labyrinth
Labyrinth connects by an excretory tubule to dorsal bladder that opens to exterior pore
Hydrostatic pressure within a hemocoel provides a force for filtration of fluid into the end sac
Subphylum Crustacea
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Nervous and Sensory Systems More fused ganglia than in other arthropods
Pair of ganglia connects to eyes and two pairs of antennae
Nerves join this brain to the mouth, appendages, esophagus, and antennal glands
Ventral nerve cord has a pair of ganglia for each somite to control appendages
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
Compound eye migrates pigments for day or night vision
Subphylum Crustacea
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Compound eyes work differently during day and night.
Pigment cells will expand or constrict to allow different amounts of light to hit the photoreceptor cells
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Reproduction, Life Cycles, and Endocrine Function Diversity of Reproduction
Most crustaceans group eggs in brood chambers, in brood sacs attached to the abdomen, or attached to abdominal appendages
Crayfishes develop directly without a larval form
Subphylum Crustacea
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Most crustaceans have a larva unlike the adult in form, and undergo metamorphosis
The nauplius is a common larval form
Appendages and somites are added in a series of molts
Metamorphosis of a barnacle proceeds from a free-swimming nauplius to a larva with a bivalve carapace and finally to a sessile adult with plates
Subphylum Crustacea
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Life cycle of a Gulf Shrimp
Metamorphosis
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Ecdysis 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
Outermost epicuticle and 2 layer procuticle dissolve and are discarded.
Subphylum Crustacea
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Pre-molt Stage:Protocuticle sperates from epidermis.
Epidermis secretes new epicuticle.
Pre-molt Continued:Molting fluid dissolves endocuticle, and
Solutions are rebsorbed.
New exocuticle develops
Ecdysis Stage:Old epicuticle and exocuticle are discarded.
Post-ecdysis:New cuticle is stretched and hardens.
Endocuticle is secreted.
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A. Membrane between carapace and abdomen ruptures (2 hours)
B. Head Thorax and Abdomen withdraw (15 minutes)
C. Lobster continues rapid absorption of water to increase length by 20% and weight by 50%.
Tissue water will be replaced by protein later. (weeks)
Lobster Molt
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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 medulla region of
the brain
Promotes release of molting hormone from the
glands near mandible which promotes ecdysis
Androgenic Glands make a male a male. Females
lack these glands.
Subphylum Crustacea
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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
Crayfishes have a two-part stomach Gastric mill grinds up food in 1st compartment
Subphylum Crustacea
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Diplopoda have a 2 part stomach: Cardiac and Pyloric
Contain teeth for mastication and setae for straining
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Class Remipedia “Oar footed)
Class Cephalocarrida
Nine species
Hermaphrodite releasing both eggs and
sperm
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Class Branchiopoda Over 10,000 species, 4 orders
Order Anostraca, includes fairy shrimp and
brine shrimp
Lack a carapace
Order Cladocera, includes water fleas
(daphnia)
Carapace encloses the body but not the head
Brief Survey of Crustaceans
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In all, legs serve as respiratory organs, assist in suspension feeding, and locomotion
Most are freshwater
Important component of freshwater zooplankton
May reproduce by parthenogenesis to rapidly boost summer populations and then by sexual reproduction with the onset of unfavorable conditions
Fertilized eggs highly resistant to cold Critical for winter survival of population
Brief Survey of Crustaceans
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Class Maxillopoda General body plan
No appendages on abdomen
Subclass copepoda- fish parasites
Subclass Cirripedia - barnacles
Brief Survey of Crustaceans
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Subclass Cirripedia Includes barnacles and three orders of
burrowing or parasitic forms
Adults are sessile and attach directly (acorn barnacles) or by a stalk (goose barnacles)
Carapace surrounds body and secretes a set of calcareous plates
Head is reduced, abdomen is absent
Jointed feeding legs bear setae and extend from the plates to feed on small particles
Brief Survey of Crustaceans
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A. Acorn Barnacle B. Gooseneck Barnacle
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Barnacles on healthy grey whale
Contains commensalistic barnacles
And parasitic amphipods (arrows)
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Life cycle of parasitic barnacle.
Enters crab, root-like processes grow throughout body.
Reproductive structure develops externally.
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Class Malacostraca soft shell Largest and most diverse class of Crustacea with over 20,000
species
Contains three subclasses, 14 orders, and many suborders
Order Isopoda Only truly terrestrial crustaceans
Also have marine and freshwater forms
Dorsoventrally flattened, lack a carapace, and have sessile compound eyes
Common land forms include sow bugs and pill bugs
Some isopods are highly modified as parasites of fishes or crustacean
Amphipoda
Beach hopper
Brief Survey of Crustaceans
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A. Pill Bugs
B. Freshwater Sow bug - aquatic isopod
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Isopod Parasite
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Order Euphausiacea
Approximately 90 species
Includes important ocean plankton
called krill
Brief Survey of Crustaceans
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Order Decapoda
5 pairs of walking legs
In crabs, first pair of walking legs form
pincers (Chelipeds)
Approximately 18,000 species
Includes crayfishes, lobsters, crabs, and
true shrimp (size of cephalothorax and
abdomen vary)
Brief Survey of Crustaceans
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A. Tropical Rock Crab
B. Hermit Crab
C. Male Fiddler Crab
D. Red Night Shrimp
E. Spiny Lobster
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Sponge Crab - masks itself with materials from environment, sponge
