Transcript Brief Survey of Crustaceans

CHAPTER 20
Crustaceans
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Sally Lightfoot Crab,
from the Galapagos
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Overview
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Over 67,000 living species
Divided into 5 classes
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We will study 3 classes, Branchiopoda and
Malacostraca, Maxillopoda
Branchiopoda = water fleas, brine shrimp
 Malacostaca = isopods, krill, crab, lobster, etc.
 Maxillopoda = barnacles
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Subphylum Crustacea
General Nature of a Crustacean
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Main distinguishing characteristic of
crustaceans
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Two pairs of antennae
Head also has a pair of mandibles and 2 pairs
of maxilla
One pair of appendages on each of the
additional segments
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Some segments may lack appendages
All appendages, except perhaps first antennae, are
biramous
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Subphylum Crustacea
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Tagmata (segments) are usually head,
thorax, and abdomen
Sometimes thorax and head are fused =
cephalothorax
Arrangement of tagmata in Malacostraca
is the ancestral plan
Head has 5 fused segments
 Thorax has 8
 Abdomen has 6
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Head (5) and thorax (8)- compose 13 cephalothorax segments
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Subphylum Crustacea
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Anterior end is a non-segmented rostrum
(covers eyes in some)
Telson, the last abdominal segment
(contains anus), and uropods forms a tail
Dorsal covering is the carapace
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May cover most of body or just cephalothorax
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Subphylum Crustacea
Form and Function
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External Features
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Secreted cuticle is made of chitin, protein, and
calcareous material
Heavy plates have more calcareous deposits
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Joints are soft and thin, allowing flexibility
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Subphylum Crustacea
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Appendages
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Most have appendages on each segment, with
homology
Appendages of crayfish: 3 main parts to each appendage
Protopod = brown
Endopod = blue
Exopod = yellow
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Crawfish Appendage and Function
(Number if pairs)
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
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Subphylum Crustacea
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Internal Features
 Coelomates  Protostomes (mouth first)
 Complete Gut
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Circulatory System
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Open circulatory system
with blood (Hemocoel) Dorsal heart
 Single-chambered sac of striated muscle
Respiratory System
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Smaller crustaceans may exchange gases across thinner areas of cuticle
Larger crustaceans use featherlike gills for gas exchange
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Subphylum Crustacea
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Muscular System
Striated muscles - most of body
 Most muscles arranged as antagonistic
groups
 Abdominal flexors of a crayfish allow it to
swim backward
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Green Gland = Kidney
Internal Anatomy of the crayfish.
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Subphylum Crustacea
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Excretory System
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Antennal 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
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Subphylum Crustacea
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Nervous and Sensory Systems
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Pair of ganglia connects to eyes and two pairs of
antennae
Ventral nerve cord has a pair of ganglia for each
segment to control appendages
Tactile hairs occur on the body
Chemical sensing of taste and smell occurs in hairs
on antennae and mouth
Compound eye migrates pigments for day or night
vision
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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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Subphylum Crustacea
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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
 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
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Life cycle of a Gulf Shrimp
Metamorphosis
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Subphylum Crustacea
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Ecdysis
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Necessary for a crustacean to increase in size the
 Exoskeleton does not grow
Underlying epidermis secretes cuticle
Outermost epicuticle and 2 layer procuticle
dissolve and are discarded.
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Pre-molt Stage:
Protocuticle separates 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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Lobster Molt
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)
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Subphylum Crustacea
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Hormonal Control of Ecdysis
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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
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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
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Brief Survey of Crustaceans
Class Branchiopoda
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Over 10,000 species, 4 orders
 Order Anostraca, includes fairy shrimp and
brine shrimp
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Order Cladocera, includes water fleas
(daphnia)
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Lack a carapace
Carapace encloses the body but not the head
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Brief Survey of Crustaceans
Class Maxillopoda
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General body plan
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No appendages on abdomen
Subclass Cirripedia - barnacles
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Adults are sessile
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
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A. Acorn Barnacle
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B. Gooseneck Barnacle
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Barnacles on healthy grey whale
Contains commensalistic barnacles
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Brief Survey of Crustaceans
Class Malacostraca
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Largest and most diverse class of Crustacea with over 20,000
species
Order Isopoda
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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 (Rolly
Pollies)
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A. Pill Bugs
B. Freshwater Sow bug - aquatic isopod
ISOPODS
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Isopod Parasite
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Brief Survey of Crustaceans
Order Decapoda
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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)
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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
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