Transcript Document
CHAPTER 20
Crustaceans
20-1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Sally Lightfoot Crab,
from the Galapagos
20-2
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Overview
Over 67,000 living species
Insects and crustacea compose over
80% of all named animal species
Divided into 5 classes
We will study 3 classes, Branchiopoda and
Malacostraca, Maxillopoda
Branchiopoda = water fleas, brine shrimp
Malacostaca = isopods, krill, crab, lobster, etc.
Maxillopoda = barnacles
20-3
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
20-4
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
20-5
Some segments may lack appendages
All appendages, except perhaps first antennae, are
biramous
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Crustacea
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
20-6
Head has 5 fused somites
Thorax has 8
Abdomen has 6
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
20-7
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Crustacea
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
20-8
May cover most of body or just cephalothorax
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Crustacea
Form and Function
External Features
Secreted cuticle is made of chitin, protein, and
calcareous material
Heavy plates have more calcareous deposits
Telson is not a somite
20-9
Joints are soft and thin, allowing flexibility
Bears anus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
20-10
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Crustacea
Appendages
Most have appendages on each somite
Appendages represent homology
20-11
Have evolved a wide variety of walking legs, mouthparts,
swimmerets, etc. from modification of the basic biramous
appendage
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Appendages of crayfish: 3 main parts to each appendage
Protopod = brown
Endopod = blue
Exopod = yellow
20-12
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
20-13
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Crawyfish 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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Crustacea
Internal Features
Coelomates - reduced
Persistent blastocoel that becomes filled with
blood Hemocoel
Protostomes (mouth first)
Complete Gut
20-15
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Crustacea
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
20-16
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Green Gland = Kidney
Internal Anatomy of the crayfish.
20-17
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Crustacea
Respiratory System
Smaller crustaceans may exchange gases across thinner areas of cuticle
Larger crustaceans use featherlike gills for gas exchange
Circulatory
20-18
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Hemolymph travel: Heart, Body, Sinus, Gills, Heart via Ostium (opening)
20-19
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Crustacea
Excretory System
20-20
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
20-21
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Crustacea
Nervous and Sensory Systems
20-22
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
20-23
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Crustacea
Reproduction, Life Cycles, and Endocrine
Function
20-24
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Crustacea
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
20-25
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Life cycle of a Gulf Shrimp
Metamorphosis
20-26
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Crustacea
Ecdysis
20-27
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.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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.
20-28
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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)
20-29
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Crustacea
Hormonal Control of Ecdysis
20-30
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Crustacea
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
20-31
Gastric mill grinds up food in 1st compartment
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Diplopoda have a 2 part stomach: Cardiac and Pyloric
Contain teeth for mastication and setae for straining
20-32
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Brief Survey of Crustaceans
Class Branchiopoda
Over 10,000 species, 4 orders
Order Anostraca, includes fairy shrimp and
brine shrimp
Order Cladocera, includes water fleas
(daphnia)
20-33
Lack a carapace
Carapace encloses the body but not the head
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
20-34
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Brief Survey of Crustaceans
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
20-35
Critical for winter survival of population
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Brief Survey of Crustaceans
Class Maxillopoda
General body plan
No appendages on abdomen
Subclass Cirripedia - barnacles
20-36
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Brief Survey of Crustaceans
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
20-37
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
A. Acorn Barnacle
20-38
B. Gooseneck Barnacle
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Barnacles on healthy grey whale
Contains commensalistic barnacles
And parasitic amphipods (arrows)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Life cycle of parasitic barnacle.
Enters crab, root-like processes grow throughout body.
Reproductive structure develops externally.
20-40
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Brief Survey of Crustaceans
Class Malacostraca
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
crustaceans
20-41
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
A. Pill Bugs
B. Freshwater Sow bug - aquatic isopod
20-42
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Isopod Parasite
20-43
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Brief Survey of Crustaceans
Order Euphausiacea
Approximately 90 species
Includes important ocean plankton
called krill
20-44
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Brief Survey of Crustaceans
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)
20-45
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
A. Tropical Rock Crab
B. Hermit Crab
C. Male Fiddler Crab
D. Red Night Shrimp
E. Spiny Lobster
20-46
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Sponge Crab - masks itself with materials from environment, sponge
20-47