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Arthropods Again:
The Crustacean
HW: Study These Notes &
Complete page 16 in RB 2.
The Crustacean
The first type of arthropod that we will
study is the crustacean.
There are about 25,000 species in this
class. They include:
 Shrimp
 Lobster
 Crayfish
 Crab
Crustacean Body Plan
Crustaceans have a body plan that
consists of:
Cephalothorax consisting of:
Head, consisting of five segments giving off
paired appendages
 Thoracic Segments – generally modified for
food handling or movement
Abdomen – usually segmented, but may or
may not have appendages.
The Crayfish
Our crustacean of choice to study is the
Like other crustaceans, the crayfish has
a head, thorax, and abdomen.
Specifically it has:
5 head segments
 8 thoracic segments (body segments)
 6 abdominal segments
Crayfish Segments
In the crayfish, each segment gives rise to a
specific appendage which has specific
You will need to know and study what these
are, and what
their functions
Head Appendages
Head Segment 1: give off antennules shorter
pair) that are used as sensory receptors.
Head Segment 2: give off antennae (longer
pair) that are also used as sensory receptors.
Head Segment 3: give off mandibles around
the mouth that are used to bite and crush
Head Segment 4 & 5: give off maxillae that
are used to move the food around so that it
can be put in the mouth.
Thoracic Appendages
Thoracic Segments 6-8: give off
maxillipeds which are also used to
manipulate food.
Thoracic Segment 9: chelipeds
(pinchers!!) are used for self-defense,
getting, and manipulating food.
Thoracic Segments 10-13: walking legs,
which are used for locomotion.
Abdominal Appendages
Abdominal Segments 14-18: give off
swimmerets, which create water currents,
enhance air movement to gills, hold eggs in
females, and are modified as reproductive
structures in males.
Abdominal Segment 19: telson (which
houses the anus)– used for waste excretion
and uropods. Both structures can be used
as a paddle to allow for rapid (backwards)
locomotion underwater.
Crayfish Internal Structures
Do not lose these notes, as this picture
will greatly help you with your self-test.
Get to Know the Exoskeleton
The dorsal and lateral parts of the
cephalothorax are covered with the carapace.
The carapace has an anterior extension known as
the rostrum.
The ventral plates is called the sternum.
The abdominal skeletal plates are known as
the tergum.
All of these structures comprise the
exoskeleton and act as protection for internal
Crayfish Muscular System
Inside the thoracic and abdominal segments
are muscle bundles, nerves, and vessels.
The abdominal segments are nearly filled with
muscle tissue. This muscle is commonly
consumed with crayfish & lobsters.
These muscles are used to power the
appendages of the abdominal regions; that is,
the swimmerets.
Crayfish Digestive
Mouth -> esophagous -> stomach ->
digestive gland -> intestine -> anus
Their stomach is divided into a cardiac region
and a pyloric region.
The cardiac chamber has calcified plates that act
like teeth to grind up food into digestible bits.
The food then moves to the pyloric region and
moves on as listed above. Ground up food is
digested here in the crayfish.
Crayfish Excretory System
The excretory system is made up of
green glands. These are consumed by
some people when eating the whole
While these glands are capable of some
excretion, they cannot handle all of the
chemical & water balance needs.
The gills play the largest role in regulating
body fluids.
Crayfish Circulatory System
Crayfish have open circulatory systems.
They have vessels, but the vessels empty
into sinuses.
 The blood from the sinuses is then
returned to the heart in channels, not
 So, though there are vessels, they empty
into sinuses – so it is still considered an
open system.
Crayfish Respiration
Respiration occurs through the gills
(found from thoracic segment 2-6).
Water is circulated over the gills by
movement of a paddle-like gill bailer
which moves with the second maxilla.