Crustaceans – Jointed Appendages
for locomotion and feeding
Ashton Mouton
2432509
Dept. of Biodiversity and Conservation Biology
University of the Western Cape
Available at http://planet.uwc.ac.za/nisl/Eco_people/Presentations/
A Brief Description of Crustaceans
http://en.wikipedia.org/wiki/Image:Blue_crab_on_market_in_Piraeus_-_
Callinectes_sapidus_Rathbun_20020819-317.jpg
 Crustaceans are a large group of arthropods that are treated as a
subphylum and are found in marine, freshwater and terrestrial
environments although they are mostly found in aquatic ecosystems.
 They have three distinct body divisions that include the head, the thorax
and abdomen or when there is no clear distinction between the head and
thorax then it's called the cephalothorax.
 The most important groups found abundantly of the crustaceans are the
copepods, barnacles, malacostraca (Craps, shrimps, lobster and krill),
branchiopoda.
 Groups that posses a well developed abdomen, usually have six specially
adapted appendages for locomotion of which 5 are called swimmeret
(pleopod) and one pair called the uropod
The Scientific Classification of Crustaceans
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Kingdom:
Phylum:
Subphylum:
Class:
Animalia
Arthropoda
Crustacea
Branchiopoda
Remipedia
Cephalocarida
Maxillapoda
Ostracoda
Malacostraca
Source: www.Wikipedia.com
http://en.wikipedia.org/wiki/Image:Christmas_Island_red_crab.jpg
Crustacean Composition
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The exoskeleton is divided into a number of plates and cylinders
the jointed appendages are described as the point where the
exoskeleton remains flexible and thin at the junction of the plates
and cylinders Many of the crustacean's appendages are biramous
They have a hardened exoskeleton that contains calcium carbonate.
The head bears a pair of compound eyes and three pairs of mouth
parts
a pair of mandibles and two pairs of maxilla used for handling food.
Three Limb types
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are three different kinds of appendages in crustaceans that allow their
appendages to be diverse, which are the cylindrical walking legs, biramous
appendages and the leaf like limbs. (Kaestner A (1970)
The first sets of appendages are the biramous appendages that consist of a
protopodite with two branches (Kaestner A (1970)
The cylindrical walking legs bear a resemblance to that of other arthropods, which
have one set of articles that belong to either the protopodite or endite if present,
which are used for locomotion or holding onto its prey and rarely used for
swimming in super order, Portunidae and Munnopsidae(Kaestner A (1970)
The leaf-like appendages are only fond in the Branchiopoda and the Phyllocaridae
and function like leaf-limbs that are adapted to do include swimming, respiration
and filter current production (Kaestner A (1970)
http://cas.bellarmine.edu/tietjen/Laboratories/Bio%20Pix%204%20U/Image111.gif
Figure 1 shows the biramous appendage
The Evolution of Crustaceans
The study of the diversity of crustacean limbs was made possible by the
results of molecular and genetic modules of Drosophilia and mice
that were made available(Panganiban et al 1995).
 The two genes that are the main focus of the development of
appendages on different segments are the ultrabithorax (Ubx) and
the abdominal-A (abd-A) in crustaceans(Panganiban et al 1995).
 The appendages that assist in feeding are called the maxilliped and
do not express the Ubx/abd-A genes during early embryological
development(Panganiban et al 1995).
 Branchiopods have preserved many ancestral characters like the
lack of maxillipeds (Panganiban et al 1995).
The Evolution of Crustaceans (continue)
 Copepods have one maxilliped present but the appendage has evolved
separately from the maxilliped found in the Malacostracans(Panganiban et
al 1995).
 Therefore the gene expression responsible for the change in the
morphology of limbs through evolution can represent the change of the
maxilliped in some crustaceans through the mutation of the Ubx/abd-A
expression; therefore it is reasonable to say that the altering patterns of
Ubx/abd-A genes can form part of the developmental foundation of the
evolution of crustacean appendages(Panganiban et al 1995)
The Body Parts of crustaceans
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body of each crustacean is divided into three different groups, which contain
the preoral two pairs of antennae, the mouthpart and the trunk appendages(Kaestner A
(1970).
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trunk appendage is further divided into the thoracopods and pleopods. The first
three thoracopods are transformed into accessory mouthparts that have strong
endites, basal articles and less developed branches(Kaestner A (1970).
When there is many pairs the modifications tend to be more similar in the posterior
end and are then called maxilliped while the other limbs are called walking legs
(perepods) (Kaestner A (1970).
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Occasionally
the grouping of the trunk somites match the distribution of the limbs,
this results in many thoracopods transforming into maxilliped while the fusion of the
head and thoracomeres to form the cephalothorax, examples are Isopods,
Amphipods, Mysidacea and Cumacea(Kaestner A (1970).
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/crustaceans.gif
Figure 2 shows the different body appendages and body shapes
Thoracic Appendages
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The appendages found at the thoracic region are transformed into maxilliped to
be used for feeding; their articles frequently allocate thorns on the inner
surface, which help in the movement of two pairs of protopodites or endites
and are analogous to the labium of insects(Kaestner A (1970).
The thoracic region may not bear modified appendages like in most
Malacostracan but the pereopods are modified to appear like walking legs and
in other crustaceans these limbs could be modified and used for swimming if
there are large exopodites present (Kaestner A (1970).
In the branchiopoda the appendages found at the thorax are biramous with two
parallel branches while the Ostracods have only two pairs of legs, which are
highly specialized (Kaestner A (1970).
Crustaceans have a constant feeding activity and will undergo certain times of
fasting during development, which occurs through molting (Sanchez-Pazza et
al 2004). Molting involves different stages with different feeding behaviors
and requires sufficient energy from the food available to crustaceans (SanchezPazza et al 2004)
Abdominal Appendages
 Malacostracans are the only crustaceans that have pleopods, which are
used for swimming and are therefore covered by setae furthermore their
branches are possibly alike (Kaestner A (1970).
 However they may also respire through these appendages by creating
respiratory currents that serve has gills.
 The males first two pairs of appendages form into gonopods, which are
copulatory appendages The uropods are the last pair of the pleopods found
in the Malacostracans and is joined with the telson to form the tailfan,
which increase the thrusting action that the abdomen creates when moving
(Kaestner A (1970).
Integument
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The integument is a membranous structure that contains various
layers to protect the body of crustaceans
The hypodermis secretes a layered chitinous membrane or
cuticle and the epicuticle protects it (Kaestner A (1970).
The integument in larger crustaceans may be used as ventral
skeletal system to provide support for the continuous growth of
these crustaceans (Kaestner A (1970).
Chromatophores are responsible for the different colors
available in crustaceans, which are caused by these soluble
pigments found in the cuticle (Kaestner A (1970).
The Malacostranans
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These consist of all the crustaceans that have eight thoracic somites six or seven
abdominal somites and a few species have a abdomen that has a furca (Kaestner
A (1970).
The appendages have pleopods that are found on the abdomen and the pleopods
are divided into uropods.
Malacostracans can be characterized by having larger complex morphologies
that are more advanced than other crustaceans, larger and heavier exoskeletons
and are larger in size (Kaestner A (1970).
The species that are the most economically important are found in this group,
which contain species like the Euphausid, shrimps, lobsters and crabs. Shrimps,
lobsters and crabs fall in the order Decapoda and they are characterized by
having a carapace that is fused to the thoracic metameres that extend to each
side of the legs, which encloses the gills within the branchial chambers
(Kaestner A (1970).
The appendages consist of three maxilliped while the other is walking legs but
the first pereopods is structurally modified to be cheliped that is used to protect
itself or handling prey (Kaestner A (1970).
http://www.gmushrooms.com/Posters/EDIBLECRUSTACEANS.jpg
Figure 3 shows the different Malacostracans that are edible for humans
History of Crustaceans
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Most crustaceans have hardened exoskeletons that can be preserved in rocks
and have.
Fossils of crabs have been found in rocks that date back to the Cretaceous
period, as well as those of the Cenozoic era.
Although soft shelled crustaceans have a poor fossil record.
This includes the barnacles and the shrimps
Crab fossils are found in rocks like the Gault clay that date back to the
Cretaceous period, where these crustaceans lived on the bottom of sea or in
reefs
Feeding and Locomotion
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The Anastraca are mostly the fairy shrimps that are constantly swimming at a
slow pace with he venter twisted upwards, therefore they are found swimming
just below the sea surface and only occasionally are found at the bottom of the
sea bed.
They do not have maxillae but the locomotory limbs have a leaf-like
appearance that enables the body to be pushed forward as well as by
contracting and extending the trunk rapidly they can dash themselves off.
These crustaceans are filter feeders that rely on plankton, small suspended
organic particles on plant and larger animals that create currents, which release
any stubborn particles attached to these examples.
Food is caught by creating waves by rapidly vibrating the limbs that attract
food to the mouth region where the small particles are sucked up into.
http://evolution.berkeley.edu/evolibrary/images/crayfish_ventral2.gif
Figure 4 shows what the different appendages are used in the order Malacostraca
Feeding and Locomotion (Continue)
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The Cirripedia (barnacles), these crustaceans are either sedimentary or
symbiotic and they all occur in marine habitats (Kaestner A (1970).
The body is consists of a head, thorax and abdomen region that
enclosed in a bivalved carapace. Some Cirripedia maintain their
primitive body order by still having six somites on the thorax and the
abdomen by having five somites (Kaestner A (1970).
All Copepods are floaters and therefore rely on the currents to keep
them afloat, if there were no currents available, they would sink and
die.
In many tropical and Mediterranean species the setae on the
appendages underwent specialized modification to increase resistance
(Kaestner A (1970).
In the order Cyclopidae where the swimmers are found, many features
have been modified to allow these crustaceans to remain longer
suspended, for example the featherlike appearance of the caudal rami
of Calocalanus (Kaestner A (1970).
Parasitic Crustaceans
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Parasitic Copepods have swollen unsegmented bodies and the legs are
either reduced or lost due to evolutionary processes but once they are
removed from the host they will be unfit to survive because they
cannot swim or are capable of floating (Kaestner A (1970).
Pennella balaenopterae is the largest parasitic copepod, which is
found on the finback of whales and a total body length of 32cm.
The living fossils of the Copepods are the free-living cyclopoid and
harpacticoid Copepods although parasitic forms would have existed
much earlier because of the occurrence of cysts found on Jurassic
echinoids (Kaestner A (1970).
http://www.fao.org/docrep/field/003/Q8694E/Q8694E46.gif
http://www.eeob.iastate.edu/faculty/DrewesC/htdocs/argulus.jpg
These figures show two parasitic crustaceans
Are changes possible due to climate change?
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A rise in global temperature may effect the distribution of crustaceans because
they are exothermic organisms or their prey may have different migration
patterns that will affect them, the higher the temperature the more difficult it
will be for the crustacean to take in oxygen because of poor ventilation and
insufficient aerobic capacity of mitochondria at low temperatures. .
” In a cause and effect hierarchy, the progressive increase in oxygen limitation
at extreme temperatures may even enhance oxidative and denaturation stress.”
(Panganiban et al 1995)
Tropical storms can affect the abundance of microscopic crustaceans by
changing the frequency occurrence
If the climate were to change rapidly, most of the larger crustaceans would be
heavily affected by it but the microscopic crustaceans especially the
crustaceans that live in the sediments would be less affected.
Reference
Kaestner A (1970) Invertebrate Zoology, volume 3, John Wiley & Son Inc,
university of Munich, pg 523
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Panganiban G, Sebring A, Nagy L, Caroll S, Science, (1995) The
development of Crustacean Limbs and the evolution of arthropods, Vol. 270,
No.5240 pp1363-1366
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http://en.wikipedia.org/wiki/Crustaceans
www.Wikipedia.com
Sanchez-Paza A, Garcý F,Carren OC, Muhlia-Almaza A,. Peregrino-Uriarteb A
B, Herna ndez-Lo J, Yepiz- G (2004) Usage of energy reserves in crustaceans
during starvation: Status and future directions, Centro de Investigaciones
Biolo´gicas Del Noroeste (CIBNOR), Unidad Hermosillo, Centenario Norte
#53 Col. Prados Del Centenario, Hermosillo, Sonora C.P. Mexico