Transcript PowerPoint

ARTHROPOD
S
Instructor: Almonther I. Alhamedi
The Islamic University of Gaza
Department of Biology
E-mail : [email protected]
Web page :http://site.iugaza.edu.ps/mhamedi
CHARACTERISTICS OF PHYLUM ARTHROPODA
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1. Bilateral symmetry; metameric body, consisting of head and
trunk; head, thorax, and abdomen; or cephalothorax and abdomen
2. Jointed appendages; primitively, one pair to each somite;
appendages often modified for specialized functions
3. Exoskeleton of cuticle containing protein, lipid, chitin, and
often calcium carbonate secreted by underlying epidermis and
shed (molted) at intervals.
4. Complex muscular system, with exoskeleton for attachment,
striated muscles for rapid actions, smooth muscles for visceral
organs; no cilia.
5. Reduced coelom in adult; most of body cavity consisting of
hemocoel (sinuses, or spaces, in the tissues) filled with blood
6. Complete digestive system; mouthparts modified from
appendages and adapted for different methods of feeding
CHARACTERISTICS OF PHYLUM ARTHROPODA
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7. Open circulatory system, with dorsal contractile heart,
arteries, and blood sinuses
8. Respiration by body surface, gills, tracheae (air tubes),
9. Paired excretory glands called coxal, antennal, or maxillary
glands present in some, homologous to metameric nephridial
system of annelids; some with other excretory organs, called
malpighian tubules
10. Nervous system of annelid plan, with dorsal brain
connected by a ring around the gullet to a double nerve chain of
ventral ganglia; fusion of ganglia in some species; well developed
sensory organs
11. Sexes usually separate, with paired reproductive organs
and ducts; usually internal fertilization; oviparous or
ovoviviparous; often with metamorphosis; parthenogenesis in
some
SUBPHYLUM CRUSTACEA
General Nature of a Crustacean
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crustaceans are the dominant arthropods in the sea.
The bodies of crustaceans are covered with a secreted cuticle
composed of chitin, protein, and calcareous material.
Crustaceans are the only arthropods with two pairs of antennae.
In addition to two pairs of antennae and a pair of mandibles,
crustaceans have two pairs of maxillae on the head, followed by a
pair of appendages on each body segment or somite.
In some crustaceans not all somites bear appendages. All
appendages, except perhaps the first antennae, are primitively
biramous (two main branches).
Crustaceans are specialized for life in water, and most possess gills
to obtain oxygen.
The appendages are specialized for swimming, crawling, attaching
to other animals, mating, and feeding.
SUBPHYLUM CRUSTACEA
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The largest group of crustaceans is class Malacostraca,
which includes lobsters, crabs, shrimps, beach hoppers, sow
bugs, and many others.
SUBPHYLUM CRUSTACEA
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These show a surprisingly constant arrangement of body
segments and tagmata, This typical body plan has a head of five
(six embryonically) fused somites, a thorax of eight somites, and
an abdomen of six somites (seven in a few species).
At the anterior end is a non-segmented rostrum and at the
posterior end is a non-segmented telson, which with the last
abdominal somite and its uropods forms a tail fan in many
forms.
In many crustaceans the dorsal cuticle of the head may extend
posteriorly and around the sides of the animal to cover or be fused
with some or all of the thoracic and abdominal somites. This
covering is called a carapace.
In decapods (including lobsters, shrimp, crabs, and others), the
carapace covers the entire cephalothorax but not the abdomen.
CHARACTERISTICS
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Head: 2 pairs antennae, pair mandibles (jaws), 2 pairs of
maxillae (handle food)
Usually 1 pair appendages for each segment
Tagmata either cephalothorax & abdomen or head (5 fused
somites), thorax (8 somites), and abdomen (6 somites)
Rostrum—anterior end
Telson & uropods form tail—posterior end
External structure of crayfishes. A, Dorsal view. B, Ventral view.
Appendages of a crayfish showing how they have become modified
from the basic biramous plan, as found in a swimmeret. Protopod,
pink; endopod, purple; exopod, yellow.
EXTERNAL FEATURES
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Dorsal covering is carapace; may cover most of body or just
cephalothorax
Somites without carapace have tergum (dorsal) or sternum
(ventral) plates which are heavy and have more calcareous
deposits
Cuticle made of protein, chitin, and calcareous deposits.
Joints soft & thin for flexibility
Telson analogous to pygidium (posterior body part)
APPENDAGES
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Specialization of appendages; all show serial homology
(derived from same biramous type)
All variations of biramous (two jointed) plan with a basal
portion called the protopod (1-2 joints) and a side portion
called an exopod (1-several joints), and a mid portion called
a endopod (1-several joints)
Joints will have further modifications called endites or
exites
BODY CAVITY
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Metamerism but no intersepta
No coelom, this is lost during development; blood-filled
hemocoel instead with no peritineal lining.
BODY CAVITY
MUSCULAR SYSTEM
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Striated muscle forms most of body
Antagonistic pairs; flexors and extensors
Flexors in abdomen allow crayfish to swim backward
Muscles alongside stomach control mandibles
RESPIRATORY SYSTEM
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Small crustaceans exchange gases through cuticle on
thin areas of body like legs.
Large crustaceans use feather-like gills.
The gills may be in thorax cavity or on thoracic legs.
CIRCULATORY SYSTEM
Open circulatory system: no veins to separate
blood from interstitial fluid
 Hemolymph (blood) leaves dorsal heart (1
chamber) by arteries but washes through tissue
sinuses; goes to sternal sinus and then on to gills
for gas exchange before returning through
pericardial sinus
 Hemolymph
colorless;
hemocyanin
and/or
hemoglobin are respiratory pigments
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NERVOUS AND SENSORY SYSTEMS
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More fusion of ganglia than other arthropods
Supra-esophageal ganglia connect eyes and antennae
Neurons join this to sub-esophageal ganglion that controls
mouth, appendages, esophagus, and antennal glands
Double ventral nerve cord with ganglion/somite to control
appendages
Eyes-compound and made of many units (ommatidia) (one
of the optical unit in compound eyes in crustaceans)
restricted to mosaic vision in bright light; in dim light sees
continuous image
Statocysts located at base of 1st antennae
Tactile hairs on, mouthparts, and telson
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Copepods are extremely abundant and important in the
plankton. They use their mouthparts to filter out or
capture food. Many planktonic species keep from sinking by
using their enlarged first pair of antennae ( Fig. 7.30 ) to
swim. Many species are parasitic, some being so simplified
that they look like little more than small bags of tissue.
The structurally simplest crustaceans, like this planktonic copepod, tend to be small
and have appendages that are similar to each other—that is, less specialized. One
exception here is the first antenna, which is specialized for swimming. All
appendages are paired, but the ventral view shows only those on one side.
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Barnacles are filter feeders that usually live attached to
surfaces, including living surfaces like whales and crabs.
Adults are sessile and attach directly (acorn) or by a stalk
(goose) Carapace surrounds body and is secreted as
calcareous plates, Head reduced, abdomen absent, legs
(cirri) long with setae for filter feeding
The plates on the upper surface open to allow the feathery
filtering appendages (cirri), which are actually the legs, to
sweep the water.
(a) Barnacles conceal a crustacean body beneath thick plates. They lie on their
backs and use their legs to filter feed. Note that barnacles are hermaphrodites.
(b) The thatched barnacle (Tetraclita squamosa) from the Pacific coast of North
America.
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Amphipods are small crustaceans with a curved body that
is flattened sideways.
The head and tail typically curve downward, and the
appendages are specialized according to function. Beach
hoppers, common in shore debris, are strong jumpers.
Other amphipods crawl among seaweeds. Burrowing in the
skin of whales (as whale lice) and living as part of the
plankton are some other lifestyles of this large, mostly
marine group of over 5,000 species.
beach hopper (Orchestoidea)
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Isopods are found in many of the same environments as
amphipods. They are about the same size as amphipods.
the body is dorsoventrally flattened and thus has a flat back. Pill
bugs are common land isopods that are similar to many marine
species. Fish lice (no relation to lice of birds and land mammals,
which are insects) and other isopods are parasites of fishes.
The sea louse, or sea roach (Ligia
oceanica) , is neither a louse nor a
roach but an isopod. It feeds
mainly on decaying seaweeds
carried in to shore by the waves.
Some isopods live as parasites on
fishes.
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Krill, or euphausiids, are planktonic, shrimp-like crustaceans.
The head is fused with some of the body segments to form a
distinctive carapace that covers the anterior half of the body like
armor. Most krill are filter feeders that feed on diatoms and other
plankton. Krill are extremely common in polar waters,
aggregating in gigantic schools of billions of individuals. They are
an almost exclusive food source for many Antarctic whales,
penguins, and fishes.
Krill (Euphausia superba)
form dense schools in
Antarctic waters and were
thought to be potential
human food.
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Shrimps, Lobsters, and Crabs With around 10,000 species,the
decapods (means“10 legs”) are the largest group of crustaceans
Decapods feature five pairs of legs, or pereopods, the first of which
is heavier and usually has claws used for feeding and defense.
Decapods also have three pairs of maxillipeds, which are closer to
the mouth, turned forward, and specialized to sort out food and
push it toward the mouth. Maxillipeds are used as filtering devices
in decapods that eat small food particles.
The carapace is well developed and encloses the part of the body
known as the cephalothorax. The rest of the body is called the
abdomen.
Limulus polyphemus is
a horseshoe crab
Pleuroncodes planipes, also called the lobster krill or tuna crab, is
a pelagic crab that has been suggested as a potential source of
human food.
DECAPODA
The American lobster ( Homarus americanus ) illustrates the basic
body plan of decapod crustaceans.
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Hermit crabs, which are not true crabs, are also scavengers.
They hide their long, soft abdomens in empty gastropod shells.
Some hermit crabs cover their shells with sea anemones or
sponges for added protection and camouflage.
In the true crabs the abdomen is small and tucked under the
compact and typically broad cephalothorax. The abdomen is
visible as a flat, V-shaped plate in males; in females it is
expanded and U -shaped for carrying eggs .
Hermit crab (Dardanus sp.) with sea anemones living on its shell.
The hermit crab is protected by the nematocysts on the sea
anemone’s tentacles, and the sea anemones get to eat food
particles that are let loose when the hermit crab feeds.
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Crabs have broader cephalothorax and reduced abdomen
compared to crayfish or lobsters