The document discusses the phylum Arthropoda, which includes insects, arachnids, crustaceans, and others. It notes that arthropods are the most successful animals due to their diversity, numbers, and traits like an exoskeleton, metamerism, hemocoel, and metamorphosis. It describes the three subphyla of arthropods - Crustacea, Chelicerata, and Uniramia. Crustaceans are mostly aquatic and have biramous limbs and a nauplius larva. Chelicerates have a prosoma and opisthosoma, six pairs of appendages including chelicerae, and include spiders, scorp

1. Phylum Arthropoda
Introduction
• By any measure, the most successful animals on the
planet are the arthropods.
• They have conquered land, water and air
• They make up over 3/4 of all known living and fossil
organisms and >85% of animal species, over one
million species in all. Estimated to be 6M
• Arthropoda (from Greek arthron, "joint", and podos
"foot", which together mean "jointed feet")
• Successful in terms of diversity, no. of spp and no of
individuals.

2. Described species of animals minus micro-organisms
Coleoptera
30%
Lepidoptera
12%
Hymenoptera
10%
Diptera
9%
Other insects
12%
Arachnida
6%
Crustaceans
3%
Other arthropods
2%
Other invertebrates
5%
Molluscs
6%
Nematodes
1%
Vertebrates
4%

3. Intro cont…
Despite their great diversity, the basic body plan of arthropods
is fairly constant.
 characteristics of the phylum Arthropoda
1.Metamerism modified by specialization of body regions for
specific functions (tagmatization)
2.Chitinous exoskeleton that provides support and protection
and is modified to form sensory structures
3.Paired, jointed appendages
4.Growth accompanied by ecdysis (casting off outer cuticle) or
moulting (shed of hair,skin or old shell)
5.Coelom reduced to cavities surrounding gonads and sometimes
excretory organs
6.Open circulatory system in which blood is released into tissue
spaces (hemocoel) derived from blastocoel
7.Complete digestive tract
8.Metamorphosis is often present. This reduces competition
between immature and adult stages

4. Why are they so successful?
 Four aspects of arthropod biology have
contributed to their success:
1. Metamerism and Tagmatization
2. The Exoskeleton
3. The Hemocoel
4. Metamorphosis

5. Metamerism and tagmatization
Arthropod body is often composed of a series of
similar segments, each bearing a pair of
appendages
Metamerism of arthropods is most evident
externally. Internally, however, septa do not divide
the body cavity of an arthropod, and most organ
systems are not metamerically arranged
Metamerism permits the specialization of regions
of the body for specific functions.
This regional specialization is called tagmatization.
These body regions, called tagmata (sing. tagma),
are specialized for feeding and sensory perception,
locomotion, and visceral functions

6. • Each tagma of an arthropod, including those fused
together, typically bears a pair of jointed appendages.
• In the head region, one or two pairs are modified into
long sensory structures called antennae.
• Tooth-like jaw appendages termed mandibles are also
usually present. Maxillae are limbs in the head region
that are modified to pass food to the mouth.
• Most of the other appendages function as walking or
swimming limbs; in aquatic forms they may have
attached gills

7. Exoskeleton
Enclosing arthropod body is an external, jointed skeleton
called an exoskeleton or cuticle
The Exoskeleton is often considered the major reason for
arthropod success.
It provides structural support, protection, impermeable
surfaces for the prevention of water loss, and a system of
levers for muscle attachment and movement
 The exoskeleton covers all body surfaces. It is nonliving and
is secreted by a single layer of epidermal cells
The epidermal layer is sometimes called the hypodermis
because, unlike other epidermal tissues, it is covered on the
outside by exoskeleton, rather than being directly exposed
to air or water
Limit size of organism
The exoskeleton is periodically shed in moulting process
called ecdysis.
 Ecdysis is controlled by nervous and endocrine systems

8. Advantages & disadvantages of
exoskeleton
• Advantages
• Protection
• Support
• Site for muscle
attachment
• Flexible at the joints
•Disadvantages
-Heavy
-Must be molted

9. Heamocoel
Hemocoel provides an internal cavity for the open
circulatory system of arthropods. Internal organs are
bathed by body fluids in the hemocoel to provide for the
exchange of nutrients, wastes, and sometimes gases
The coelom was reduced in ancestral arthropods. The
presence of the rigid exoskeleton and body wall means
that the coelom is no longer used as a hydrostatic
compartment. In modern arthropods, the coelom forms
small cavities around the gonads and sometimes the
excretory structures
In arthropods, "blood" is confined to vessels during only a
portion of its circuit through the body. The remainder of its
journey takes place within the body cavity (called the
hemocoel). For this reason, arthropod blood is called
hemolymph.

10. Metamorphosis
Metamorphosis is a radical change in body
form and physiology as an immature stage
becomes an adult
The evolution of arthropods has resulted in
an increased divergence of body forms,
behaviours, and habitats between
immature and adult stages
Having different adult and immature stages
means that the stages do not compete with
each other for food or living space. Limit
Intraspecific competition
 In some arthropod, larvae also serve as the
dispersal stage
Metamorphosis can be complete or
incomplete

11. Classification
• Despite the apparent unity of arthropods, it is now
believed that they have separate origins, and thus they
don’t form a single monophyletic group.
• Modern taxonomy recognizes 3 major lines of evolution,
resulting into 3 sub-phyla:
1. Crustacea 2. Chelicerata 3. Uniramia
There is also one extinct subphyla Trilobitomorpha which
dominated from Cambrian to Carboniferous period.

12. Sub Phylum Crustacea
• The majority of marine
arthropods are crustaceans.
These include shrimps,
crabs, lobsters, barnacles,
copepods and others
• Others are freshwater, and
very few are terrestrial
(isopods and amphipods)

13. Cyclops sp. (Bottom left), Isopods (down right)
Most crustaceans are used as food

14. Structure
• The Crustacea is a very
large group (about
70,000 known species),
and very variable in size
and shape
• Most possess gills for
obtaining oxygen and
various structures for
swimming
•They possess two pairs
of antennae for sensing
the environment (Main
different with other
group of arthropods)
•Their exoskeleton is
made of chitin hardened
using calcium carbonate–
sometimes forming a
carapace

15. • Gills on legs, for example, in a lobster
• Crustaceans are distinguished from other Arthropods
by their possession of a pair of biramous (two-parted)
limbs, and by a nauplius (free swimming and
planktonic) larval stage

16. Biology
• The biology of
crustaceans, like
their structure, is
very diverse
• Some are filter
feeders (e.g.
barnacles), while
others are predators
(crabs, lobsters) or
scavengers (shrimps
•Some are planktonic
and have appendages
for Swimming (e.g.
copepods) while
others are bottom
dwellers with walking
legs (lobsters)
•Larval development is
variable

17. Sub Phylum Chelicerate
• Have piecing and sucking mouth parts called
chelicerae
• The Chelicerata includes spiders and scorpions, mites
and ticks, horseshoe crabs, and their relatives.
• It is the second most prominent group of terrestrial
arthropods, after the uniramians.
• Majority terrestrial

18. Characteristics
Body divided into
two parts: PROSOMA
and OPISTHOSOMA
6 pairs of
appendages
(CHELICERA,
PEDIPALPS and 4
pairs of legs)

19. Characteristics Cont….
• They have six pairs of appendages
• Lack of Antennae
• Lack of mandibles (mouth parts)
• Body divided into two distint regions Prosoma (Head and thorax) and
Opisthosoma(Abdomen)
• Most suck liquid food from their prey

20. Characteristic Cont….
• The pedipalps, are modified in various ways e.g. in scorpions they
form the large pair of claws, while the chelicerae are tiny structures
near the mouth.
• The pedipalps of the male spiders are modified for copulation.
• In spiders, the chelicerae are modified into fangs with poison glands

21. Breathing
• Aquatic species have abdominal gills used for
breathing.
• Terrestrial groups cover the gills to form a special
breathing organ, the book lungs.
• Others use the tracheal system opening through a
spiracle.

22. Feeding
• The majority of chericerates are predators on other arthropods.
• Others are ecto-parasites (mites and ticks).
• A few (mites) are plant feeders.