Arthropods are the most diverse and abundant group of animals. They make up over 80% of all known animal species. Arthropods are found in nearly all habitats on Earth and have been highly successful in adapting to life on land, in water, and air. They have a segmented body, jointed appendages, a hard exoskeleton that is periodically molted, and bilateral symmetry. Insects are the largest class of arthropods, making up over 50% of all known animal life. Insects go through complete or incomplete metamorphosis from egg to adult. Their body segments are specialized for different functions and they have an exoskeleton, jointed legs, and often wings.

1. ARTHROPODS

2. 1.1 Diversity and abundance of arthropods
• The arthropods are by far the most successful
phylum of animals, both
– in diversity of distribution and
– in numbers of species and individuals.
• They have adapted successfully to life in water, on
land and in the air.

3. 1.1 Diversity and abundance of arthropods
• Relative abundance.
– 3/4 (About 80%) of all known species of animals are
arthropods.
– More known species of arthropods than known
species of plants and animals combined.
– about 800,000 species have been described, and
– recent estimates put the total number of species in
the phylum at about 6 million.

4. Diversity and abundance….
• Diversity
– Great diversity in form and habitat.
– Found in a greater variety of habitats than any
other animal group;
• On top of mountains,
• At great depths in the ocean and
• In the icy wilderness of antarctica.
– They can survive great extremes of temperature,
toxicity, acidity and salinity.

5. 2. Characteristics of Arthropods

6. 2. General characteristics
• Arthropoda = Jointed foot
• Comprises invertebrate animals with:
– Segmented body
– Several pairs of jointed appendages
– Bilateral symmetry
– Rigid, chitinous exoskeleton that is periodically
molted as the animal grows.
6

7. 2.1 Metamerism
• Metamerism- body is segmented.
• Exoskeleton and metamerism causes molting

8. 2.2 Exoskeleton
• Exoskeleton- body covered with a hard external
skeleton
• Why an exoskeleton?
• Why not bones? Exoskeleton good for small
things, protects body from damage (rainfall,
falling, etc.).
• Bones better for large things

9. 2.3 Bilateral Symmetry
• Bilateral Symmetry- body can be divided into two
identical halves

10. 2.4 Jointed Appendages
• Jointed appendages- each segment may
have one pair of appendages, such as:
• Legs
• Wings
• Mouthparts

11. 2.5 Open Circulatory System
• Open Circulatory System- blood washes over
organs and is not entirely closed by blood vessels.
Our system is a closed one

12. 2.6 Ventral Nerve Cord
• Ventral Nerve Cord- one nerve cord, similar to
our spinal column

13. 3. Classifications

14. 3.Classification
Animali
a
Arthropoda
Chilopoda
Diplopoda
Crustacea
Arachnida
Insecta
Metazoa
Protozoa
SUB KINGDOM
KINGDOM CLASS
14

15. 3.Classification
Arthropoda
Chilopoda
Diplopoda
Insecta
Arachnida
Crustacea
SUB KINGDOM CLASS
15

16. Arthropoda
Chilopoda
Diplopoda
Insecta
Siphonoptera (Fleas ) = Complete
metamorphosis
Hemiptera (Bugs) = Incomplete
metamorphosis
Anoplura (Lice) = Incomplete
metamorphosis
Diptera (Mosquitoes & Flies) =
Complete metamorphosis
Arachnida
Crustacea
SUB KINGDOM ORDER
CLASS
16

17. 4. Classes

18. 4.1 SUBPHYLUM Crustacean (Formerly a
Class)
• Lobsters, crayfish, shrimp, and others
• Primarily aquatic
• Free-floating larval stage
• 26,000+ known species
• Branched appendages:
• gills on legs, for example, in a lobster

19. 4.2 Class Diplopoda….
• Millipedes milli means thousand, pede means
legs, so ('thousand legged creature'?)
• Most feed on decaying matter
• Diplo means two, poda means feet, so two pair
of legs per segment

20. 4.2 Class Diplopoda…
• Generally harmless detritus feeders
• pests in nursing homes.
• Some species can eject cyanide (poison).

21. 4.4 Class Chilopoda-Centipede
• Centi means hundred, pede means legs, so
"hundred legged creature"?
• 1 pair of legs per segment
• Usually shiny, reddish brown, less than 3
inches long

22. 4.4 Class Chilopoda…
• Move rapidly, often found under logs; some in
homes
• Can bite
• have poison claws- modified 1st pair of legs
• supposedly feels like a bee sting

23. 4.5 Class Arachnida
• Ticks, mites, and spiders
• No antennae
• Two body regions: cephalothorax and abdomen
• Feeding appendages are chelicerae Most are
carnivorous

24. 4.5 Class Arachnida…
• They hold the prey with chelicerae, and pour
enzyme-rich salivary juices over the victim
• Digestion is mostly external
• Most are terrestrial
• 57,000 known species

25. 4.6 Class Insecta
• Insect means in (into) sect (cut).
• insects are the most numerous and diverse of all
the groups of arthropods.
• There are more species of insects than species
in all the other classes of animals combined!!

26. 4.6 Class Insecta…
• Insects differ from other arthropods in having
– Three pairs of legs.
– In size
• Insects range from < 1 mm to 20 cm in length,
• The majority being less than 2.5 cm long.

27. Class insecta
Characteristics:
• Body divided in to head, thorax, abdomen
• Head carries one pair of antennae
• Thorax carries 3 pairs of legs
• Wings may be present (one or two pairs) or
absent

28. 4.6.1 Morphology and Biology of insects
• 3 body segments-
head, thorax (chest),
abdomen (stomach
area).

30. 4.6.1 Morphology…
• Head carries one pair of antennae

31. 4.6.1 Morphology…
• Head consisted of 6 fused segments
– 2nd, 4th, 5th & 6th bore
appendages in the adult stage
• Thorax consisted of 3 distinct
segments
• The thoracic segments later
developed wings
• Prothorax, Mesothorax,
Metathorax
• Mesothorax has scutum,
scutellum and post - scutellum
31

33. 4.6.1 Morphology…
• The abdomen consisted of 12 distinct segments
each with a pair of appendages
• The digestive system consisted of three parts:
• Foregut : starts with the mouth followed by the
pharynx, oesophagus, crop and proventriculus
(gizzard).
• Sacculate midgut or ’’Stomach’’
• Hindgut : ileum, colon and rectum & emptying
through anus
33

34. Insect morphology
Legend of body parts
Tagmata: A – Head, B – Thorax,
C – Abdomen.
1. antenna
2. ocelli (lower)
3. ocelli (upper)
4. compound eye
5. brain (cerebral ganglia)
6. prothorax
7. dorsal blood vessel
8. tracheal tubes (trunk with spiracle)
9. mesothorax
10. metathorax
11. forewing
12. hindwing
13. mid-gut (stomach)
14. dorsal tube (heart)
15. ovary
16.hind-gut (intestine, rectum & anus)
17.anus
18.oviduct
19.nerve cord (abdominal ganglia)
20.Malpighian tubes
21.tarsal pads
22.claws
23. tarsus
24. tibia
25. femur
26. trochanter
27. fore-gut (crop, gizzard)
28. thoracic ganglion
29. coxa
30. salivary gland
31. subesophageal ganglion
32. mouthparts

35. 4.6.1 Morphology…
• Wings- usually two pairs of wings, although some
have one pair of wings, or none. No other class of
arthropods has wings. (Have you ever seen a flying
Lobster?!)

36. 4.6.1 Morphology…
• Thorax carries 3 pairs of legs
• 1pair to each of the 3 thoracic segments.
• Compound eyes, with facets (ommatidia).

37. 4.6.1 Morphology…
• Insect mouthparts
– 1. chewing (beetles, cockroaches).
– 2. piercing-sucking (mosquitoes, bugs).
– 3. lapping and sponging (flies).

38. Insect Mouth Parts and Transmission of
Parasites
• Piercing-sucking - mosquito, tube structure
penetrate skin and blood flows out the tube.
Usually releases anticoagulating substance to
prevent blood clotting.
• Cutting-sponging - sharp mandibles that break
the skin and a labium that acts like a sponge.
Important in transmission of organisms.
Horsefly

40. Insect mouth….
• Sponging mouth type:
– Labium acts as a large sponge that absorbs liquids.
– Often regurgitates chemicals to breakdown the
material.
– The housefly, Musca domestica is perhaps the most
important insect to man because of its spread of
disease

43. 4.6.1 Morphology…
• The circulatory system:
• A pulsating dorsal tube (the heart) with valves,
pumps the blood (haemolymph) in one direction
forwards into the aorta.
– Bathes all organs and tissues
43

44. 4.6.1 Morphology…
• The respiratory system:
– A branching system of tracheal tubes
reaches all parts of the body and opens
to outside by respiratory spiracles(holes)
– So, they do not have lungs at all.

45. 4.6.1 Morphology…
• The excretory system:
• Tubes of varying number (Malpighian tubes). They play a key
role in the production of primary urine and osmoregulation,
selectively reabsorbing water, ions, and solutes.
• Waste products (urine) from the haemolymph and excrete them
into the gut to come out with faeces from the anus
45

46. 4.6.1 Morphology…
• The nervous system is composed of:
• Nerve ganglia in the head (brain)
• Ventral nerve cord
• Nerves extend from these ganglia to different parts of th
body
46

47. Body parts of an insect
47

48. LARVAL FORMS OF CRUSTACEA
• Crustaceans are Arthropods whose body is covered with
chitinous exoskeleton for protection. But the same
exoskeleton does not allow body growth and hence must be
shed in order to allow growth. The larval stages feed and grow
in order to become adults and must undergo moulting or
ecdysis to grow. After each moulting they change their
structure and size and hence are different from the previous
stage. Therefore, each species of crustaceans demonstrates
several successive larval stages before it becomes adult. These
larval stages are described below.

49. NAUPLIUS LARVA
• Discovered by Muller in 18th century, the Nauplius larva is the first
fundamental stage in all crustaceans that sometimes hatches from the egg
and sometimes passes inside the egg. Body is oval in shape and
unsegmented with a large cephalothorax and rudimentary abdomen.
There are three pairs of appendages, namely, antennules, antenna and the
mandible; the last two pairs are biramous and are used for swimming.
There is a single median eye. It has a well developed digestive system for
feeding on planktons. In Branchiopoda and Copepoda, Nauplius hatched
from eggs.
Cyclops (Adult)

50. METANAUPLIUS LARVA
• In some Branchiopods such as Apus, the nauplius larva transforms into
metanauplius, which is slightly larger than nauplius and has cephalothorax
and abdomen and a caudal furca. It also has a single median eye.
Antennule is uniramous and sensory but antenna is large, biramous and
locomotory in function. Mandibles reduce in size and are used for chewing
food. In addition, 2 pairs of maxillae and 2 pairs of maxillipedes make their
appearance in metanauplius for handling food.
Apus (Adult)

51. PROTOZOEA LARVA
• In the case of marine prawns and lobsters, eggs hatch into protozoea
which has a large cephalothorax and elongated unsegmented abdomen
with a caudal fork and a pair of small uropods. Antennule is uniramous
and segmented while antenna is biramous. There is a single median eye.
Mandibles are small and masticatory in function. There are 2 pairs of
maxillipedes for food gathering. Three pairs of thoracic limbs make their
appearance as buds. Cephalothorax is covered by a carapace.
Euphausia (Adult)

52. ZOEA LARVA
• Zoea is the common larva of decapods and hence it has variations in its features in
different species. It has a large cephalothorax that is covered with a helmet-like
carapace that also sports spines and it protruded into a rostrum in front. There is
one pair of compound eyes. Antennule and antenna are short and sensory in
function. First and second maxillipedes are large and biramous, used for
swimming. Thoracic appendages are still in bud form and non-functional.
Abdomen is 6-segmented, without appendages and has a caudal furca on the tip
along with a telson. In some Malacostraca, zoea changes in to metazoea, which
grows abdominal appendages for swimming.

53. MYSIS LARVA
• In shrimps and some lobsters zoea transforms into mysis that resembles
Mysis in general features. It has a cylindrical and elongated body bearing a
cephalothorax and 6- segmented abdomen. Carapace is produced in front
into a pointed rostrum. Antennule and antenna are sensory in function.
There are 6 pairs of biramous thoracic appendages for locomotion and 6
pairs of abdominal appendages for swimming, out of which the last one is
modified as uropod. There is a pointed telson on the tip of abdomen.
Penaeus (Adult)

54. PHYLLOSOMA LARVA
• In spiny lobsters, the egg hatches into phyllosoma larva in which body is divisible
into head, thorax and abdomen. There is a pair of stalked compound eyes and a
pair each of antennules and antenna as sense organs. Body is dorsoventrally
flattened and transparent. The first maxillipede is rudimentary and the second one
is uniramous. The third maxillipede is large, biramous and is used for swimming.
The abdomen is small, segmented and does not bear appendages. Three pairs of
thoracic appendages are very long and their tips are flattened oar-like for
swimming near the surface of water.

55. Identification of Vectors(Arthropods)
• Keys for identification:
1. How many legs does it have?
• 6 for insect
• 8 for arachnid
2. Does the insect have any wings?
• Walking insect
• Flying insect
55

56. Identification…..
3. Does the insect have any antennae or feelers?
– End in a point
– ‘Knotted' at the ends
4. Are there any moving jaw or mouthparts?
– Biting pincer-like parts
– Straw-like mouth part for sucking

58. Structure Class Insecta
(Hexapoda)
Class
Arachnida
(Octapoda)
Class Crustacea
Body Head
Thorax
Abdomen
Cephalothorax
Abdomen
Cephalothorax
Abdomen
Antennae One pair Absent Two pairs
Legs 3 pairs 4 pairs 4 pairs
Wings 1 – 2 pairs
Some times absent
Absent Absent
Examples Mosquitoes
Flies
Bugs
Lice
Fleas
Ticks
Mites
Scorpion
Cyclops
58

59. 5. Insect Growth Basics

60. 5. Insect Growth Basics
• Insects develop from egg.
• Eggs come in a variety of shapes and sizes.
• They hatch from the egg, and begin eating
• Sooner or later they become too big for their
exoskeletons.

61. 5. Insect Growth Basics
• Development of arthropods:
– Arthropods develop from eggs to adult (known as
metamorphosis)
– They Molt , or shed their skins.
– Molting is the shedding of old cuticle and
expanding into a new and larger one.
– Changes in the insect may occur with each molt.
This is called metamorphosis , or a change in form.

62. 5.1 Types of Metamorphosis
• Partial metamorphosis (gradual, incomplete)
• Complete metamorphosis *most advanced*

63. 1. Incomplete metamorphosis (Hemimetabolous):
• Egg  Nymph  Adult
• Immature forms are called NYMPHS resemble the
adult stage.
• Gradual change in appearance.
• For example, wing pads grow longer with each molt, and
eventually into wings in the adult.
• Generally have the same food source as the adult.

65. 2. Complete metamorphosis (Holometabolous):
• The intermediate stages (larva & pupa) differ from
the adult stage.
Egg  larva  pupa  adult
• Larva and adult may have radically different food
sources, with very different environments.
• Example: butterflies. Or, they may have same food source:
bees.

68. 6. Medical importance of arthropods

69. 6.1 Harmful effects of arthropods
1. Direct harm
a. Annoyance-flies interfere with your work and
rest. (biting flies, fleas, lice, ants or flies at a
picnic, cockroaches)
b. Venom-stings of scorpions and spiders may
even cause death.
c. Accidental injury to sense organs (insect in eye,
ear, swallow an insect

70. Harmful effects of arthropods
1. Direct harm
Parasites-Fly larvae may cause myiasis, scabies et
• Dermatosis (lice, mites)
• Myiasis (infestation of fly larvae)
• Allergy and related conditions (dust mites)
• Blood loss from blood feeding insects (mosquitos,
Fleas, etc)

71. 6. Harmful …
2. Transmission of diseases:
a. Mechanical transmission.
b. Biological transmission.
Fig. Transmission of vector – borne diseases

72. 72
1. Mechanical transmission:
• no reproduction or developmental changes of
the Pathogen. E.g. House fly

73. 2. Biological transmission:
2. Biological (obligatory or natural vector)
• The pathogen either reproduces, develops or
both in the vector.
a. Types
a. Propagative
b. Cyclopropagative
c. Cyclodevelopmental
d. Transovarian.

74. a. Propagative:
• Multiplication of the pathogen without
developmental change.
E.G plague (flea), yellow fever (aedes aegypti)
b. Cyclopropagative:
• Multiplication and developmental change of the
pathogen.
– E.G malaria (anopheles), trypanosomiasis (tse
tse fly)

75. c. Cyclodevelopmental:
– The pathogenic organisms undergo a change in
form without multiplication.
Eg. Filaria in mosquitoes
d. Transporting :
– the pathogen remains without multiplication or
development.
– E.g. D. Latum (cyclops)
75

76. d. Transovarian:
– organisms transmitted to progeny through Ova.
– E.g Scrub typhus (Trombicula)

77. Ways insects are beneficial to man
• Transfer of pollen in plants
• Useful products (honey, bees wax, silk)
• Major component of the food chain
• Biological control, decomposition of organic matter
• Beauty - butterflies
• Medicine - some used for medicinal purposes
especially in Eastern medicine

78. Summary
• Arthropods comprise invertebrate animals with
segmented body, jointed appendages and bilateral
symmetry
• Arthropods are the most populated group of animal
kingdom
• Arthropods have several benefits to the mankind (useful
products, decomposition of organic matter, medicine...)
• Arthropods affect the human health in many ways
(annoyance, entomophobia, blood loss, vectors...)

79. Summary
• Arthropods develop from egg to adult by
metamorphosis
• Transmission of disease by vectors could be by
mechanical or biological means
• Propogative, cyclopropogative, transovarian,
cyclodevelopmental changes are the types of
biological transmission
• Subkingdom arthropoda is classified in to five
classes: chilopoda, diplopoda, crustacea, arachnida
and insects

80. Summary
• The number of legs, presence or absence of legs,
antennae and moving jaw or mouth parts are keys for
identification of insects
• Head, thorax and abdomen are the three body
divisions of insects
• The digestive system of insects consist of foregut,
mid gut and hind gut
80

81. References
1. Ibrahim A, Geme U, Melaku T, Jigssa G(2004 ) Lecture Note
on Vector Biology for Medical Laboratory Technologists.
Addis Ababa University,(Carter Center). Ethiopia
2. Higley, L.G.L.L. Karr, L.P. Pedigo.( 1989) . Manual of
Entomology and Pest Mangement. Macmillan, New
York.
3. Patric R. Murray, Ken S. Rosenthal, G.S. Kobrayashi,
M.A. Pfaller (1998). Medical Microbiology, Third edition.
Mosby.USA.