- Arthropoda is the largest phylum of animals, including insects, arachnids, crustaceans, and others. They are bilaterally symmetrical, segmented, and have jointed appendages and a chitinous exoskeleton. - The phylum contains over 80% of all animal species. It is divided into subphyla including Trilobita, Chelicerata, and Mandibulata. Trilobites are extinct marine arthropods. Chelicerates include spiders, scorpions, and others. Mandibulates include insects, crustaceans, centipedes, and millipedes. - Arthropods live in nearly all environments and have

1. ARTHROPODA
• Arthropods were first studied by Aristotle.
• Von-sie-Bold coined the Name Arthropoda
• Arthropoda, animals having jointed appendages or legs.
• Arthro= Jointed; poda= foot
• Bilaterally symmetrical, triploblastic, metamerically segmented , haemocoelomic,
protostomes , invertebrates having head, thorax and abdomen, a chitinous
exoskeleton and jointed legs and appendages.

2. INTRODUCTION
• Most successful phylum on the Earth that has ever existed. The phylum includes
such animals as spiders, insects, shrimps and craps among many others that
can be found in a wide range of environments from the ocean floor to the
mountain peaks.
• Largest class- Hexapoda/ Insecta
• Largest order- Coleoptera
• Chitinous exoskeleton- prevents dessication and helps in attachment of muscles
• Ecdysis/moulting

3. GENERAL CHARACTERS
• Cosmopolitan in distribution found in aquatic, terrestrial and aerial
forms. Some are ectoparasitic and vectors of disease.
• Body have jointed appendages or legs (which are modified to different
structures to perform different functions like jaws, gills, walking legs,
paddle). There may be 3 pairs, 4 pairs, 5 pairs, many pairs.
• Body is triploblastic.
• Bilaterally symmetrical.
• Organ system level of organization.
• Body is divisible into head, thorax and abdomen. Tagmosis

4. GENERAL CHARACTERS
• This is the first group to develop a true head, which contains sense
organs and feeding organs specialized for their particular habitats.
• Body is covered with chitinous exoskeleton. Sclerites, tergum, sternum
and pleura, ecdysis/ moulting to facilitate growth
• They are haemocoelomate. Coelom i.e. body cavity is filled with blood
or fluid.
• Head bears a pair of compound eyes and antenna.
• Locomotion takes place by jointed appendages. Swimming, creeping,
burrowing, running, flying can be accomplished with the jointed
appendages

5. GENERAL CHARACTERS
• Digestive system is complete, straight and well developed. forgut,
midgut and hindgut,
• foregut and hindgut covered internally by cuticle, midgut by endoderm
The mouth bears mouth parts for ingestion of foods. Mouths are
modified for chewing, biting, sponging, piercing, siphoning.
• Respiration takes place by general body surface or gills (in
Crustaceans) or trachea ( in insects, diplopoda and chilopoda) or
booklungs (Arachnida) and book gills (in king cobra).

6. GENERAL CHARACTERS
• Circulatory system is of open type i.e. do not have blood vessels and enters
directly into the body chambers. The blood /Haemolymph is colorless. In
crustaceans it is blue due to haenocyanin. Heart is dorsal to haemocoel
• Excretion takes place through Malphigian tubules (in terrestrial form) or green
glands or coxal glands (in aquatic forms).
NOTE: Aquatic forms are ammonotelic, terrestrial forms are uricotelic.
• Nervous system is of annelidian type, which consists of brain and ventral nerve
cord.
• Sensory organ include antennae, sensory hairs for touch and chemoreceptor,
simple and compound eyes, auditory organs (in insects) and statocysts (in
crustacean).

7. GENERAL CHARACTERS
• Muscles are striated, very few non striated
• Unisexual i.e. sexes are separate. Sexual dimorphism can be seen in
some
• Fertilization is internal or external.
• They are either oviparous or ovoviviparous.
• Development may be direct or indirect. Parthenogenesis can be seen in
some insects
• Life history includes one to many larval forms and a metamorphosis

8. • Phylum Arthropoda – Six Sub-Phyla
1. Tardigrada
2. Pentastomatida
3. Trilobitomorpha or Triolobita
4. Picnogonida or Pantopoda
5. Chelicerata
6. Mandibulata
Of these six phyla now Tardigrada, Pentastomatida and Picnogonida are included under minor phyla
Consequently only three sub phyla are discussed here.
CLASSIFICATION OF ARTHROPODA

10. I.SUB-PHYLUM- TRILOBITA
• Extinct marine arthropods – fossils found inn Cambrian
period
• Body – head, trunk and pygidium
• Body is protected by chitinous plates- exoskeleton
• Body is oval divided into three lobes by longitudinal furrows
• A pair of many jointed antennae are present on head
• Four pairs of biramous appendages
• Trunk appendages are also biramous and chitinous
gnathobase was attached to each leg
• Respiration by gill like structure
• Larva – Protaspis
• Examples : Triarthrus, Agnostus

11. II. SUB-PHYLUM- CHELICERATA
• Terrestrial or marine animals
• Body – Prosoma or Cephalothorax(6 segments) and Opisthosoma(13 segments)
• Devoid of antennae
• Cephalothorax bears six pairs of appendages 1st pair- Chelicerae, 2nd pair-Pedipalpii remaining
four pairs of walking legs
• At the hind end of opisthosoma- a telson is present
• Second abdominal segment bears genital aperture covered by genital operculum.
• Median ocelli are present
• Respiration by book lungs
• Excretion by malphigian tubules and coxal glands.
• Sexes are separate and development is direct
• Chelicerata includes– Merostomata, Arachnida

12. 1.CLASS- MEROSTOMATA
• Marine animals
• Prosoma bears a pair of compound eyes
• Opisthosoma is divided into mesosoma and metasoma
• Prominent caudal spine is present
• Mesosoma has 4-5 pairs of appendages
• Respiration through gills
• It includes two sub-classes
i) Xiphosura and
ii) Eurypterida

13. SUB CLASS: XIPHOSURA
• Cephalothorax is dome shaped/ convex shaped
• Two pairs of eyes present on dorsal side of
cephalothorax
• Mouth is on ventral side surrounded by six pairs of
appendages
• In the abdomen mesosoma is 6 segmented and
metasoma is unsegmented and is like a long spine
called telson
• Coxal glands – excretory organs
• Example : Limulus (King crab)

14. SUB-CLASS-EURYPTERIDA
• It includes fossil
animals which had
stout bodies
• Examples : Eurypterida
and Pterygotus

15. CLASS- ARACHNIDA
• Terrestrial animals
• Body – cephalothorax and abdomen
• Exoskeleton is made of chitin
• Simple eyes are present. Compound eyes when present are degenerated
• Prosoma/cephalothorax bears chelicerae and strong pedipalpi, four pairs of walking legs
• Antennae are absent
• Respiration is by book lungs or tracheal tubes
• Take only liquid food
• Sexes are separate.
• Divided into Nine orders.

16. Sl.No Orders Examples
1 Scorpionida (Scorpions) Palamnaeus , Buthus
2 Araneida(Spiders) Lycosa( hunting spider),Cteniza(trap door spider)
3 Pseudoscorpionida Chelifer, Garypus
4 Solifuga Galeodes
5 Palpigrada Eukoenenia
6 Pedipalpida Mastigoproctus
7 Phalangida Oligolophus, Gaddo
8 Podogona Cryptocellus
9 Acarina(Ticks & Mites) Ixodes(Tick), Sarcoptes (Mite)

17. SUB-PHYLUM- MANDIBULATA
• Animals with mandibles
• Aquatic or terrestrial animals
• Body is made of two parts- head and trunk. Trunk in some cases may be divided into thorax and
abdomen
• Appendages include 1or 2 pairs of antennae and walking legs
• Compound eyes and simple eyes are present
• Respiration by gills, trachea or skin
• It includes four classes
• Crustacea
• Chilopoda
• Diplopoda
• Insecta / Hexapoda

18. CLASS- CRUSTACEA
• Marine animals. Some live in fresh water and
others in damp places
• Live independently or as parasites or as
symbiotic animals
• Body – head, thorax and abdomen
(cephalothorax in some)
• Five pairs of cephalic appendages –antennules,
antennae, mandibles and two pairs of maxilla
• A pair of stalked compound eyes
• Eight pairs of thoracic and six pairs of abdominal
appendages are also seen

19. CLASS- CRUSTACEA
• Exoskeleton is made of plates or sclerites.
The cuticle is in the form of thin membrane
between sclerites
• Respiration is by gills
• Circulatory system consists of heart ,
arteries and haemocoelomic spaces
• Excretion is by antennal glands
• Sexual dimorphism is present
• Free swimming Nauplius stage in the life
cycle

20. • Crustacea is divided into six sub-classes
• Sl .No Sub – class Examples
1 Branchiopoda Daphnia(water flea) Apus
2 Ostracoda Cypris
3 Copepoda Cyclops , Diaptomus
4 Branchyura Argulus , Dolops
5 Cirripedea Barnacles (Lepas, Balanus )
6 Malacostraca Squilla , Palaemon, Cancer(Crab)

21. CLASS-CHILOPODA(OPISTHOGONEATA)
• Commonly called centipedes
• Body dorsoventrally flattened
• Head is formed by 6 segemnts and trunk by many
segments
• Nocturnal animals live in humid places
• Head bears two pairs of maxillae and a pair of
legs in each segment of trunk except last two
• First pair of legs of the trunk bear poisonous claws
into which poisonous glands open
• Genital openings are present between the
penultimate legs. Gonads are dorsal to the gut.
• Respiration by tracheal tubes.
• Examples: Scutigera, Scolopendra

22. CLASS- DIPLOPODA(PROGONEATA)
• Commonly called millipedes- have numerous legs.
Each segment with two pairs of legs
• Each segment has two pairs of ganglia, two pairs of
spiracles and two pairs of ostia
• Vegetarians and nocturnal.
• Body is cylindrical and divisible into 5 segmented
head and a large number of body segments.
• Maxillae unite to form a special structure called
gnathochilarium. Besides maxillae head bears a
pair of antennae and a pair of mandibles also
• Gonads are ventral to alimentary canal and are
unpaired but gonoducts are paired
• Poisonous glands and claws are absent.
• Examples: Julus, Spirostreptus

23. CLASS- INSECTA/ HEXAPODA
• Commonly called hexapods
• Body is divisible into head, thorax and abdomen
• Head is made of 6 segments . Externally
segmentation is not seen
• Head bears a pair of antenne, a pair of mandibles,
two pairs of maxillae and a pair of compound eyes
• Thorax is divisible into three segments- Prothorax,
mesothorax and metathorax
• Two pairs of wings and three pairs of jointed legs
in the thorax

24. CLASS- INSECTA/ HEXAPODA
• Abdomen is without appendages
• A pair of well developed salivary glands help in
digestion
• Excretion – Malphigian tubules associated with
gut
• Tracheal respiration
• Sexual dimorphism, development is
direct/indirect with larval and pupal stages

25. • Hexapoda is divided into two sub- classes. They are
Sub classs- Apterygota(Ametabola) Sub-class- Pterygota
Wings are absent Wings are present. In some they are
secondarily absent
Metamorphosis is absent Metamorphosis is present
Examples : Lepisma, Campodea, Podura
etc
Examples : Dragon fly, Mantis, Locust,
Cimex, Cockroach, Butterfly etc.