2. What are Arthropod
• Arthropod, (phylum Arthropoda), any member of the
phylum Arthropoda, the largest phylum in the animal
kingdom, which includes such familiar forms
as lobsters, crabs, spiders, mites, insects, centipedes,
and millipedes.
• About 84 percent of all known species of animals are
members of this phylum. Arthropods are represented in
every habitat on Earth and show a great variety
of adaptations. Several types live in
aquatic environments, and others reside in terrestrial
ones; some groups are even adapted for flight.
3. Features of All Arthropods
• All have exoskeletons for support and protection
• All have jointed appendages
• Body regions include: a head, thorax, and an
abdomen.
• Some have a cephalothorax (head and thorax are
fused together)
• All arthropods molt (shed exoskeleton)
4. General Characteristics Cont’d
• Arthropods use either gills, tracheal tubes, or book lungs for
gas exchange.
• Acute senses include simple and compound eyes, brains, and
many ganglia.
• Arthropods use pheromones to communicate.
• They have open circulatory systems, complete digestive
system, and efficient means of wastes excretion.
• Arthropods reproduce sexually, but some exhibit
parthenogenesis.
5. Phylum Arthropoda is classified into
four subphylla
• 1- Trilobita Extinct (Fossilised )
• 2- Crustacia (All aquatic forms )
• 3- Chelicerata
• Class Arachnida
• ( includes three important orders)
• (A) Acarina (Ticks and mites)
• (B) Scorpionida (All forms of scorpions)
• (C) Areinida (all spiders)
• 4- Uniramia – Three classes-Hexapoda;
Chilopoda; and Diplopoda
6. Class Arachnida
• Spiders, scorpions and mites belong to this class.
• Spiders are the largest group of arachnids.
• Most arachnids have only 2 body regions- a cephalothorax and the
abdomen.
• Arachnids have 2 chelicerae for poisoning prey and 2 pedipalps for sensing
and handling food.
• 4 remaining appendages aid in locomotion.
7. Arachnids Cont’d
• Spiders have silk glands for spinning webs and for wrapping their eggs in a
cocoon.
• Ticks and mites have only one body segment.
• Ticks feed on mammalian blood and can expand up to 1 cm.
• Mites are very small and cannot be seen by the naked eye. However their
bites, called chiggers, can be felt.
• Scorpions have many body segments and 2 pincers and have a long tail
with a venomous stinger at the end.
8. Class Crustacea
• Most crustaceans are aquatic and use gills for gas exchange.
• 2 pairs of antennae for sensing.
• Mandibles for crushing food that move side to side.
• Eyes are located on movable stalks.
• Many have five pairs of walking legs used for seizing prey and cleaning
other appendages.
• First pair is often modified into strong claws.
9. Crustaceans Cont’d
• Crabs, lobsters, shrimp, crayfish, barnacles, water
fleas, and pill bugs are crustaceans.
• Some have three body sections, and others have only
two.
• Land crustaceans like pill bugs must live in damp
environments for efficient gas exchange.
10. Class Chilopoda and Diplopoda
• Centipedes belong to class Chilopoda and millipedes belong to class
Diplopoda.
• Centipedes are carnivorous and eat soil arthropods, snails, slugs, and
worms.
• Centipede bites are painful to humans.
• Both have Malphigian tubes for waste excretion.
• Both have tracheal tubes for gas exchange.
• Millipedes eat mostly plants and dead material.
• Millipedes also have stink glands for scaring predators.
11. Class Merostomata
• Horseshoe crabs belong to this class.
• Have remained unchanged since Cambrian period.
• Have exoskeletons similar to trilobites
• Feed on seaweed, mollusks, and worms on bottom of oceans.
• Females lay eggs on land.
12. Class Insecta
• Insects are the largest group and most successful arthropods.
• Insects may only mate once or twice in their lifetimes.
• Internal fertilization
• Large number of eggs are produced to ensure a large number of offspring.
• Females lay eggs in wood or the ground.
• May go through complete or incomplete metamorphosis depending on
species.
13. Insects Cont’d
• Complete metamorphosis: egg, larva, pupa, and adult.
• Incomplete metamorphosis: egg, nymph, and adult.
• Nymphs compete with adults for same resources and are not
sexually mature.
