Introduction & Classification of Arthropods

1. Introduction & Classification of Arthropods

Introduction & Classification
of
Arthropods
Dr. Mohammed Iqbal Siddiqui

2. 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)

3. 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.

4. 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

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.