1 of 12

General characters & Classification of�Arthropods

B. SUJATHA

GOVT DEGREE COLLEGE, RAJAMPET

2 of 12

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 of 12

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 of 12

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 of 12

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 of 12

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 of 12

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 of 12

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 of 12

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 of 12

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 of 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.

12 of 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.