Introduction & Classification of Arthropods

1. Introduction & Classification ofArthropods 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.