Entomology 101Arthropod Groups

David J. Shetlar, Ph.D.The “BugDoc”

The Ohio State University, OARDC & OSU Extension

Columbus, OH

© Sept, 2009, D.J. Shetlar, all rights reserved

Characteristics of the PhylumArthropoda

• Coelomate protostomates that posses a segmented chitinous exoskeleton that must be shed during growth.

• Segments have paired appendages (e.g., legs, antennae) that are jointed.

• Segments are grouped into regions, called tagmata (e.g., head, thorax, abdomen).

• The nervous system is ventral

• The circulatory system is open and dorsal.

Arthropod Groups (taxa)

The arthropods are divided into two large groups that exist today:

The Chelicerates

and

The Mandibulates

Chelicerate Arthropod Characters:

• Pincher-like mouthparts - chelicerae - and pedipalps

• NO antennae

• Two body regions, usually - cephalothorax & abdomen

• Four pairs of legs

• Horseshoe crabs and arachnids are only living groups

Mandibulate Arthropod Characters:

• Mouthparts are mandibles - normally chewing sideways

• One or two pairs of antennae

• Various body region arrangements - cephalothorax & abdomen / head & trunk / head, thorax & abdomen

• Variable leg numbers

• Insects, crustaceans & myriapods

Classes of Arthropods:

Chelicerates –Class Xiphosura – horseshoe crabs

Class Arachnica – arachnids

Mandibulates –Class Crustacea – crustaceans

Class Diplopoda – millipedes

Class Chilopoda – centipedes

Class Symphyla – garden centipedes

Class Hexapoda – insects

Class Arachnida• 2 body regions

• Cephalothorax• Abdomen

Major Orders of Arachnids

• Scorpiones - scorpions

• Pseudoscorpiones - false scorpions

• Opiliones - daddy-long-legs or harvestmen

• Acari - mites & ticks

• Araneae - spiders

Scorpion Tick(a mite)

Pseudoscorpion

Daddy-long-legs

WolfSpider

Order Scorpiones

{pedipalps

chelicerae eyes pedipalp

Pseudoscorpion

pedipalps &chelicerae

cephalothorax

abdomen

Mite and Tick Body Regions

American dog tick male

Blacklegged (deer) tick female

American dog tick female laying egg mass (1000-2000 eggs!).

Clover mites

Twospotted spider mites

Predatory mite

Opiliones (=daddy-long-legs, harvestmen)

cephalothorax abdomen

pedipalp

chelicera (fang)

cephalothorax

abdomen

narrow waist

Spider Anatomy

Abdomen

Pedipalp

Chelicera (fang)

Cephalothorax

Jumping Spider

Wolf spider with egg case Spitting spider

Tarantula Orbweaving spider

Black widow with egg case

Brown recluse (fiddleback)

Classes of Myriapods(many legged arthropods)

(all have one pair of antennae, a head region, and trunk with many pairs of legs, use trachea)

• Diplopoda - millipedes

• Chilopoda - centipedes

• Symphyla - garden centipedes

Myriapods

Millipede (Diplopoda)

Two pair of legs per visible segment, attached under body.

Centipede (Chilopoda)

Pair of fangs under head, one pair legs per visible segment - attached to side of body.

Symphylan (Symphyla)[garden centipede]

No fangs, no eyes, legs attached to side of body.

[one pair of antennae, head & trunk regions, trunk with many pairs of legs]

Millipede (Diplopoda)

Centipede (Chilopoda)

Garden centipede (Symphyla)

Classes of Crustacea(mostly marine, fresh water, a few terrestrial)

(all have two pair of antennae, five or more pairs of legs, segmented abdominal appendages, head & trunk or

cephalothorax & abdomen body arrangement, have gills)

• Isopoda - sowbugs or pillbugs

• Amphipoda - sand fleas, amphipods

• Cirripedia - barnicles

• Decapoda - crabs, lobster, shrimp

• several other minor orders

Crayfish External Morphology

Sowbugs (Isopoda), terrestrial crustaceans