Kingdom Animalia Subkingdom Eumetazoa

Bilateria Phylum Arthropoda

Professor Andrea Garrison Biology 3A

Illustrations ©2014 Cengage Learning unless otherwise noted

Phylum Arthropoda

• Insects, spiders, crabs, millipedes, centipedes, etc. (arthron = joint; podos = foot)

• Largest animal phylum (>3/4 all species)

• All habitats • Triploblastic • Protostomes • Bilateral w/cephalization

– Sensory structures • Antennae, compound and/or

simple eyes, sensory hairs, auditory organs, statocysts

Ecdysozoa; photo http://www.cdc.gov/dpdx/trichinellosis/ 2

Hard Exoskeleton

• Chitin w/varying amounts of calcium carbonate

• Muscles attached to inside of exoskeleton

• Molt to grow – Develop soft exoskeleton under

the old exoskeleton – Shed old exoskeleton – Aquatic

• Swell with water, then exoskeleton hardens

– Terrestrial • Swell with air then exoskeleton

hardens

– Vulnerable to predators until new exoskeleton hardens

Arthropoda; photo by A. Garrison 3

Segmented Body

• External joints allow movement • Tagmosis

– Segments fused or grouped together in body regions • May be covered by carapace so you

don’t see segments (can count appendages)

– Segments within a region are similar

– Segments differ between regions

• 1 pair appendages/segment • Appendages may vary in

function – Feeding, defense, walking,

swimming

Arthropoda 4

Body Regions

• Head – Brain – Sensory structures

• Eyes (compound or simple) • Touch, chemical, hearing

– Feeding appendages

• Thorax – Walking or swimming

appendages – Some with wings

• Abdomen – May or may not have

appendages

Arthropoda; top photo by Didier Descouens; ,://creativecommons.org/licenses/by-sa/3.0/deed.en’ bottom photo by Fir0002/Flagstaffotos

5

Fir0002/Flagstaffotos

Body Regions

• Some body regions may be fused

– Cephalothorax • Head and thorax fused

– Abdomen

Arthropoda 6

Phylum Arthropoda

• Coelomate

• Complete digestive system – Head appendages

modified as mouthparts

• Open circulatory system – Hemocoel fills with

hemolymph

• 2 ventral nerve cords with ganglia – Attached to nerve ring

around mouth w/ “brain”

Arthropoda 7

Phylum Arthropoda

• Respiratory system – Aquatic

• Gills

– Terrestrial • Book lungs • Trachea

• Excretory system – Aquatic

• Paired glands at base of antennae

– Terrestrial • Malphigian tubules joined to gut

• Reproductive system – Dioecious – Internal fertilization – Several stages of development

between molts • Successive stages may be similar

or abruptly different

Arthropoda 8

Phylum Arthropoda

• 5 subphyla

– Trilobita

– Chelicerata

– Crustacea

– Myriapoda

– Hexapoda

Arthropoda 9

Subphylum Trilobita

• Trilobites (tri = three; lobos = lobe) • All extinct • Lots of fossils

– Arthropods first organisms with hard parts, molt several exoskeletons

• 3 lobes of body – 1 median lobe, 2 lateral lobes

• Dorsoventrally flattened • Heavy exoskeleton • 3 body regions

– Head • sensory antennae • compound eyes

– Thorax w/appendages – Abdomen w/appendages – Appendages on thorax and abdomen all

similar

Arthropoda 10

Subphylum Chelicerata

• Horseshoe crabs, spiders, scorpions, mites, ticks (chela = claw; keras = horn)

• Marine, freshwater, few terrestrial • Predators or parasites • Cephalothorax

– 6 pr appendages • 1 pr chelicerae—pincers to assist in

feeding • 1 pr pedipalps—grasping, sensory,

walking (pincers in scorpion to right) • 4 pr walking legs

• Abdomen – May have appendages

Arthropoda 11

Subphylum Chelicerata

• Class Merostomata – Horseshoe crabs – Very ancient, primitive group – Nocturnal feeder

• Worms, molluscs

– Compound and simple eyes – Carapace covers cephalothorax

• 1 pr chelicerae • 5 pr walking legs

– Abdomen • 6 pr swimming appendages • Book gills

– Telson

Arthropoda 12

Subphylum Chelicerata

• Class Arachnida – Spiders, scorpions, mites,

ticks

– Cephalothorax • Simple eyes may be image

forming

• 1 pr chelicera

• 1 pr pedipalps

• 4 pr walking legs

– Abdomen • No appendages

– Spinnerets exception to this

Arthropoda 13

Subphylum Chelicerata, Arachnida

• Spiders – Active hunters or spin webs to

capture prey • Spinnerets on abdomen • Liquid silk hardens on contact with

air

• Mites – Tiny – Cephalothorax and abdomen fused – Agricultural pests – Mange – Dust mites cause allergies

• Ticks – Blood-sucking ectoparasites – Cephalothorax and abdomen fused – Transmit bacterial pathogens

• Rocky Mountain spotted fever • Lyme disease

Arthropoda 14

Subphylum Crustacea

• Shrimps, lobsters, crabs (crusta = crust, hard shell)

• Marine, freshwater, very few terrestrial

• Most with cephalothorax and abdomen, but some with all three body regions

• Tagmosis well developed – Different regions with

different functions and different appendages related to function • Walking vs swimming

Arthropoda 15

Subphylum Crustacea

• Cephalothorax – Often covered by carapace

– 5 pr appendages on head • 2 pr antennae

• 3 pr mouthparts – 1 pr mandibles

» Bite, chew

– 2 pr maxillae

» Pass food to mouth

– More appendages on thorax and abdomen • Decapods

– 5 pr legs on thorax

Arthropoda 16

Subphylum Crustacea

• Well-developed nervous system – Large ganglia – Antennae with chemical

and touch receptors – Compound eyes – Statocysts on head – sensory hairs in

exoskeleton

• Respiration – Gills under carapace

• Excretion • Antennal gland

Arthropoda 17

Subphylum Myriapoda

• Centipedes and millipedes (myrias = ten thousand; pod- = feet)

• Terrestrial – Under rocks, leaves

• 2 body regions – Head

• 1 pr antennae

– Segmented trunk

• Centipedes – 1 pr walking legs/trunk segment – Predators

• Invertebrates and small vertebrates • Powerful toxins

• Millipedes – 2 pr walking legs/trunk segment – Feed on decaying leaves, organic

matter in soil

Arthropoda 18

Subphylum Hexapoda

• Insects (hex = six; pod- = feet)

• Most successful animal group – Every habitat

– Wings • Cross environmental

barriers, disperse

– Wingless groups • not as successful as

winged groups

Arthropoda 19

Subphylum Hexapoda

• 3 body regions – Head

• 1 pr compund eyes • 2-3 simple eyes (ocelli) • Mouthparts

– 1 pr antennae – 1 pr mandibles – 1 pr maxillae – 1 labium & 1 labrum cover

mouthparts – Mouthparts vary with feeding

style of insect

– Thorax • 3 pr legs • 2 pr wings in most

– Abdomen • No walking legs • Appendages for copulation

Arthropoda 20

Subphylum Hexapoda

• Respiration via tracheal system

– Spiracles open into system

– Tracheal tubes extend to tissues

• Excretion via Malphigian tubules

– Carry nitrogenous wastes to intestine to be released with feces

Arthropoda 21

Insect Development and Ecdysis

• Developmental stages beyond the egg called instars

• 3 types of development – No metamorphosis

• All instars look like mini-adults

– Incomplete metamorphosis • Only minor differences with each instar

• Early nymphs lack wings

– Complete metamorphosis • Drastic changes with each instar

Arthropoda 22

Insect Development and Ecdysis

Arthropoda 23

Insect Development and Ecdysis

Arthropoda 24

Insect Development and Ecdysis

Arthropoda 25