Arthropoda

Characteristics of Arthropoda

• Segmented body (tagma & tagmatization)• Hard exoskeleton (cuticle)of chiton + protein• Paired, Jointed appendages– Legs, antennae, feeding parts

Exoskeleton

• Can be thick/rigid or thin/flexible• Functions:– Structural support– Muscle attachment– Protection– Prevents/reduces desiccation

• Facilitated colonization of land• Must be molted• Energetically costly

Arthropod SystemsWell developed sensory systems• Eyes that produce visual images (compound & simple)• Chemo (olfactory receptors)• Inc. antennae which function as both chemo and tactile

receptors

Open circulatory system• Hemocoel is main body cavity

Respriatory system• Aquatic typically gills• Terrestrial internalized tubes

– Tracheal system– Book lungs

Diversity

3 lineages, 4 main sub-phyla• Chelicerata• Myriapodia• Pancrustaceans– crustaceans– Hexapoda (inc. insects)

Chelicerates (spiders, horseshoe crabs, scorpions, ticks, mites):

• Chelicerae– Feeding appendages (fangs or “claws”)

• pedipalps – sensing, reproduction, defense, manipulating food

• 2 body segments– cephalothorax & abdomen

• Simple eyes (single lens) (often multiple• No antennae• uniramous

Figure 33.32

Scorpion

Dust mite

Web-building spider

50 µm

Arachnids (chelicerates)Appendages• 4 pairs of walking legs• chelicerae—fangs which posses poison glands• Toxin contains digestive enzymes that soften & semi digest the tissues of prey and

then they are slurped up the slurry.• Pair of pedipalps

Book lungs• Internalized, highly branched from lots of gas exchange.• Stacked plates with spaces between, hemolymph flows next to spaces

Silk and webs:• protein produced by glands in the abdomen• spun by spinerette • Each species produces a unique web and the spiders innately know how to create

it –genetically determined behavior

Myriapods — millipedes and centipedes

• All living examples are terrestrial• Uniramous legs • Head segment: 1 pair of antanae, 3 pairs of appendages that are modified into

mouthparts which includes the jawlike mandible

Millipedes: • Two pairs of legs/segment • They are detrivores and/or herbivores• Rounded in cross section

Centipedes• One pair of legs/segment• Dorsoventrally flattened• Carnivores

– Poison claws (maxillaped) on the 1st trunk segment that paralyze prey and help in defense

Crustaceans (crabs, lobsters, shrimp, krill, barnacles, isopods, copepods) exp. decapod

• Freshwater, marine, and some terrestrial

Appendages• Biramous appendages• Two pairs of antennae• Walking legs on thorax• Swimmerets on abdomen (marine versions only)

Segments:• Cephalothorax

– Carapace w/ calcium carbonate

• abdoman

Crustaceans (crabs, lobsters, shrimp, krill, barnacles, isopods, copepods) exp. decapod

Gas exchange• Small ones cuticle• Larger gills

Reproduction: aquatic crustanceans have larval stages• Crustacean larvae help form a large part of the zooplankton• Some adults (copepods) are also part of plankton Barnacles—cuticle with calcium carbonate (refered to as a shell)• Filter feeders filter with feeding appendages• Glue themselves to substrate

Cephalothorax Abdomen

ThoraxHead

Eye

Swimming appendages(one pair per abdominalsegment)

Walking legsMouthparts(feeding)

Pincer(defense)

Antennae(sensory

reception)

Figure 33.36

Hexapoda (6 legged arthropods – includes insects)Appendages• Antennae• 3 pairs of walking legs• uniraous

Segments• 3 parts

– Head– Thorax

• Many with two pairs of wings• Extensions of exoskeleton, not limbs• Adaptive advantage of flight

• Abdomen

Reproduction:• Dioecious• Internal fertilization• Sperm in spermatheca, fertilize egg at later time • Incomplete v.complete metamorphosis

Figure 33.38Abdomen Thorax Head

Compound eye

Antennae

Anus

Vagina

Malpighiantubules

HeartDorsalartery Crop Cerebral ganglion

Mouthparts

Nerve cords

Tracheal tubes

Ovary

Tracheal system• Pores on surface trachea tracheoles tissues (perfuses

all tissues)• Air sacs• Both gas exchange and gas transport• No hemolymph involved

Malphigian Tubules• Terrestrial arthropods• Closed tubes in hemoceol• Actively transport waste

and ions (no filtration)• Water follows osmotically• Connects to rectum• Rectum reabsorbs water

and ions• Nitrogenous waste (uric

acid) released as solid w/ feces

Video: Butterfly Emerging

Figure 33.40

(a) Larva(caterpillar)

(b) Pupa(c) Later stage

pupa (d) Emergingadult

(e) Adult

Figure 33.41Archaeognatha (bristletails; 350 species)

Zygentoma (silverfish; 450 species)

Winged insects (many orders; six are shown below)

Complete metamorphosis Incomplete metamorphosis

Coleoptera(beetles; 350,000 species)

Diptera(151,000 species)

Hymenoptera(125,000 species)

Lepidoptera(120,000 species)

Orthoptera(13,000 species)

Hemiptera(85,000 species)

Proboscis

• Consult your lab guide for selected details about specific insect orders