Arthropoda (Joint - Foot)

Characteristics 1• Jointed appendages• Versatile exoskeleton• Fusion of segments (tagmosis) to form specialized tagmata

• Open circulation (Coelom ≈ hemocoel) Little or no respiratory pigment needed. Why?

• Complete digestive system• Respiration by diffusion, book lungs, gills, or trachae

• Dorsal brain with ventral nerve cord • Dioecious

Characteristics contd.• Complex muscular system (smooth & striated)

• Malpighian tubules, coxal, or antennal glands (excretion)

• Metamorphosis– Holometabolous (complete metamorphosis) butterfly

– Hemimetabolous (incomplete metamorphosis) grasshopper

– Ametabolous (direct development) scorpion, silverfish

• Social organization– Bees– Ants– Termites

Subphyla• Trilobita (extinct for 200 million years)

• Chelicerata– Horseshoe crabs, spiders, ticks, mites, sea spiders, sun spiders, scorpions & whip scorpions

• Crustacea– Lobsters, Crayfish, Crabs, Barnacles, Shrimps, Isopods, Amphipods, & others

• Uniramia– Insects, Millipedes, Centipedes, Pauropods, & Symphyla

Chelicerata

• Cephalothorax & abdomen

• 6 pr. of cephalo-thoracic appendages

• 1 pr. Chelicerae (mouth parts)

• One pair of Pedipalps• 4 pr. of walking legs• Horsehoe crab: 5 pr. legs and one pr. of chelicerae.

• Classes:– Merostomata

• Horsehoe crabs

– Pycnogonida• Sea spiders

– Arachnida• Araneae - spiders• Scorpiones• Acari - ticks & mites

• Opiliones - harvestmen

Xiphosurida: Horseshoe crabs

• Ancient (over 400 million years old)• Generalists• Feeds on molusks & worms• Book gills• Carapace, abdominal plates, & telson• Marine• Come to beach to mate• Larvae appear like trilobites

Horseshoe Crabs

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Pantopoda: Sea Spiders

• All legs!• intertidal to deep ocean; Polar waters• Thin body• 4 pairs of long legs• Mouth @ end of a long proboscis• Feed on soft bodied organisms (e.g.. cnidarians)

• No respiratory or excretory systems needed due to a large surface area to volume ratio

• Open circulatory system

Sea Spider

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Araneae: spiders

• 40,000 species• Cephalothorax and abdomen

• Chelicerae with fangs• Pedipalps (sensory & reproductive function)

• Sensory setae• Four pair of walking legs

• Most fluid feeders (some have teeth )

• Female spins cocoon

• Malpighian tubules & coxal glands in some

• Book lungs• 8 simple eyes (SALTICIDAE)• Silk glands & spinnerets (2-3 pr.)

• Liquid scleroprotein with many uses.

• Venom– Neurotoxins– Hemolytic

Brown Recluse bite

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Jumping Spider

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Scorpiones• 1400 species• Oldest terrestrial arthropods

• Hunt using sensilla on legs to detect surface waves.

• Pectines (comb-like sensors; ventral side of abdomen)

• Cephalothorax, preabdomen (7) and postabdomen (5)

• Small chelicerae• Large chelipeds (pincers)

• Mating dance: males pulls female over spermatophore

• Viviparous (live bearing)

• Direct development

Scorpion under UV light

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Acari: Ticks & Mites• 40,000 species identified

• Est. of 50,000+• Terrestrial & aquatic (fresh water, few marine)

• 1mm to 3cm• Fusion of cephalothorax & abdomen

• Mouth on capitulum• Legs: usually 4 pr.• Oviparous• Nymphal stages

• Spider mites - web– Plant parasite

• Important disease vectors!– RMSF– Lyme disease (deer tick)

– Tularemia– Cattle fever– Dust mites– Scabies (mite)

• Viruses, bacteria, fungi, etc.

Blood Engorged Tick, Right

Opiliones: Daddy Longlegs

• Related to scorpions• 5000 species• Cephalothorax & abdomen broadly joined• 2 eyes• 4 pr. spindly legs• Carnivorous• Non-venemous• Oviporous; male uses penis for sperm transfer

Opiliones Left, Cellar Spider Right

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CrustaceansCrustaceans Insects of the seaInsects of the sea

Crusta = shell Crusta = shell (CaCO(CaCO33)) More

Crustacea we know…• Crabs• Lobsters• Crayfish• Shrimp• Isopods (eg. pill bugs)There are more than 67,000 species that have been identified. Together with Insects, they make up over 80% of all animal species!

Lesser known Crustacea:

• Copepods• Ostracods• Water fleas• Whale lice• Tadpole shrimp• & KrillExamples

Features of Crustacea• Biramous appendages • Paired Antennae (2)• Maxillae (eg. Crayfish

Bailor = 2 maxillae)• Mandibles• Chelipeds (claws)• Cephalothorax

– Carapace• Abdomen• Brain (ganglia)• Primarily Marine• Gills (most) or..

– Lungs (hermit crabs)– Diffusers

(phyllopodia)– Pseudotrachea

(terrestrial isopods)

• Cuticle …procuticle (outer) impregnated with calcium

• Tactile hairs• Smell & taste - antennae• Compund Eyes

– Ommatidia - apposition image– Dark adaptation (retracted

pigment)• Statocysts (antennal base) &

Statolyths– Iron filings alter

perception• Excetory organs

– Antennal glands (Green Glands)• ionic balance

– Gills & cuticle • Nitrogenous waste

– No Malpighian Tubules• Hemocoel

– Open circ. System• Hemocyanin or hemoglobin

– Dorsal Heart & venous sinuses

Reproduction• Most are dioecious - sexual reproduction by separate males and females

• Oviparous • Barnacles are Monoecious• Some are Parthenogenic (male scarcity or need for rapid population growth)– Ostracods (mussel shrimp)– Some Copepods– Cladocerans (eg. Daphnia)

Growth and Development:

Two strategies

1. Direct development: eg. Crayfish

2. Metamorphosis: eg. Barnacles, crabs, shrimp, lobsters

Three typical metamorphic larvae:

1. Nauplius (most common form)

2. Zoea (swimming crabs)

3. Megalopae (dungenous crabs)

4. There are other types as well

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ZOEA

Megalopae

Largest class = Malacostra

• Rostrum - anterior• Telson - posterior• Carapace• Tergum• Paired Appendages

– Each segment

• Serial Homology– Cheliped vs. 2nd legs

1. Isopoda2. Amphipoda3. Euphausiacea4. Decapoda

Serial Homology

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- all appendages derived from the same ancestral structures

Molting: making a larger cuticle

Example

Necessary for Growth

Hormonal control

X-organ (brain/eye stalks) MIH

removal ecdysis

Y-organs (mandibles) MH

Helpless state - quiescent

Feeding

• Complete digestive systems• Filter feeders

– Cirripedia (Barnacles)– Branchiopoda (…respire through feet! Fairy

shrimp, Daphnia, etc.)

• Parasites– Order Rhizocephala (crab parasites) – Order Isopoda (some are fish exoparasites)

• Lobster & Crayfish– Mandibles, Esophagus, Gastric mill (cardiac

stomach), Setae (pyloric s.), Intestine, and digestive gland

Feeding contd.•Some are parasitic.

•Whale lice >>

•Most are predatory.

•Mantis shrimp fluoresce >>

•Pistol shrimp (see video)

•Some are suspension feeders

•Barnacles

•Fairy shrimps

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Terrestrial

Mandibulates

Classes:

•Chilopoda•Diplopoda•Pauropoda•Symphyla•Insecta

• PauropodA

• Symphyla B

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A

B

Chilopoda: Centipedes

• One pair of legs per segment• Up to 177 segments (per text)• Venomous• Carnivorous• Up to 30 cm in length• 3000 species• Rapid locomotion

Diplopoda: Millipedes

• 2 pair of legs per segment• 25 -100 segments• Up to 30 cm in length• Herbivorous• Repugnatorial glands• 10,000 species• Slow moving• Larvae have 1 pair of legs per segment!

Pauropoda

• Soft bodied• Small head• No true eyes• No trachae, spiracles, or circulatory system

• Moist soil & leaf litter• 12 segments and 9 pair of legs• 500 species

Symphyla

• .2 to 1cm (small)• Humus, leaf debris• 14 segments and 12 pair of legs• Eyeless• Only anterior trachae and spiracles

• 160 species

Insecta (Hexapoda)• Three segments• Six legs (tripod)

– 1 Pair each segment of thorax

• Usually 2 pair of wings (fig. 20.13)

• All habitats but marine

• Highly adaptable• Durable eggs• Scleroproteins (cuticle)

• Compound eyes• Sophisticated sense organs

• 1 pair of antennae (smell, hearing, or tactile sense)

• Extensive tracheal system & spiracles

• Open Circulation• Malpighian tubules (uric acid)

• Complete, Incomplete & Direct metamorphosis

• 1.1 million species identified

Insects contd.• Feeding:• Three section gut• Food specialization reduces competition.– Among species– Within species

• Predaciious, parasitic, herbivorous, or saprophagus.

• Specialized mouth parts

• Sensory functions:• Vision (simple or

compound)• Tympanum

(moths & bats)• Chemoreception (CO2,

pheromones, etc.) - mosquitoes, Sphinx moth

• Proprioception, gravity, etc.

• Mechanoreception– Sensilla on antennae,

legs, and body

Insect Growth and Reproduction

• Complete or Holometabolous Metamorphosis– 88% of all insects

– Egg, larva, pupa, & adult.

– Eg. Butterflies

• Incomplete or Hemimetabolous Metamorphosis– Egg, larva, adult

– Larva goes through several instars

– Eg. Grasshoppers

Growth contd.

• Direct or Ametabolous development.– Egg, juvenile, & adult– Juveniles almost identical to adults

– Eg. Silverfish

Complete Metamorphosis

• Under hormonal control• Brain secretes PITH which inhibits

• Ecdysone (molting hormone)– Secreted by prothoracic gland

• Juvenile hormone– Corpora allata (p.739 of text)– Ceases production as insect approaches adult stage.

– This signals pupation.

Quiescent Periods

• Hibernation (winter)• Estivation (Summer)• Diapause (Either - Adverse environmental conditions)– Genetically determined– @ end of growth stage (before molt)

Defense styles

• Mimicry of noxious species– Eg. Viceroy and Monarch

• Aposematic coloration• Crypsis (camouflage)

Insect Behavior• Communication

– Chemical signals• Pheromones

– Visual signals• fireflies

– Sound signals• Crickets

• Social Insects (altruistism)– Hymenoptera (honey bee dance)– Isoptera - termites