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Chapter 18: Arthropoda (Greek=jointed foot/appendage) 75% of all described species >1,100,000 species described >1,000,000 species still undescribed rich fossil history dating to the late Precambrian >600 mya Macrocheira kaempferi Demodex folliculrum

size ranges: Japanese crab (4 m leg span) follicle mite (0.1 mm long) abundance/wide ecological distribution  most diverse animal group serious disease agents & compete with humans for food; others beneficial all feeding modes: but most herbivorous

Unicellular (acellular) Multicellular (metazoa)

protozoan protists

Poorly defined Diploblastic Triploblastic tissue layers Cnidaria Porifera Ctenophora Placozoa

Uncertain Acoelomate Coelomate Pseudocoelomate

Priapulida Rotifera Chaetognatha Platyhelminthes Nematoda Gastrotricha Rhynchocoela Kinorhyncha Entoprocta Mesozoa Acanthocephala Loricifera Gnathostomulida Nematomorpha

Protostomes Uncertain (misfits) Deuterostomes

Annelida Mollusca Echinodermata Brachiopoda Arthropoda Hemichordata Phoronida Onychophora Bryozoa Chordata Pentastomida Pogonophora Sipuncula Echiura

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General Arthropodan Characteristics

1) exoskeleton 2) eucoelomate protostomes with well-developed organ systems 3) similar to annelids distinct segments a) molecular analyses: annelids & arthropods from different ancestor

b) primitive pattern: linear series of somites with jointed appendages c) many somites fused/combined into specialized groupstagmata d) appendages often highly specialized for division of labor

Arthropodan Evolution

1) ancestral arthropodan soft cuticle: stiffened by deposition of protein & inert polysaccharide chitin 2) joints provide flexibility: sequence of molts necessary to allow for growth 3) molting required hormonal control 4) hydrostatic skeleton function lost: coelom regressed; open sinuses replaced them 5) motile cilia lost 6) if this not a monophyletic group: these features would all have to arise independently 7) exoskeleton: cuticle highly protective but jointed for mobility

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Segmentation & Appendages for Efficient Locomotion 1) usually each somite pair of jointed appendages 2) segments & appendages modified for various adaptive functions 3) limb segments: hollow levers with internal striated muscles 4) function a) sensing b) food handling c) walking d) swimming

Modern Exoskeleton

1) procuticle lightweight, flexible  protection against dehydration 2) chitin: 40% of the procuticle in insects: 80% in crustaceans 3) impregnation with calcium salts: procuticle very hard in lobsters/crabs 4) cuticle: laminated & further hardened by a chemical tanning process 5) cuticle thin between segments allows movement at joints 6) cuticle folds inward to line the foregut, hindgut & trachea 7) molting (ecdysis): process of shedding old exoskeleton & replacing with a larger one 8) typically molt 4 to 7 times: weight limit to ultimate body size

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Exoskeleton 1) outer thin epicuticle 2) inner thick procuticle a) exocuticle secreted before a molt b) endocuticle secreted after molting c) both layers contain chitin bound with protein

Estradiol

Testosterone

Molting Hormone (MH)

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Comparison of Vertebrate Steroidal Reproductive & Molting Hormones

aromatase

Testosterone Estradiol

20-OH hydroxylase

Ecdysone 20-OH ecdysone

Y-organ

X organ-sinus glandMolt-Inhibiting Hormone (MIH) peptide 4000-5000 MW

Y-organ

Y-organ: Molting Hormone

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Phylum: Arthropoda Subphylum: Trilobitomorpha Class: Trilobita Subphylum: Chelicerata Class: Merostomata Class: Arachnida Class: Pycnogonida Subphylum: Crustacea Class: Malacostraca Order: Decapoda Order: Euphausiacea Order: Amphipoda Order: Isopoda Class: Maxillopoda Subclass: Copepoda Subclass: Cirripedia Class: Branchiopoda Subphylum: Uniramia Class: Chilopoda Class: Diplopoda Class: Hexapoda

Phylum: Arthropoda Subphylum: Trilobitomorpha Class: Trilobita (no living species) 4,000 spp. fossil records before Cambrian >600 mya; common 500 mya extinct 250 mya; end of Paleozoic

2 to 67 cm length

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Subphylum: Chelicerata (claw) 75,000 spp Cheliceratan Characteristics 1) 6 pairs of cephalothoracic appendages a) chelicerae b) pedipalps c) four pair of legs 2) lack mandibles & antennae 3) most suck liquid food from prey

Subphylum: Chelicerata Class: Merostomata (extinct except for 4 spp)

eurypterid (3 m) Cambrian Permian 570------245 mya

horseshoe crab (3 m) Limulus Triassic 245-208 mya

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Figure 18.02b

Subphylum: Chelicerata Class: Arachnida (Greek: spiders) 74,000 spp ancestors marine

50% spiders

1400 scorpions

40000 mites & ticks

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Figure 18.04

Figure 18.05

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Water Conservation uric acid: low solubility & precipitates readily; allows water to be conserved

Nitrogen Endproducts

Garden spider, Argiope aurantia Fisher spider, Dolomedes triton

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tarantula, Brachypelma vegans brown recluse, Loxosceles reclusa

Harvestmen, Mitopus sp.

Brown Recluse Spider 6 eyes ( 3 pairs separated) violin shape on cephalothorax most spiders: 8 eyes (two rows of four) Other Characteristics -Uniformly light-colored legs - no stripes, no bands -Uniformly colored abdomen: vary from cream to dark brown (dependent on food) -Never have two colors of pigment at the same time. -No spines on the legs, only fine hairs -Small retreat webs behind objects, never out in open -Body length ~3/8 inch

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Hobo spider Characteristics Legs show no distinct rings and have short hairs. Abdomens several chevron shaped markings Males: two large palps that look like boxing gloves Palps mistaken for fangs or venom sacs, but are male genitalia Females: palps, but the ends are not 'swollen' like males Females larger abdomen when compared to males Body length: ~12 to 18 mm

Emperor scorpion, Paninus imperator

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Ticks: 2nd to mosquitos as carrier of bacterial, viral, fungal, protozoan agents

Rocky Mountain spotted fever: Dermacentor Texas cattle fever: Boophilus annulatus: carrier of bacterium, Rickettsia rickettsii carrier of protozoan parasite Lyme disease: Ixodes: carrier of bacterium Tularemia (rabbit fever): tick carrier of bacterium, Francisella tularensis Equine encephalitis: tick (lice, mites, mosquitos) carrier of virus

SEM of house dust mite, Dermatophagoides farinae chiggers: larval mites: skin cell fluids Asia: carrier of scrub typhus Human itch mite, Sarcoptes scabiei

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red velvet (harvest) mite, Trombidium sp. damage caused by mites

Subphylum: Chelicerata Class: Pycnogonida (Greek = thick knees or all legs) (sea spiders) 1000 spp

Proboscis

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Figure 18.17

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