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Subphylum ChelicerataSubphylum Chelicerata

• Horseshoe crabs, spiders, ticks, mites, scorpions

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Subphylum Chelicerata Subphylum Chelicerata (cont(cont’’d)d)

• Cephalothorax (prosoma)– Fused head and thoracic

region

– Sensory, feeding, locomotion

• Abdomen (opisthosoma)– contains digestive,

reproductive, excretory, and respiratory organs

3

Subphylum Chelicerata Subphylum Chelicerata (cont(cont’’d)d)

• Appendages attached to cephalothorax– Pair of chelicerae (pincer-like feeding

appendages)

– Pair of pedipalps (usually sensing or feeding)

– four pairs of legs (5 in horseshoe crabs)

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Subphylum Chelicerata Subphylum Chelicerata (cont(cont’’d)d)

• Usually has eyes

• Never has antennae

• Most suck liquid food from prey

mite

Class MerostomataClass Merostomata

• Two subclasses: – Xiphosura (horseshoe crabs)

•Covered by carapace

•Have chelicerae, pedipalps, 3 pairs walking legs, & 1 pair digging legs

•book gills to obtain oxygen from sea water

– Euryptida (giant water scorpions) --extinct

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Class ArachnidaClass Arachnida• Spiders, ticks,

scorpions

• Most are predators

• Most harmless to humans

Order Araneae

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Class Arachnida (contClass Arachnida (cont’’d)d)

Special features to know:

•Use coxal glands and/or Malpighian tubules for nitrogenous waste/excretion

•Have book lungs (folds of body wall to form lungs)

•Air intake tubes: trachaea, which open to outside via spiracles

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Class Arachnida (contClass Arachnida (cont’’d)d)

Special features to know, continued:

•Sensory structures: sensilla

•Dioecious (separate male/female individuals)

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Class Arachnida (contClass Arachnida (cont’’d)d)

• Some ticks and mites spread disease, cause irritation

Dust mite mite

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Class Arachnida (contClass Arachnida (cont’’d)d)

• Lyme disease– Caused by tick

tick

Order ScorpionidaOrder Scorpionida• The Scorpions

– Prosoma fused into shield-like carapace

– Opisthoma contains digestive & reproductive organs

– Oviparous: lay eggs that develop and hatch outside the body

– Pedipalps and chelicerae

– Posterior stinger

•Only a few scorpions are toxic to humans

» Found in Northern Africa and Mexico, Arizona, New Mexico 11

Scorpion

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Order AraneaeOrder Araneae(the spiders)(the spiders)

• Some spiders (ie. black widow, brown recluse spider) give painful, dangerous bites

• Know how to identify them!

Black widow

Brown recluse

Black widow has red “hourglass” on ventral surface of opisthoma

Brown recluse has “violin” mark on dorsal side of prosoma

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SpidersSpiders• Prosoma: anterior segment

• Opisthoma: posterior segment

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Spiders (contSpiders (cont’’d) d)

• All predaceous– Mostly insects

• Chelicerae may have fangs

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Prey capture among the Prey capture among the spidersspiders

• Some species are cursorial predators– stalk and ambush

their prey (trap door spider)

– they usually have well-developed eyes

Jumping spider

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Prey capture among the Prey capture among the spiders (contspiders (cont’’d)d)

• Some are web-building spiders– Eyes not as well

developed

– sensory hairs for detecting vibrations

Grass spider

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• Many spiders (and mites) producing silk– Used for trapping prey, building nests,

forming egg cases

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Orb web construction

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• silk glands that open to the exterior part of the abdomen through spinnerets

spinnerets

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• Spider venom is used to subdue prey

• Venom liquifies tissues with a digestive fluid

• Spider sucks up soupy prey (ewwww!)

Wolf spider

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Spiders: Class AraneaeSpiders: Class Araneae

Spider love…..

• Spiders, like most arthropods, are dioecious

• Mating habits– Pheromones- chemicals that elicit

behavioral change

– Rituals- males pluck female’s web (pattern is species-specific)

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Spiders: Class AraneaeSpiders: Class Araneae

• Male builds small web, deposits sperm– Collects sperm in cavities of pedipalps

– Pedipalps have ejaculatory duct + embolus

– inserts pedipalps into female genital opening

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Spiders: Class AraneaeSpiders: Class Araneae

• Eggs laid in silk case– Carried, attach to web, bury

Wolf spider preparing egg sac

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A lycosid (wolf spider) preparing egg sac

M. C. Barnhart

25M. C. Barnhart

26M. C. Barnhart

27M. C. Barnhart

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Wolf spider parental care- after the eggs hatch, the young ride on mom for several days.

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CrustaceansCrustaceans

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The CrustaceansThe Crustaceans

shrimpcrabs

lobsters

amphipods

euphausids (krill)amphipods

Daphnia

• Phylum Arthropoda– Subphylum

Crustacea

•crusta= shell

• Lobster, crayfish, shrimp, crab, water flea, barnacles

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The Crustaceans (contThe Crustaceans (cont’’d)d)

• Aquatic (mostly marine)– a few terrestrial forms

• Major ecological and economical importance.

shrimp

lobsters

euphausids (krill)amphipods

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• Biramous appendages (at least primitively)– 2 main branches

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• Only arthropods with 2 pairs of antennae

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• Great specialization of appendages– Mouthparts chewing, grinding, handling

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– appendages strengthened for walking or protection (chelipeds, pincer-like claws)

cheliped

walking legs

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• Like other arthropods (+ unlike annelids), coelom is highly reduced

• Major body cavity is hemocoel (contains colorless blood)

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Respiration – gills (usually)

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• Compound eye is typical of phylum

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• Same Order, but different families

• Lobsters are bigger

• Lobsters are marine; crayfish live in freshwater creeks, ditches, or lakes

WhatWhat’’s the difference s the difference between a crayfish and a between a crayfish and a

lobster?lobster?

crayfish lobster

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Brine Shrimp (Artemia salina)

• cosmopolitan

• restricted to highly saline lakes and evaporation basins

• Dormant cysts= encased embryo

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BarnaclesBarnacles

“nothing more than a little shrimplike animal standing on its head in a limestone house and kicking food into its mouth” -Louis Agassiz

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BarnaclesBarnacles

• living and nonliving substrates

• most species secrete CaCO3 shell

• Head reduced, rudimentary abdomen

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KrillKrill

• Component of plankton

• Major food for whales