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Subphylum Chelicerata • Horseshoe crabs, spiders, ticks, mites, scorpions 1 Subphylum Chelicerata (cont’d) • Cephalothorax (prosoma) – Fused head and thoracic region – Sensory, feeding, locomotion • Abdomen (opisthosoma) – contains digestive, reproductive, excretory, and respiratory organs 2 Subphylum Chelicerata (cont’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) 3 Subphylum Chelicerata (cont’d) • Usually has eyes • Never has antennae • Most suck liquid food from prey mite 4 Class 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 5 Class Arachnida • Spiders, ticks, scorpions • Most are predators • Most harmless to humans Order Araneae 6 Class Arachnida (cont’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 7 Class Arachnida (cont’d) Special features to know, continued: • Sensory structures: sensilla • Dioecious (separate male/female individuals) 8 Class Arachnida (cont’d) • Some ticks and mites spread disease, cause irritation Dust mite mite 9 Class Arachnida (cont’d) • Lyme disease – Caused by tick tick 10 Order Scorpionida • The Scorpions Scorpion – 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 Order Araneae (the spiders) • Some spiders (ie. black widow, brown recluse spider) give painful, dangerous bites • Know how to identify them! Brown recluse has “violin” mark on dorsal side of prosoma Black widow Black widow has red “hourglass” on ventral surface of opisthoma Brown recluse 12 Spiders • Prosoma: anterior segment • Opisthoma: posterior segment 13 Spiders (cont’d) • All predaceous – Mostly insects • Chelicerae may have fangs 14 Prey capture among the spiders • Some species are cursorial predators – stalk and ambush their prey (trap door spider) – they usually have welldeveloped eyes 15 Jumping spider Prey capture among the spiders (cont’d) • Some are web-building spiders – Eyes not as well developed – sensory hairs for detecting vibrations Grass spider 16 • Many spiders (and mites) producing silk – Used for trapping prey, building nests, forming egg cases 17 18 • silk glands that open to the exterior part of the abdomen through spinnerets spinnerets 19 • Spider venom is used to subdue prey • Venom liquifies tissues with a digestive fluid • Spider sucks up soupy prey (ewwww!) Wolf spider 20 Spiders: 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) 21 Spiders: 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 22 Spiders: Class Araneae • Eggs laid in silk case – Carried, attach to web, bury Wolf spider preparing egg sac 23 A lycosid (wolf spider) preparing egg sac M. C. Barnhart24 M. C. Barnhart25 M. C. Barnhart 26 M. C. Barnhart27 Wolf spider parental care- after the eggs hatch, the young ride on mom for several days. 28 Crustaceans 29 The Crustaceans lobsters • Phylum Arthropoda – Subphylum Crustacea • crusta= shell • Lobster, crayfish, shrimp, crab, water flea, barnacles Daphnia shrimp crabs amphipods amphipods euphausids (krill) 30 The Crustaceans (cont’d) lobsters • Aquatic (mostly marine) – a few terrestrial forms • Major ecological and economical importance. shrimp amphipods euphausids (krill) 31 • Biramous appendages (at least primitively) – 2 main branches 32 • Only arthropods with 2 pairs of antennae 33 • Great specialization of appendages – Mouthparts chewing, grinding, handling 34 – appendages strengthened for walking or protection (chelipeds, pincer-like claws) cheliped walking legs 35 • Like other arthropods (+ unlike annelids), coelom is highly reduced • Major body cavity is hemocoel (contains colorless blood) 36 Respiration – gills (usually) 37 • Compound eye is typical of phylum 38 What’s the difference between a crayfish and a lobster? • Same Order, but different families • Lobsters are bigger • Lobsters are marine; crayfish live in freshwater creeks, ditches, or lakes crayfish lobster 39 Brine Shrimp (Artemia salina) • cosmopolitan • restricted to highly saline lakes and evaporation basins • Dormant cysts= encased embryo 40 Barnacles “nothing more than a little shrimplike animal standing on its head in a limestone house and kicking food into its mouth” -Louis Agassiz 41 Barnacles • living and nonliving substrates • most species secrete CaCO3 shell • Head reduced, rudimentary abdomen 42 Krill • Component of plankton • Major food for whales 43