Subphylum Chelicerata Horseshoe crabs, spiders, ticks, mites, scorpions

Subphylum Chelicerata (cont’d) Cephalothorax (prosoma) Fused head and thoracic region Sensory, feeding, locomotion Abdomen (opisthosoma) contains digestive, reproductive, excretory, and respiratory organs Opistho- behind

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)

Subphylum Chelicerata (cont’d) Usually has eyes Never has antennae Most suck liquid food from prey mite

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

Class Arachnida Spiders, ticks, scorpions Most are predators Most harmless to humans Order Araneae

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

Class Arachnida (cont’d) Special features to know, continued: Sensory structures: sensilla Dioecious (separate male/female individuals)

Class Arachnida (cont’d) Some ticks and mites spread disease, cause irritation Dust mite mite

Class Arachnida (cont’d) Lyme disease Caused by tick tick

Order 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

Order Araneae (the spiders) Some spiders (ie. black widow, brown recluse spider) give painful, dangerous bites Know how to identify them! Black widow Brown recluse has “violin” mark on dorsal side of prosoma Brown recluse Black widow has red “hourglass” on ventral surface of opisthoma

Spiders Prosoma: anterior segment Opisthoma: posterior segment

Spiders (cont’d) All predaceous Chelicerae may have fangs Mostly insects Chelicerae may have fangs

Prey capture among the spiders Some species are cursorial predators stalk and ambush their prey (trap door spider) they usually have well-developed eyes 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

Many spiders (and mites) producing silk Used for trapping prey, building nests, forming egg cases

Orb web construction

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

Spider venom is used to subdue prey Venom liquifies tissues with a digestive fluid Spider sucks up soupy prey (ewwww!) Wolf spider

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)

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

Spiders: Class Araneae Eggs laid in silk case Carried, attach to web, bury Wolf spider preparing egg sac

A lycosid (wolf spider) preparing egg sac M. C. Barnhart

M. C. Barnhart

M. C. Barnhart

M. C. Barnhart

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

Crustaceans

The Crustaceans Phylum Arthropoda lobsters Phylum Arthropoda Subphylum Crustacea crusta= shell Lobster, crayfish, shrimp, crab, water flea, barnacles Daphnia shrimp crabs amphipods euphausids (krill) amphipods

The Crustaceans (cont’d) lobsters Aquatic (mostly marine) a few terrestrial forms Major ecological and economical importance. shrimp amphipods euphausids (krill)

Biramous appendages (at least primitively) 2 main branches

Only arthropods with 2 pairs of antennae

Great specialization of appendages Mouthparts chewing, grinding, handling

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

Like other arthropods (+ unlike annelids), coelom is highly reduced Major body cavity is hemocoel (contains colorless blood)

Respiration gills (usually)

Compound eye is typical of phylum

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 lobster crayfish

Brine Shrimp (Artemia salina) cosmopolitan restricted to highly saline lakes and evaporation basins Dormant cysts= encased embryo

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

Barnacles living and nonliving substrates most species secrete CaCO3 shell Head reduced, rudimentary abdomen

Krill Component of plankton Major food for whales Plankton- small organisms that drift in water