Transcript Arachnid & crustacean 2012-2013

Subphylum Chelicerata
• Horseshoe crabs,
spiders, ticks, mites,
scorpions
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Subphylum Chelicerata (cont’d)
• Cephalothorax (prosoma)
– Fused head and thoracic region
– Sensory, feeding, locomotion
• Abdomen (opisthosoma)
– contains digestive,
reproductive, excretory, and
respiratory organs
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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)
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Subphylum Chelicerata (cont’d)
• Usually has eyes
• Never has antennae
• Most suck liquid food from prey
mite
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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
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Class Arachnida
• Spiders, ticks, scorpions
• Most are predators
• Most harmless to humans
Order Araneae
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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
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Class Arachnida (cont’d)
Special features to know, continued:
• Sensory structures: sensilla
• Dioecious (separate male/female individuals)
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Class Arachnida (cont’d)
• Some ticks and mites spread disease, cause
irritation
Dust mite
mite
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Class Arachnida (cont’d)
• Lyme disease
– Caused by tick
tick
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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
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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
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Spiders
• Prosoma: anterior segment
• Opisthoma: posterior segment
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Spiders (cont’d)
• All predaceous
– Mostly insects
• Chelicerae may have fangs
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Prey capture among the spiders
• Some species are
cursorial predators
– stalk and ambush their
prey (trap door spider)
– they usually have welldeveloped eyes
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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
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• Many spiders (and mites) producing silk
– Used for trapping prey, building nests, forming
egg cases
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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 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 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 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. Barnhart24
M. C. Barnhart25
M. C. Barnhart
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M. C. Barnhart27
Wolf spider parental care- after
the eggs hatch, the young ride on
mom for several days.
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Crustaceans
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The Crustaceans
lobsters
• Phylum Arthropoda
– Subphylum Crustacea
• crusta= shell
• Lobster, crayfish,
shrimp, crab, water
flea, barnacles
Daphnia
shrimp
crabs
amphipods
amphipods
euphausids
(krill)
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The Crustaceans (cont’d)
lobsters
• Aquatic (mostly marine)
– a few terrestrial forms
• Major ecological and
economical importance.
shrimp
amphipods
euphausids
(krill)
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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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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
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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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Barnacles
“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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Barnacles
• living and nonliving substrates
• most species secrete CaCO3 shell
• Head reduced, rudimentary abdomen
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Krill
• Component of plankton
• Major food for whales
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