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1. Versatile exoskeleton2. Segmentation and appendages for
more efficient locomotion3. Air piped directly to cells4. Highly developed sensory organs5. Complex behavior patterns6. Reduced competition through
metamorphosis
Highly protective, yet highly mobile Exoskeleton: several layers of cuticle
covering secreted by underlying epidermisProcuticle
Inner, thicker cuticle Composed of chitin bound with protein
Tough, resistant, nitrogenous polysaccharide that is insoluble in water, alkalies, and weak acids
Crustaceans procuticle impregnated with calcium salts (<flexibility, >hardness)
Divided into two parts:Exocuticle (secreted before a molt)Endocuticle (secreted after molting)
Epicuticle Thin Composed of protein and lipids
Each segment has a pair of jointed appendages can be modified:
Segments and appendages can be specialized for adaptive functions
Limb segments- hollow levers moved by striated muscles (good for rapid actions)
Jointed appendages- equipped with sensory hairs Modified for sensory functions, food
handling, and swift/efficient walking or swimming
Land arthropodsHighly efficient tracheal system of air tubesTubes deliver oxygen directly to tissues and
cells for high metabolic rate
Aquatic arthropodsBreath mainly from some form of gill
Arthropods are very alert to environmental stimuli
Compound (mosaic) eyes Other senses of:
Touch (what organ system?)Smell (what organ system?)Hearing (what organ system?)Balance (what organ system?)Chemical reception (what organ system?)
Innate behaviorUnlearned behavior controls much of what
arthropods do Learned behavior
Habituation (ignore repeated harmless stimuli)
Imprinting (colony scents)Classical conditioning (food scents)Waggle dance (bees)
Larval formsQuite different from adults = less
competition within species
Larval forms adapted for fulfilling a different niche than adults Different foods Different habitats
Subphylum Trilobita Subphylum Chelicerata Subphylum Crustacea Subphylum Myriapoda Subphylum Hexapoda
Extinct for over 200 million years
Abundant during the Cambrian & Ordovican periods
Named for tri-lobed shape of body caused by a pair of longitudinal grooves
Bottom dwellers, probably scavengers
Could roll up like rollie-pollies
Horseshoe crabs, spiders, ticks, mites, scorpions, sea spiders, etc
Characterized by:Two tagmataSix pairs of appendages
Pair of chelicerae Pair of pedipalps Four pairs of walking legs (exception: horseshoe
crabs)No mandiblesNo antennaeMost suck liquid food from their prey
Subclass Xiphosurida Class Pycnogonida Class Arachnida
Order Araneae Order Scorpionida Order Opiliones Oder Acari
Dates from Cambrian periodPractically unchanged back to
Triassic Period Lives in shallow water along
North American Atlantic coast
Swims (awkwardly) with abdominal plates; walks with walking legs
Feed at night – worms & small mollusks
Physical Features:Carapace: Unsegmented,
horseshoe-shaped, and hard dorsal shield
Broad abdomenTelson: long spine-like
tailpieceBook gills: flat leaf-like gills
Exposed on some abdominal appendages
One pair chelicerae and 5 pairs of walking legs
Physical Features: 4 pairs of thin, walking legsPair of ovigers ovigers (ovigerous legs)
Males carry egg masses on these legs Reduced abdomenElongated cephalothoraxLarge suctorial proboscisproboscis: suck juices from
hydroids and soft-bodied animals Ocean-dwellers Few mm in length
uber diverse: > 50,000 species described
Includes: spiders, scorpions, pesudoscorpions, whip scorpions, ticks, mites, harvestmen (daddy longlegs), etc…
Arachnid tagmata: cephalothorax & abdomen
>35,000 species worldwide
Predacious Feed mainly on insects Chase prey, ambush prey, or trap them in silk net Feeding:
Chelicerae function as fangs with ducts from venom glands
Digestive enzymes liquefy tissue so broth can be sucked up
Some have teeth at base of chelicerae to crush or chew in addition to use of enzymes
Physical Features Tagmata joined by pedicelpedicel
Narrow, waist-like structure connecting cephalothorax & abdomen
2 or 3 spinnerets contain hundreds of microscopic tubules connect to abdominal silk silk glandsglands
Silk thread created when liquid protein secretions hardens on contact with air
Fun facts: silk threads stronger than steel threads of same
diameter 2nd in torsional strength (fused quartz fiber is 1st) Threads will stretch 1/5 of their length before
breaking webs used for:
Trap insects, line nests, form sperm webs or egg sacs, build draglines, make bride lines, warning threads, molting threads, attachment discs, nursery webs, or to securely wrap prey
Most spiders are harmless to humans Australia has some of the deadliest spiders
(they have some of the deadliest organisms actually)Atrax robustis
South America has a few dangerous spiders tooPhoneutria fera
In the U.S.Black widows
Latrodectus mactans Venom is neurotoxic (acts on the
nervous system) Shiny black, red hourglass on ventral
side of abdomen
Brown recluse Loxosceles reclusa Venom is hemolytic
(destroys tissues and skin surrounding bite)
Brown, violin-shaped dorsal stripe on cephalothorax
Book lungsBook lungs or tracheaetracheae (or both) Book lungsBook lungs-- many
parallel air pockets extending into a blood-filled chamber Air enters chamber
by a slit in body wall TracheaeTracheae- system
of air tubes that carry air directly to tissues from opening called spiraclesspiracles
Malpighian tubulesMalpighian tubulesK, other solutes & wastes secrete
into tubulesTubules drain urine-like fluid into
intestinesRectal gland reabsorb K & H20
Wastes like uric acid Nearly dry mixture of urine & feces left
Great adaptation (especially for arid conditions)- conserve fluids
Coxal glandsCoxal glandsModified nephridia open @ base
(coxa) of first & third walking legs
8 simple eyesLens, optic rods, retinaPerception of moving objectsMay form images for hunting/jumping
spidersGenerally poor vision
Sensory setaeHair-like structures that sense surroundings
i.e. air currents, changing tensions in the spider’s web
Web vibrations allow spider to sense size/activity of its prey, mate, or predator
Courtship rituals before mating Indirect mating
Male deposits sperm on a web he has spun prior to mating
Sperm package picked up/stored in cavities of pedipalps
PedipalpsPedipalps = second pair of appendages that males use to transfer sperm into a female’s genital opening
Females can store sperm packets in seminal receptacle until eggs are ready (weeks or months)
Females lay fertilized eggs in silken cocoon Carries around or attaches to web or plant
Cocoon may contain hundreds of eggs Eggs hatch and young remain in egg sac for a
few weeks feeding and growing for several molts
Range: tropical, subtropical, some temperate zones
Secretive: hiding in burrows or under objects by day; feeding @ night
Predacious: insects & spiders Reproduction
Bear live youngMother carries on her back until after their first
molt Venom can be fatal in a few species from
Africa, Mexico, Arizona, New Mexico, Australia, etc…AndroctonusCentruroides
Physical featuresClaw-like pedipalps Jaw-like cheliceraeShort cephalothorax
1 – 6 pairs of eyes appendages
segmented abdomen Preabdomen- broad Postabdomen- tail-like; ends in a stinging
apparatus that injects venom
Physical Features Broad joining of abdomen with cephalothorax
without pedicel Presence of external segmentation of abdomen 4 pairs of long, spindly legs
Legs can regenerate Ends of chelicerae are pincer-like
Scavenger feeders Fun Fact: NOT the
most poisonous spider.They do not even have venom glands!
Habitat: fresh/saltwater, vegetation, ground, parasitic on vertebrates/invertebrates
>25,000 species Many of which are
important to humans
Physical Features Fused cephalothorax & abdomen
(no external tagmatization) CapitulumCapitulum- little anterior
projections carrying mouthparts
Many free livingDermatophoides farinae live in
house dust and cause allergies & dermatoses
Aquatic species (mostly fresh, some marine)Long, hair-like setae on legs for swimmingLarvae may be parasitic on aquatic
inverts
Spider mites (Family Tetranychidae)Agricultural pests on fruit trees, cotton,
clover, etc…
Genus TrombiculaLarvae are called chiggers or redbugsFeed on dermal tissues of terrestrial
vertebrates Process:
Cause irritating dermatitisSome species transmit Asiatic scrub typhus
Genus DemodexHair-follicle mites
FeedingPierce skin; suck
blood until distended; drop off; digest meal
Molts; feeds again Disease vectors
Carry protozoans, rickettsial, viral, bacterial, and fungal organisms
Genus IxodesLyme’s Disease
Genus DermacentorRocky Mountain
spotted fevertularemia
Boophilus annulatus (cattle tick)Texas cattle fever
(red-water fever)
>67,000 species
Primarily aquatic (mainly marine), few terrestrial
Free living; can be sessile, commensal, parasitic
Important to aquatic ecosystems and economy
2 pairs of antennae Mandible and two pairs of maxillae Typically pair o’ biramous appendages biramous appendages on
each segment (except first antennae) Gills (no malpighian tubules) 16-20 segments (> 60 segments) Major tagmata: head, thorax, abdomen
Varying degrees of fusion CarapaceCarapace- dorsal cuticle of head covers/fuses
with some/all thoracic & abdominal segments; clamshell-like vales that cover most/all body; covers entire cephalothorax not abdomen
FoliaceousFlat & leaf-likemaxillae
Biramous2 branchesSwimmerets, maxillipeds,
uropods, antennae Uniramous
1 branchWalking legs
Swimmerets- abdominal appendages, biramous
Endopod- inner branch of swimmerets Exopod- outer branch of swimmerets Protopod- basal segments, endo/exopods
attached to Maxillipeds- 1st 3 pairs of thoracic appendages Chelipeds- 1st pair of walking legs enlarged
with chela
Gonopods- 1st pair of abdominal swimmerets used for copulation for males, nursery for eggs/young for females
Uropods- last pair of appendages;paddles for backward movement
Telson- uropods & telson protect young/eggs
Epidermis-endocuticle-exocuticle-epicuticle Exoskeleton must be molted during
maturation and growth Molting occurs in steps
1. Old procuticle separates from epidermis, which secretes a new epicuticle
2. As a new exocuticle is secreted, mottling fluid dissolves old endocuticle, and solution products are reabsorbed
3. @ ecdysis, the old epicuticle and exocuticle are discarded
4. In postecdysis, new cuticle is stretched and unfolded and endocuticle is secreted
ChromatophoresChromatophores Pigments in specialized branched cells Change color by:
Concentrating pigment granules in center of cells, which causes lightening
Dispersing pigment throughout each cell, which causes darkening
Neurosecretory hormonesNeurosecretory hormones Neurosecretory cells in eyestalk control Neurosecretory cells in eyestalk control
pigment behaviorpigment behavior Hormones control:Hormones control:
Pigment in eyes for light & dark adaptationPigment in eyes for light & dark adaptation Control rate and amplitude of heartbeatControl rate and amplitude of heartbeat
Androgenic glands Androgenic glands Secretions stimulate expression of male Secretions stimulate expression of male
sexual characteristicssexual characteristics
Controls molting Molt-inhibiting hormone Molt-inhibiting hormone
created by neurosecretory cells in the X-organ of the eyestalk
released through sinus glands in the eyestalk
Level of hormone decreased Molting hormone Molting hormone
produced by Y-organs near mandible Initiates premolt
Mandibles/maxillae involved in ingestion Maxillipeds hold/crushes food Suspension feeders
Plankton, detritus, bacteria Use legs to create water currents that sweep food
particles through fringe of setae Scavengers
Larvae, worms, crustaceans, snails, fishes Predatory
Lygiosquilla- a walking leg has specialized digit that can be drawn into a groove and released to pierce passing prey
Alpheus- enlarged chela that forms bubble that implodes to stun prey (like cocking a gun)
Crayfish2-part stomach
Gastric mill in 1st stomachFood shredded by mandibles ground by 3
calcareous teeth into fine particles that will pass to 2nd stomach
Particles pass into intestines for chemical digestion
Some small crustaceans breath through body surface
GillsVary in shape: tree-like, leaf-like, filamentousAssociated blood vessels or sinusesAttached to appendages usually
Movement through H2O keeps gills ventilated
Branchial chambersBranchial chambers Protected by overlapping carapaceProtected by overlapping carapace
Open circulatory systemHeart (compact or tubular)ArteriesMovement of organs and limbs circulates
blood more effectively in open sinuses than heartbeats and capillaries
Blood May contain respiratory pigments
Hemocyanin (decapods) hemoglobin
Property of clotting to prevent loss of blood in injuries
transport blood to different areas of hemocoel
Excretory & osmoregulatory organs are paired glands in head
Antennal glands/Maxillary Antennal glands/Maxillary glands/green glands glands/green glands (decapods)- Excretory pores opening @ base of antennae or maxillae
Some wastes diffuse through gills as well as excretory glands
Waste products: ammonia with some urea and uric acid
Cerebral ganglion Located above esophagus sends nerves to anterior sense organs Connect to a subesophageal ganglion by a pair of
connectives around esophagus Double ventral nerve cord has a ganglion in
each segment that sends nerves to viscera, appendages, & muscles
Giant fiber systems Sensory organs
Eyes Statocysts- balance organs Tactile setae (on cuticle) Chemosensitive setae (on antennae, antennules, &
mouthparts)
Median (nauplius) eyesMedian (nauplius) eyes2-3 pigment cups containing retinal cellsmay have lensFound in nauplius larvae and in some adults
Compound eyesCompound eyescan be on moveable eyestalks (i.e.
crabs/crayfish)Detect motion, analyze polarized lightWide visual field due to convex corneal
surfaceComposed of ommatidiaommatidia
Mainly dioecious Barnacles monecious (cross-fertilization) Parthenogenic in some ostracods
Most brood their eggs Branchiopods/barnacles- special brood chamber Copepods- attached egg sacs to abdominal sides Malacostracans- carry eggs and young attached
to appendages Life Cycles
Crayfish juvenile small version of adult Most produce larvae that must go through series
of changes as it molts NaupliusNauplius- unsegmented body, frontal eye, three pairs
of appendages (2 pairs of antennae & mandibles) Post-larval forms vary among subphyla
Class BranchiopodaOrder AnostracaOrder NotostracaOrder ConchostracaOrder Cladocera
Class MaxillopodaSubclass OstracodaSubclass CopepodaSubclass BranchiuraSubclass Cirripedia
Class MalacostracaOrder IsopodaOrder AmphipodaOrder
EuphasiaceaOrder Decapoda
Physics FeaturesReduced 1st antennae
2nd maxillae
PhyllopodaPhyllopoda Flattened, leaf-like legs Main respiratory organs Suspension feeding Locomotion
Order Anostraca Fairy shrimp; brine shrimp Lack a carapace
Order Notostraca Tadpole shrimp (i.e. Triops) Carapace forms large dorsal shield covering most
trunk segments Order Conchostraca
Clam shrimp (i.e. Lynceus) Bivalved carapace encloses entire body
Order Cladocera Water fleas (i.e. Daphnia) Carapace covers body, but not head Large portion of freshwater zooplankton
Physical features:Segmented
5 cephalic, 6 thoracic, 4 abdominalTelson Maxillopodan eye in the nauplii
Subclass OstracodaMarine, fresh H2O habitatsClam-like….bivalved carapaceSeveral trunk segments fused# of thoracic appendages reduced to 2 or 0Burrow in sedimentsScavenge food, feed on detritus, suspension
feeding
Subclass CopepodaFree-living in planktonic & benthic
habitats (marine & fresh)10 consumer in many aquatic nichesMany symbiotic, some parasiticSmall, elongate, tapered toward
posteriorLacks carapaceSimple, median, nauplius eye Appendages
4 pairs of flat, biramous, thoracic swimming appendage
5th pair reduced No legs on abdomen
Subclass BranchiuraParasitize marine or freshwater fish5-10 mm longPhysical features:
No gills Broad, shield-like carapace Compound eyes 4 biramous thoracic appendages for swimming Short, unsegmented abdomen 2nd maxillae modified as suction cups
Subclass CirripediaBarnaclesBurrowing or parasitic formsEnclosed shell of calcareous platesSessile as adults
Some can attach to substrate by a stalk Physical features:
Carapace (mantle) surrounds body, secretes calcareous-plated shells
Reduced head No abdomen Long thoracic legs Many-jointed cirri with hair-like setae
Cirri extend through small opening between the plates to filter feed
Largest class of Crustacea & diverse
Marine & freshwater
Physical features:8 thoracic segments6 abdominal
segmentsEach segment has a
pair of appendages
Order IsopodaAsellus- freshwaterLigia- sea beaches, rocky shoresPorcellio & Armadillidium- terrestrial under
stones or damp places (rollie pollies)Some parasites of fish or other crustaceansPhysical features:
Dorsoventrally flattened No carapace Sessile compound yes Gills on abdominal appendages
Order AmphipodaMarine and freshwatersOrchestria- beach fleasPhysical features:
No carapace Sessile compound eyes Compressed laterally gills on thoracic segments
Order Euphausiacea Important as oceanic plankton- “krill”
Uber important in ocean ecosystems3-6 cm longEaten by baleen whales and many fishes
Order DecopodaLobsters, crayfish, shrimps, crabsPhysical features:
5 pairs of walking legs First pair of legs modified to form chelae True crabs have broader carapace & reduced
abdomen
Ura (fiddler crabs) – burrow in sand just below high-tide
Decorator crabs- cover carapace with sponges and sea anemones as camouflage
Libinia (hermit crabs)- live in snail shell; abdomen not protected by exoskeleton
2 tagmata: head & trunk
One pair of antennae
Mandibles & 2 pairs of maxillae(1 pair in millipedes)
Uniramous legs
Respiratory system: respiratory exchange through body surface and tracheael systems (aquatic juveniles may have gills)
Centipedes Predators- earthworms, insects Dioecious & oviparous Physical features:
Somewhat flattened dorsoventrallyCan have up to 177 segmentsSegments bear one pair of appendages
First body segment- modified- venom clawsHead with pair of eyesRespiration- tracheal tubes with pair of
spiracles @ each segment
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