Lab 5 - Arthropods


Introduction to Arthropods

This is not, together the Victorians dubbed it, the age of Mammals. Theplanettoday is almost totally dominated by a solitary phylum of animal life.On land, in the sea, even in the waiting itself, they space the true mastersof the Earth. They are the arthropods. Arthropods areeucoelomateprotostomes, overcoming the protostome branch the the animal tree, justas vertebrates dominate the deuterostome branch. Arthropods re-publishing acommonancestor with polychaete worms, and may also be a direct descendant ofpolychaetes. Yet unlike various other eucoelomate invertebrates, the arthropodcoelom is greatly diminished in the adult animal.

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There space over 800,000 named varieties in the Phylum Arthropoda,named indigenous the Greek arthros (= jointed) and also poda (=foot),including the familiar arachnids, crustaceans, and insects, togetherwitha host of less acquainted critters, like centipedes, millipedes and also seaspiders.All arthropods have jointed appendages. This evolutionaryinnovationis more than likely the crucial to the stunning success of this diverse group.Thereare around 1018 (10 billion billion) arthropods alive at any one time.Thereare over three times together many types of arthropods together there space of allother pets on Earth, and also there might be millions more that we haven"teven discovered. Arthropods do everything with foot or amendment legs.Theywalk, castle swim, castle creep and also crawl, they usage legs to sense with (theantennae), to bite and also sting with, and also even come chew with. That"s onereasonarthropods look so alien once we see them up close. They chew sideways,and it"s every done through legs.

Their body are protected by an hard cuticle do of proteins andchitin,a polysaccharide with included nitrogen groups. A cuticle is atoughouter great of non life organic material. The cuticle the arthropodsactsas one exoskeleton. many are really small, despite a couple of lobstersreachup come a meter, and also one gigantic crab grow to 3.5 meter long.

Fossil insects to be also very large. Old dragonflies hadwingspansof a foot or more. But living insects room uniformly small. Perhapssmallerinsects were much better at hiding or escaping indigenous their countless predators.Terrestrialarthropods remain small primarily due to the fact that of the limitation applied bytheir exoskeleton. A huge insect would require such a special exoskeletontowithstand its strong muscles that the weight of the cuticle would certainly betoogreat because that the animal to carry around. Because that a little animal, having actually yourskeletonon the exterior is together logical as having it ~ above the inside. But it poses afundamental trouble for arthropods. Lock must melted their exoskeleton,ormolt,in order come grow. The exoskeleton splits open. The animal emerges andswellsto a bigger size till the newer, larger exoskeleton is hardened. Whilethe animal molts, that is specifically vulnerable - simply ask a bowl ofsoft-shelledcrabs!

Arthropods have actually segmented bodies, choose the annelid worms. Thesesegmentshave end up being specialized, however, v one pair that jointed appendagesaddedto each segment. Among living arthropods, the millipedes most closelysuggestwhat the genealogical arthropod could have looked like. Arthropod segmentshave additionally fused together right into functional units called tagma.Thisprocess that segment fusion, or tagmosis, usually outcomes in anarthropodbody that is composed of three significant sections, a head, thorax, andabdomen.Sometimes the head and thorax room fused together into a cephalothorax.Each the these body sections still bear the appendages the went withit,though this appendages are regularly highly modified. Arthropods room veryhighly cephalized, frequently with intricate mouthparts and also elaboratesensoryorgans, consisting of statocysts, antennae, an easy eyes andcompound eyes. Sensitive hairs on the surface ar of the body candetecttouch, water currents, or chemicals. Your nervous systems space highlydeveloped,with chain of ganglia serving miscellaneous parts of the body, and also threefusedpairs of cerebral ganglia forming a brain.

Aquatic arthropods respire through gills. Terrestrial formsrelyon diffusion with tiny tube called trachea. Trachea arecuticle-linedair ducts the branch transparent the body, and open in tiny holes calledspiracles, located along the abdomen. Insects have the right to open and also closethesespiracles, to conserve water that would certainly otherwise be shed toevaporationfrom the open tubes. Your reliance on diffusion because that respiration is oneof the factors that insects space small.

Arthropods excrete by method of malphigian tubules,projectionsof the digestive street that aid conserve water. Terrestrial formsexcretenitrogen as uric acid, as execute birds. Their waste is practically dry, asuperb adaptation to life top top land. Arthropods have an open up circulatorysystem, and also separate sexes. Fertilization is normally internal, anotheradaptation for terrestrial life. Males and also females regularly showpronouncedsexualdimorphism.


Phylum Arthropoda:

Subphylum Chelicerata

class Merostomata - horseshoe crabs,

course Arachnida - spiders,scorpions,ticks, mites

Subphylum Crustacea - crustaceans

Subphylum Uniramia

course Chilopoda - centipedes

class Diplopoda - millipedes

course Insecta - insects

bespeak Hymenoptera- ants, bees, wasps

order Coleoptera -beetles

bespeak Lepidoptera- butterflies, moths

stimulate Diptera -flies,mosquitoes

order Orthoptera -grasshoppers, crickets, roaches

bespeak Odonata -dragonflies

stimulate Isoptera -termites

Terms jointed appendages cuticle chitin exoskeleton molt tagma tagmosis head thorax abdomen cephalothorax statocyst antennae straightforward eyes compound eyes gills trachea spiracles malphigian tubules uric acid sex-related dimorphism chelicerae fangs pedipalps spinnerets web Rocky Mt. Spotted fever Lyme an illness biramous appendages uniramous appendages nauplius larvae detritus detritivores pheromones maxillae simple metamorphosis complete metamorphosisCharacteristics the Subphyla and Classes

Subphylum Chelicerata:

In chelicerates, the an initial pair of appendages are dubbed chelicerae,and room modified come manipulate food. Castle are regularly modified as fangsorpincers. Chelicerates lack antennae.

Class Merostomata - horseshoe crabs (Limulus)

Horseshoe crabs have actually larvae that are very similar to trilobites, andthey might be descendants of this long vanished group. Horseshoe crabsarenocturnal, feeding top top annelids and also molluscs. They swimming on their backs,or walk upright on 5 pairs of wade legs. They live in the deepocean,migrating inshore in huge numbers in the feather to friend on the beachesduring moonlight and high birds - much like undergraduates ~ above SpringBreak.

Class Arachnida - (57,000 sp.), spiders, scorpions, ticks,mites,and dad longlegs

This really successful group of arthropods have 4 pair of walkinglegs(8 legs). The first pair the appendages room the chelicerae, andthesecond pair are pedipalps, appendages modified for sensoryfunctionsor because that manipulating prey. Lock are largely carnivorous (many mites areherbivores).Most secrete an effective digestive enzyme which room injected right into thepreyto liquify it. Once liquified in its own epidermis, the food is sippedlike a root beer float.

Order Scorpiones (2,000 sp.) - Scorpions have actually pedipalpsmodifiedas pincers, along with a poisonous sting in their tail. Scorpions datebackto the Silurian, around 425 mya, and also may be the very first terrestrialarthropods.

Order Araneae (32,000 sp.) - Spiders have special modifiedposteriorappendages dubbed spinnerets, i m sorry they usage to spin their webs.Not every spiders turn webs. Wolf spiders space the many tigers of the leaflitter,and the usual jumping spider leaps numerous times that body length tocatchits prey. Spiders usage pedipalps together copulatory organs. Spiders breathebybook lungs

Order Acari - (30,000 sp.) - Ticks and also mites space the largestand most diverse group the arachnids. Many are an extremely tiny, less than 1 mmlong. The thorax and head room fused into a solitary unit (cephalothorax).Ticksarebloodsucking parasites, and also can bring diseases choose Rocky MountainSpottedFever and also Lyme Disease.

Order Opiliones (5,000 sp.) - daddy Longlegs is a familiararachnid.It has actually an oval human body with extremely long legs, which castle frequentlylosein various accidents and brushes through predators. They room predators,herbivores,and scavengers. Look in ~ them very closely next time you check out one. They carrytheir eyes atop a little tower on their back (weird!).

Subphylum Crustacea - (38,000 sp.), crabs,shrimp,lobsters, crayfish, isopods, barnacles, brine shrimp

Crustaceans are mostly marine, and also dominate the s to the samedegreethat insects overcome the land and also air. Regardless of their aquaticdiversity,there space very few terrestrial crustaceans, just as there are an extremely fewtruly aquatic insects. Crustaceans have biramous appendages.Eachleg has second process, prefer a little miniature leg branchingofffrom the main leg. Many groups the crustaceans have lost this extraappendageduring succeeding evolution. The Order Decapoda have five pairofwalking legs, and also include the familiar crabs, lobsters, and crayfish.Thefirst pair that appendages space usually modified as antennae.Crustaceanshave 2 pair the antennae. Another collection of anterior appendages aremodifiedas mandibles, which function in grasping, biting, and chewingfood.Male crayfish additionally use one pair the legs as a copulatory organ. Allcrustaceansshare a common type of larva dubbed a nauplius larva.

Order Isopoda, Isopods have many typical names, such together Pillbugs,Roly-Polys, Woodlice, Bibble Bugs, Cheesybugs, Cud-worms,Coffin-cutters,Monkey Peas, penny Pigs, Sink-lice, Slaters, Sowbugs, Tiggyhogs, and(inNew Orleans) Doodlebugs. They are one of the couple of successful terrestrialcrustaceans. They feed on disc vegetation in the sheet litter.

Subphylum Uniramia - centipedes, millipedes,insects

Uniramians have actually a single pair the antennae, and also uniramousappendages.They probably progressed from oligochaete worms.

Class Chilopoda - (2,500 sp.) Centipedes dwell in wet placesunder old logs and stones. They space carnivorous, eating largely insects.They are highly segmented, and also have one pair that legs every segment.Despitethe name, the variety of legs comes the end to substantially less than onehundred(centi = 100). The very first trunk segment bears poison fangs.Centipedesare very dangerous, and their bite is incredibly painful.

Class Diplopoda - (10,000 sp.) Millipedes re-superstructure the samehabitatas centipedes, yet they are mostly herbivorous, feeding top top decayingvegetationin the sheet litter. Animals that feeding on detritus are dubbed detritivores.They have actually two pair that legs every segment, (less than a thousand <=milli>,but lots more than a centipede). Every segment of the millipede isactuallytwo segment fused with each other (hence the dual set of legs). They cansecretea protective fluid the smells bad, and also a couple of species actually secretetinyamounts the cyanide gas to defend themselves!

Class Insecta - (750,000 sp.) If us knew every the differentinsectson Earth, there could be as countless as 30 million species. Insects evolvedabout 200 mya, v cockroaches and also dragonflies amongst the first toappear.Insects have a head, thorax, and abdomen, with 3 pair of foot (6legs)on the thorax. (Crustaceans have legs ~ above the abdomen as well as on thethorax). Many insects have one or 2 pairs of wings. They room the onlyinvertebrates the fly. Most have actually compound eyes, and also cancommunicateby sound and scent, using an effective chemical hormones calledpheromones.

Insects have actually extremely elaborate mouthparts, consists of pairs ofappendages fused right into a reduced lip (labium), and an upper lip (labrum),with other appendages referred to as maxillae aiding in chewing. Thesemouthpartsare extremely modified in various teams for chewing, sucking, andpiercing.Insects undergo metamorphosis as they develop, transforming fromoneform to another as they mature. Some (about 10%) show simplemetamorphosis,in which there is no resting stage. The juvenile step look like tinyversions that the adults. Many (90%) present complete metamorphosis,in which one phase is one inactive pupa, prefer the cocoon of themothor the chrysalis that the butterfly. Your larvae are regularly radicallydifferentfrom the mature adult (like the butterfly and also the caterpillar). Theynotonly look different, they live in various places and eat differentfood.

To Do and also View

Observe the preserved arthropods ~ above display. Exactly how do thevariousgroups use their foot to walk, swim, feeding or mate?

Watch the means the millipede moves. Look in ~ the legs. View howthe waves of muscle contraction pass down through the segments? Thepolychaeteworm Nereis move in precisely the very same way. Take care of themillipedesvery gently. They are someone"s pets. They likewise make good pets fordormrooms - they need small care, don"t take up much room, and also don"t makenoise or messes, unlike her roommate.

Disturb the centipedes to acquire them moving around. Deserve to you seethe toxicity fangs? an alert how level the body is, and contrast the numberof legs with those that the millipede. Why does each container hold onlya solitary centipede? Don"t open up the jars uneven you have a thing forextremepain.

Play about with the roly-polys. Oh, walk ahead, it"s cool.Theywon"t bite. Watch the means they role up right into a ball when disturbed. Notall isopods can do this, however rolling up into an armored ball is a greatdefensive tactic. To compare our teeny tiny terrestrial version v theenormous(preserved) maritime isopods.

Look at the live brine shrimp, hermit crabs and also fiddler crabs.Treat them gently (more pets). Watch the method they use their legs,includingthe modified legs that kind their mouthparts. You might see the malefiddlercrabs raise their big claw and also wave it around to claim a territoryinsidethe tank, in the wishes of attracting a mate (Can girlfriend blame them?).

Observe the live crayfish. What does the crayfish do once itfeels threatened? how does it use its swimmerets as soon as it is stationary?

Observe the diversity in insect mouthparts etc. Don"t worryaboutbeing maybe to determine the individual slides. Shot to acquire a feeling for theway modified legs room employed in these animals for a wide variety ofsucking,sponging, piercing and also biting.

Observe the insects on display. You should be familiar (forlaband lecture) v the typical orders that insects noted in this guide.

Tips because that Dissection

Crayfish are relatively easy to dissect. Numerous of friend have had amplepractice dissecting them at Jazz Fest. Your first task is come determinewhether you have actually a male or woman crayfish. Turn the animal on itsback,and research the area that the thorax whereby the legs sign up with the body. Femalecrayfish have a one opening, like a small doughnut, i beg your pardon is theirseminalreceptacle. Male crayfish have actually a hardened pair of swimmerets (legson the abdomen) the extends earlier towards the head, and also fits neatlyintothe groove between the go legs. This modified legs are stiff,likehard plastic. They space curved like fifty percent a soda straw, and also when lock arejoined together, they make a small tube through which the sperm travelduringcopulation. Crayfish accurate copulate v their legs.

Observe their external anatomy. Determine the complying with structures: rostrum,antennae, eyes, thorax, carapace, chelae (claws), cheliped,walkinglegs, abdomen, swimmerets, telson, and uropod. study the variousappendages and modified appendages closely. Keep in mind that some room biramous(ex. Uropods, many swimmerets), when some are uniramous (ex.cheliped).The uniramous appendages result from the evolution loss the thesecondbranch. Note that every pair the antennae are biramous appendages.Examinethe telson and also uropod. How does the crayfish use these biramousappendagesto escape predators? utilizing a probe, try to discover the mouth and anus.Notethe thick triangular mandibles, a main trait that crustaceans.

Place the crayfish in the pan through its dorsal next up. Closely cutthe carapace simply to one next of the midline with your scissors, anddownalong both sides. Peel it back to expose the gills. Notification howthegills interface with the legs, and observe the 2nd underlying heat ofgills. Reduced away the gills whereby they sign up with the body. Try to uncover thetinyheart(good luck!). Just under the heart are the gonads (ovaries ortestes).Look because that the esophagus and stomach (you have the right to alwaysinserta probe with the mouth to watch where that emerges). Carefullyremovethe inner organs, and look because that the tiny brain near the baseofthe antennae.

Crayfish Anatomy seminal receptacle rostrum antennae eye thorax carapace chelae cheliped walking foot abdomen swimmerets telson uropod mandibles gills love gonads stomach mouth stomach brainEconomic, Ecological, and Evolutionary Importance

The plenty of ways the arthropods help us and hurt us are nearly toonumerousto mention.

They carry out seafood, and also pollinate fruit crops.

The additionally cause billions of dollars a year in chop damage.

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They reason or carry a hold of diseases, such together malaria and theplague.

Ecologically, they room critically crucial herbivores. Arthropodsarethe major converters of plant tissue to animal tissue top top the planet!

Consider This

How perform segmentation and tagmosis account because that the success ofarthropods?

Why aren"t bugs the size of Buicks?

Trilobites were among the most successful arthropods top top Earth, oncenumbering end 10,000 species. Why room they all gone?

How walk the smooth flow of muscle contractions in the movingmillipederelate to the evolution of segmentation in annelids and also arthropods? (Hint:Why is a segmented body arrangement useful because that a burrowing animal?)

Links come Explore

There are numerous arthropods wait quietly in obscure cornersof the web, prepared to pounce top top the unwary undergraduate and also grab yourattention.Where come start? The UCMP server is great for all teams exceptcrustaceans: remarkable wealth of material on spiders, scorpions, ticks and also mitesawaits you in ~ the center of the arachnid web. Contains systematics,arachniddatabases, stuff for kids, art, literature and movies: crawl transparent the murky reaches of the cybersea. You"llfind a good starting suggest at the house page of the Crustacean Society,which consists of lots of links to this crunchy critters: are practically as plenty of insect home pages together there are varieties ofbutterflies.A good place to begin is Gordon"s Entomological house page, whichincludesa riches of web links to all significant orders, and also lots that cool ingredient aboutbugs: the drop on jumping spiders, including PG-13 Quicktime movie oftheircurious courtship rituals at: an faq on scorpions, including beaucoup links, at: power of lice compels you, so learn around ticks and also mites andthingsthat bite from the Lyme condition Network"s house page at: http://www.lymenet.orgRead the Cockroach regulate Manual at: of butterflies and moths have actually been captured in the web: A goodpictorialguide to common species, through tips top top their hold plants deserve to be uncovered at: about the moths of north America at: books, videos, caterpillars etc. At: of countless pages committed to raising Painted Lady butterflies:

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