NICHOLLS BIOL 156 - Phylum Arthopoda - Arthropods

Unformatted text preview:

Phylum Arthopoda - Arthropodsincludes spiders, scorpions, horseshoe crabs,centipedes, crustaceans, insectsThe largest and most diverse animal phylum.Almost 2/3 of all species that have been described are arthropodsThere may be as many as 30,000,000 species of insects aloneAbundant in all habitats, but dominate terrestrial regionsMost arthropods are small, but a few may be as large as 3.6 mEconomically important, especially insectsPollinate crops, control insects and weedsMany species are eaten - especially crustaceansCompete with humans for foodCause extensive damage to food cropsSpread diseasesKey Innovations of Arthropods: Jointed appendages, completeexoskeleton, segmental body with specialization of body regionsArthropod means "jointed feet"Jointed appendages are specialized for different functions: legs, mouthparts,antennaeJoints in appendages make them highly functional forwalking, and graspingAntennae are sensory -sounds and chemicalsMouth parts specialized for different food sourcesRigid exoskeleton, made of chitin and protein helps to protect against predators and reduces water loss - allows life in dry environmentsSkeleton functions as attachment for musclesmuscles attach to interior of skeletonExoskeleton limits arthropods maximum sizealthough chitin is tough, it is brittle and cannot support great weight without increasing its thickness greatlyExoskeleton must be shed in order for increase in size - “ecdysis”Segmental body plan clear in all forms, but segments often fused to form specialized body regions - “tagmats”Insect: head, thorax, abdomenCrustacean: cephalothorax, abdomenChelicerata:first appendages are forfeeding - chelicerae - fangs of spidersfeeding appendages of horseshoe crabsLiving arthropods divided into three subphyla - based on appendagesCrustacea and Uniramia (Tracheata) together called the Mandibulates: first appendages are antennae, first feeding appendages are called mandiblesMandibulates are divided into two subphyla - Crustaceans andUniramians (Tracheata) - based on appendagesCrustaceans have biramous (branched) appendagesUniramians (insects, millipedes, centipedes) have uniramous(unbranched) appendagesGeneral Biology of ArthropodsExoskeletonAll arthropods covered by hardened exoskeletonmade of chitin and protein - secreted by and fused with epidermisvaries in toughness and thicknessmany crustaceans add calcium carbonate - increases rigidityFunctions of exoskeletonprevents excessive water lossprotects from predators and injuryMolting - a liability of the exoskeletonGrowth requires periodic ecdysis, shedding of outer cuticleNew exoskeleton grows beneath old oneSeparated by a fluid that dissolves components of old skeletonOld skeleton cracks open and is shedNew skeleton is soft and must be expanded to full sizeHardens with exposure to air or waterA new exoskeletonforms inside old -old one must beshed - “ecdysis”The newexoskeleton and allof the body parts itencloses must bepulled out of oldexoskeleton -includes legs,claws, gills, etc.Each new lifestage is called an“instar”EyesOcelli are simple eyes with single lensesSometimes occur together with compound eyesFunction in distinguishing light and darkCompound eyesComposed of many ommatidia - independent unitsEach covered with a lens - contains eight retinular cells and central light-sensitive rhabdomEach ommatidium receives its ownimage and is connected to a nervecell - entire image is integrated inthe brainGut is tubular and extends from mouth to anus - with specialized regions - crop, stomach (midgut), hindgut, intestine, rectumCirculatory System is openheart extends through thorax and abdomencontraction sends blood forwardrelaxation draws blood from tissuesone-way valves in heart allows blood to flow forward onlyblood from anterior end flows through tissues toposterior endRespiratory SystemCrustaceans have feathery gills under carapaceChelicerates have book gills and book lungs - series of plates withthin respiratory epitheliumTerrestrial Uniramians and some Chelicerates have trachaeaTrachea are branched tubules that allow air to diffuse into the bodysmaller tracheoles bring air to individual cellsair entry controlled through external spiraclesclosing spiracles conserves waterflow is mostly passive - muscular movements can increase flowlimits body size because all cells must be able receive oxygenExcretory SystemSeveral forms of excretory systemsTerrestrial Uniramians have Malpighian tubulesSlender tubular projections off the digestive tract at the junction of the midgut and hindgutWater and solutes pass through walls of tubulesnitrogenous wastes are precipitated as uric acid or guanineFluid with waste is emptied into hindgut and eliminatedMost water and valuable solutes reabsorbed by hindgutAn efficient systemthat conserves water- a good adaptationfor terrestrial lifeNervous SystemDouble chain of ganglia runs along ventral surfaceThree fused pairs of dorsal ganglia form the brainventral ganglia control local activity of body regionsmany activities continue with brain removedBrain appears to be inhibitor, not stimulator (as in vertebrates)some activities begin spontaneously when head is removedThree Classes of Chelicerates Class Arachnida - spiders, scorpions, ticksClass Merostomata - horseshoe crabsClass Pycnogonida - sea spidersClass Arachnida - ArachnidsLargest class of chelicerates includes spiders, daddy longlegs, scorpions, mites & ticksAll have a pair of chelicerae, pair of pedipalps, four pairs of legsChelicerae are first appendages, fangs with poison glandsPedipalps are next, similar to legs - rarely used for locomotionoften used for catching and handling preymay also chew with basal portionmay function as copulatory organs or sensory organsscorpion pincers are pedipalpsMost are carnivorous, some mites are herbivorousMost ingest only liquified foods, digestion begins externallyMost are terrestrial, direct transfer of sperm for reproductionRespire with trachea, book lungs or bothClass Merostomata - Horseshoe CrabsExample: Limulus, common on North Atlantic coastsAncient group, Limulus fossils date to 220 million years old Live in deep water, migrate to shallow coastal waters to mateFeed at night on mollusks and annelidsShell-like carapace over cephalothorax protects most body partsSwim with carapace down moving abdominal platesPossess four pairs of walking legs, chelicerae, and pedipalpsRespire via five pairs of book gillsClass Pycnogonida - Sea SpidersCommon in marine


View Full Document

NICHOLLS BIOL 156 - Phylum Arthopoda - Arthropods

Download Phylum Arthopoda - Arthropods
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Phylum Arthopoda - Arthropods and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Phylum Arthopoda - Arthropods 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?