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 m
Economically important, especially insects
Pollinate crops, control insects and weeds
Many species are eaten - especially crustaceans
Compete with humans for food
Cause extensive damage to food crops
Spread diseases
Key Innovations of Arthropods: Jointed appendages, completeexoskeleton, segmental body with specialization of body regions
Arthropod means "jointed feet"Jointed appendages are
specialized for different functions: legs, mouthparts,antennae
Joints in appendages make them highly functional forwalking, and grasping
Antennae are sensory -sounds and chemicals
Mouth parts specialized for different food sources
Rigid exoskeleton, made of chitin and protein helps to protect against predators and reduces water loss - allows life in dry environments
Skeleton functions as attachment for musclesmuscles attach to interior of skeleton
Exoskeleton limits arthropods maximum sizealthough chitin is tough, it is brittle and cannot support great weight without increasing its thickness greatly
Exoskeleton 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, abdomen
Chelicerata:first appendages are forfeeding - chelicerae - fangs of spidersfeeding appendages of horseshoe crabs
Living arthropods divided into three subphyla - based on appendages
Crustacea and Uniramia (Tracheata) together called the Mandibulates: first appendages are antennae, first feeding appendages are called mandibles
Mandibulates are divided into two subphyla - Crustaceans andUniramians (Tracheata) - based on appendages
Crustaceans have biramous (branched) appendages
Uniramians (insects, millipedes, centipedes) have uniramous(unbranched) appendages
General Biology of ArthropodsExoskeletonAll arthropods covered by hardened exoskeleton
made of chitin and protein - secreted by and fused with epidermis
varies in toughness and thicknessmany crustaceans add calcium carbonate - increases rigidity
Functions of exoskeletonprevents excessive water lossprotects from predators and injury
Molting - 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 water
A 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 lenses
Sometimes occur together with compound eyesFunction in distinguishing light and dark
Compound eyesComposed of many ommatidia - independent unitsEach covered with a lens - contains eight retinular cells and central light-sensitive rhabdom
Each ommatidium receives its ownimage and is connected to a nervecell - entire image is integrated inthe brain
Gut is tubular and extends from mouth to anus - with specialized regions - crop, stomach (midgut), hindgut, intestine, rectum
Circulatory System is openheart extends through
thorax and abdomencontraction sends blood
forwardrelaxation draws blood
from tissuesone-way valves in heart
allows blood to flow forward only
blood from anterior end flows through tissues toposterior end
Respiratory SystemCrustaceans have feathery gills under carapaceChelicerates have book gills and book lungs - series of plates with
thin respiratory epithelium
Terrestrial Uniramians and some Chelicerates have trachaeaTrachea are branched tubules that allow air to diffuse into the body
smaller 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 oxygen
Excretory SystemSeveral forms of excretory systemsTerrestrial Uniramians have Malpighian tubules
Slender tubular projections off the digestive tract at the junction of the midgut and hindgut
Water and solutes pass through walls of tubulesnitrogenous wastes are precipitated as uric acid or guanine
Fluid with waste is emptied into hindgut and eliminatedMost water and valuable solutes reabsorbed by hindgut
An efficient systemthat conserves water- a good adaptationfor terrestrial life
Nervous SystemDouble chain of ganglia runs along ventral surfaceThree fused pairs of dorsal ganglia form the brainventral ganglia control local activity of body regions
many activities continue with brain removedBrain appears to be inhibitor, not stimulator (as in vertebrates)
some activities begin spontaneously when head is removed
Three Classes of Chelicerates Class Arachnida - spiders, scorpions, ticks
Class Merostomata - horseshoe crabsClass Pycnogonida - sea spiders
Class Arachnida - ArachnidsLargest class of chelicerates includes spiders, daddy longlegs,
scorpions, mites & ticksAll have a pair of chelicerae, pair of pedipalps, four pairs of legs
Chelicerae are first appendages, fangs with poison glandsPedipalps are next, similar to legs - rarely used for locomotion
often used for catching and handling preymay also chew with basal portionmay function as copulatory organs or sensory organsscorpion pincers are pedipalps
Most 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 both
Class 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 gills
Class Pycnogonida - Sea SpidersCommon in marine habitats, especially in cool watersrarely observed because of small sizeNot closely related to spidersAdults are parasites or predators on other animalsHave sucking proboscis with terminal mouthBody consists mostly of cephalothorax, no well-defined headPossess four to six pairs of legsMales exhibit parental care of young,
carry eggs on legs
Subphylum Crustacea - Crustaceansincludes shrimp, crabs, crawfish, lobsters, pillbugs, copepods,brine shrimp, barnacleshave biramous (two branch) appendages, two pairs of antennae,and 3 pairs of feeding appendages,larger forms have feathery gills near base of legs
Most have a nauplius larva
Have legs on thorax and abdomen like millipedes and centipedes but unlike insects
Having two pairs of antennae is unique to crustaceansMany have compound eyesHave tactile (touch sensitive) hairs over whole bodyExcretion of nitrogen wastes occurs mostly across surface of cuticleVariety of sexual styles and care of young
Crustacean DiversityDecapod ("ten-footed") Crustaceans -
includes lobsters, shrimp, crabs, crawfishExoskeleton reinforced with calcium carbonateAnterior segments fused into cephalothorax, covered by carapaceCrushing pincers common, used to obtain food and in defense
Swimmeretsused inreproduction andlocomotionSnapping oftelson anduropods causesforceful, rapidmovement to therear
Crustaceans DiversityTerrestrial forms - pillbugs, sowbugs, isopods
Amphipods are both terrestrial and aquatic
Planktonic crustaceansCopepods (Copepoda)Water fleas (Cladocera)Ostracods (Ostracoda)Fairy shrimp and brine shrimp (Anostracoda)
Sessile CrustaceansInclude barnacles (Cirripedia)
Sessile adults, free-swimming larvaeHead attaches to substrate, food swept
into mouth by feathery legshave shell-like plates covering body
Subphylum Uniramia (or Tracheata) - has three classesClass Chilopoda - centipedesClass Diplopoda - millipedesClass Insecta - insects
Well adapted to terrestrial lifeRespire with tracheaMalpighian tubules for excretionWaxy cuticle on exoskeleton
Centipedes and Millipedes - both have head tagmat followed bynumerous repeating segments - each with paired appendages
Centipedes (hundred legs) have one pair of legs per segmentMillipedes (thousand legs) have two pairs of legs per segment
Centipedes - carnivorous, most eat insectsAppendages of first body segment are poisonous fangs
Millipedes - most are herbivorousCan roll bodies into a flat coilMay secrete defensive fluids and cyanide gas
Reproduction similar in both groupsSexes separate, fertilization is internal, copulate to
transfer sperm, all species lay eggsJuveniles are similar to adults in appearance
Class Insecta - InsectsLargest group of organisms on earth - with great diversityEspecially numerous in the tropics
Most are terrestrial but many are aquatic in freshwaterHave three body segments: Head, thorax, abdomenHave three pairs of legs, all attached to thoraxHave one pair of antennaeMay have one or two pairs of wingsSexes separate with internal fertilization
Wings arise as sack-likeoutgrowths
Wings are solid exceptfor veins
Wings are not homologous to otherappendages
Digestive tract is tubular and slightly coileddigestion occurs within stomach or midgut
Excretion by Malpighian tubulesRespiration via trachea that extend throughout body
may have air sacs with muscles that create a bellows system to allow deeper air circulation in bodySpiracles can be closed by muscles to retard water loss
Possess wide variety of sensory systems - in addition to eyesSensory hairs located all over bodies especially on legs andantennae
Sounds detected by tympanumSensory hairs may also detect sound wavesProduce sounds which may inaudible to humans
Chemicals (pheromones) are also used tocommunicate
DevelopmentMost insects hatch from laid eggs - rarely develop within motherAfter hatching young insects undergo regular ecdysis through a
series of instarsOften the larva is very different from the adult and undergoes
metamorphosis to become adultIn simple metamorphosis, wings develop during juvenile stage
there is no "resting stage" before last moltImmature stages are called “nymphs”Seen in beetles, grasshoppers, dragonflies, cockroaches, silverfish
Simple Metamorphosis
In complete metamorphosis, wings develop during a resting stage just prior to final moltresting stage called a pupa or chrysalis - at this time cellular
reorganization occurs to form adult bodyPupa does not normally move, except in mosquitoes
CompleteMetamorphosis
Juveniles and adults live in distinct habitats -larvae often worm-like, lacking large eyes, and legs
Larvae usually have chewing mouth-parts, even if adults havesucking mouth-parts
Pupae are usually inactive and do not feedseen in moths, butterflies, beetles, bees, wasps, ants, flies, fleas