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