Biology - An Illustrated Guide to Science (794127), страница 20
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There are both more individualinsects and more species of insectsthan all the species of all otherAnimalia groups combined.antennaforewingcompoundeyeInsect bodystructureInsect bodies have threeregions: the head, thorax, andabdom en .
They have six jointed legsand many have pairs of wings. Thewhole of the body is covered by atough exoskeleton made of a tough,fibrous material called chitin.● The head is well supplied with senseorgans, including compound eyes thatare capable of forming accurateimages. The antennae can detectvibrations, and some insects haveextremely sensitive chemical detectorsthat can smell things over hugedistances.● Insects do not possess lungs. Gaseousexchange takes place through holes inthe exoskeleton called spiracles.These communicate with a network oftubes running throughout the insectbody. Insects have no circulatorysystem and this, combined withthe absence of lungs, means thatthey cannot grow beyond acertain size or they will be unableto get oxygen to the innermost partsof their bodies.● Some insects (ants, bees) havecomplex social structures withintricate behavior patterns. These sortsof insects often live in largecommunities with a single queen,producing most of the young.© Diagram Visual Information Ltd.●legsspiraclesLegLateral view of headcoxacompound eyetrochantergenamaxillafemurantennaocellifronstibiaclypeusmandiblelabrummaxillarypalptarsuslabiumpretarsuslabial palp117Kingdom Animalia:CrustaceaDIVERSITYKey wordsabdomenexoskeletonsegmentthoraxCrayfishLateral viewantennacephalothoraxThe Crustaceaabdomenchela●The Crustacea are a mainly marinegroup including crabs, lobsters,crayfish, and woodlice.
Woodlice areterrestrial but need to live in cooldamp places to avoid drying out.Crustacean body structureCrustaceans have highly segmentedbodies, although in some of the moreadvanced species the segm en ts havefused together into larger blocks. Theoverall body plan follows standardarthropod structure with head, thorax,and abdom en , although the head andthorax are fused into a region calledthe cephalothorax.● The head is well supplied with senseorgans, including two pairs ofantennae.
In many crayfish and lobsterspecies, a pair of front legs has beenhighly modified into pincers(chelipeds).● The marine crustaceans like lobstersand crayfish grow in size by moltingtheir exoskeleton , growing rapidly, andthen reforming a tough exoskeleton.This can occur a number of timesduring an animal’s life. The moltingand redevelopment of the exoskeletonimposes a significant cost on theanimal in terms of calcium, and this isrecovered from the old exoskeletonbefore it is shed.● Crustaceans can lay eggs containingeither larvae (small shrimps, lobsters,and crabs) or fully formed, but small,adult forms (crayfish).●walking legspleopodsVentral viewsecondantennafirstantennaDorsal viewchelipedlabrumcompound eyepalp of mandiblemandiblethirdmaxillipedcephalicgroovefirst pereiopod(walking legs)carapacefourthpereiopodpleopodsuropod protopoditeuropod exopoditet elsonuropod endopodite© Diagram Visual Information Ltd.t ergite (dorsal exoskeleton)sternite (ventral exoskeleton)118DIVERSITYKey wordsherbivoremaxillipedpredatorsegmentKingdom Animalia:Chilopoda and DiplopodaChilopoda (centipede)Diplopoda (millipede)Dorsal viewExternal viewantennaantennaThe ChilopodaThe Chilopoda are commonly knownas centipedes.
There are roughly 3,000species of centipedes, ranging fromabout 1 inch (3 cm) in length to 10inches (26 cm) for some tropicalspecies.● Centipedes have a single pair of legson each segm en t, with the front-mostones being modified into clawsequipped with poison glands. Thesefront legs are called m axillipeds andallow the centipedes to be effectivepredators.● Eyes are simple rather thancompound.● The upper and lower surfaces of thetrunk segments are armored withthickened plates called tergal platesand are joined by a flexible membrane.● The last division of the body, thetelson, is not considered a truesegment because it lacks legs.● Centipedes live mainly in soil andhumus and under stones and rocks.●maxilliped(poison claw)eyeslegs(jointed)legs (jointed)diplosegmentt ergal plateThe DiplopodaThe Diplopoda, commonly known asmillipedes, have two pairs of legs oneach body segment.
The averagemillipede species (of which there are10,000) will have between 100 and 300legs in total, although the Illacm eplen ipes species has 750 legs.Millipede length ranges from 0.08 to12 inches (2–300 mm) with mostspecies between 2 and 6 inches(50–150 mm).● Most millipedes are detritivores orherbivores. They eat decaying organicmatter and plants.● Eyes tend to be simple.● Milipedes are nocturnal and avoidbecoming prey to the more aggressivecentipedes by producing an irritatingsubstance from glands in the thorax.This substance is released when theyfeel threatened.© Diagram Visual Information Ltd.●t elsonChilopoda (Scutigera)Lateral view of headsecond maxillafirst maxillaeyesmaxilliped (poison claw)first tergal platefirst legsecond legsecond tergal plate119Kingdom Animalia:ArachnidaDIVERSITYKey wordsabdomenexoskeletonpedipalpsegmentspiracleSpideropisthosomaDorsal viewprosomaThe Arachnidawalking leg●The Arachnida has over 6,000 species,including all spiders and scorpions.SpidersSpiders are segm en ted, but theirsegments are fused into two mainparts—the prosoma at the front andthe opisthosoma at the rear.● Arachnids do not have true lungs.Instead, respiration occurs throughrudimentary book lungs, which are aseries of plates.
Air bathes the outersurface of the plates, and bloodcirculates within them, facilitating theexchange of gases.● Spiders have eight walking legs thatarise from the prosoma. A pair ofsegmented legs, called pedipalps, atthe front of the animal are used tograb and hold prey. The chelicera areused for holding, piercing, andinjecting poisons that paralyze theprey.●pedipalpcheliceralung book spiracleVentral viewScorpion (Pandinus)Dorsal viewopisthosomaprosomapedipalpScorpionsScoprions are large arachnids thatlive in desert areas.
They have astrong exoskeleton and anelongated body.● The scorpion body is divided intotwo main segments: prosoma(head) and the opisthosoma(abdomen). The abdomen consistsof the mesosoma—containing itsbook lungs, digestive tract, andsexual organs—and the metasomaor tail, which bears the telson(stinger). The movable tail is curledover the back so that thevenomous stinger is in positionto strike prey.● Like spiders, scorpions use theirpedipalps (claws) to grasp prey anddefend against predators. Jawlikechelicera crush the prey and bringfood to the mouth.metasomastingVentral viewmesosomaspiracle of book lungwalking legchelicera© Diagram Visual Information Ltd.●120DIVERSITYKey wordsgameteKingdom Animalia:EchinodermataStarfishOral viewarmThe EchinodermataThe Echinodermata include over 6,000species, all of which live in marineenvironments.
The phylum includesthe sea urchins and starfishes, but notfish, because echinoderms possessneither gills nor vertebrae.● Echinoderms are radially symmetrical,which means that their body consistsof legs or rays radiating out from acentral hub, like a bicycle wheel.mouth●ambulacral groovemadreporitestone canalAboraI dissectioncardiacstomachanuspyloric stomachrectal sacStarfish body structureThe central area of the starfishcontains the stomach and intestines,though these are continuous withtubes that run out along each of therays. Starfish can take food into theirgut but often eat by everting thestomach onto the prey and digesting itoutside the starfish body.
They can eatbivalves like mollusks by prying apartthe shells slightly and then insertingtheir stomach into the gap. Afterdigestion is completed, the mollusk isjust an empty shell.● Starfish move using many tiny feet onthe lower surface of the body. Thesestructures, called tube feet, havesuckers on the end that can hold tightto prey.● Starfish have limited powers ofregeneration and can grow back anarm that has been removed givensufficient time and good conditions. Insome species, a severed ray candevelop into a complete new starfish.● Starfish commonly reproduce by aprocess called free-spawning.
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