Invertebrate Zoology

Invertebrate Zoology

اسلاید 1: www.tabaye.ir

اسلاید 2: Invertebrate ZoologyChapter 13 – Phylum Annelida Part Two

اسلاید 3: Taxon ClitellataTwo classesClass OligochaetaClass HirudinomorphaPosses a clitellumSeveral (6 or 7 in Lumbricus) anterior segments with a thick, glandular epidermisConspicuous during reproductionClose proximity to gonoporesProduces mucus for copulation, albumen for eggs, and cocoonsLack parapodia, prostomial and pygidial appendagesCopulating hermaphrodites with direct development

اسلاید 4: Class OligochaetaName means “few chaetae”3500 spp.Earthworms are most familiar, but also small FW and marine varieties200 marine spp., mostly interstitialGiant Australian earthworm (Megascolides australis)Up to 3 m long

اسلاید 5: Body FormOnly exceptions to generalized annelid are listedFour bundles of chaetae per segment Two ventralTwo lateralChaetae are structurally simpleGenital chaetae are more complexOne to 25 chaetae per bundleTwo per bundle in most earthwormsProtractor and retractor muscles attached to each chaetaSmall in terrestrial varieties and longer in aquatics

اسلاید 6: CoelomEarthworms posses coelomoporesConnect coelomic cavities with exteriorPosses a sphincterPores are located in intersegmental furrowsExude coelomic fluid dorsallyKeeps animal moistDeters predators“Squirter worm” (Didymogaster) can squirt fluid 30 cm high

اسلاید 7: LocomotionCrawl or burrow using peristalsisMucus and egested soil coat burrow wallsLumbricus terrestris covers burrow openingLarger worms can burrow deeperChaetae are extended or retracted as needed to apply optimal tractionAnimal moves forward in steps2 – 3 cm per stepApproximately 30 cm per minute in someCan even crawl backwards

اسلاید 8: NutritionScavengers of dead organic matter (such as leaves) and / or deposit feedersSwallow soilTakes 1 – 2.5 hr to processCastings are excretedGreat for soil (aerates, mixes, and transfers nutrients)Aquatic varieties may be carnivores of amebas, ciliates, rotifers, etc.Some may parasitize FW snails

اسلاید 9: Nervous SystemOne large ventral nerve cord instead of two lateral cordsFive giant axonsStimulation of either end of worm elicits an escape response (wriggling, or withdrawal into burrow)Subpharyngeal ganglion is motor control centerMost lack eyes but have simple ocelliSome have rings of chemoreceptors (called tubercles) that project from cuticle

اسلاید 10: Digestive SystemPharyngeal bulbEversible in aquatic spp.Muscular pump in terrestrial spp.Esophageal glands secrete mucus and enzymesCompartmentalized esophagusCrop for food storageGizzard for grindingLined with chitin-like cuticle

اسلاید 11: Calciferous GlandsLocated in wall of esophagusProduce calcite crystals that are secreted into esophageal lumen and pass in fecesTwo functional hypothesis1) Removal of excess CO2Soil CO2 is high (relative to atmospheric levels), due to bacterial respirationTherefore there is a negative concentration gradient for diffusion of worm’s CO2CO2 combines with calcium ions to form calcite 2) Removal of excess calcium

اسلاید 12: Digestive System Cont…Intestine makes up posterior 3/4 of digestive systemAnterior half secretes digestive enzymesCellulase and chitinase (breaks down fungal cell walls) are released by mutualistic bacteriaPosterior half is absorptiveTyphlosole is a large dorsal fold in the intestine that increases its surface areaChlorogogen cells surround intestineWaste - laden cells are released into coelomExit body via nephridiopores or coelomopores

اسلاید 13: Circulation and Gas ExchangeOften have hearts (described earlier)Five pairs in Lumbricus (segments 7-11)Gas exchange is carried out across body wallLarge species have capillary loops in epidermis and hemoglobin dissolved in plasmaMoist surface facilitates diffusionOxygen levels in soil drop after heavy rains, forcing earthworms to the surface

اسلاید 14: ExcretionUreotelic but excrete some ammoniaDepends on environmental conditionsOsmoregulationUrine is hyposmoticOften several types of nephridiaAllows them to tolerate dry soilsThose without special nephridia must burrow deeper during dry periods

اسلاید 15: EncystmentCan secrete tough mucus covering Summer cysts to avoid desiccationWinter cysts during periods of low temperatureUndergo diapauseSome migrate deeper into soil during dry or cold periodsUp to three meters down in some70% of body water can be lost

اسلاید 16: ReproductionClonal reproduction always occurs via transverse fissionSexualMonoecious (hermaphroditic)Reproductive organs located in a few anterior segmentsPaired ovaries release eggs which develop in ovisacsPaired testes release sperm which develop in seminal vesiclesGenital segments each posses a pair of gonoducts (sperm ducts or oviducts), which open to the ventral surfaceFemale genital segments have ventral openings that lead to seminal receptacles (store sperm prior to fertilization)

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اسلاید 18: Lumbricus breeds continually, but some have one yearly reproductive seasonOften reabsorb reproductive system and grow back later Copulation with mutual sperm transferVentral contact between oppositely oriented wormsGenital chaetae and mucus produced by clitellum hold worms togetherSperm swim in a ventral sperm groove from male gonopores to openings of partner’s seminal receptaclesIndirect sperm transferEntire process can take 2 – 3 hoursSome worms have copulatory organ for direct sperm transfer

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اسلاید 20: CocoonsSecreted a few days after copulationClitellum secretes mucus tubeClitellum secretes chitinous material which becomes wall of cocoonAlbumen from clitellum deposited into cocoonTube slides forward as worm moves backwardsEggs and partner’s sperm (from seminal receptacles) deposited into cocoonExternal fertilizationCross fertilizationCocoon slides of head, and ends pinch off; mucus tube disintegrates

اسلاید 21: Terrestrial species deposit cocoons in soilAquatic species deposit cocoons in debris or mud, or attach to vegetationOvoid and yellow in colorContain 1 to 20 eggs7.5 cm X 2 cm in Megascolides

اسلاید 22: DevelopmentDirect developmentTherefore create eggs containing yolk or albumenEight days to several months before juveniles emerge from cocoonsLive several yearsSix years in captivityReach sexual maturity at approximately 200 days

اسلاید 23: Class HirudinomorphaLeeches and closely related worms500 sppMarine, mostly freshwater, a few terrestrial species (restricted to moist environments)Lack chaetaeHave a fixed number of segments (typically 33)All have a posterior sucker for adhering to prey or substratumMost have an anterior sucker as well

اسلاید 24: Blood-sucking ectoparasites or carnivores1 cm to 30 cm long (Haementeria, giant Amazonian leech)Black, brown, olive, or red in colorMay have striped / spotted patternsTypically inhabit stagnant or slow moving freshwaterEstivate in mud during periods of droughtCan lose 90% of body waterOften extremely abundant

اسلاید 25: Body FormDorsoventrally flattenedTapered at anterior endSuckersAnterior (if present) is smaller and surrounds mouthPosterior is disc-shaped; anus located directly anterior Annulations that don’t accurately depict segmentsNumber of annulations per segment variesClitellum spans segments 9-11, but is only conspicuous during reproduction

اسلاید 26: Body WallConnective tissue is much thickerMakes up a larger proportion of the animalSlightly different musculatureDorsoventral musclesFor flatteningHelical musclesFor twisting

اسلاید 27: CoelomLarger connective tissue compartment means a reduction of the coelomLack septa, so therefore lack bilateral coelomic cavitiesAlso lack mesenteriesContinuous coelom which serves as a hemal systemTwo large lateral coelomic vesselsDorsal and ventral coelomic vesselsLined with mesothelium (chlorogogen cells)Muscle contractions propel fluidBody surface conducts gas exchange

اسلاید 28: LocomotionNot equipped for burrowing due to:Reduction of coelomLoss of septa and chaetaeMany inchworm by anchoring with anterior and posterior suckersMany swimFirst contract dorsoventral muscles to increase surface areaThen undulate

اسلاید 29: Nervous SystemSimilar to other annelidsFusions of ganglia in the sucker regionsPosses ocelliPosses sensory papillaeProjecting discs consisting of many sensory cellsTypically found dorsally, in rows, on one annulation of a particular segment Sense organs mainly used for prey detection, and respond to:Moving shadows and water-pressure vibrations in fish leechesChemicals from body fluids such as oils, sweat, and bloodWavesTemperature differences

اسلاید 30: Excretory System10 – 17 pairs of metanephridiaOne pair per segment in middle 1/3 of animalNephrostomes project into coelomic vesselsNephridial tubules are embedded in connective tissuePosses a bladder that fills before urine is released through nephridioporeImportant for osmoregulation

اسلاید 31: Digestive SystemPharynx typesProtrusible pharynx that is forced into prey / host tissueNon-protrusible sucking pharynxMay or may not have jawsEnzymes usually facilitate penetration in those lacking jawsSalivary glands empty secretions into pharynxHirudin – anticoagulantAnestheticVasodilatorsOften 1 – 11 pairs of lateral intestinal ceca

اسلاید 32: NutritionThree fourths are blood suckersUsually not host specificUsually parasitize a group of organisms (i.e. crayfish, fish, reptiles, birds, mammals, etc.)Some are carnivores of small invertebrates

اسلاید 33: Water from plasma is excreted via nephridioporesDigestion is very slowGut produces hardly any enzymesSymbiotic bacteria may produce digestive enzymes and vitaminsMay take 200 days to digest a blood mealRarely feedOne blood meal may increase animals weight by 10XMay only need to feed twice a year in order to growSome can fast for 1.5 years

اسلاید 34: Medical ApplicationsHistorically used in Europe for bloodlettingSupposedly, George Washington died two days after a bloodletting for a soar throatHirudo medicinalis is still used today for restoring circulation and reducing swelling after:Skin graftsDigit / appendage reattachmentNatural antibiotic propertiesSymbiotic bacteria produce antibiotics to reduce competition with other bacteria

اسلاید 35: ReproductionNo sexual reproduction, including regenerationHermaphroditic, but not simultaneousProtandricMale portion of reproductive system develops firstSpend first part of existence as males, then later reproduce as femalesCopulation and fertilization is always internalMost have copulatory organ for direct sperm transferOthers hypodermically impregnate using a spermatophorePressure and cytolytic chemicals rupture body wall of mateSperm are released and migrate toward eggs

اسلاید 36: Eggs are laid after copulationTime variesClitellum secretes a cocoon and albumenThe cocoons of fish leeches are attached to fish hostsSome brood eggs by attaching cocoon to substratum and ventilate eggs by fanning flattened ventral surfaceSome attach cocoon to ventral surface