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Biology 320 Invertebrate Zoology Fall 2005 Chapter 18 – Phylum Arthropoda Subphylum Chelicerata.

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Presentation on theme: "Biology 320 Invertebrate Zoology Fall 2005 Chapter 18 – Phylum Arthropoda Subphylum Chelicerata."— Presentation transcript:

1 Biology 320 Invertebrate Zoology Fall 2005 Chapter 18 – Phylum Arthropoda Subphylum Chelicerata

2 70,000 species 70,000 species Spiders, scorpions, mites, and horseshoe crabs Spiders, scorpions, mites, and horseshoe crabs Most are terrestrial Most are terrestrial Very diverse, with many interesting adaptations to terrestrial existence Very diverse, with many interesting adaptations to terrestrial existence

3 General Body Form Possess two tagmata Possess two tagmata Cephalothorax Cephalothorax Abdomen Abdomen Cephalothorax Cephalothorax No antennae, but typically two compound eyes and four ocelli No antennae, but typically two compound eyes and four ocelli Chelicerae – most anterior appendages; used for feeding Chelicerae – most anterior appendages; used for feeding Pedipalps – second appendages with various functions Pedipalps – second appendages with various functions Walking legs – four pairs Walking legs – four pairs Abdomen Abdomen Typically lacks appendages Typically lacks appendages Houses many visceral organs Houses many visceral organs Respiratory structures Respiratory structures

4 Class Xiphosura Horseshoe crabs Horseshoe crabs Largest chelicerates Largest chelicerates Up to 75cm long Up to 75cm long Only three genera, comprised of four species Only three genera, comprised of four species Limulus is the most famous; lives off N. American Atlantic coast Limulus is the most famous; lives off N. American Atlantic coast Remaining three species inhabit the Indo-Pacific Ocean Remaining three species inhabit the Indo-Pacific Ocean

5 Body Form Cephalothorax is shaped like a horse’s hoof Cephalothorax is shaped like a horse’s hoof Dorsal exoskeleton is called a carapace Dorsal exoskeleton is called a carapace Two large lateral compound eyes and two medial ocelli Two large lateral compound eyes and two medial ocelli Appendages are located ventrally; most have chelae Appendages are located ventrally; most have chelae Chelicerae Chelicerae Pedipalps Pedipalps Three pairs of walking legs Three pairs of walking legs Pusher legs for pushing soft sediment Pusher legs for pushing soft sediment

6 Abdomen Abdomen Ventral concavity that forms branchial chamber Ventral concavity that forms branchial chamber One pair of large flat genital opercula, with two gonopores (either male or female) One pair of large flat genital opercula, with two gonopores (either male or female) Five pairs of book gills are housed here Five pairs of book gills are housed here Long tail spine (telson) that extends posteriorly from last abdominal segment Long tail spine (telson) that extends posteriorly from last abdominal segment Used for pushing Used for pushing Righting body Righting body Anus located near base of tail spine Anus located near base of tail spine

7 Nutrition Omnivorous Omnivorous Eat molluscs, worms, algae, etc. Eat molluscs, worms, algae, etc. Walking leg coxae have gnathobases Walking leg coxae have gnathobases Medial space between gnathobases forms a food groove Medial space between gnathobases forms a food groove Gnathobases crush food and particles are moved towards mouth Gnathobases crush food and particles are moved towards mouth

8 Digestive System J-shaped gut J-shaped gut Mouth opens posteriorly at anterior end of food groove Mouth opens posteriorly at anterior end of food groove Stomach Stomach Has two pairs of large digestive ceca Has two pairs of large digestive ceca For extracellular digestion and absorption For extracellular digestion and absorption May be white as they take up extra calcium from blood, which is later voided with feces May be white as they take up extra calcium from blood, which is later voided with feces Not edible; some have high concentrations of saxotoxin Not edible; some have high concentrations of saxotoxin

9 Hemal System Hemocoel is main body cavity Hemocoel is main body cavity Heart has 9 pairs of ostia Heart has 9 pairs of ostia Blood contains: Blood contains: Hemocyanin Hemocyanin Two types of hemocytes (for clotting and producing more hemocyanin) Two types of hemocytes (for clotting and producing more hemocyanin)

10 Respiratory System Book gill surface area is approximately 2m 2 Book gill surface area is approximately 2m 2 Gill movements ventilate branchial chamber Gill movements ventilate branchial chamber Inhalant aperture on each lateral aspect of carapace (at junction of cephalothorax and abdomen) Inhalant aperture on each lateral aspect of carapace (at junction of cephalothorax and abdomen) Exhalant aperture at both sides of tail spine Exhalant aperture at both sides of tail spine

11 Excretory System Ammonotelic, so wastes removed across gill surface Ammonotelic, so wastes removed across gill surface Four pairs of saccate nephridia assist with osmoregulation in brackish water Four pairs of saccate nephridia assist with osmoregulation in brackish water Two nephridiopores located near the last pair of walking legs Two nephridiopores located near the last pair of walking legs

12 Nervous System CNS CNS Large brain Large brain Two longitudinal nerve cords Two longitudinal nerve cords Five pairs of segmental ganglia that serve book gills Five pairs of segmental ganglia that serve book gills Sensory structures Sensory structures Lateral compound eyes Lateral compound eyes 1000 ommatidia each 1000 ommatidia each Do not form images, but detect movement Do not form images, but detect movement Flabellum Flabellum Located on pusher leg, in the path of the inhalant current Located on pusher leg, in the path of the inhalant current Chemosensor that monitors water quality Chemosensor that monitors water quality

13 Reproduction Gonochoric Gonochoric External fertilization via flagellated sperm External fertilization via flagellated sperm Have specific mating seasons in spring and summer Have specific mating seasons in spring and summer Influenced by lunar cycles and tides Influenced by lunar cycles and tides Mating occurs near shore Mating occurs near shore Smaller male climbs onto female’s dorsal abdomen and claps her with pedipalps Smaller male climbs onto female’s dorsal abdomen and claps her with pedipalps Female digs a depression in the sand and oviposits 2000 – 30,000 eggs Female digs a depression in the sand and oviposits 2000 – 30,000 eggs Male releases sperm into depression Male releases sperm into depression

14 Larvae are called trilobite larvae Larvae are called trilobite larvae One cm long One cm long Small tail spine and two pairs of book gills Small tail spine and two pairs of book gills Burrow in sand Burrow in sand 9 – 12 years to reach sexual maturity 9 – 12 years to reach sexual maturity May live up to 19 years May live up to 19 years

15 Class Arachnida 70,000 described, with an estimated one million more undescribed 70,000 described, with an estimated one million more undescribed Spiders, scorpions, solifuges, and mites Spiders, scorpions, solifuges, and mites Almost entirely terrestrial Almost entirely terrestrial Very well adapted for terrestrial existence Very well adapted for terrestrial existence Waxy epicuticle Waxy epicuticle Book gills transformed into book lungs for breathing air Book gills transformed into book lungs for breathing air Malpighian tubules Malpighian tubules Possess other interesting adaptations Possess other interesting adaptations Silk Silk Poison glands Poison glands

16 Body Form Two tagma are sometimes connected by a pedicel Two tagma are sometimes connected by a pedicel Similar appendages in all Similar appendages in all Chelicerae – one pair that may have fangs and poison glands Chelicerae – one pair that may have fangs and poison glands Pedipalps – one pair that have many functions, and may have gnathobases Pedipalps – one pair that have many functions, and may have gnathobases Walking legs – four pairs that may terminate in claws Walking legs – four pairs that may terminate in claws

17 Nutrition Mostly carnivorous, but some are ectoparasites Mostly carnivorous, but some are ectoparasites Digestion begins extraorally Digestion begins extraorally Prey is captured and killed Prey is captured and killed Chelicerae and gnathobases of pedipalps macerate Chelicerae and gnathobases of pedipalps macerate Digestive enzymes digest Digestive enzymes digest Liquids are ingested Liquids are ingested Gut is adapted for a liquid diet Gut is adapted for a liquid diet Either pharynx or stomach functions as a muscular pump Either pharynx or stomach functions as a muscular pump Gut has a very small diameter Gut has a very small diameter No gizzard No gizzard

18 Gas Exchange Small arachnids use body surface Small arachnids use body surface Large arachnids have two types of organs Large arachnids have two types of organs Book lungs Book lungs Invaginations of ventral abdominal wall with a slit-shaped spiracle Invaginations of ventral abdominal wall with a slit-shaped spiracle Atrium contains lamellae supported by pedestals Atrium contains lamellae supported by pedestals Muscle contractions expand atrium to facilitate ventilation Muscle contractions expand atrium to facilitate ventilation Atrium surrounded by pulmonary sinus Atrium surrounded by pulmonary sinus Trachea Trachea Do not make direct contact with cells as in insects Do not make direct contact with cells as in insects Blood delivers gasses (possesses hemocyanin) Blood delivers gasses (possesses hemocyanin) Tracheae conserve more water than book lungs (huge SA) Tracheae conserve more water than book lungs (huge SA)

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20 Excretion Uricotelic Uricotelic Possess either saccate nephridia, Malpighian tubules, or both Possess either saccate nephridia, Malpighian tubules, or both Also possess nephrocytes Also possess nephrocytes Large phagocytic cells that police the hemocoel Large phagocytic cells that police the hemocoel Sequester metabolic wastes indefinitely Sequester metabolic wastes indefinitely May detoxify wastes and return to blood May detoxify wastes and return to blood

21 Nervous System Highly cephalized Highly cephalized Sensory organs Sensory organs Trichobothria Trichobothria Setae found in high concentrations on legs Setae found in high concentrations on legs Can sense air currents from fly wings, and aid in prey capture Can sense air currents from fly wings, and aid in prey capture Slit sense organs Slit sense organs Slits in exoskeleton with a thin membrane covering Slits in exoskeleton with a thin membrane covering Detect strain on exoskeleton Detect strain on exoskeleton May be found in clusters called lyriform organs May be found in clusters called lyriform organs Some have as many as 3000 slit sense organs Some have as many as 3000 slit sense organs Flagellum Flagellum Lack antennae, so some posses a posterior sensory flagellum Lack antennae, so some posses a posterior sensory flagellum

22 Reproduction Always gonochoric Always gonochoric Always internal fertilization Always internal fertilization Sperm transfer Sperm transfer Direct Direct Penis Penis Indirect Indirect Spermatophore placed on ground, or transferred by pedipalp Spermatophore placed on ground, or transferred by pedipalp

23 Order Scorpiones 1200 species 1200 species Found on all continents except Antarctica Found on all continents except Antarctica Baja California has greatest diversity Baja California has greatest diversity Secretive and nocturnal Secretive and nocturnal Hide under rocks, logs, or in burrows during the day Hide under rocks, logs, or in burrows during the day Emerge at night to hunt Emerge at night to hunt Fluoresce green under UV light Fluoresce green under UV light Most are 3 – 9 cm, but Hadogenes from Africa can reach 21 cm Most are 3 – 9 cm, but Hadogenes from Africa can reach 21 cm

24 Body Form Long segmented abdomen Long segmented abdomen Posses a telson (sting) Posses a telson (sting) Pedipalps are enlarged to form pincers Pedipalps are enlarged to form pincers No pedicel No pedicel Two comb-like sensory structures (pectines) on ventral surface Two comb-like sensory structures (pectines) on ventral surface Several segments possess spiracles that open into book lungs Several segments possess spiracles that open into book lungs

25 Nutrition Feed on other inverts, especially insects and arachnids Feed on other inverts, especially insects and arachnids Ambush predators Ambush predators Wait at burrow entrance Wait at burrow entrance Claws open and ready to strike Claws open and ready to strike Some dig up prey Some dig up prey Some can catch prey in midair Some can catch prey in midair

26 Prey is held with pedipalps and stabbed with sting (if needed) Prey is held with pedipalps and stabbed with sting (if needed) Metabolic rates are among the lowest recorded for animals Metabolic rates are among the lowest recorded for animals Can survive over one year between meals Can survive over one year between meals Conversion of prey to biomass is very efficient Conversion of prey to biomass is very efficient One meal can increase body weight by 1/3 One meal can increase body weight by 1/3 Poison glands Poison glands Only 25 species are potentially lethal to humans Only 25 species are potentially lethal to humans Centruoides in SW US Centruoides in SW US Androctonus in N. Africa Androctonus in N. Africa

27 Organ Systems Respiratory Respiratory Four pairs of book lungs, with spiracles located ventrally Four pairs of book lungs, with spiracles located ventrally Hemal Hemal Standard Standard Excretory Excretory Two pairs of Malpighian tubules Two pairs of Malpighian tubules One pair of saccate nephridia One pair of saccate nephridia

28 Nervous system Nervous system Ventral nerve cord Ventral nerve cord Seven segmental ganglia Seven segmental ganglia Giant axons for rapid closing of claws and stinging motion Giant axons for rapid closing of claws and stinging motion Pectines Pectines Sensory role is unclear Sensory role is unclear Sensitive to ground vibrations Sensitive to ground vibrations Suspected chemosensory role in spermatophore deposition Suspected chemosensory role in spermatophore deposition Ablation of pectines results in failure of male to deposit spermatophore Ablation of pectines results in failure of male to deposit spermatophore

29 Adaptations to Arid Existence Lowest evaporative water loss of any invertebrate Lowest evaporative water loss of any invertebrate 0.01% body weight / hour 0.01% body weight / hour Tolerate up to 40% body water loss Tolerate up to 40% body water loss Obtain water from food and rarely drink Obtain water from food and rarely drink Uricotelic Uricotelic Impermeable exoskeleton Impermeable exoskeleton Burrow up to one meter in some Burrow up to one meter in some Nocturnal Nocturnal Raise bodies off of ground (stilting) Raise bodies off of ground (stilting)

30 Reproduction Indirect sperm transfer via spermatophore Indirect sperm transfer via spermatophore Usually a courtship ritual where claws are grasped and the two walk around as if dancing Usually a courtship ritual where claws are grasped and the two walk around as if dancing Male deposits spermatophore Male deposits spermatophore Stands approximately 6 mm high Stands approximately 6 mm high Consists of a lever, stalk, ejection apparatus and sperm reservoir Consists of a lever, stalk, ejection apparatus and sperm reservoir Male positions female over it Male positions female over it Female pectines cause sperm reservoir to eject into open gonopore Female pectines cause sperm reservoir to eject into open gonopore

31 Viviparous Viviparous Direct development Direct development 1 to 95 young depending on species 1 to 95 young depending on species Juveniles crawl onto mother’s back and remain through first molt (4 weeks) Juveniles crawl onto mother’s back and remain through first molt (4 weeks) High degree of parental care High degree of parental care Six months to six years to reach sexual maturity Six months to six years to reach sexual maturity May live 25 years May live 25 years

32 Order Uropygi 100 species of whip scorpions 100 species of whip scorpions Some such as the North American vinegaroon (Mastigoproctus giganteus) can reach 8 cm in length Some such as the North American vinegaroon (Mastigoproctus giganteus) can reach 8 cm in length Interesting structures Interesting structures Large pedipalps with pincers Large pedipalps with pincers Flagellum Flagellum Repugnatorial glands near anus, that spray acetic acid at predators Repugnatorial glands near anus, that spray acetic acid at predators In some, males use pedipalps to transfer spermatophore to female’s gonopore In some, males use pedipalps to transfer spermatophore to female’s gonopore Females lay eggs in a sac that she attaches to her body Females lay eggs in a sac that she attaches to her body

33 Order Amblypygi Whip spiders Whip spiders Secretive and nocturnal Secretive and nocturnal 4 to 45 mm 4 to 45 mm Flattened bodies that share characteristics of spiders and crabs Flattened bodies that share characteristics of spiders and crabs Often move sideways like crabs Often move sideways like crabs Lack poison glands Lack poison glands Large spiny pedipalps Large spiny pedipalps First legs are extremely long and thin First legs are extremely long and thin Sensory Sensory One pointed forward and one sideways while animal moves One pointed forward and one sideways while animal moves Have a pedicel Have a pedicel

34 Order Araneae 40,000 species of spiders 40,000 species of spiders Huge population densities Huge population densities Five million / hectare in one field in Great Britain Five million / hectare in one field in Great Britain Silk is probably most important adaptation to spider existence Silk is probably most important adaptation to spider existence Only arachnids with silk spinning appendages (spinnerets) Only arachnids with silk spinning appendages (spinnerets) Possess a pedicel, which allows abdomen to move independently of cephalothorax, in order to distribute silk Possess a pedicel, which allows abdomen to move independently of cephalothorax, in order to distribute silk Carnivorous Carnivorous

35 Body Form Large variation in body size (0.5 mm to 9 cm) Large variation in body size (0.5 mm to 9 cm) Typically have eight eyes Typically have eight eyes Chelicerae possess fangs and poison glands Chelicerae possess fangs and poison glands Distal tips of male pedipalps are knoblike and modified for sperm transfer Distal tips of male pedipalps are knoblike and modified for sperm transfer Four pairs of walking legs that terminate in either two (cursorial) or three (web building) claws Four pairs of walking legs that terminate in either two (cursorial) or three (web building) claws Gonopore and book lung spiracles located ventrally Gonopore and book lung spiracles located ventrally Tracheal spiracle located posteriorly, near spinnerets Tracheal spiracle located posteriorly, near spinnerets

36 Silk Produced by abdominal silk glands Produced by abdominal silk glands Extruded from spigots on distal tips of spinnerets Extruded from spigots on distal tips of spinnerets Different types of glands (six known) that produce different silks Different types of glands (six known) that produce different silks It is a protein that is emitted as a liquid, but hardens as it is drawn out It is a protein that is emitted as a liquid, but hardens as it is drawn out Strong, but resistance to breakage is mainly due to its elasticity Strong, but resistance to breakage is mainly due to its elasticity Many functions: Many functions: Prey capture (web building) Prey capture (web building) Shelters Shelters Egg cases Egg cases Draglines Draglines Balooning in spiderlings Balooning in spiderlings

37 Prey Capture Web building spiders Web building spiders Webs are strategically placed and oriented according to prey habits Webs are strategically placed and oriented according to prey habits Web type differs between species, which partitions resources Web type differs between species, which partitions resources Most famous type of web is the orb web Most famous type of web is the orb web One plane One plane Radial threads aren’t sticky (spider walks on these) Radial threads aren’t sticky (spider walks on these) Catching spiral is sticky Catching spiral is sticky Spiders are sensitive to web vibrations Spiders are sensitive to web vibrations Can sense type, size and location of prey Can sense type, size and location of prey

38 Cursorial (hunting) spiders Cursorial (hunting) spiders Do not build webs Do not build webs Ambush or actively forage Ambush or actively forage Heavier legs Heavier legs Possess scopulae Possess scopulae Tufts of setae near claws Tufts of setae near claws Each seta may have over 1000 branches (huge SA) Each seta may have over 1000 branches (huge SA) Use for adhering to slick surfaces and prey Use for adhering to slick surfaces and prey Can walk up walls, glass, or upside-down across ceilings Can walk up walls, glass, or upside-down across ceilings

39 Nutrition Fangs on chelicerae penetrate prey Fangs on chelicerae penetrate prey Muscles surrounding poison glands contract Muscles surrounding poison glands contract Low metabolic rates Low metabolic rates Can double body weight with one meal Can double body weight with one meal Mainly carnivores of insects, but some wasps (tarantula hawks and mud daubers) use spiders as food for larvae Mainly carnivores of insects, but some wasps (tarantula hawks and mud daubers) use spiders as food for larvae

40 Most spider venom is not toxic to humans Most spider venom is not toxic to humans A few genera are toxic, but rarely lethal A few genera are toxic, but rarely lethal Latrodectus Latrodectus Black widows have neurotoxic venom Black widows have neurotoxic venom Symptoms of bites include nausea, pain, and muscles spasms Symptoms of bites include nausea, pain, and muscles spasms Loxosceles Loxosceles Recluses have hemotoxic venom Recluses have hemotoxic venom Six eyes, and a violin shape on cephalothorax Six eyes, and a violin shape on cephalothorax Causes tissue necrosis Causes tissue necrosis A few genera are lethal A few genera are lethal Atrax Atrax Australia’s funnel-web spider Australia’s funnel-web spider World’s deadliest spider World’s deadliest spider Trechona Trechona Lives in South America Lives in South America

41 Gas Exchange Respiratory structures located ventrally Respiratory structures located ventrally Primitive spiders (such as tarantulas) possess two pairs of book lungs Primitive spiders (such as tarantulas) possess two pairs of book lungs Most possess one anterior pair of book lungs and one posterior set of tracheae (with one spiracle) Most possess one anterior pair of book lungs and one posterior set of tracheae (with one spiracle) Some only possess tracheae Some only possess tracheae

42 Hemal and Nervous Systems Hemal Hemal Heart only has 2 or 3 pairs of ostia Heart only has 2 or 3 pairs of ostia Spiders lack extensor muscles, so legs are extended by elevating hemocoel pressure Spiders lack extensor muscles, so legs are extended by elevating hemocoel pressure Legs are always flexed in dead spiders Legs are always flexed in dead spiders Jumping spiders can jump 50X body length by quickly elevating blood pressure Jumping spiders can jump 50X body length by quickly elevating blood pressure Nervous Nervous Eyes lack ommatidia Eyes lack ommatidia Vision is important to cursorial spiders Vision is important to cursorial spiders Jumping spiders have best vision of all arachnids Jumping spiders have best vision of all arachnids Main eyes form images while secondary eyes detect movement Main eyes form images while secondary eyes detect movement

43 Reproduction Sexually dimorphic (males usually much smaller) Sexually dimorphic (males usually much smaller) Highly modified pedipalps are used for sperm transfer Highly modified pedipalps are used for sperm transfer Have a sperm reservoir Have a sperm reservoir Male builds sperm web and extrudes sperm (not spermatophore) onto web Male builds sperm web and extrudes sperm (not spermatophore) onto web Dips pedipalp into sperm, fills reservoir, and searches for receptive female Dips pedipalp into sperm, fills reservoir, and searches for receptive female

44 Courtship behavior, chemical and tactile cues are important so that the female doesn’t eat the male Courtship behavior, chemical and tactile cues are important so that the female doesn’t eat the male Orb-weaver males pluck radial threads of female’s web during courtship Orb-weaver males pluck radial threads of female’s web during courtship Number, frequency and intensity of plucks is species specific Number, frequency and intensity of plucks is species specific Female lays up to 300 eggs in a silk case Female lays up to 300 eggs in a silk case

45 Egg case is attached to web, inside of home, or spider itself Egg case is attached to web, inside of home, or spider itself Spiderlings remain in egg case until completing first molt Spiderlings remain in egg case until completing first molt Disperse via ballooning Disperse via ballooning Most live one to two years, but some have lived for 25 years in captivity Most live one to two years, but some have lived for 25 years in captivity

46 Order Pseudoscorpiones Small, less than 7mm Small, less than 7mm 2500 species 2500 species Live in leaf litter Live in leaf litter Large chelate pedipalps with poison glands Large chelate pedipalps with poison glands Feed on small arthropods such as mites Feed on small arthropods such as mites Exhibit a phenomenon known as phoresy Exhibit a phenomenon known as phoresy Grab leg of a flying insect and hitch a ride Grab leg of a flying insect and hitch a ride

47 Order Solifugae Many names: solifuges (with many variations on spelling), sun spiders or wind scorpions Many names: solifuges (with many variations on spelling), sun spiders or wind scorpions Body size: a few mm to 7 cm Body size: a few mm to 7 cm Large chelicerae with the largest mandibles (relative to size) in the entire animal kingdom Large chelicerae with the largest mandibles (relative to size) in the entire animal kingdom Two median eyes Two median eyes Long, leg-like pedipalps Long, leg-like pedipalps

48 First legs are used as antennae First legs are used as antennae Carnivorous or omnivorous Carnivorous or omnivorous Many eat termites Many eat termites Tracheae are similar to those of insects Tracheae are similar to those of insects Oddly shaped sensory organs Oddly shaped sensory organs Called racquet organs Called racquet organs Two to five pairs hang from fourth legs Two to five pairs hang from fourth legs

49 Order Opiliones 5000 species of daddy longlegs or harvestmen 5000 species of daddy longlegs or harvestmen Lack silk glands and poison glands Lack silk glands and poison glands Many are herbivores or feed on dead organic matter Many are herbivores or feed on dead organic matter Gut is adapted for ingesting and processing particulate matter Gut is adapted for ingesting and processing particulate matter

50 Body length sometime reaches 22 mm, but leg length ca reach 160 mm Body length sometime reaches 22 mm, but leg length ca reach 160 mm May be brightly colored May be brightly colored Long legs are excellent for maneuvering over rough terrain Long legs are excellent for maneuvering over rough terrain Males possess a penis and females possess an ovipositor Males possess a penis and females possess an ovipositor

51 Order Acari 40,000 species of mites 40,000 species of mites Most mites are free-living, but some are parasites of people, animals, and crops Most mites are free-living, but some are parasites of people, animals, and crops Mites are the smallest arachnids Mites are the smallest arachnids Some can inhabit the tracheae of honeybees Some can inhabit the tracheae of honeybees Some live in human hair follicles Some live in human hair follicles The largest mites (called ticks) can reach 3 cm when engorged with blood The largest mites (called ticks) can reach 3 cm when engorged with blood

52 Lack segmentation; cephalothorax is fused with abdomen Lack segmentation; cephalothorax is fused with abdomen Can be internal or external parasites Can be internal or external parasites Larvae of Trombicula are referred to as chiggers Larvae of Trombicula are referred to as chiggers Mange mite burrows under skin, lays eggs, and causes a skin condition known as scabies Mange mite burrows under skin, lays eggs, and causes a skin condition known as scabies Can also be vectors of diseases Can also be vectors of diseases Example – Lyme disease Example – Lyme disease

53 Class Pycnogonida 1000 species of sea spiders 1000 species of sea spiders Marine, but not really spiders Marine, but not really spiders Crawl around on eight long legs Crawl around on eight long legs One mm to 10 mm long normally, but Colossendeis can achieve leg spans of 70 cm One mm to 10 mm long normally, but Colossendeis can achieve leg spans of 70 cm

54 Mostly feed on sessile animals like hydroids, soft corals, and anemones Mostly feed on sessile animals like hydroids, soft corals, and anemones Some are ectoparasites Some are ectoparasites Ovary has branches that extend into femurs Ovary has branches that extend into femurs Gravid females have swollen legs Gravid females have swollen legs Males have ovigerous legs (ovigers) that are used to carry egg masses Males have ovigerous legs (ovigers) that are used to carry egg masses Gathers released eggs and cements them to ovigers Gathers released eggs and cements them to ovigers


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