Phylum Arthropoda The Arthropoda (from the Greek Arthron, joint and podus, foot) are the largest...

Phylum ArthropodaPhylum Arthropoda

The Arthropoda (from the Greek Arthron, The Arthropoda (from the Greek Arthron, joint and podus, foot) are the largest group joint and podus, foot) are the largest group of organisms and they occur in all of organisms and they occur in all environments on earth.environments on earth.

The group includes: spiders, ticks, mites, The group includes: spiders, ticks, mites, centipedes, millipedes, crustaceans, centipedes, millipedes, crustaceans, insects and others.insects and others.

Characteristics of the ArthropodaCharacteristics of the Arthropoda

Bilaterally symmetrical with a segmented Bilaterally symmetrical with a segmented (metameric) body divided into head, thorax (metameric) body divided into head, thorax and abdomen; cephalothorax and and abdomen; cephalothorax and abdomen; or fused head and trunk.abdomen; or fused head and trunk.


Jointed appendages. Primitively one pair Jointed appendages. Primitively one pair per segment, but number often reduced. per segment, but number often reduced.

Appendages often greatly modified for Appendages often greatly modified for specialized tasks.specialized tasks.


Exoskeleton of cuticle. Exoskeleton of cuticle.

Exoskelton secreted by underlying Exoskelton secreted by underlying epidermis. Made of chitin, protein, lipid epidermis. Made of chitin, protein, lipid and often calcium carbonate.and often calcium carbonate.

Exoskeleton is shed periodically (ecdysis) Exoskeleton is shed periodically (ecdysis) as the organism grows.as the organism grows.


Muscular system is complex and muscles Muscular system is complex and muscles attach to the exoskeleton. attach to the exoskeleton.

Striated muscles for voluntary movement Striated muscles for voluntary movement and smooth muscles for the viscera.and smooth muscles for the viscera.

Coleom is reduced. Most of body cavity is Coleom is reduced. Most of body cavity is a hemocoel (sinuses or spaces) filled with a hemocoel (sinuses or spaces) filled with blood.blood.


Complete digestive system. Mouthparts Complete digestive system. Mouthparts are specialized being modified from are specialized being modified from appendages and specialized for dealing appendages and specialized for dealing with various types of food.with various types of food.

Open circulatory system with a dorsal Open circulatory system with a dorsal contractile heart arteries and hemocoel.contractile heart arteries and hemocoel.


Respiration occurs in multiple possible Respiration occurs in multiple possible waysways across the body surfaceacross the body surface via a system of tracheal tubesvia a system of tracheal tubes gillsgills book lungsbook lungs


Nervous system is similar to that of Nervous system is similar to that of annelids. A dorsal brain connected via a annelids. A dorsal brain connected via a ring around the pharynx to a double ring around the pharynx to a double ventral nerve cord.ventral nerve cord.


Sexes are usually separate with internal Sexes are usually separate with internal fertilization. fertilization.

Can be oviparous or ovoviviparous. Can be oviparous or ovoviviparous. Offspring often go through process of Offspring often go through process of

metamorphosis.metamorphosis. Parthenogenesis occurs in a some Parthenogenesis occurs in a some

species (e.g. aphids).species (e.g. aphids).

Classification of Phylum ArthropodaClassification of Phylum Arthropoda

Subphylum Chelicarata: horseshoe crabs, Subphylum Chelicarata: horseshoe crabs, spiders, tick, mites, scorpions, spiders, tick, mites, scorpions,

Subphylum Crustacea: crabs, lobsters, Subphylum Crustacea: crabs, lobsters, copepods, barnacles, pill bugs copepods, barnacles, pill bugs

Subphylum Myriapoda: millipedes and Subphylum Myriapoda: millipedes and centipedescentipedes

Subphylum Hexapoda: springtails, insectsSubphylum Hexapoda: springtails, insects

Classification of the ArthropodaClassification of the Arthropoda

Subphylum ChelicerataSubphylum Chelicerata Class MerostomataClass Merostomata

• Subclass Xiphosurida: Horseshoe crabsSubclass Xiphosurida: Horseshoe crabs Class Pycnogonida: sea spidersClass Pycnogonida: sea spiders Class Arachnida: spiders, scorpions, ticks, Class Arachnida: spiders, scorpions, ticks,

mites, harvestmen, whip scorpions.mites, harvestmen, whip scorpions.

Subphylum ChelicerataSubphylum Chelicerata

Body is divided into two tagmata (fused Body is divided into two tagmata (fused segments) head and abdomen.segments) head and abdomen.

Six pairs of appendages:Six pairs of appendages: a pair of chelicerae, first pair of appenadges used for a pair of chelicerae, first pair of appenadges used for

feeding.feeding. a pair of pedipalps (not in horseshoe crabs)a pair of pedipalps (not in horseshoe crabs) 4 pairs of walking legs (5 in horseshoe crabs).4 pairs of walking legs (5 in horseshoe crabs).

No mandibles or antennae.No mandibles or antennae.


The chelicrates are a very ancient group The chelicrates are a very ancient group that includes the extinct Eurypterids (giant that includes the extinct Eurypterids (giant water scorpions (200-500 mya), which water scorpions (200-500 mya), which were the largest known arthropods were the largest known arthropods reaching up to 3m long.reaching up to 3m long.

Eurypterus (left) from the Silurian of New York State. Eurypterus remipes was voted the New York state fossil in 1983.

Mixopterus (right) from the Devonian reached about one meter in length


Subclass Xiphosurida: Horseshoe crabs. Subclass Xiphosurida: Horseshoe crabs. These are an ancient group that date from These are an ancient group that date from the Cambrian (543-495 mya).the Cambrian (543-495 mya).

Five living species. Five living species. LimulusLimulus, which lives in , which lives in shallow waters on the Atlantic coast of the shallow waters on the Atlantic coast of the U.S. is almost unchanged since the U.S. is almost unchanged since the Triassic (251-206 mya).Triassic (251-206 mya).

12.2

Figure 18.02

Subphylum Chelicerata: Horseshoe Subphylum Chelicerata: Horseshoe crabscrabs

Horseshoe crabs have an unsegmented Horseshoe crabs have an unsegmented carapace, which is sort of horseshoe carapace, which is sort of horseshoe shaped, hence the name.shaped, hence the name.

There is also a wide abdomen with a long There is also a wide abdomen with a long spinelike tailpiece (telson).spinelike tailpiece (telson).

Flat leaf-like gills, called book gills, are Flat leaf-like gills, called book gills, are present on the underside.present on the underside.

Horseshoe crabsHorseshoe crabs Horseshoe crabs feed on foods such as worms and Horseshoe crabs feed on foods such as worms and

molluscs, such as clams, which brings them into conflict molluscs, such as clams, which brings them into conflict with fishermen.with fishermen.

The synchonized breeding of horseshoe crabs which The synchonized breeding of horseshoe crabs which come to spawn on the beaches of the mid-Atlantic coast come to spawn on the beaches of the mid-Atlantic coast of the U.S. at the lunar high tides is a striking sight in of the U.S. at the lunar high tides is a striking sight in summer. summer.

The eggs produced in the millions are an important food The eggs produced in the millions are an important food source for migrating shorebirds such as Knot, which source for migrating shorebirds such as Knot, which flock to areas such as the Delaware Bay to fatten up for flock to areas such as the Delaware Bay to fatten up for migration.migration.

Horseshoe crabsHorseshoe crabs

Horseshoe crabs are harvested Horseshoe crabs are harvested commercially for bait and also for their commercially for bait and also for their blood, which is used in laboratory testing blood, which is used in laboratory testing for endotoxins in medical products.for endotoxins in medical products.

Currently, the horseshoe crab is at the Currently, the horseshoe crab is at the center of a series of legal battles about the center of a series of legal battles about the size of harvests and their sustainability.size of harvests and their sustainability.

Subphylum Chelicerata: Class Subphylum Chelicerata: Class Pycnogonida: sea spidersPycnogonida: sea spiders

Another name used for these animals is Another name used for these animals is Pantopoda (“all legs”), which is an excellent Pantopoda (“all legs”), which is an excellent description. description.

The body is greatly reduced in size, whereas the The body is greatly reduced in size, whereas the legs are long and clawed. In some species legs are long and clawed. In some species modified legs called ovigers are used by males modified legs called ovigers are used by males to carry egg masses.to carry egg masses.

There is a long proboscis on the head, which the There is a long proboscis on the head, which the pycnogonid uses to feed on soft-bodied pycnogonid uses to feed on soft-bodied invertebrates, especially cnidarians.invertebrates, especially cnidarians.

12.3

Figure 18.03

Class Pycnogonida: sea spidersClass Pycnogonida: sea spiders

Most pycnogonids are small being only a Most pycnogonids are small being only a few millimeters long, but a few reach 70cm few millimeters long, but a few reach 70cm measured by leg spread.measured by leg spread.

Pycngonids are exclusively marine Pycngonids are exclusively marine (occuring from the intertidal to the deep (occuring from the intertidal to the deep seas) and there are about 1000 species.seas) and there are about 1000 species.

Subphylum Chelicerata: Class Subphylum Chelicerata: Class Arachnida: Order Aranae: spidersArachnida: Order Aranae: spiders

Spiders are a very large group with more than 35,000 Spiders are a very large group with more than 35,000 described species that occur worldwide except in described species that occur worldwide except in Antarctica.Antarctica.

The body is divided into a cephalothorax and an The body is divided into a cephalothorax and an abdomen.abdomen.

Spiders breathe using book lungs or tracheae. Book Spiders breathe using book lungs or tracheae. Book lungs are unique to spiders and consist of a large lungs are unique to spiders and consist of a large number of air pockets extending into a blood-filled number of air pockets extending into a blood-filled chamber. Tracheae are tubules that carry air directly chamber. Tracheae are tubules that carry air directly from outside to tissues. They can be closed to prevent from outside to tissues. They can be closed to prevent excessive water loss.excessive water loss.

SpidersSpiders

Spiders and insects have an excretory system Spiders and insects have an excretory system that uses structures called Malphigian tubules.that uses structures called Malphigian tubules.

Potassium, other salts, and other waste solutes Potassium, other salts, and other waste solutes drain into these tubules, which empty into the drain into these tubules, which empty into the intestine. Rectal glands selectively reabsorb intestine. Rectal glands selectively reabsorb most of the potassium and water leaving behind most of the potassium and water leaving behind nitrogenous wastes in the form of uric acid, nitrogenous wastes in the form of uric acid, which requires little water for its excretion.which requires little water for its excretion.

SpidersSpiders

Spiders possess eight eyes, but their Spiders possess eight eyes, but their image forming ability is limited. image forming ability is limited.

Hairlike setae, however, provide a lot of Hairlike setae, however, provide a lot of information about the environment sensing information about the environment sensing e.g. vibrations and air currentse.g. vibrations and air currents

SpidersSpiders

All spiders are predators and their chelicerae All spiders are predators and their chelicerae function as fangs. function as fangs.

The fangs are connected via ducts to venom The fangs are connected via ducts to venom glands that produce a lethal venom the spider glands that produce a lethal venom the spider uses to dispatch its prey.uses to dispatch its prey.

After killing a prey item the spider injects After killing a prey item the spider injects digestive fluid into the organism and sucks up digestive fluid into the organism and sucks up the resulting soup.the resulting soup.

12.4

Figure 18.05

SpidersSpiders

Spiders use a variety of techniques to Spiders use a variety of techniques to catch prey. catch prey.

Some chase their prey or leap on it, some Some chase their prey or leap on it, some ambush prey often using trip wires, and, of ambush prey often using trip wires, and, of course, many use webs. course, many use webs.

One small group, the bolas spiders, One small group, the bolas spiders, capture their prey by deception.capture their prey by deception.

Bolas spidersBolas spiders

Bolas spiders at night spin a line of thread with a sticky Bolas spiders at night spin a line of thread with a sticky globule (the bolas: akin to the bolas used by South globule (the bolas: akin to the bolas used by South American Gauchos to hunt) at the free end. American Gauchos to hunt) at the free end.

The bolas contains pheromones which attract certain The bolas contains pheromones which attract certain male moths which think they are approaching a female. male moths which think they are approaching a female. When the spider senses the vibrations in the air caused When the spider senses the vibrations in the air caused by a nearby flying moth it twirls its bolas in response. by a nearby flying moth it twirls its bolas in response.

Once the bolas strikes the moth it sticks and the moth is Once the bolas strikes the moth it sticks and the moth is hauled in.hauled in.

Silk-spinningSilk-spinning Spiders spin silk, which they use to make webs Spiders spin silk, which they use to make webs

to trap prey. to trap prey.

Webs come in a variety of shapes and sizes and Webs come in a variety of shapes and sizes and contain and are coated with an adhesive that contain and are coated with an adhesive that holds prey. holds prey.

Webs are typically placed in insect flyways and Webs are typically placed in insect flyways and the spider sits and waits for an insect to become the spider sits and waits for an insect to become entangled. The vibrations of the struggling prey entangled. The vibrations of the struggling prey signal the spider to emerge and dispatch it.signal the spider to emerge and dispatch it.

Silk-spinningSilk-spinning

The silk is produced by two or three spinnerets, The silk is produced by two or three spinnerets, which are connected to abdominal silk glands. which are connected to abdominal silk glands. The silk is formed from a protein secretion that The silk is formed from a protein secretion that hardens on contact with air. hardens on contact with air.

The silk is extremely strong (stronger e.g. than The silk is extremely strong (stronger e.g. than steel of equivalent weight) and is being used as steel of equivalent weight) and is being used as a kevlar substitute. Unlike steel, silk can stretch a kevlar substitute. Unlike steel, silk can stretch which makes it an extremely useful material.which makes it an extremely useful material.

Silk-spinningSilk-spinning

The silk is used to make webs, but also for The silk is used to make webs, but also for a variety of other purposes:a variety of other purposes: Line nestsLine nests Form egg sacsForm egg sacs For dispersal by ballooningFor dispersal by ballooning To wrap preyTo wrap prey

Reproduction in spidersReproduction in spiders

Courtship rituals are a major feature of Courtship rituals are a major feature of spider mating in which the (usually much spider mating in which the (usually much smaller) male attempts to mate without smaller) male attempts to mate without being eaten by the female. being eaten by the female.

Males produce a sperm packet wrapped in Males produce a sperm packet wrapped in silk which he holds in a cavity in one of his silk which he holds in a cavity in one of his pedipalps (second pair of appendages).pedipalps (second pair of appendages).

Reproduction in spidersReproduction in spiders

The male, if he lives long enough, inserts a The male, if he lives long enough, inserts a pedipalp into a female’s genital opening and she pedipalp into a female’s genital opening and she stores the sperm in a seminal vesicle. stores the sperm in a seminal vesicle.

The female later fertilizing eggs when she is The female later fertilizing eggs when she is ready to lay them. Eggs are laid in a silk cocoon ready to lay them. Eggs are laid in a silk cocoon where the young hatch and remain for a short where the young hatch and remain for a short time and molt before departing for an time and molt before departing for an independent life.independent life.

Toxic spidersToxic spiders

The vast majority of spiders are harmless The vast majority of spiders are harmless to humans, but a handful are toxic and to humans, but a handful are toxic and potentially deadly.potentially deadly.

In the U.S. there are a few venomous In the U.S. there are a few venomous spiders: several black widow species spiders: several black widow species (genus (genus LatrodectusLatrodectus), the brown recluse ), the brown recluse ((Loxosceles reclusaLoxosceles reclusa) and the hobo spider ) and the hobo spider ((Tegenaria agrestisTegenaria agrestis) introduced from ) introduced from Europe to the Pacific Northwest.Europe to the Pacific Northwest.


Spiders eat a liquid diet by injecting Spiders eat a liquid diet by injecting digestive juices into their prey and some digestive juices into their prey and some spider venoms contribute to this process spider venoms contribute to this process by destroying tissue. by destroying tissue.

Bites of such spiders can lead to tissue Bites of such spiders can lead to tissue necrosis. This is the type of venom necrosis. This is the type of venom possessed by the hobo and brown recluse possessed by the hobo and brown recluse spiders.spiders.

Hobo spider

Brown recluse spider


A bite from one of these spiders results in A bite from one of these spiders results in a bite site that develops a painful ulcer a bite site that develops a painful ulcer where tissue dies (necrosis) and in the where tissue dies (necrosis) and in the case of hobo spiders severe headaches.case of hobo spiders severe headaches.

One component of brown recluse venom One component of brown recluse venom is sphingomyelinase D which attacks and is sphingomyelinase D which attacks and dissolves cell membranes. dissolves cell membranes.


Sphingomyelinase D and other components in Sphingomyelinase D and other components in the venom apparently also turn on the patient’s the venom apparently also turn on the patient’s inflammatory defenses against his or her own inflammatory defenses against his or her own tissues.tissues.

White blood cells destroy themselves releasing White blood cells destroy themselves releasing other enzymes that attack the victim’s own flesh other enzymes that attack the victim’s own flesh and blood clots form in tiny vessels cutting off and blood clots form in tiny vessels cutting off the blood supply to the bite area and causing the blood supply to the bite area and causing necrosis.necrosis.


Generally, bites are not fatal but if the Generally, bites are not fatal but if the venom gets into the bloodstream it may venom gets into the bloodstream it may destroy red blood cells or attack the bone destroy red blood cells or attack the bone marrow, which may lead to fatal marrow, which may lead to fatal complications.complications.


Black widow spiders and the funnel web Black widow spiders and the funnel web spider (one of the world’s most dangerous spider (one of the world’s most dangerous species [naturally it’s from Australia!]) species [naturally it’s from Australia!]) produce potent neurotoxins that affect the produce potent neurotoxins that affect the nervous system.nervous system.

Female Black Widow spider with egg sac


Venom is complex and many components Venom is complex and many components only affect invertebrates, but one only affect invertebrates, but one substance in black widow venom called substance in black widow venom called alpha latrotoxin stimulates cells to release alpha latrotoxin stimulates cells to release neurotransmitters such as acetylcholine. neurotransmitters such as acetylcholine.

Nerves contract uncontrollably and this Nerves contract uncontrollably and this can cause small muscle rigidity and can cause small muscle rigidity and intense, agonizing pain.intense, agonizing pain.


Additional symptoms include nausea and Additional symptoms include nausea and vomiting, increased blood pressure, and vomiting, increased blood pressure, and the heart may begin racing or slowing the heart may begin racing or slowing significantly.significantly.

Brain functions may also be affected Brain functions may also be affected producing anxiety, amnesia, and even producing anxiety, amnesia, and even psychosis.psychosis.


Black widow bites were historically often Black widow bites were historically often associated with outhouses, but now usually associated with outhouses, but now usually occur when working in the fields or clearing junk occur when working in the fields or clearing junk in outbuildings.in outbuildings.

Fatality rates have been estimated at 1-5%, but Fatality rates have been estimated at 1-5%, but this figure certainly is an overestimate as many this figure certainly is an overestimate as many people bitten do not seek medical attention. people bitten do not seek medical attention. Those most at risk are small children and the Those most at risk are small children and the elderly.elderly.


Funnel web spiders (especially the Sydney Funnel web spiders (especially the Sydney funnel web spider) are extremely dangerous. funnel web spider) are extremely dangerous.

Funnel web spiders inject a venom whose lethal Funnel web spiders inject a venom whose lethal component is called atrotoxin. component is called atrotoxin.

The toxin travels in the lymphatic system and The toxin travels in the lymphatic system and binds to nerve endings all over the body where it binds to nerve endings all over the body where it causes nerves to discharge wildly, especially causes nerves to discharge wildly, especially those of the autonomic nervous system.those of the autonomic nervous system.

Funnel web spiders

Funnel web spider burrow site


The constant discharging of the autonomic The constant discharging of the autonomic nervous system results in fever, irregular nervous system results in fever, irregular heart rhythm and wild changes in heart heart rhythm and wild changes in heart rate and blood pressure that can cause rate and blood pressure that can cause respiratory failure, coma and cardiac respiratory failure, coma and cardiac arrest.arrest.

Death may occur anything from 15 Death may occur anything from 15 minutes to 6 days after a bite. minutes to 6 days after a bite.


Work by Dr. Struan Sutherland and Work by Dr. Struan Sutherland and colleagues in Melbourne has led to colleagues in Melbourne has led to success in treating funnel web spider bites success in treating funnel web spider bites and greatly reduced mortality. and greatly reduced mortality.

Dr Sutherland pioneered the use of Dr Sutherland pioneered the use of pressure bandages to prevent the pressure bandages to prevent the spreading of the venom and led the team spreading of the venom and led the team that developed successful antivenins.that developed successful antivenins.

Phylum Arthropoda The Arthropoda (from the Greek Arthron, joint and podus, foot) are the largest...

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Transcript of Phylum Arthropoda The Arthropoda (from the Greek Arthron, joint and podus, foot) are the largest...