Phylum Onychophora Phylum Onychophora: Velvet worms, Peripatus. All modern Onychophorans are terrestrial but fossils, which date back to the Cambrian, are mainly from marine sediments. Onychophorans look a bit like slugs with legs and when first described in 1825 were thought to be mollusks. However, now placed at the base of the Arthropod family tree.
Phylum Onychophora About 10 genera and approximately 110 species cm in length. Geographically widely distributed in suitable moist, humid habitats such as tropical (e.g. Congo, northern South America, Himalayas) and southern temperate forest (e.g. New Zealand, Australia, South Africa, Andes). Limited habitat distribution (and exclusively nocturnal behavior) related to problem of water loss. Like other arthropods, Onychophorans have a chitinous cuticle, which is molted as they grow, but it is thin and flexible, non-waxy and permeable.
Phylum Onychophora Onychophorans do not have jointed legs, but possess other arthropod characteristics including a reduced coleom and a hemocoel. The pairs of legs are large and conical with terminal pads and claws. They move using their legs and by extending and contracting the body.
Phylum Onychophora Most are predators and use glue which they can spray from a pair of oral papillae to catch their prey. They can spray two streams of glue up to 50cm and this hardens almost immediately trapping the prey in a net of sticky threads.
Phylum Onychophora Peripatus video 3 minutes SiH-Vw
Phylum Arthropoda The Arthropoda (from the Greek Arthron, joint and podus, foot) are the largest group of organisms and they occur in all environments on earth. The group includes: spiders, ticks, mites, centipedes, millipedes, crustaceans, insects and others.
Characteristics of the Arthropoda Bilaterally symmetrical with a segmented (metameric) body divided into head, thorax and abdomen; cephalothorax and abdomen; or fused head and trunk.
Characteristics of the Arthropoda Jointed appendages. Primitively one pair per segment, but number often reduced. Appendages often greatly modified for specialized tasks.
Characteristics of the Arthropoda Exoskeleton of cuticle. Exoskeleton secreted by underlying epidermis. Made of chitin, protein, lipid and often calcium carbonate. Exoskeleton is shed periodically (ecdysis) as the organism grows.
Characteristics of the Arthropoda Muscular system is complex and muscles attach to the exoskeleton. Striated muscles for voluntary movement and smooth muscles for the viscera. Coelom is reduced. Most of body cavity is a hemocoel (sinuses or spaces) filled with blood.
Characteristics of the Arthropoda Complete digestive system. Mouthparts are specialized being modified from appendages and specialized for dealing with various types of food. Open circulatory system with a dorsal contractile heart arteries and hemocoel.
Characteristics of the Arthropoda Respiration occurs in multiple possible ways across the body surface across the body surface via a system of tracheal tubes (e.g. beetle) via a system of tracheal tubes (e.g. beetle) Gills (e.g. crabs) Gills (e.g. crabs) book lungs (spiders) book lungs (spiders)
Horseshoe crab book gills
Characteristics of the Arthropoda Nervous system is similar to that of annelids. A dorsal brain connected via a ring around the pharynx to a double ventral nerve cord.
Characteristics of the Arthropoda Sexes are usually separate with internal fertilization. Can be oviparous or ovoviviparous. Offspring often go through process of metamorphosis. Parthenogenesis (reproduction without fertilization) occurs in a some species (e.g. aphids).
Classification of the Arthropoda Subphylum Chelicerata Class Merostomata Class Merostomata Subclass Xiphosurida: Horseshoe crabsSubclass Xiphosurida: Horseshoe crabs Class Pycnogonida: sea spiders Class Pycnogonida: sea spiders Class Arachnida: spiders, scorpions, ticks, mites, harvestmen, whip scorpions. Class Arachnida: spiders, scorpions, ticks, mites, harvestmen, whip scorpions.
Subphylum Chelicerata Body is divided into two tagmata (fused segments) head and abdomen. Six pairs of appendages: a pair of chelicerae, first pair of appendages used for feeding. a pair of chelicerae, first pair of appendages used for 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.
Subphylum Chelicerata The chelicerates are a very ancient group that includes the extinct Eurypterids (giant water scorpions ( mya), which were the largest known arthropods reaching up to 3m long.
Eurypterus (left) from the Silurian of New York State. Eurypterus remipes was voted the New York state fossil in Mixopterus (right) from the Devonian reached about one meter in length
Subphylum Chelicerata Subclass Xiphosurida: Horseshoe crabs. These are an ancient group that date from the Cambrian ( mya). Five living species. Limulus, which lives in shallow waters on the Atlantic coast of the U.S. is almost unchanged since the Triassic ( mya).
Subphylum Chelicerata: Horseshoe crabs Horseshoe crabs have an unsegmented carapace, which is sort of horseshoe shaped, hence the name. There is also a wide abdomen with a long spinelike tailpiece (telson). Flat leaf-like gills, called book gills, are present on the underside.
Horseshoe crabs Horseshoe crabs feed on foods such as worms and molluscs, such as clams, which brings them into conflict with fishermen. The synchronized breeding of horseshoe crabs which 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 summer. The eggs produced in the millions are an important food source for migrating shorebirds such as Knot, which flock to areas such as the Delaware Bay to fatten up for migration.
Horseshoe crabs Horseshoe crabs are harvested commercially for bait and also for their blood, which is used in laboratory testing for endotoxins in medical products. Currently, the horseshoe crab is at the center of a series of legal battles about the size of harvests and their sustainability.
Subphylum Chelicerata: Class Pycnogonida: sea spiders Another name used for these animals is Pantopoda (“all legs”), which is an excellent description. The body is greatly reduced in size, whereas the legs are long and clawed. In some species modified legs called ovigers are used by males to carry egg masses. There is a long proboscis on the head, which the pycnogonid uses to feed on soft-bodied invertebrates, especially cnidarians.
Class Pycnogonida: sea spiders Most pycnogonids are small being only a few millimeters long, but a few reach 70cm measured by leg spread. Pycngonids are exclusively marine (occuring from the intertidal to the deep seas) and there are about 1000 species.
Subphylum Chelicerata: Class Arachnida: Order Aranae: spiders Spiders are a very large group with more than 35,000 described species that occur worldwide except in Antarctica. The body is divided into a cephalothorax and an abdomen. Spiders breathe using book lungs or tracheae. Book lungs are unique to spiders and consist of a large number of air pockets extending into a blood-filled chamber. Tracheae are tubules that carry air directly from outside to tissues. They can be closed to prevent excessive water loss.
Spiders Spiders and insects have an excretory system that uses structures called Malphigian tubules. Potassium, other salts, and other waste solutes drain into these tubules, which empty into the intestine. Rectal glands selectively reabsorb most of the potassium and water leaving behind nitrogenous wastes in the form of uric acid, which requires little water for its excretion.
Spiders Most spiders possess eight eyes (some have a few as two), but their image forming ability is limited. Hairlike setae, however, provide a lot of information about the environment sensing e.g. vibrations and air currents
Spiders All spiders are predators and their chelicerae function as fangs. The fangs are connected via ducts to venom glands that produce a lethal venom the spider uses to dispatch its prey. After killing a prey item the spider injects digestive fluid into the organism and sucks up the resulting soup.
Spiders Spiders use a variety of techniques to catch prey. Some chase their prey or leap on it, some ambush prey often using trip wires, and, of course, many use webs.
One small group, the bolas spiders, capture their prey by deception. AzvbI&list=PLr96eNfxmgJRv9AlzVs35Qm ybWaKUlPsb AzvbI&list=PLr96eNfxmgJRv9AlzVs35Qm ybWaKUlPsb AzvbI&list=PLr96eNfxmgJRv9AlzVs35Qm ybWaKUlPsb Bolas spider 2’55”
Bolas spiders Bolas spiders at night spin a line of thread with a sticky globule the bolas (akin to the bolas used by South American Gauchos to hunt) at the free end. The bolas contains pheromones which attract certain male moths which think they are approaching a female. When the spider senses the vibrations in the air caused by a nearby flying moth it twirls its bolas in response. Once the bolas strikes the moth it sticks and the moth is hauled in.
Gladiator spider The gladiator spider throws a net of silk to catch its prey KMi0I&list=PLr96eNfxmgJRv9AlzVs35Qm ybWaKUlPsb KMi0I&list=PLr96eNfxmgJRv9AlzVs35Qm ybWaKUlPsb KMi0I&list=PLr96eNfxmgJRv9AlzVs35Qm ybWaKUlPsb 2 min
Silk-spinning Spiders spin silk, which they use to make webs to trap prey. Webs come in a variety of shapes and sizes and contain and are coated with an adhesive that holds prey. Webs are typically placed in insect flyways and the spider sits and waits for an insect to become entangled. The vibrations of the struggling prey signal the spider to emerge and dispatch it.
Silk-spinning The silk is produced by two or three spinnerets, which are connected to abdominal silk glands. The silk is formed from a protein secretion that hardens on contact with air. The silk is extremely strong (stronger e.g. than steel of equivalent weight) and is being used as a kevlar substitute. Unlike steel, silk can stretch which makes it an extremely useful material.
Web building WdQao WdQao WdQao 3 minutes
Silk-spinning The silk is used to make webs, but also for a variety of other purposes: Line nests Line nests Form egg sacs Form egg sacs For dispersal by ballooning For dispersal by ballooning To wrap prey To wrap prey
Reproduction in spiders Courtship rituals are a major feature of spider mating in which the (usually much smaller) male attempts to mate without being eaten by the female. Males produce a sperm packet wrapped in silk which he holds in a cavity in one of his pedipalps (second pair of appendages).
Reproduction in spiders The male, if he lives long enough, inserts a pedipalp into a female’s genital opening and she stores the sperm in a seminal vesicle. The female later fertilizes eggs when she is ready to lay them. Eggs are laid in a silk cocoon where the young hatch and remain for a short time and molt before departing for an independent life.
Toxic spiders The vast majority of spiders are harmless to humans, but a handful are toxic and potentially deadly. In the U.S. there are a few venomous spiders: several black widow species (genus Latrodectus), the brown recluse (Loxosceles reclusa) and the hobo spider (Tegenaria agrestis) introduced from Europe to the Pacific Northwest.
Toxic spiders Spiders eat a liquid diet by injecting digestive juices into their prey and some spider venoms contribute to this process by destroying tissue. Bites of such spiders can lead to tissue necrosis. This is the type of venom possessed by the hobo and brown recluse spiders.
Hobo spider Brown recluse spider
Toxic spiders A bite from one of these spiders results in a bite site that develops a painful ulcer where tissue dies (necrosis) and in the case of hobo spiders severe headaches. One component of brown recluse venom is sphingomyelinase D which attacks and dissolves cell membranes.
“Many medical conditions are mistaken for brown recluse bites. The wound on the left is from a brown recluse spider, the one on the right from a bacterial infection.”
Toxic spiders Sphingomyelinase D and other components in the venom apparently also turn on the patient’s inflammatory defenses against his or her own tissues. White blood cells destroy themselves releasing other enzymes that attack the victim’s own flesh and blood clots form in tiny vessels cutting off the blood supply to the bite area and causing necrosis.
Toxic spiders Generally, bites are not fatal but if the venom gets into the bloodstream it may destroy red blood cells or attack the bone marrow, which may lead to fatal complications.
Toxic spiders Black widow spiders and the funnel web spider (one of the world’s most dangerous species [naturally it’s from Australia!]) produce potent neurotoxins that affect the nervous system.
Female Black Widow spider with egg sac
Toxic spiders Venom is complex and many components only affect invertebrates, but one substance in black widow venom called alpha latrotoxin stimulates cells to release neurotransmitters such as acetylcholine. Nerves contract uncontrollably and this can cause small muscle rigidity and intense, agonizing pain.
Toxic spiders Additional symptoms include nausea and vomiting, increased blood pressure, and the heart may begin racing or slowing significantly. Brain functions may also be affected producing anxiety, amnesia, and even psychosis.
Toxic spiders Black widow bites were historically often associated with outhouses, but now usually occur when working in the fields or clearing junk in outbuildings. Fatality rates have been estimated at 1-5%, but this figure certainly is an overestimate as many people bitten do not seek medical attention. Those most at risk are small children and the elderly.
Toxic spiders Funnel web spiders (especially the Sydney funnel web spider) are extremely dangerous. Funnel web spiders inject a venom whose lethal component is called atrotoxin. The toxin travels in the lymphatic system and binds to nerve endings all over the body where it causes nerves to discharge wildly, especially those of the autonomic nervous system.
Funnel web spiders Funnel web spider burrow site
xIMURc xIMURc xIMURc Sydney funnel web spider 4’30”
Toxic spiders The constant discharging of the autonomic nervous system results in fever, irregular heart rhythm and wild changes in heart rate and blood pressure that can cause respiratory failure, coma and cardiac arrest. Death may occur anything from 15 minutes to 6 days after a bite.
Toxic spiders Work by Dr. Struan Sutherland and colleagues in Melbourne has led to success in treating funnel web spider bites and greatly reduced mortality. Dr Sutherland pioneered the use of pressure bandages to prevent the spreading of the venom and led the team that developed successful antivenins.
Subphylum Chelicerata: Order Scorpionida: Scorpions There are about 1,500 species of scorpions and the group includes some of the largest of the arachnids as some scorpions reach up to 18cm in length. Scorpions are best known for their prominent front claws, which are modified pedipalps and their stinging tail, with which they inject venom.
Scorpions Scorpions have a body that consists of a quite short cephalothorax, which bears 4 pairs of walking legs and a long, segmented abdomen which is divided into a thick preabdomen and a thinner postabdomen that carries the stinging apparatus.
Giant desert hairy scorpion by Rhonda Spencer
Scorpions Scorpions glow when a black light (UV light) is shone on them. This is because the cuticle contains a variety of fluorescent compounds. This characteristic makes nocturnal surveys of scorpions quite easy.
Scorpions Scorpions occur on all continents except Antarctica. They are commonest in tropical and subtropical areas, but some occur in colder areas including high mountain tops.
Scorpions Scorpions are generally secretive and hide from potential predators during the day in crevices before emerging to feed at night on insects and similar prey. The largest species may kill small reptiles and mammals. Scorpion’s liking for dark places to hide is why it’s important to shake out your shoes in the morning in scorpion country.
Feeding Scorpion pincers are covered in highly sensitive hairs and respond quickly to prey that brush against them. Prey is gripped with the pincers (pedipalps) and either crushed or stung to death. Scorpions consume only liquids so the prey is torn into tiny pieces using the jawlike chelicerae and predigested in a pre-oral cavity below the chelicerae until it liquifies and is then consumed.
Scorpion toxicity The venom of most species of scorpions is not harmful to humans, but that of some African species and some found in Mexico and the southwestern U.S. can be fatal. In all about 25 species are potentially dangerous to humans. The venom is a mix of compounds that includes neurotoxins and enzyme inhibitors. One short chain scorpion toxin is known to block K + channels in cell membranes.
Scorpions Because scorpions have a low metabolic rate and are relatively inactive they can go for long periods between meals. Some species can survive 6-12 months of starvation.
Scorpion courtship Most scorpions reproduce sexually although a few species are known to reproduce parthenogenetically. There is a complex courtship ritual in which the male grips the females claws and dances with her as he attempts to maneuver her over a spermatophore he has produced.
Scorpions Scorpions are viviparous (give birth to live young) and these stay with their mother and ride on her back until they undergo their first molt. They depend on their mother for protection and to regulate humidity levels. The young go through 5-7 molts (instars) before reaching maturity.
Order Uropygidi: whip scorpions and Order Amblypygi: tail-less whip scorpions The members of these two groups are similar in appearance to scorpions, but lack the stinging apparatus in the tail. The abdomen of these organisms either ends in a long tail [which has a sensory function] or there is no tail (hence the common names of the two groups).
Amblypygid (bottom left and below) Uropygid (left)
Order Uropygidi: whip scorpions and Order Amblypygi: tail-less whip scorpions Uropygids are often called vinegaroons because they can spray an acidic solution from their tails. Both groups are predatory and there are about 100 described species of Uropygids and about 130 species of Amblypygids. Both groups are found in tropical and subtropical areas and a few species occur in the southern U.S.
Uropygids and Amblypygids Both groups use 6 legs for walking the first pair having been modified into antennae- like sensory organs. Both groups are carnivorous nocturnal hunters that feed mostly on insects and other arthropods.
Uropygids and Amblypygids Many behaviors of Uropygids and Amblypygids are similar to those of scorpions. They avoid light as do scorpions, hide in crevices and the young travel on their mother’s back when small
Subphylum Chelicerata: Order Opiliones: harvestmen Harvestmen or “daddy longlegs” are common and easily separated from spiders by a number of features: Their abdomen and cephalothorax are not separated by a narrow “waist” or pedicel as they are in spiders. Their abdomen and cephalothorax are not separated by a narrow “waist” or pedicel as they are in spiders. They usually have extremely long thin legs. They usually have extremely long thin legs. They cannot spin silk. They cannot spin silk. They have only two eyes rather than then the eight of spiders. They have only two eyes rather than then the eight of spiders.
Harvestmen The chelicerae of harvestmen are pincerlike and they use them to catch small insects and also commonly scavenge dead items. Unlike spiders they can eat solid food There are about 6400 described species.
Harvestmen Most harvestmen reproduce sexually although pathenogenesis occurs in some species In some species the male guards the female after mating and in others the male defends a territory where females come to lay eggs. The male tends the eggs until they hatch and defends the eggs against predators including females who come to lay.
Subphylum Chelicerata: Order Acari: ticks and mites The members of the Acari differ from the other Arachnids in that their cephalothorax and abdomen are completely fused with no evidence of a division between the segments. The mouthparts are mounted on a small projection called a capitulum.
Ticks and mites An estimated 25,000 species of Acarines occur worldwide in a wide variety of habitats on the ground, in vegetation, in freshwater and marine habitats often as ectoparasites. The group includes a number of major pests including spider mites, which are serious agricultural pests, chiggers and ticks which are ectoparasites and spread a variety of unpleasant diseases.
Disease carrying ticks Ticks are usually bigger than mites and feed on the blood of vertebrates. They wait on vegetation until they sense the presence of a suitable host and then grasp on. They will attach by inserting their chelicerae and a feeding tube called a hypostome and generally feed for several days (increasing enormously in size) and eventually drop off.
Disease carrying ticks Once a tick drops off it will digest its meal and molt before feeding again. Because they feed on blood, ticks, like mosquitoes, are major vectors of disease.
Disease carrying ticks A wide variety of diseases are tick borne, with ticks being second only to mosquitoes in the variety and seriousness of the conditions they spread. Diseases spread include Rocky Mountain spotted fever, tularemia, red-water fever and best known of course Lyme Disease.
Lyme Disease Lyme Disease (named for Lyme Connecticut where it was first described from) is caused by a bacterium Borrelia burgdorferi. Symptoms of Lyme disease, which is spread by the bite of a deer tick, include fever, headache, fatigue, and a diagnostic skin rash called erythema migrans, which has a bull’s eye appearance.
Lyme Disease If not treated, an infection with Borrelia burgdorferi can spread to the joints producing arthritis-like symptoms as well as to the heart, and nervous system, which may result in facial palsy. Lyme disease can be treated with antibiotics if caught early enough. Prompt removal of ticks from clothing and of attached ticks is important in avoiding infection.
Commensal mites A variety of mites live commensally with us including tiny species that live in hair follicles especially around the nose and eyes. These mites (<0.4mm long) are vaguely wormlike having quite long bodies and live head down in follicles feeding on dead skin cells and secretions.
Eyelash mites. Above left: three embedded head down in a follicle; above right an individual Demodex folliculorum and right close up of the anterior end.
Commensal Mites In addition to follicle mites, dust mites are extremely common and feed on the dead flakes of skin that we shed every day (that’s what most dust is). Your pillow is home to thousands of them!
Chiggers Chiggers are tiny mites (< 0.05 mm long), but cause skin irritations out of all proportion to their size. Chigger larvae climb on to vegetation and wait to hitch a ride on a passing animal. The larva pierces the skin and injects a salivary secretion of powerful, digestive enzymes that break down skin cells into a liquid, which the chigger ingests.
Chiggers The digestive enzymes also causes the surrounding tissue to become harder, which generates a feeding tube (called a stylostome) of hardened flesh through which more semi- digested skin cells are consumed. After about four days the larva finishes feeding and drops off its host, leaving behind a red welt that itches severely. Although very irritating U.S. chiggers do not spread disease.