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Arthropods. Insects were a winning combination. Insects cause hugh economic losses (but a lot of benefits, as well) each year They are the dominant group of animals on the earth today The diversity of insects is far greater than all other taxa combined

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insects were a winning combination
Insects were a winning combination
  • Insects cause hugh economic losses (but a lot of benefits, as well) each year
  • They are the dominant group of animals on the earth today
  • The diversity of insects is far greater than all other taxa combined
  • There are an estimated 200 million insects alive for every human today
characteristics of arthropoda
Characteristics of Arthropoda
  • Arthropods includes spiders, scorpions, ticks, mites, crustaceans, millipedes, centipedes, insects, and some smaller groups as well
  • There is a rich fossil record extending back to the mid-Cambrian period
  • Arthropods have a well-developed organ system and a chintinizedcuticular exoskeleton
  • Segments have coalesced into tagmata
  • They range in size from .1 mm to 13 feet!
  • Arthropods compete with us for food and spread disease; they also produce silk, honey, and beeswax
ecological relationships
Ecological Relationships
  • They are found in all environments and virtually all altitudes and latitudes
  • Species are adapted to land and to fresh, brackish, and marine water
  • Most species fly to their favored habitats
  • All modes of feeding occur among arthropods though the majority are herbivorous
  • Nothing else matches their divesity
characteristics of the arthropoda
Characteristics of the arthropoda
  • An exoskeleton with a cuticle that is highly protective but is jointed, providing mobility
  • Both layers of the cuticle contain chitin bound with protein
  • Chitin is a tough resistant polysaccharide insoluble in water
characteristics of the arthropoda1
Characteristics of the arthropoda
  • Terrestrial arthropods use an efficient tracheal system that delivers oxygen directly to cells
  • Aquatic arthropods respire by various forms of efficient gills
  • Arthropods have highly developed sensory organs
    • Sensory organs vary from a compound mosaic eye to other senses of touch, smell, hearing, balancing and chemical reception
segmentation and appendages
Segmentation and Appendages
  • Each segment usually has a pair of jointed appendages
  • Segments and appendages are modified for various adaptive functions
  • Appendages may function in sensing, food handling, walking or swimming
characteristics of the arthropoda2
Characteristics of the arthropoda
  • As the cuticle is thin between segments, it allows movement at the joints
  • Muscles attach to the cuticle
  • The cuticle also folds inward to line the foregut, hindgut, and the trachea
  • Ecdysis, or molting, is the process of shedding its outer exoskeleton
  • Arthropods usually molt 4 to 7 times; the weight of the exoskeleton limits their body size
taxonomy of the arthropods
Taxonomy of the arthropods
  • There are four subphyla:
    • Trilobita
    • Chelicerata
    • Crustacea
    • Uniramia
subphylum trilobita
Subphylum Trilobita
  • Trilobita arose before the Cambrian, flourished, and then became extinct 250 million years ago
  • They have a trilobed body shape due to a pair of longitudinal grooves
  • They were bottom dwellers and probably were scavengers
  • They ranged from an inch to 20 inches or more and could roll up like pill bugs
subphylum chelicerata
Subphylum Chelicerata
  • Include the horseshoe crabs, spiders, ticks, mites, scorpions, and sea spiders
  • Chelicerates have six pairs of appendages including chelicerae, pedipalps and four pair of legs
  • They lack mandibles and antennae
  • Most suck liquid food from prey
class merostomata
Class Merostomata
  • Includes the modern horeshoe crab; Limulus polyphemus
  • This species is nearly unchanged from its Cambrian ancestors
  • Five species in three genera survive
the horseshoe crab
The Horseshoe Crab
  • Most live in shallow water
  • They have an unsegmented carapace that covers the body in front of a broad abdomen
  • A telson or spinelike tail
  • Book gills are exposed on some of the abdominal appendages
  • They walk with their walking legs and swim with abdominal plates
  • They feed at night on worms and small molluscs
class pycnogonida the sea spiders
Class Pycnogonidathe sea spiders
  • They vary from a few millimeters to centimeters; all have small, thin bodies
  • Some males use legs to carry developing eggs
  • The mouth at the tip of a proboscis, drinks juices from cnidarians (hydroids) and soft-bodied animals
  • They have a greatly reduced abdomen attached to an elongated cephalothorax
class arachnida
Class Arachnida
  • Consists of a great diversity among scorpions, mites, ticks, daddy longlegs and others
  • Of 80,000 species, most are free living and more common in warm, dry regions
  • Arachnids are dived into a cephalothorax and abdomen
order araneae the spiders
Order Araneaethe spiders
  • About 40,000 species of spiders are known
  • The body consists of an unsegmentedcephalothorax and abdomen joined by a slender pedicel
order araneae the spiders1
Order Araneaethe spiders
  • The anterior appendages are a pair of chelicerae with terminal fangs
  • All spiders are predaceous, mostly on insects, which are killed b poison and fangs
  • The injected venom liquefies and digests the tissues which are then sucked into the spider’s stomach
  • Spiders breath by book lungs and/or trachae
characteristics of the spiders
Characteristics of the spiders
  • Book lungs are found only in the spiders; parallel air pockets extend into a blood-filled chamber
  • Air enters the chamber through a slit in the body wall
  • The tracheae system is less extensive than in insects; it carries air directly to tissues
  • Spiracles are openings to the trachea
  • Most spiders have eight simple eyes, each with a lens, optic rods and a retina
  • They detect movement and may for images
  • Sensory setae detect air currents, web vibrations, and other stimuli
web spinning habits
Web-spinning Habits
  • Spinning silk is a critical ability for spiders and some other arachnids
  • Two or three pairs of spinnerets contain microscopic tubes that run to silk glands
  • A liquid protein secretion hardens as it is extruded from the spinnerets
  • Silk threads are very strong and will stretch considerably before breaking
  • Spiders are often camouflaged or cryptic
web spinning habits1
Web-spinning Habits
  • Jumping spiders (Salticidae) have excellent vision and stalk their prey
  • Silk is used for orb webs, lining burrows, forming egg sacs, and wrapping prey
  • Wolf spiders, jumping spiders, and fisher spiders chase and catch their prey
reproduction in spiders
Reproduction in spiders
  • Males court females before mating
  • The male spins a small web, deposits a drop of sperm on it, and then stores the package in his pedipalp
  • Mating involves inserting the pedipalps into the female genital openings and depositing the spermatophore
  • Sperm are stored in a seminal receptacle for weeks or months until the eggs are ready
  • Eggs may develop in a cocoon in the web or may be carried by the female
  • The young hatch in a few weeks and may molt before leaving the cocoon
venomous spiders
Venomous spiders
  • Most are feared for no reason at all
  • Spiders help to control the populations of insects
  • American tarantulas rarely bite and the bite is not dangerous
  • The black widow (Lactrodectusmactans) however, can be fatal
    • The venom is neurotoxic
  • The brown recluse spider, Loxosceles recluse, has hemolytic venom that destroys tissue around the bite
  • Some Australian and South American Spiders are the most dangerous and aggressive
order scorpionida scorpions
Order Scorpionida: Scorpions
  • More common in tropical and subtropical (such as Florida!) zones but do occur in temperate areas
  • They are nocturnal and feed largely on insects and spiders
  • The short cephalothorax has the appendages and 1 to 6 pair of eyes
  • The postabdomen has the long slender tail of five segments that end in a stinging apparatus
  • Scorpions bear live young carried on the mothers back
order opiliones harvestmen
Order Opiliones: Harvestmen
  • Harvestmen or Daddy longlegs are common, especially in tropical areas
  • Unlike spiders, their abdomen and cephalothorax join broadly without a narrow pedicel
  • They can lose one or mor legs of their eight legs without ill effect
  • Their chelicerae are pincer-like and they feed more as scavengers than do spiders
order acari ticks and mites
Order Acari: Ticks and Mites
  • They are medically and economically the most important arachnids
  • Their mouthparts are on the tip of the anterior capitulum
  • They are both aquatic and terrestrial; some parasitize vertebrates and invertebrates
  • About 40,000 species have been described; many more are estimated to exist
diversity of mites and ticks
Diversity of mites and ticks
  • House mites are free-living and cause allergies
  • Spider mites are one of the many important agricultural pest mites that suck out plant nutrients
  • Chiggers are larval Trombicula mites; they feed on dermal tissues and cause skin irritation
  • The hair follicle mite Demodex is harmless but related species cause mange in domestic animals
  • Ticks are usually larger than mites
  • Tick species of Ixodes carry Lyme disease
  • Tick species of Dermacentor transmit Rocky Mountain Spotted Fever
  • The cattle tick transmits Texas cattle fever
subphylum myriapoda
Subphylum Myriapoda
  • Includes the centipedes, millipedes, pauropods and symphylans
  • Several classes have two tagmata – a head and trunk with paired appendages on the trunk
  • Myriapods only have one pair of antennae, mandibles, and maxillae
  • Legs are always uniramous
  • Respiration occurs through the body surface, trachea, or gills in juveniles
class chilopoda centipedes
Class Chilopoda: Centipedes
  • Centipedes are terrestrial carnivorous predators found under logs, bark and stones eating earthworms, cockroaches and other insects
  • Their flattened bodies have up to 177 segments
class chilopoda centipedes1
Class Chilopoda: Centipedes
  • Each segment, except the one behind the head and the last two, bears a pair of appendages
  • Appendages of the first body segment form venom claws
  • The head has a pair of eyes on either side of the head that consist of groups of ocelli
  • A pair of spiracles in each segment allows air to diffuse through branched air tubes of the trachae
  • The sexes ar separate; all are oviparous and the young resemble the adults
  • One genus of house centipede has 15 pairs of legs and another has 21 pairs
  • Most are harmless to humans but a few large, tropical centipedes are dangerous
class diplopoda
Class Diplopoda
  • Millipedes have many legs, but not a thousand as they are sometimes called
  • Their cylindrical bodies have from 25 to 100 segments
  • Two pairs of legs are present per segment, probably from the fusion of two segments
  • Each abdominal segment has two pair of spiracles opening into air chambers and tracheal air tubes
  • Most eat decayed plants but a few eat living plant tissue
  • After copulation, the female lays eggs in a nest and guards them
  • Larvae have only one pair of legs to each segment
subpylum crustacea
  • 67,000 species include lobsters, crayfish, shrimp, crabs, and copepods
  • Most are aquatic, and free living, many are sessile, commensal, or parasitic
  • The main distinguishing characteristic of crustaceans is that they have two pairs of antennae
  • The head also has a pair of mandibles and two pair of maxillae
subphylum crustacea
Subphylum Crustacea
  • There is one pair of appendages on each of the additional segments; some segments lack appendages
  • All appendages, except perhaps the first antennae, are biramous with two main branches
  • Primitive crustaceans may have up to 60 segments; modern crustaceans have 16-20
  • The tagmata are usually head, thorax and abdomen
  • The dorsal covering is the carapace; it may cover most of the body or just the cephalothorax
form and function of crustacea
Form and Function of Crustacea
  • Crayfish and lobsters show modifications to their appendages
  • Swimmerets retain the primitive biramous condition and consist of an endopod and exopod which are attached to one or more basal segments collectively called a protopod
form and function of crustacea1
Form and Function of Crustacea
  • Crayfish appendages have evolved into walking legs, mouthparts, swimmerets, etc from modification of the basic biramous appendage
    • The evolutionary trend is reduction and modification of appendages
  • Three pairs of thoracic appendages are called maxillipeds; the first pair of walking legs are called chelipeds, and the last pair of appendages are called uropods
form and function of crustacea2
Form and Function of Crustacea
  • Abdominal swimmerets are used in locomotion, the first pair are named gonopods
  • Gonopods in males are modified for copulation; females attach eggs and young to them
  • Uropods serve as paddles for swift backward movement
  • The telson also protects eggs and young on the swimmerets
important internal features
Important Internal Features
  • Major body space is a blood-filled hemocoel
  • Muscular and nervous sysems show the metamerism of annelid-like ancestors
  • Most muscles are antagonistic; flexors draw a limb toward the body and extensors straighten a limb out
  • Abdominal flexors of a crayfish allow it to swim backward
  • Strong muscles located on each side of the stomach control the mandables
the molting process
The molting process
  • Molting is necessary for a crustacean to increase in size; the exoskeleton does not grow
  • The physiology of molting affects reproduction, behavior and many metabolic processes
  • Inorganic salts are withdrawn from the old cuticle during premolt
  • The underlying epidermis secretes the cuticle
  • Enzymes released into the area above the new epicuticle dissolve the old endocuticle
  • The animal then swallows water or air to expand and burst the old cuticle
  • The new soft cuticle stretches and then hardens with the deposition of inorganic salts during postmolt
  • Molting occurs often in young animals and may cease in adults
  • Temperature or day length may trigger molting
feeding habits
Feeding Habits
  • Many crustaceans shift from one type of feeding to another, depending on food availability
  • The same fundamental mouthparts are adapted to a wide array of food availability
  • Mandibles and maxillae ingest food; maxillipeds hold and crush food
  • Suspension feeders generate water currents in order to eat plankton, detritus and bacteria
  • Predators consume larvae, worms, crustaceans, snails and fishes
feeding habits1
Feeding Habits
  • The shrimp-like Lygiosquilla pierces prey with a specialized digit on a walking leg
  • The pistol shrimp Alpheus catches prey with a large chela that snaps shut
  • Scavengers eat dead animal and plant matter
  • Crayfishes have a two-part stomach; a gastric mill grinds up food in the first compartment
internal anatomy of crustaceans
Internal anatomy of crustaceans
  • Gills that vary in shape
  • Excretory and osmoregulatory organs are located in the head
  • Decapods have antennal glands called green glands
  • Waste products consist of ammonia with some urea and uric acid
  • Crustaceans and other arthropods have an open circulatory system; there is no system of veins to separate blood from interstitial fluid
internal anatomy of crustaceans1
Internal anatomy of crustaceans
  • Movement of organs and limbs circulate blood in the open sinuses
  • Hemocyanin and hemoglobin are respiratory pigments; clotting also occurs
  • There is a brain with a double ventral nerve cord
  • A median eye and compound eyes are present
  • The median eye consists of three pigment cups, retinal cells, and possible a lens
  • Crustacean compound eyes are similar to insect eyes
  • Attached to moveable stalks, compound eyes detect motion and analyze polarized lights
  • Statocysts, tactile setae, and chemosensitive setae are also present
reproduction and life cycles
Reproduction and Life Cycles
  • Crustaceans have separate sexes with specializations for copulation
  • Almost all barnacles are monecious but generally cross-fertilize
  • In some ostracods, males are scarce and reproduction is by parthenogenesis
  • Most crustaceans brood eggs in brood chambers, in brood sacs attached to the abdomen, or attached to abdominal appendages
  • Crayfish develop directly without a larval form
  • Most crustaceans have a larva unlike the adult in form, and under metamorphis
  • The Nauplius is a common larval form
brief survey of crustaceans
Brief Survey of Crustaceans
  • Ostracods are enclosed in a bivalve carapace and resemble tiny clams and are less than 1/16 inch long
  • Most live in marine or freshwater sediments but some scavenge or feed on detritus

Copepods have numerous species

  • They lack a carapace and retain the simple, median eye in the adult
  • They have four pairs of flattened, biramous, thoracic swimming appendages
  • Free-living copepods may be the dominant primary consumer in aquatic communities
  • Parasitic forms are highly modified and reduced, often unrecognizable as arthropods

Brachiurans lack gills and most are parasites of fish

  • Found on both marine and freshlwater fish
cirripedia the barnacles
Cirripedia – the barnacles
  • Barnacles as adults are sessile and attach directly or by a stalk to the substrate
  • The carapace surrounds the body and secretes a set of calcareous plates
  • The head is reduced, the abdomen is absent and the thoracic legs are long with hair-like setae
  • The many-jointed cirri that bear the setae are extended from the plates to feed on small particles

Isopods are dorsoventrally flattened, lack a carapace and have sessile compound eyes

  • The abdominal appendages bear gills
  • Common land forms include the sow bugs and pill bugs
  • Some isopods are highly modified as parasites of fish or crustaceans

Amphipods resemble isopods except they are somewhat compressed laterally

  • They lack a carapace and have sessile compound eyes
  • Many are marine, others are beach-dwelling, freshwater or parasitic

Euphausiacidsor “Krill” has only 90 species but includes the important ocean plankton called krill

  • They form a major component of the diet of baleen whales and of many fishes.
  • Some are over 2 inches long

Decapods have five pairs of walking legs, the first forming pincers or chelae

  • They range from a few millimeters to the larges arthropod, a Japanese crab with a 12 foot leg-span
  • They are true crabs with a broader cephalothorax and reduce abdomen, compared to crayfish or lobsters
  • Fiddler crabs have a reduced abdomen and burrow in the sand
  • Hermit crabs are adapted to live in snail shells