Arthropods Flashcards
Where do Arthropods sit in a phylogeny?
A phylum within the super-phylum Ecdysozoa.
Describe water bears/Tardigrada?
Water dwellers.
Can survive extreme temperatures, pressures, space vacuums, radiation, lack of water.
Cryptobiosis (a physiological state in which metabolic activity is reduced to an undetectable level to survive extremely dry conditions).
Describe velvet worms/onychophora?
Convergent, similar to annelids.
Shoot slime from appendages on their heads.
Give birth to live young.
Describe hexapods?
Insects - winged and unwinged.
Beetles, butterflies, moths, ants, wasps and bees, flies.
30 million species
Some undergo metamorphosis
Describe myriapods?
Centipedes and millipedes.
Centipedes have an odd number of leg pairs, poison fanged and nocturnal active hunters.
Millipedes eat rotting vegetation and wood. Secrete noxious chemicals as a defence mechanism.
Describe Chelicerates?
Ticks and mites, Scorpions and spiders.
Named due to their chelicerate appendages.
Independent invasion of land to insects.
Describe Trilobites
They were abundantly and widely distributed in the sea.
Extinction due to competition with crustaceans and predation pressure from early fish.
Describe Crustaceans?
Lobsters, Crabs, Crayfish, Shrimp, Krill, Barnacles, and Woodlice.
Key link between primary producers and higher level consumers in marine ecosystems.
Paraphyletic group as hexapods evolved from a crustacean ancestor. Solved with use of pancrustaceans.
Key anatomy of Arthropods?
Segmentation
Jointed appendages
Exoskeleton
Hemocoel - circulation fluid
Ventral nervous cord
Brains
Segmentation of arthropods?
Common ancestor of arthropods had a series of similar segments.
Segments in extant derived taxa are often fused and/or lost. Some have become specialised - heteronomous.
All arthropods group segments to form a head. Specialised for feeding, sensing and neural integration.
Chelicerates fuse head with thorax to produce a cephalothorax.
Most divide rest of the body into a thorax and abdomen region.
What is tagmosis?
Grouping of segments with similar functions/segments.
Appendages in arthropods?
Arthropod ancestor had an appendage on each segment.
Evolved a wide range of specialised paired appendages:
head: feeding and sensing
others: locomotion, reproduction, respiration, food manipulation
Jointed appendages - joints allow articulation despite hard exoskeleton.
Flexible cuticle at the joint allows bending.
Antagonistic muscles control joint movement.
Exoskeleton in arthropods?
The cuticle provides support, maintains shape, allows joint articulation and provides protection against pathogens and mechanical forces.
Made of chitin - polysaccharide.
Moulting in arthropods?
To permit growth, the cuticle must be periodically moulted - ecdysis.
Stages: 1. Pre moult Detach old cuticle and develop new cuticle 2. Moult Shed old cuticle 3. Post moult Harden new cuticle 4. Inter moult 10% of arthropod life
Which arthropods act as parasites?
Ticks Mites Flies Fleas Lice Crustaceans
Mainly ectoparasites
What body segments do chelicerates have?
Cephalothorax and abdomen.
Arachnid body features?
Fused cephalothorax with carapace
Pedipalps (short at front, used for feeding or inseminating females)
Book lungs
4 pairs of legs
Carnivorous with liquid diet
Spider features?
Silk
Pedicel (waist)
Poison glands
Sperm transfer via pedipalp.
How many times has silk evolved?
23 times
What are the pedipalps?
On all arachnids.
Used for feeding and inseminating females.
Gives out digestive enzymes, sucks in liquid using pumping stomach.
Chelicerae are the only form of teeth, and are hardened with zinc ions to make them harder than other arthropods’ exoskeletons.
Silk in spiders?
Spider silk is stronger than any other known natural/synthetic fiber on Earth.
Ballooning is a behaviour in which spiders and some other invertebrates use airborne dispersal to move between locations. A spider (usually limited to individuals of a small species), or spiderling after hatching, will climb as high as it can, stand on raised legs with its abdomen pointed upwards (“tiptoeing”), and then release several silk threads from its spinnerets into the air. These automatically form a triangular shaped parachute which carries the spider away on updrafts of winds where even the slightest of breezes will disperse the arachnid.
Before entering the duct, the silk consists of liquid proteins. When entering the duct, cells raw water away from the silk proteins. Hydrogen is pumped into another part of the duct, creating an acid bath.
The unspun silk transforms from a gel into a final solid fiber as it is pulled through the acidic silk strands (spinnerets).
Spiders usually have 2-8 spinnerets.
Spiders are vibration specialists. Have both air borne and substrate borne vibration sensors present in large numbers on all 8 legs.
Main features of crustaceans?
Mainly marine, but also freshwater and terrestrial.
Large variation in morphology.
Moulting
Body composed of head, thorax and abdomen.
Carapace (hard upper shell).
Gas exchange by gills
