Arthropods I Flashcards
Describe the classification of the Ecdysozoa
superphylum
Which subphyla do the Ecdysozoa contain?
- Panarthropoda
- Nematoda
- Nematomorpha
- others
Describe the Panarthropoda
- Tardigrada
- Onychophora
- Arthropoda
Describe the Arthropoda
- emerged approximately 540Mya
- 80% of all known animals
Describe the arthropod common ancestor
- homonomous
- tagmosis
Homonomy
a series of similar segments, with one appendage on each segment
Give the key characteristics of the extant arthropods
- segmentation
- jointed appendanges (the terminal of which is termed the telson), and an exoskeleton.
Describe arthropod segmentation - the basics
- some have been specialised (sometimes in pairs)
- some have been fused or lost in heteronomy
Heteronomy
segmentation remains apparent during embryonic development, but not in adult form
Describe arthropod segmentation - the basics
- intersegmental articulation
- tagmosis
Describe intersegmental articulation
the segmentation of appendages
Describe tagmosis
grouping of segments with similar functions or structure
Describe jointed appendages
- allows for bending between appendage articles through a flexible cuticle of the continuous exoskeleton at the joint
- evolutionary innovation that overcomes the hard exoskeleton
Describe the mechanism of jointed appendages
to control hinged appendage movements, the antagonistic flexor and extensor muscles allow for lateral movement between sclerites, and protractor and retractor muscles allow for extension and retraction.
Describe tagmosis
- evolved independently in the insect, crustacean and chelicerate groups
- most arthropods exhibit some form of division tagmosis into the thorax and abdomen, where some develop a trunk
- often specialised for other key life history functions, such as locomotion, reproduction, respiration and food manipulation
Describe the ubiquitous tagmosis within the arthropods
is the head, creating a specialised region for feeding, sensing and neural integration.
Give an example of tagmosis
Chelicerates fuse their head and thorax segments to form a tagmosed cephalothorax.
Describe the chitinous exoskeleton
- integral to joint articulation
- necessary for support provision and shape maintenance, as well as pathogen and injury protection
- diverse properties, from stretchy tendons to hard carapace shells
Describe sclerotisation
tanning leads to cross-linking within the exoskeleton; enhanced strength
Describe the evolutionary constraints of the exoskeleton
- lack of flexibility prevents dyanmic growth
- ecdysis process
Describe ecdysis
- periodic moulting of the cuticle to allow for growth
- multi-staged process
Describe the process of ecdysis
1) pre-moult
2) moult
3) post-moult
4) inter-moult growth phase
Describe pre-moult
the old cuticle is detached and the new cuticle developed
Describe moult
the old cuticle is shed
Describe post-moult
- new cuticle hardens
- increased vulnerability associated pre-sclerotisation
- 80-90% of arthropod mortality
Describe inter-moult growth phase
can make up as a little as an approximate 10% of an arthropod’s life history
Describe the evolutionary advantages of moult
- contiunuouation of the exoskeleton for protection
- facilitating growth to increase body size
- explains why the majority of the arthropod’s life history is spent in-moult
Describe the taxonomic classification of the Arthropoda (Regier et al., 2010)
- four extant Subphyla: the Hexapoda, the Myriapoda, the Crustacea and the Chelicerata
- one extinct subphylum, the Trilobites
How many species does the Hexapoda contain?
> 800k species
How many species does the Myriapoda contain?
16k species
How many species does the Crustacea contain?
67k species
How many species does the Chelicerata contain?
85k species
Describe the Hexapoda
winged insects, as well as other wingless arthropod groups
Describe the winged insects
- 30 million species
- 5 Major Orders: ants, Coleoptera, Lepidoptera, Diptera, and bees and wasps
- metamorphosis
Coleoptera
beetles
Lepidoptera
butterflies and moths
Diptera
flies
Describe the basics of metamorphosis
- either complete or incomplete
- requires a moulting stage to reach sexual maturation
Describe incomplete metamorphosis
demonstrating a nymphal stage
Describe the Crustacean subphylum
- huge morphological diversity
- mostly marine
- some species able to exist in freshwater and terrestrial environments
- the key trophic link in marine ecosystems between primary producers and higher level consumers. - ten million tonnes of krill eaten and consumed each year
Give the 6 Major Orders in the Crustacea
- barnacles and woodlice
- crabs
- crayfish
- krill
- lobsters
- shrimp
Describe the Myriapod Subphylum
- two Major Orders: the centipedes and and the millipedes
- segmentation forms a head and trunk region with a single specialised antennae appendage and an open trachaea
Describe the centipedes
- approximtely 2.8k species
- always have an odd number of legs
- nocturnal active hunters
- structurally specialised poison claw on the first trunk segment
- modified anal legs on the last trunk segment
Describe the millipedes
- saprotrophs
- secrete defensive toxic chemicals
- diplosegments – two legs per segment
Describe the open trachea structure of Myriapods
constrained to humid environments.
Describe the anal legs of the centipedes
not locomotory, used for defence
Describe the Chelicerata
- chelicerae
- independently invaded and radiated various dry land habitats
- characteristic segmentation: two body segments (the cephalothorax and the abdomen)
- compound eyes
chelicerae
specialised pincer mouthpart appendages
Describe the 5 Major Subphyla of the Chelicerata
- Acari (mites and ticks)
- Araneae (spiders)
- Scorpiones (scorpions)
- Pycnogonida (sea spiders)
- Xiphosura (horse shoe crabs)
Describe the Arachnids - the basics
- pedipalps
- box lungs
- four pairs of legs
- spinnerets
- liquid carnivory
Pedipalps
specialised appendages associated with the head
spinnerets
modified appendages at the abdomen terminus
Box lungs adaptations
extraordinarily high SA
liquid carnivore adaptations
lack of mouthparts associated with solid food
Describe the Arachnids - the specifics
- approximately 40k species of spider
- not particularly trophically diverse: almost exclusively predatory or parasitic
- pedipalps for sperm transfer
- innovated poison glands, some of which have been lost secondarily
What is the most important innovation of the Arachnids
- silk
- composition varies across species
- multi-optimisation innovation used in all aspects of the spider biology, from feeding, to reproduction, sensing, locomotion and dispersal
How is silk used in feeding?
allows web building for vibration assessment
How does silk aid locomotion?
silk draglining and abseiling
How is silk used in dispersal?
ballooning spiderlings
How have spiders colonised volcanic habitats?
passive flight
Describe the Trilobites
- extinct subphylum
- highly abundant (approximately 17k species under 10 orders)
- widely distributed
- marine
- survived for approximately 300My
- fossils date back approximately 520Mya
