14. Arthropods Flashcards
Most diverse eukaryotic group?
Arthropods!
Arthropods are in what group?
Ecdysozoans
Name a few arhtropods to show how diverse they are.
- Sea spider
- Scorpion
- Crustaceans
- Centipede
- Insects: bees!
Arthropods - segmentation?
Reduced
- Cephalothorax + abdomen
Arthropods have jointed….
Appendages (each have specialized functions
Body structure of arthropods?
Rigid exoskeleton
- non-living
- secreted by epidermis
- Covers all external surfaces, digestive tract, tracheae
- Composed of layers
- Composed of chitin, protein and CaCO3 (for crustaceans)
Advantages of a rigid exoskeleton?
- Physical support
- Place for muscle attachment
- Physical protection (from abrasion, predation, parasite, desiccation)
- Pigments (camouflage, mating, etc.)
- Jointed appendages & exoskeleton allows faster locomotion
- Opportunity to change morphology between larval and adult stages
Disadvantages of a rigid exoskeleton?
- Inflexible and heavy
- Impossible continuous growth in size - must be shed (moulted) periodically
- Requires energy (to form and shed)
- Prevents use of cilia as effectors
- Respiration through skin not possible - must have spiracles (pores) and tracheae
In arthropods, mass grows …… and/but size changes ….
Mass: continuously
Size: stepwise fashion
Musculo-Skeletal systems in arthropods
- Skeletal muscles: need a resistor to act against (a skeleton); are often found in antagonistic pairs
4 major groups of arthropods? (under revision)
- Myriapods (millipedes, centipedes)
- Chelicerates (spiders, mites, scorpions)
- Crustaceans (marine)
- Hexapods (insects) (terrestrial)
Body regions of myriapods?
2 - head + trunk
Myriapods - feeding?
- Centipedes: carnivorous
- Millipedes: detritivores, herbivores
Chelicerates - body regions
- Cephalothorax (has appendages)
- Abdomen (no appendages)
- –> no jaws, but mandibles
Chelicerates - #1 appendages?
Chelicerae - fangs
Chelicerates - #2 appendages
Pedipalps - copulatory organs, pincers
Chelicerates - #3, 4, 5, 6 appendages?
Walking (4 pairs of walking legs)
Daphnia are…
Crustaceans
Where are crustaceans found?
Dominant in marine environment, but also in freshwater and terrestrial
Crustaceans - body shape?
- Head + thorax (cephalothorax) + abdomen
- Appendages off each segments
Crustaceans make up a large part of…
Zooplankton
Hexapods = ….
Insects and other groups
Hexapods - habitat?
Abundant in freshwater + land, very few marine
Hexapods - body regions?
- Head (antennae, mouthparts)
- Thorax (3 pairs of walking liegs, may have wings)
- Abdomen (no appendages)
Springtails are not …. but are considered to be ….
- Insects (internal mouthparts)
- A hexapod
What is unique to insects?
External mouthparts
Insect - feeding mode?
Herbivores, detrivitores, fluid-drinkers, predators, scavengers, parasites
Wings have been …… by some insect species
Secondarily lost
The wing of an insect and the gill of a crayfish are….
Homologous (common ancestral root)
Insects (+most myriapods) respiratory systems?
Holes (spiracles) open into tubular tracheae which branch to finer tubes. Carry O2 to body cells
Crustaceans - respiratory system?
Gills
Chelicerates - respiratory system?
Some have spiracles & trachae, book gills (horseshoe crabs) or book lungs (spiders, scorpions)
Arthropod circulatory system?
- Open
- Dorsal tubular heart (1 chamber) with pores (ostia); drives hemolymph into hemocoel spaces
- One-way valves
Arthropods sexual reproduction
- Most species are dioecous and lay eggs
On land: internal fertilization (unless they use spermatophores - packets of sperm)
In water: internal (crabs) or external (barnacles)
Metamorphosis of arthropods?
Moulting enables changes in morphology
When do insects and crustaceans cease moulting?
Insects: as adults (metamorphosis to adult form may be complete or incomplete)
Crustaceans: continue moulting as adults
Which one is not a disadvantage of having a cuticle to shed?
- Energy is required to shed exoskeleton
- Vulnerable to predation
- Body cannot continuously increase in mass
- Respiration through cuticle is not possible
3
for 4, see nematodes
Complete metamorphosis =
Indirect or holometabolous development
Complete metamorphosis characteristics?
- Abrupt changes in form (includes a “resting stage” - pupa)
- Often major habitat changes
Incomplete metamorphosis = …
Gradual or hemimetabolous metamorphosis
Incomplete metamorphosis characteristics?
- Gradual changes in form (no resting stage)
- Often no habitat change
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