Class Notes (1,100,000)
CA (630,000)
McGill (30,000)
BIOL (600)
BIOL 111 (400)
Lecture 14

BIOL 111 Lecture Notes - Lecture 14: Dytiscidae, Hydrostatic Skeleton, Dytiscus

Biology (Sci)
Course Code
BIOL 111
Irene Gregory- Eaves

of 7
Biology Lecture 14: Arthropods I- Skeletons, Molting
and Muscles Negin Arbabi
Nematodes: pseudocoelomates
Arthropods: coelomates
Arthropods are the most diverse eukaryotic group
The Diversity of Arthropods
Dytiscus: predaceous diving beetle, adults collect air under wings and use this to breathe
Honey bee (Apis) has the most complex social lifee.g. worker bees dance to communicate
location of new food source
- Angle of waggle relative to sun communicates position of food source
- Duration of waggle communicates distance of food source
- This work was awarded a Nobel prize
- However new data shows that up to 93% of the time other bees ignore the dance
- Early experiments were conducted with artificial feeders and few food sources
- Other cues such as odor are likely important
Arthropods “joined foot”
Largest eukaryotic phylum
Very abundant (1018 individuals alive at any one time)
Ex: insects, crustaceans, arachnids
Reduced segmentation
- body regions
jointed appendages
- specialized functions
Rigid exoskeleton
- ecdysozoan: molting animal
Arthropods Rigid Exoskeleton
Secreted by epidermis
Covers all external surfaces, digestive tract, and tracheae
Composed of layers
Chitin, protein + CaCO3 (in crustaceans)
Advantages of a Rigid Exoskeleton
Physical support
Place for muscle attachment
Physical protection
- from abrasion, predation, parasite entry
- from desiccation
Location of pigments (camouflage, warning coloration, mating)
Jointed appendages and exoskeleton allow faster locomotion
Opportunity to change morphology between larval and adult stages
Disadvantages of a Rigid Exoskeleton
Inflexible and heavy (if thick and protective)
Continuous growth in size is not possiblemust be periodically shed (molted)
Requires energy to form and shed
Prevents use of cilia as effectors
Respiration through skin is not possiblespiracles (pores) and tracheae (tubes)
Discontinuous Growth
Mass grows continuously, but size changes in stepwise fashion
1. Hydrostatic skeleton
Ex: cnidarians, worms, shell-less mollusks
2. Exoskeleton
Ex: shelled mollusks, arthropods
3. Endoskeleton
Ex: echinoderms, vertebrates
Musculo-Skeletal Systems in Arthropods
Skeletal muscles:
A) need a resistor to act against (i.e. a skeleton)
B) are often found in antagonistic pairs
- act in opposite directions
- “muscles can only pull, not push”
- ex: biceps/triceps
Discontinuous Growth
Mass grows continuously, but size
changes in stepwise fashion
More on molting next lecture
Musculo-Skeletal Systems
Internal skeletonExternal skeleton
How Muscle Contractions are Initiated
Action Potential
VertebratesSaltatory Conduction
How are contractions initiated?
Lets review action
potential and learn
about synapses
Review of Action Potential
Vertebrates have saltatory