lecture 12: soft bodies 2 Flashcards
main idea of how hydrostatic skeletons work
despite pressure, a constant volume is maintained
bodies are soft but deformable
not just large volumes of fluid, muscles and cells are essentially bags of water –> muscular hydrostats
how does shape deformation work?
reducing diameter a little makes for a large increase in length
- like tentacles of squid or cuttlefish
reducing length and increasing width with a lot of force
- like worm peristalsis
how to solve the problem of circumferential tensile stress (like a balloon filling with air on one side (unequally) first creating an aneurism)
muscular reinforcement - best solution being support diagonally – like crossed collagenous connective tissue
**this allows for the number of muscles to stay the same but just change their orientation
- when they get to parallel with the body, are very strong, until then they’re flexible
dual anchor crawling: what are the two anchors?
1) penetration anchor
- push against this anchor
2) terminal anchor
- pull on this anchor
EXAMPLES:
= leeches and caterpillars using ‘looping’ technique
= annelids using peristalsis
- where fat segments & chaetae as anchors
how does an annelid burrow?
using a dual-anchor
lengthening burrow by “cracking”
using fracture edge and terminal anchor
Anterior expansion is both terminal anchor and fracture wedge
*** puts out front part to “crack” then widens it to make anchor
how and why are mechanical properties of sediments important?
- fine muddy sediments are cohesive
- muddy sediments behave as elastic solids like oobleck
- coarse sandy sediments are non-cohesive
- do not behave as elastic sediment that can be fractured - the particles just move relative to eachother
how does a bivalve burrow in coarse sand?
dual anchor burrowing and fluidization of sediment
step 1)
penetration anchor points down (skinny)
- shell valves gape
- lengthens foot thru hydrostatic skeleton
step 2)
foot forms anchor
- adductor muscles contract to close valves quickly and the foot jets into sand on the sides (gets fat thru fluid) - expands terminal end
step 3)
contracts foot muscle
- expansion of foot forms terminal anchor
- whole organism pulls down
gastropod foot: how do they crawl with muscular hydrostatic (no morphological anchors) - 4 types of waves
1) direct wave
- wave of compression
- smaller waves = better grip
- not lifting off foot
2) retrograde wave
- stretching first
- direction of waves is reversed, but direction of travel = same
- larger waves = smaller foot = faster
3) pedal waves
- direct monotaxic
(simple)
- direct ditaxic (complex)
- retrograde monotaxic (simple) - retrograde ditaxic (complex)
4) composite waves
- ex// cowries
– lots of control over muscles
how do different materials behave under stress? (mucus)
dynamic properties of snail slime?
as twist, strain goes up,
then liquifies, and vice versa
gives the ability for both anchor and then movement (smooth gliding surface) - timed properly - acts as 2 different things
when stop adding stress, will change properties
- pushing against = behave like solid
- when need it to be liquid it will be, and you can lift things
mucus energy cost and uses
7-26% of energy budget on mucus
- abt a quarter of energy budget
EXAMPLES:
1) homing limpets
- allow them to track back
- farming their own microalgae (so on the way back they have source of food)
2) “webs” to trap small particles
- Vermetid snails
*anchored to ground
send out a web of
mucus - and bring it in
and get food from it
- Bivalves
*mucus in gills
- Polychaetes
- Larvaceans
etc
3) inhibits nematocysts
- nudibranchs use mucus to stop discharge of stinging cells when they feed
4) dried mucus for temporary adhesion
- periwinkles glue themselves to pier during low tide
5) locating conspecifics
- cues like attracting mates
6) mucus trails followed by predators (to find prey)
