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Lecture 7

BIO325H5 Lecture Notes - Lecture 7: Jet Propulsion, Swim Bladder, Body Cavity

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Glenn Morris

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Lecture 7: Jetting Vortices, & Buoyancy
January 28, 2019
Jetting Vortices & Buoyancy- squid, odonate, medusa bell, salps, fish swim bladders, Nautilus chambers
Podia debonder, thrashing nematodes, burrowing clams, sliding snails
Muscular hydrostats: tongues, trunks, & tentacles
Buoyancy and Jetting: bony fish swim bladders, Nautilus, dragonflies rectal gills, jellyfish
pulsatile propulsion
Temporary Adhesion
Epidermis of the tube foot disc contains glands which produce two kinds of adhesive secretion
o Glue bonder & glue de-bonder
Glue is delivered through the disc cuticle to the substratum where it form a thin film bonding the
foot- debonding secretions act like enzymes, detaching the upper coat of the glue & leaving the
rest of the adhesive material behind attached to the substratum as a footprint
End of extensible cylinder is the disc- larger in diameter than the stem, contains central depression
Phylum Nematoda
Nematodes speciose- 20,000 spp. Described & probably more than a million to go
“If all the matter in the universe except the nematodes were swept away, our world would still be
simly recognizable, and if, as disembodied spirits, we could investigate it, we should find its
mountains, hills, vales, rivers, lakes, & oceans represented by a film of nematodes. The location of
towns would be decipherable, since for every massing of human beings there would be a
corresponding massing of certain nematodes. Trees would still stand in ghostly rows representing
our streets & highways. The location of the various plants & animals would still be decipherable,
and had we sufficient knowledge, in many cases even their species could be determined by an
examination of their erstwhile nematode parasites”
Pseudocoelom as Fluid Skeleton Caenorhabditis elegans
Helical Collagen Fibres As Nematode Muscle Antagonists
The orthogonally oriented locomotory muscles of the earthworm are circular & longitudinal
antagonists- circulars external to the longitudinals
Nematodes also have longitudinal muscle bands- but no circulars
What antagonizes nematode longitudinals? Ennos says part of the answer is a helical arrangement
of collagen fibres in the curicle, the helix angle being at about 75°
The longitudinal muscles of the worm are under constant low-intensity contraction, which would
tend to shorten the worm… such shortening would result in it getting wider, [but this increase in
girth] is pressurized instead. This pressurization produces a [more] rigid structure that can be
[thrashed to and fro] by asymmetrical contraction of the longitudinal muscles first on one side &
then on the other, allowing the worm to swim through [water films]”
High internal pressure o the pseudocoel makes it difficult to ingest food
o They need special organs “to prevent them from vomiting”
Phylum Nematoda Rundworms
- Pinworms= most too small (<2mm) to be noticed
- Pig roundworm Ascaris= unusually big
- Most free-living in soil (some are parasitic)
- Unsegmented (not modular/metameric)
- Body= circular in transverse section with acuminate (tapered) ends
- Has no circular muscles, only longitudinal
- Remarkably high internal pressure of pseudocoel fluid

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Lecture 7: Jetting Vortices, & Buoyancy
January 28, 2019
Cycle of Burrowing Movements
Stage A: adductor relaxed so shells braced on surrounding sand by ligaments
Stage B: protractors start to contract, pushing blood into foot & the foot probes down, gaining
ground into the mud
Stage C: pushing force of foot makes body move up a little (relative to start point)
Stage D: adductors contract, pulling valves together (red indicates the space they DID occupy)
Stage E: valves push blood into foot to make an anchor, simultaneously squirting seawater out
around valves from mantle- this water* ‘puddles’ sand
o Foot swells the foot maximally into the bottom anchor of the two anchor system
Stage F: cycle renews
** it’s not clear whether this involves ocean water drawn in by siphons
o Perhaps it does if the clam is burrowing near the surface & perhaps if lower down it
oscillates its valves to draw in pore water
Class Bivalva= 20000 species in 75 families
Class Gastropoda= 35000 species
Pulmonates are a subclass of Gastropoda & include land snails
Name is from conversion of mantle cavity into a lung
Gastropods move on their foot using ‘muscular waves moving along [its] ventral surface’
“The force of these waves is coupled to the substratum by a thin layer of pedal mucus” (Denny)
There are monotaxic & ditaxic gastropod species
Pedal Locomotion in Pulmonates
Mantle cavity of pulmonates has been converted into a lung
Hence ‘pulmonate snails’ of which are just one sort
Edges of mantle cavity seal to back except for pneumostome opening
Roof of mantle cavity vascularized, no gill
Muscles as Material= glycoprotein, polymeric sugar with lysozymes
How can an animal with only one foot walk on glue?
Denny’s Abstract
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