January 29 Colonial hydrozoans of the Order Siphonophora Swim bladder functions Counter current...
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January 29 Colonial hydrozoans of the Order Siphonophora Swim bladder functions Counter current retes Chaoborus: ghost midges Exoskeletons and levers Saltatoria:
January 29 Colonial hydrozoans of the Order Siphonophora Swim
bladder functions Counter current retes Chaoborus: ghost midges
Exoskeletons and levers Saltatoria: jumping animals
Slide 2
Colonial hydrozoa: what is a pneumatophore? Siphonophora
(Cnidaria) colonial Hydrozoa A pneumatophore is an individual
colonial zooid modified into a gas-filled float giving buoyancy to
the colony below. Zooids: nectophores: squirt out jets of seawater
to propel the colony gastrozooids are sac- like, specialized for
ingestion and distribution of nutrients to rest of colony
dactylozooids with batteries of nematocysts etc. ~300 species live
in the open ocean They use stinging nematocysts to capture fish
prey.
Slide 3
Velella: By-the- wind sailor Siphonophores have created a
complex metazoan body by making organs out of individual organisms
(p 386, Wilson) Wikkipedia from Meglitsch P.A. Invertebrate Zoology
Wilson, E.O. 1975. Sociobiology. Harvard, Cambridge Mass.
Slide 4
Buoyancy see Vogel Comparative Biomechanics p. 96 Archimedes
Law : objects heavier than the volume of water they displace will
sink; objects lighter than the volume of water they displace will
rise. A fish is buoyed up by a force equal to the weight of the
water it displaces. It can change this force by changing its
volume, i.e., displacing more or less water. Secreting oxygen gas
into its swim bladder from the blood, the fish increases its volume
and displaces more water, so increasing the force acting to make it
rise in the water column. Conversely it can absorb oxygen gas from
the bladder and so sink. Inland fishes of NY, Cornell Recall
remarks last lecture re Buoyancy Compensators and the virtues of
being neutrally buoyant.
Slide 5
Swim bladder /Gas bladder Many bony fishes have a single median
gas bag in their body used to change their density, giving neutral
buoyancy at different levels in the water column. This bladder,
situated just below the backbone and just above the viscera,
contains oxygen at a high concentration; the oxygen is actively
secreted from the blood. Fisheries & Oceans Canada Ancestors of
bony fishes, living in fresh water, evolved lungs to supplement
their gills in times of drought. When some of these ancestors
reinvaded the seas these lungs evolved into swim bladders.
Slide 6
How to keep oxygen tension high in the bladder when blood has a
much lower tension: oxygen will tend to diffuse from the bladder
into the blood*. Rete mirabile [Latin rete is net, i.e., network of
capillaries. Rete is a set of relatively long parallel-lying
capillaries just ahead of the gas gland, some leading to it and
some leading away: arterial blood to and venous blood from (Red
Body). Tension of oxygen in the leaving venous capillaries is high,
but by running these capillaries right beside the incoming arterial
capillaries, oxygen can diffuse between them. This is called a
countercurrent exchange and is also used to conserve heat. *The
oval is a separate chamber of the gas bladder isolated by a
sphincter muscle that allows diffusion back into the blood to
reduce buoyancy. (Tension: term applied to the partial pressure of
a gas when in solution.) Univ. S. Dakota
Slide 7
Weberian ossicles Sound waves travel well in water (and 4X
faster than in air) and they pass easily through the flesh of
animals. But they are interrupted by gas e.g., swim bladder. So the
swimbladder is a bubble of gas that is readily vibrated by
impinging sound waves. Some fish (freshwater carp overgrown minnow
-- have capitalized on this: special bones Webers Bones connect the
swim bladder to the internal ear. Freshwater carp Inland fishes of
NY >speechlab.eece.mu.edu< You strange, astonished- looking,
angle-faced, Dreary-mouthed, gaping wretches of the sea, Gulping
salt-water everlastingly, Cold-blooded, though with red your blood
be graced, ---- And mute, though dwellers in the roaring waste.
James Henry Leigh Hunt
Slide 8
Drums are fishes that use the swim bladder to make sound
signals Sonic muscles investing the swim bladder can be used by
some fishes (family Sciaenidae: drums and croakers) to create sound
signals: Aplodinotus >speechlab.eece.mu.edu
3 classes of lever: classified on the basis of the sequencing
of force in, force out and fulcrum (axis) FIRSTEFFORT FULCRUMLOAD
SECOND FULCRUMLOADEFFORT THIRDFULCRUMEFFORTLOAD One of the
commonest arrangements in animal muscle systems is a first,
together with a third-class, lever acting as an antagonistic pair.
Remember to consider the centre of gravity. First class levers:
force advantage is usually >1, speed advantage can be very good
(wing of a fly for example) Second class levers: force advantage is
always >1, speed advantage is always