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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: jumping animals

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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.

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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.

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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.

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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.

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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

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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

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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