Cnidarian Locomotion

A.  Other modes of motion/locomotion in the Cnidaria
	1.  Use of floats, sails, etc.
		a.  Hydrozoa-siphonophores
			1.  Portuguese Man-o-War (Physalia)--colonial 
				organism, one polyp forms the float
				(pneumophore), others are suspended
				from the float.  Gas can either be
				secreted into the float or released
				from the float.  In times of turbulent
				weather, gas is released and colony
				sinks to depth where wave action is
				less.
			2.  Vellela (Sailor by the wind)--colony where
				one polyp forms a disk-shaped structure
				that has sail, other individuals are
				suspended from the undersurface of the
				disk
			3.  Some hydrozoans have cone-shaped medusae that
				are budded off from each other, but remain
				attached.  Other polyps are attached to
				these structures.

		b.  In many instances there is a difference in handed-ness
			relates to the fact whether the creatures live in
			the southern versus the northern hemisphere
	2.  Using the medusae form
		a.  Scyphozoa
			1.  Animal has bell-shaped structure.  Most of
				medusae consists of acellular materials
				that form the mesoglea of the creature.
				There are muscles, circular and radial, that
				can change the shape of the bell.  Contraction
				of circular muscles makes bell smaller, 
				increases the pressure on the fluid in the
				subumbrellar area which forces the fluid
				away from animal.  This propulsion is a form
				of jet-propulsion, but very slow.
			2.  Animal moves very slowly upward by contractions
				of the bell and then takes advantage of
				gravity to drift downwards.  Feeds as it
				falls in the the water column.
		b.  Hydrozoan medusae
			1.  Function the same way, except that there are
				folds that extend from the side of the 
				bell towards the middle and occludes the
				opening.  This will produce larger forces
	3.  Medusae that don't necessarily act as medusae
		a.  Clown jellys--attach themselves to seaweed by umbrellar
			surface.  Edges of umbrellar surface extended as 
			tentacles, each of which has a ball-shaped ending
			with lots of nematocysts
		b.  Cassiopia--regular jelly that has symbiotic algae living
			in its tissues.  As a result, the jellyfish lies
			upside down on the floor of shallow water lagoons
			in tropical/subtropical areas of the world.