Gasbag
Background
The genus of gasbags evolved on Scoti to make use of as much daylight as
possible. Gasbags have a very light body with a large methane filled cavity
to provide buoyancy. The low level prevailing winds across the equator go
from winter pole to summer pole and it is thought that early gasbags carried
out a migratory existence, alternating between the two summer poles.
Initially, the gasbags would spend time during the summer months producing
stores (e.g. ethanol) that could be converted to fill the gasbag. At the end
of summer these stores are converted to methane and the organism would rise
into the airstream to begin the journey to the other pole.
Locomotion
The quantity of methane produced governs whether the destination is reached.
If too little reserves were laid down during the summer months then not
enough lift could be produced to reach an airstream that would traverse the
equatorial ice sheets. If too much was laid down then either the extra weight
would similarly prevent sufficient distance being travelled if a small amount
of methane was produced, or the gasbag would rise too far into the returning
airstream is a large amount was produced.
Some adjustment of altitude is possible by the gasbag converting further
reserves to generate extra lift or metabolising methane to reduce it. This
introduces the problem that there is an end limit to the adjustment possible
imposed by the initial size of reserves.
To overcome this, a chameleon like characteristic evolved. This allows the
gasbag to adjust buoyancy without altering the contents of the gasbag. By
making the outside of the gasbag darker, more sunlight is absorbed; the
contained gases heat up and expand increasing lift. By making the outside
lighter, more sunlight is reflected; the gas cools and lift is reduced.
Internal partitions within the gasbag allow different sections of the gas to
be warmed and cooled independently. This allows the gasbag to control
attitude and orientation in the air, as the warmest parts will be on top.
Blood vessels flowing through these partitions can also be used to conduct
heat in or out of the core of the bag to speed the rate at which density
changes occur.
Long tentacles can also be used to steer or propel the gasbag. Rowing,
swimming and screw propeller actions have all been observed.
Feeding
The gasbags have long dangling tentacles with which to gather food to the
central mouth. By adjusting buoyancy, food can be gathered from the ground or
from among the branches of plant life. Other avian creatures can also be
attacked.
Stings carried on the tentacles can be used to immobilise target creatures.
Predators
Because of their store of methane, gasbags provide valuable energy to
predators. The main difficulty is that owing to its gaseous nature it is
easily lost during a fight. This is very damaging (frequently fatal) to the
gasbag and provides no benefit to the predator.
The most dangerous predator is one large enough to entirely consume the
gasbag in one mouthful. To avoid this smaller gasbag species have unpalatable
surfaces.