Ocean Planets
In this article we are going to explore the possibilities of alien life on ocean planets and discuss what space explorers
may find. Above and below: a species of biosciform, an aquatic organism from the ocean of Undinion. These
organisms have two mouths that are adapted for filter-feeding. Each of the two highly inflatable filter-funnels sieves
out food organisms from the water and periodically contracts to expel the water. Some of the water is moved into a
highly distensible reservoir which pumps it out of the pair of movable exhalent siphons, in a series of spurts, enabling
jet propulsion. The organism is neutrally buoyant and so requires little additional effort to stay afloat. The filters also
act as gills, absorbing oxygen from the water. Filter-feeding is one of the most common feeding mechanisms in
aquatic environments on Earth and we would expect to find it in the life-supporting oceans of other planets. Most of
these organisms are only 10-20 cm long, but some reach over 10 meters in length.
Above: Planet Undinion. Ocean Planets can be divided into classes. The classification we will use is as follows: a class A
ocean planet has its surface entirely covered by liquid ocean; a class B ocean planet has more than half of its surface
covered by ocean and class c include planets with large seas and lakes. Further classification includes the nature of the
liquid: for example, subclass W means that the liquid is predominantly water (water is the main solvent), A for ammonia, H
for hydrocarbons and N for liquid nitrogen and nitrogen compounds other than ammonia. In this classification the Earth
would be a class BW planet. Some planets also have subsurface oceans, sea
ice planets like Europa, for example.

In this article, we will look at aquatic life on the planet Undinion. Undinion orbits a dim red dwarf class M star, which it
orbits at 0.3 AU (this is about as close as Mercury is to the Sun, but the parent star of Undion has only one-tenth the
luminosity of the Sun). Undion is 2.4 times as massive as the Earth and is typically shrouded in a dense cloud-layer.
Photosynthetic organisms in both the surface ocean and in the clouds themselves drive the ecosystem. Red dwarfs are
long-lived and so are good candidates for hosting life-bearing worlds, since life may have a long time to evolve on such
worlds. On Undinion, life is advanced, but still somewhat archaic in its level of sophistication compared to life on Earth.
Study the images of the biosciformes and consider the questions below:

  1. Which structures do you think have a skeletal function?
  2. Which structures do you think help the organism to float?
  3. What is the likely function of the tail (which has a fin but is not highly muscular)?
  4. What do you think is the function of the four red-blue dorsal organs?
  5. What other systems must be present?
  6. Why do you think the organism lacks skin pigment?

Some other ocean planets are shown below, compared to views of Undinion:
Above: a planet with hydrocarbon
oceans. This world is similar to
in your own Solar System.
Animal or plant? Above - a cell from the tissues of a biosciforme. The cells of these organisms are not quite like
the cells of animals on Earth. They have a flexible cell wall, more like plant cells, and they form a variety of
crystalline and fibrous tissues. The genetic material is not enclosed in a lipid envelope, as it is in both animal
and plant cells, instead the nucleic material is wound onto a protein scaffold, visible as the spirals and rods in
this cell. There are no mitochondria, though there are energy-generating organelles of respiration, they have
not evolved by endosymbiosis as they did in eukaryotes on Earth. These cells are, however, carbon and
The biosciformes sieve tiny organisms from the water such as this single-celled planktonic organism. This cell
moves about by means of the two helices which are attached to rotating protein wheels. This is a larger version
of similar structures found in
bacteria on Earth. Again, notice that the nucleus consists of protein rods on which
the nucleic material is wound. There is a related form that has lost the helices and the wheels are adorned
instead by adhesive tubes radiating from their rims. By means of these wheels these cells are able to crawl over
solid surfaces.

Many aquatic organisms use jet propulsion (just think of
cephalopods, jellyfish and salps on Earth; sponges also
generate jets, though for functions other than locomotion, namely feeding, respiration and gamete discharge).
Below are some examples of organisms from the oceans of Undinion, which utilise both filter-feeding and
Explore life in a sub-surface ocean on
the icy world
The organism above is colonial. The main central individual acts as a pump and jet-propulsion unit, as well as
filtering water for food, by filtering out larger particles. The rigid arms comprise rows of tiny individuals, each
connected to the exterior via a pore through which it draws in water, filtering out microscopic food particles and
then ejecting the water into the central canal of each arm. As the ends of the arms are down-turned, the
exhalent jets, emitted from the end of each arm, also aid locomotion. This organism can turn, by regulating the
filtration rate in each arm (though the central unit might also have some control over the direction of its exhaust)
and these organisms will slowly move up and down the water-column, or else remain floating at the surface
during daylight where micro-organisms gather to feed. They can be seen floating with the central individual
projecting above the water and occasionally flushing itself with water to clean away the drying salt that deposits
on its surface as water evaporates from it.
Left: another colonial organism, consisting of eight individuals
connected in a ring. The diagrams show one cycle in the
feeding-locomotion behaviour of this organism. The organism is
moving vertically upwards in these images and begins by taking in
water into the upper chambers. The inhalent aperture then closes and
water is pumped into the lower chambers which then pump the water
out as exhalent jets. In between the two chambers is a filter which
sieves out food particles and passes to the ring, in which they are
digested and the food disseminated to all parts of the colony. Clearly,
there has to be a valve system between the two chambers of each
pump, to ensure that water flows in the correct direction.

Q. We have seen how such organisms move, feed and respire, but
how might these organisms combat predation pressures? What
defenses might they have?

Another, larger species is shown below, in which the individuals have
more closely merged into a single compound organism.
Oceania beta-4
Left: a view looking directly down on the inhalent
apertures, which are shown uppermost in the image
above. The central region between the individuals
has fused to form a larger food-filtering mesh, with
the pumps now being mainly for locomotion. These
organisms illustrate another recurring theme in
Nature - the construction of more complex systems
by repeating simpler parts. We have also seen how
similar patterns of life, dictated to be physical;
requirements, repeat on different planets, albeit with
infinite variations. I think it was Dr Who who once
said: 'It never ceases to amaze me how the same
patterns of life repeat around the Universe', or
words to that effect. Equally amazing is the infinite
diversity within these patterns, and the occasional
rare or unique pattern is always a pleasant surprise!

Coming soon - more alien organisms from the ocean of
The organism above is a single cell, a giant cell, typically growing to 10-20 cm in length. It moves along the ocean
bed, using its cytoskeleton to put out appendages with which it walks. It is surrounded by a flexible cell wall.
Through an opening in the wall, at one end of the cell, protrude pseudopods that are sensory, though their primary
function is food collection; they collect particles, from the ooze on the ocean bed, which they phagocytose. One
problem with cells when they become too large is that diffusion becomes too slow to transport substances around
the cell. On Earth, plant and algal cells can achieve large sizes by active cytoplasmic streaming. In the organism
above, the corkscrew-like skeletal filament rotates and this mixes the viscous cytoplasm. Gas vacuoles in the tail
help ensure that the organism stays upright, though, being a single-cell, if it is overturned then it can right itself by
streaming mucus and rolling over, or it can absorb its appendages and change its polarity, with the ventral surface
swapping with the dorsal surface. The specimen shown above is getting ready to divide by budding. The tubules of
the nucleus are associated with a division ring of cytoskeletal elements which will eventually divide the nucleus in
two and then pinch-off the rear portion of the cell, which will float some distance in the plankton before sinking and
developing into a new and mature individual.
Above: another species of biosciform which has appendages rich in photosynthetic symbionts - micro-organisms
that can derive energy from sunlight by photosynthesis that live in the organism's tissues. The organism spends
much of its time drifting in the surface waters, basking in the sunlight. The symbionts produce more organic
materials than they need to sustain their numbers and they provide their surplus to the host, which utilises the
organic compounds both as fuel and as building blocks for its own cells. The biosciform's own digestive system is
much reduced and serves mainly to remove oxygen from the water for respiration. The tail is now a propulsive
organ, though it is normally only used in emergency escape responses and to steer the organism to optimum light
conditions for its symbionts. To assist in its propulsive function, the tail has a hydrostatically operated central elastic
chord against which the muscles, now arranged in segmented blocks for extra efficiency, operate. The chord can be
made rigid or flaccid. Buoyancy is also regulated and the light construction helps give the organism neutral density
so that it can float quite easily, assisted by its wing-like appendages and adjustable flotation organs (gas bladders).
The central nervous system consists of several nerve rings, inside the protective skeletal hoops.