Slimes


We believe that slimes were one of the earliest communal life forms to appear on Shalimar. Slimes are simple sheets of cells which stay attached to each other, in part by clinging to a foundation, such as a stone in the water. Each cell functions independently: there is no division of labor. The group probably derives some evolutionary advantage from clinging to the stones, perhaps by maintaining a favorable distance from the surface of the water. The cells form a very thin layer, because each one must receive some light. This means that their sheet of cells is fragile, and so tends to be found in sheltered, shallow water where the bottom is stony or sandy. In a muddy environment, slimes could too easily be buried. In rough water, the tissue of slimes is torn apart, and small pieces or individual cells are carried away in the water, perhaps to start new colonies elsewhere.

Slimes have chlorophyll, and may be green, orange, brown, or purple. Small colonies tend to be clones of a single cell, and so will all be the same color. Many different colonies may take hold on larger expanses of rock and so may show many colors.

Slimes reproduce by division. Their cells divide into two completely, but the outer walls stay attached to each other. Slimes also produce small, toughly shelled capsules that contain their genetic material. These little packets are carried all over the planet in the ocean, and can remain dormant for long periods of time. This adaptation makes it possible for slimes to survive unpredictable meteor conditions produced by meteor strikes.

Some of the slimes have developed into a thicker form which we have called carpets. In these sheets some of the cells are stacked on each other, forming little bumps. They look and feel different from the very smooth sheets of the slimes. Stacking individual cells allows the topmost ones to get closer to the light, and raises them above any drifting silt. It does, however, reduce the light that the lower cells receive.

As the little towers get taller, they are more affected by the pressure of currents in the water. Pieces of the carpet may be torn away, especially if the lowest cells, which provide attachment, are deprived of light. The towers are very close together, creating small tubes between the cells in which nutrients can be transported. The primary function of the lowest cells becomes to provide anchorage to the base of the carpet of cells. Differentiation of function begins as nutrients are transferred from cells higher up in the tower.

We believe that some of the towers continued to differentiate, with the growing towers of cells closing around the channels that allowed the topmost cells to feed the roots. Groups of towers grew taller, fusing into stems, and branching a little at their tips to capture more of the light energy available to them. Their bases grew to provide more holding surface, creating a web of proto-roots.

Growing stems made it possible for the towers to take hold at greater depths. These plants continued to reproduce by division, and new towers would start up from the roots. Having roots and stems also made it possible for the towers to grow in sand, and, later, silt. If they were being buried, they could simply keep growing and get to the light again. They began to colonize shallow areas previously not available to them.

Some of the towers widened their topmost area into disks instead of branches. We have called these plants buttons, as the simplest ones look a bit like mushrooms. Flat disks tended to collect debris unless the water was very clear, and so most forms have a downward sloping topmost disk.

Another innovation developed by these plants was branching. Stems began to grow up to a certain height, and then to put forth some short branches. Sometimes a central stem was grown where the plant branched, and so the stem continued growing upward, with the branches in tiers. Repeating the modules of the stem allowed the plants to recover more quickly if a storm broke them. (The broken part could also float away and take root elsewhere.) It allowed the plants to put their light gathering cells close to the surface of the water. Once the plants began to send up more than one shoot per branching node, they were able to increase the lighted area that they filled. These water plants grow prolifically on Shalimar in most places where the water is warm and shallow.





© Elizabeth Anne Viau, 1996. This material may be used freely for instructional purposes but not sold for a price beyond the cost of reproduction. Please e-mail me at eviau@earthlink.net if you use this material. I'd be interested to know how it works for you!