Worms

On Shalimar, the most advanced life forms seem to have evolved from worms. These worms evolved along three lines.

  • The first worms were very small, short, simple tubes of flesh which ate tiny bits of the slimes and carpets. They were slow, clumsy, primitive grazers. Their bodies consisted of an inner digestive tube, two layers of muscles (one going down the body lengthwise, one consisting of rings of muscles around the body) and an outer skin. Fluids circulated in their bodies as the muscles relaxed and contracted.

    Over time, various species evolved which differed in size, though most remained very small because their circulatory systems would only work in very small, simple bodies. Some worms developed light sensitivity, and little abdominal graspers so that they could climb up on the water plants and eat the plants at higher levels. Naked worms still exist on Shalimar, and are eaten by fiercer, faster animals.

  • The second line remained primitive and naked, like the original parents, but developed a defensive strategy.

    Members of this line of worms became fixed in one place and secreted shells for themselves out of calcium carbonate. These worms often found shelter in clumps of rocks and reached out into the currents to capture food morsels that floated by. Other species buried themselves in mud flats. This line also remained small and simple, and has changed little over the millennia. One of the most successful adaptations of this group was the development of slender mouth filaments that could strain food out of water currents.

  • The third line of worms became armored by growing shells attached to the outsides of their bodies, thus protecting themselves from predation. Many species seem to have experimented with this strategy.

    Some of the armored worms remained very short and stubby, with hemispherical shells to cover them. These animals crawled over rocks and plants like snails. They remained small but developed some body vessels through which fluid could be pumped, as wearing the shell kept some of the cells from contact with the water.


    Another line, the hemisphericals, remained long and thin, but developed jointed armor to cover themselves. This armor consisted of scales that were shaped like hemispherical bands. Some of these worms remained soft on the underside: some defended themselves by growing tougher undersides. These worms roll themselves up as a defense from predators. Some also developed short spikes as a form of self-protection. The spikes limit the mobility of the organisms somewhat, which explains why all living species have short, stubby spikes.

    Having shells created breathing problems for the worms. They developed breathing tubes that ran the length of their bodies and that lay just above the digestive tube. Water was fanned down the tube either by the prevailing current or by the beating of cilia.

  • The most prolific of the armored worms are the triangularians. Evolving from the armored worms, these worms developed three protective plates that were joined together to form a rigid triangle. A series of these triangles is linked together to form the body of the animal.
    Starting with primitive armored forms, these animals developed simple nervous and circulatory systems. They began as grazers, but some species are herbivores and some eat other animals. Triangularians proliferated into a number of species of different sizes and colors. These species evolved to live in a number of ecological niches. Many evolved small, stubby knobs on their undersides to facilitate moving, and some developed short spikes See details on the Anatomy of Triangularians

  • We called the last animals in the worm group Xers. The team hasn't figured out exactly how they evolved yet: they seem to have started as worms that crawled over the slimes and ate some of their cells. Gradually their mouths seem to have migrated so as to be placed underneath the body. The fore-part of the body was then free to search and probe for food, and eventually to be able to pull the worm up over obstacles. Later, following the habit of chromosome duplication without cell division, a lucky combination resulted in an xer with one stomach but two sets of limbs.

    Xers seem to do quite well. The most successful forms have four flexible limbs (rather like a starfish) topped by a small, football-shaped body. External flaps ensure a flow of water over oxygen-capturing tissues. Having a well-developed breathing system and sturdy limbs, these animals can get around in the environment. These animals eat other animals, as their energy needs are high. We named the taller, more agile descendants of the Xers Towers. See details on the Anatomy of Xers.





    © 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!