So, you killed off all of my Toxiwurm's descendants? Nice try, but that's not stopping me.
Toxiwurm: tidepool and freshwater filter-feeder.
Genetic diversity: very low (cloning).
Description: small tubular aatumnimal with basic musculature to enable swimming and crawling out of water, limited desiccation resistance, mild poisonous nodules, extendible cilia for capturing plankton, and a simple internal digestive chamber.
Species Name: Toxiwurm subterraneum
Ancestor Species: Toxiwurm
Selective Pressure: Lack of diversity, low population
Primary Mutation: The cilia strengthen to become tendrils, used to bury its eggs under the sea floor and capture plankton better
Secondary Mutation(s): Small (nonpoisonous) spikes appear on the skin, increased sexual activity
The Toxiwurm, having outlived all of its descendants, now faced a predicament. Only a small population survived, and although its deadly aftertaste reduced its predators, there was still the problem of readily available Toxiwurm eggs. One of the creatures developed stronger cilia, and it used them to bury their eggs underground, out of the reach of predators. This allowed a much larger amount of eggs to survive to the point where their poison developed, and caused a population boom. The increased population enabled the Toxiwurm family to have a much greater genetic diversity, and it began to flourish. A minor note is that during this period, the remaining Toxiwurm began to evolve spikes, eerily mirroring its lost descendants.