Riverfruit
Riverfruit was the name given to an apparent form of plant life native to the planet Alzarius by the Alzarian humanoid culture which developed there after the arrival of the starliner from Terradon.
Riverfruit resembled Terran watermelons to some degree and appeared to be part of the staple diet of the Alzarians. It appeared to be farmed by the Alzarians, with riverfruit theft a relatively serious offence.
Immediately prior to and during Mistfall the eggs of the Alzarian spider appeared within riverfruit. These would rapidly develop until the fruit split open and released the adult creature. Given this fact, and the accepted link between the Alzarian spider, the Marshman, and the Alzarian humanoids, it is reasonable to assume riverfruit also contains the same unusual cellular characteristics as the descendant organisms. (DW: Full Circle.)