There is a question here asking if sea sponges are Kosher. The answers seem to center around the idea that regardless of if they have animal cells, a halachic classification might depend on how it ...
Why did God make all plants, but only some animals, kosher? Sources, please.
Are there any g'dolim (or rabbis of major influence) - past or present - who are known to have owned pets/kept animals for non-agricultural purposes?