The Dwarf white isopod, Trichorhina tomentosa, sometimes also called "Devil's Rice" is these names suggest a small, white, and prolific (tomentum is Latin for "stuffing", and they do fill up their enclosures fast) isopod that looks a bit like grains of rice (if you squint a little). This species is known for it's parthenogenesis, which means that a single female will produce viable offspring without the need for a male. No males of this species are known.
Valued for their secretive and prolific nature they are most often used as tankmates in cases where predation pressure could pose a challenge. Despite looking like a shrunken down P. laevis "white", you aren't at risk of having your other pets become their snack. Some people use them as live feed, however I'm skeptical of this practice as they have a low nutritional value (can't gut stuff them like fruit flies, meal worms, or even spring tails) and pose a high risk of becoming a permanent resident in some setups, possibly trowing off the balance that you worked hard on.
Care
As long as they are provided with a deep, rich in decaying plant matter and heavily moist (NOT SOAKING!) substrate they should be happy. As with all isopods you must provide a calcium source, however note that due to their dislike of open spaces you should opt for something that can be incorporated into the substrate, such as really finely ground egg shells, or CaCO3 powder (use in moderation)
Feeding
Most of their diet will come from a properly made substrate. As supplemental food I have observed them consume fish flakes, dried shrimp, and similar protein sources, but they didn't seem to get particularly hungry for them, even with extended times between feedings. However I have seen them absolutely swarm rolled oats (use in moderation, these mold easily in the dampness the dwarf whites love), and slime mold. The second one proved interesting, as it kept growing while feeding on the media, providing a week long feast for the colony. They absolutely loved it!
Personal notes:
Far from a display species. Most of the time their enclosure looks like some damp dirt with leaves on top. You can lure them out with the aforementioned treats, but the most reliable way to view them is trough disturbing the dirt, which I prefer to avoid.
They are a good way of teaching people why you should always make sure to avoid unwanted animal transfers.
I have had situations where they came to me with another species (were likely used as the clean up crew). If they are in your tank, they are in your tank. You can't really get rid of them. Wash your hands well after handling. Make sure none are on your sleeves. Preferably do not touch the soil unless needed. They can easily become a plague in your other bins.