A "Polydesmus sp. tiny millipede" refers to a small, unidentified species from the genus Polydesmus, commonly known as flat-backed millipedes, characterized by their broad body armor and typically measuring around 1-2 cm long, though some can be smaller. These millipedes are abundant in soil and leaf litter, feeding on decaying vegetation, and are distinguished from centipedes by having two pairs of legs per body segment. Specific identification often requires examining the male gonopods, but general features include a flat appearance, varying shades of brown or yellow, and the ability to secrete defensive almond-scented fluids. 

Key Characteristics
Appearance: They are dorso-ventrally flattened, with a broad, flat body, and their chitinous extensions give them a shield-like look.
Size: While the genus is diverse, many species, like Polydesmus angustus, are relatively small, with adults often around 2 cm. Some smaller individuals can be even tinier.
Color: The color can range from dull yellow to dark brown.
Legs: Like all millipedes, they have two pairs of legs per body segment.
Defense: They can release defensive fluids with an almond-like smell to deter predators. 
 
Habitat & Behavior
Habitat: They are found in damp, dark environments like under stones, logs, bark, and deep in leaf litter and compost heaps.
Diet: They are decomposers, playing a vital role in breaking down dead plant matter.
Movement: They are slow-moving, adapted for pushing through soil and leaf litter.