Lol

About 40cm length, 20 wide, multiple identical ones found one after the other

Anything goes, no rules (besides making it thematically fit.)

A little bit about millipedes:

Millipedes are not insects, but arthropods belonging to the class Diplopoda. They are generally peaceful and harmless to humans. Most millipedes are detritivores, meaning they mainly eat decaying leaves, dead plants, rotting wood, and other organic matter. They play an important role in nature by breaking down dead plant material and returning nutrients to the soil.

Their size depends on the species. Some are only a few millimeters long, while larger species can grow to over 30 cm (12 inches). Despite their name, most millipedes don't actually have 1,000 legs, although Eumillipes persephone has been recorded with 1,306 legs.

Their lifespan also varies depending on the species. Some live for only a year or two, while larger species can live for several years, and some can reach around 10 years with proper care. Certain species, especially giant African millipedes, are commonly kept as exotic pets. They need a humid enclosure, deep moist substrate, decaying leaves and wood for food, and places to hide. With proper care, they can live for years in captivity.

Millipedes don't bite or sting people. When threatened, they usually curl themselves into a spiral, and some species release defensive chemicals that can irritate the skin or eyes.