Reaching up to 16.5 centimeters (6.5 inches) in length, it is the longest known millipede in North America.

[1][4] Like other members of the family Paeromopodidae, each body ring is marked with small parallel grooves running lengthwise, and mature males have two pair of modified legs (gonopods) on the seventh body segment (not including the head) that are used in mating.

[4] P. paniculus lives in the Sierra Nevada mountains of California, and has mainly been found within Yosemite National Park and other parts of Mariposa County.

[1] Little is known of its ecology but P. paniculus has been found in moist microhabitats under dead logs and bark and is known to co-occur with Californiulus yosemitensis, another member of the Paeromopodidae, which is distinguished from P. paniculus by having a broad yellow dorsal stripe with a black line down the middle.

The holotype is a male collected in 1969 and is housed in the Bohart Museum of Entomology at the University of California, Davis.