Is there a word to describe limbs or other body parts arranged in sets of 5?

Pentadactyl:

having five digits on each hand or foot

(Dictionary.com)

You might want to use pentapod.

Penta is a Greek prefix which means five and -pod is also from Greek which means foot/limb etc.

An organism or a machine with five legs. [Wikitionary]

You might have heard tripod stand which is a three-legged stand in laboratories.

Most of the dominant lifeforms on Pandora have six limbs, making them what's known as hexapoda (Greek for "six legs"). Some hexapods in the movie are a horse-like creature called the Direhorse, a panther-like creature called a Viperwolf, and a pterodactyl-like creature called a Mountain Banshee. All of them have six limbs.

On Earth, most creatures are tetrapods, meaning they have four limbs. That includes everything from dogs to horses to humans. The only creatures that have six limbs are insects.
[The Geek Twins]