Giant brittle stars are enormous ophiuroids related to sea stars and similar starfish. A brittle star has a disc-shaped body from which radiate long flexible arms it uses to catch food, walk and swim; most have five arms but a few species have six. These creatures have bony spines down the side of their arms whose size and density depends on the species, ranging from stubby bumps to stout spikes or dense bristles. The spines may look formidable but are blunt and harmless, they improve the limbs' traction rather than acting as a defense. Underneath the arms are sticky tube feet that can manipulate prey or cling to surfaces, such as cliff faces and cave roofs. The writhing motion of its arms gives ophiuroids another name: the serpent stars. Brittlestars, including the giant version, live on the sea floor and can be found in any climate. A few species tolerate brackish water and can live around river mouths.
 A typical giant brittle star has a body disc 4 to 5 feet across and arms 15 to 20 feet long. Bigger specimens are possible but rare; smaller giant brittle stars are commoner but rarely attack humanoids.
 Most kinds of brittle stars are either male or female, although some are both sexes at once or can alternate between male and female; they breed by floating millions of eggs away on the currents. The rare Six-Armed Brittle Star (see below) can also reproduce by splitting in two.

Predatory Scavengers. A brittle star is primarily a scavenger, sweeping up scraps of food with its arms and conveying it to the five-jawed maw on its underside. A giant ophiuroid is much larger and more active than its normal-sized kin so requires far more food, so giant brittlestars roam around the sea floor and devour anything edible they come across. While it lacks the intelligence to deliberately stalk prey, a giant brittle star will enthusiastically pursue prey for a few minutes if it senses there's a good meal close by.

Hungry Beachcombers. Air-breathing humanoids most often encounter giant brittle stars on the shoreline as they patrol the tideline for food washed up by the waves. A giant brittlestar can emerge from the water for up to an hour, so coastal specimens often supplement their diet of flotsam with careless or slow land creatures.

VARIANT: BURROWING BRITTLE STAR
A common type of brittle star lives in the silt of the sea floor. It usually hides its body under the mud or sand and reaches out its arms to snag passing food. Such brittle stars have arms that are far longer than species that actively roam about on the surface. A giant burrowing brittlestar has the following traits.

Slow Burrower. The burrowing giant brittle star has Speed 10 ft., burrow 10 ft, climb 10 ft.

Long Fragile Arms. The burrowing giant brittle star's arm attacks have reach 30 feet and usually has the Shed Arms trait (see Brittle Limbs, above). If it has the Shed Arms trait, it is triggered by at least 6 damage or a Strength of 16 or higher, and the d6 roll to determine the result uses:

VARIANT: SIX-ARMED BRITTLE STAR
A few species of brittle star have six arms instead of the usual five. These animals can multiply by fission, splitting their disc-shaped body down the middle to produce two new animals, although they are still capable of reproducing normally. A six-armed star with the three arms on one side of its body shorter than the other side is probably a youngster produced by fission that hasn't regrown the half that formed its twin sibling.
 A six-armed brittle star has the following traits.

Fission. During their reproductive season, a six-armed giant brittle star can split in half to become two new brittle stars; this slow process takes 10 to 20 (2d6 + 8) days but does not inconvenience the creature. The two new brittle stars each have 21 (2d10+10) hit points and three arms. As they gain new arms with their Regrowth ability, their hit points slowly increase until they reach 42 (5d10 + 15) hit points when they grow six full length arms and a complete body-disc. It usually takes at least three months (6d10+60 days) for a split half to regenerate into a whole six-armed giant brittlestar.

Six Arms. A giant brittle star with six limbs instead of five does not gain any extra attacks, but its Shed Arms is triggered by 7 damage or higher (5 if it has the Fragile Arms trait) and losing arms reduces its speed as follows:
 A six-armed giant brittle star's speed is lowered by 5 ft. if it loses one or two arms and halved if it loses three or four. If it loses five arms its speed becomes 5 feet and if it loses all six it has a speed of 0 feet.
 If the brittle star finishes a long rest its arm stumps regrows enough to remove one "arm's worth" of speed reduction, so it is lowered by 5 ft. with two or three arms, halved with four or five lost arms, and reduced to 5 ft. if is has lost all six arms. The brittle star regains its speed and arm attacks when its Regrowth trait replaces the lost arms.

(Original monster designed by Casimir Liber and Cleon on the Creature Catalog Monster Homebrews forum)