A darkmantle was an octopus-like subterranean creature that disguised itself as a stalactite. Larger specimens were sometimes called envelopers. Darkmantles were favored by the drow deity Ghaunadaur and the orc deity Shargaas.
A darkmantle resembled an octopus or squid with limestone-colored skin and a thick membrane of skin stretched between each of its tentacles, reaching about two-thirds of the way to the tips. Part of its body was covered in a stony dorsal shell. When perfectly still, they looked just like stalactites, stalagmites, or other lumps of stone. A darkmantle had eight eyespots, but these were not true eyes.
Each of a darkmantle's tentacles was covered in "teeth", and it had a lamprey-like mouth at their intersection. From the back of its head was a mucus-covered foot-muscle, with which it could cling to a wall or ceiling.
A typical specimen weighed about 30 pounds (ten kilograms) and stretched about four feet (one meter) from the tip of its head to the tip of one of its tentacles. They did not have bones and so pre-adult individuals could squeeze themselves through surprisingly tight spaces.
Darkmantles could "see" in natural darkness, but not with true vision. Their vestigial eyes could only sense light and dark. They primarily relied upon an echolocation similar to that of bats. Because their "blindsight" had limited range, they preferred enclosed spaces and darkness to open spaces or sunlight and very rarely wandered from their subterranean homes.
The tips of a darkmantle's tentacles had sense organs similar to taste or smell with which they could locate needed minerals to consume for their shells. They also had superb senses of hearing, by means of tiny pits spaced evenly over their tentacles.
A darkmantle could slither much like a snail using its foot, but they could move much more quickly by using their tentacles like legs. This was actually its fastest method of locomotion. Its magical flight could provide lift, but it had to flap the skin between its tentacles for propulsion and was thus a clumsy flier, and its magic only kept it airborne for limited amounts of time. Darkmantles could occasionally catch a small meal in their mouths while flying, but this was rare.
To appear like stalactites, darkmantles would hang from their foot and press their eight tentacles tightly together to form a point. They could also cling to a surface with their tentacles, hanging with their pointed heads downwards instead, but their grip with their tentacles was not nearly as good—only their muscular foot was "sticky".
Darkmantles were prey for several cave creatures. Their usual defense was to disguise themselves as stone, but they would also alternate ground movement with flight to throw off predators tracking them by scent.
Other than the high-pitched sounds used for their natural sonar, darkmantles made no other vocalizations.
Darkmantles had the magical power of flight and the ability to create an aura of unnatural darkness fifteen to twenty feet (five or six meters) in radius, maintaining such an effect from up to ten minutes or even much longer than that. They could also change their skin color to match their environment.
A darkmantle would cling to the ceiling of a cavern and remain still until prey moved below it. At such a point, it would drop suddenly down and unfurl its mantled tentacles in an attempt to engulf the victim's head, all while emitting its magical darkness. If successful, the darkmantle would blind, suffocate, and crush its prey. If a darkmantle missed, it would fly to the ceiling and try again.
Darkmantles could also slash with their tentacles, and since the tips were covered with "teeth" this could cause more damage than one might expect.
Darkmantles were hermaphrodites with both male and female reproductive organs. After mating, each of the pair would lay eggs in clutches of six to eight. These eggs were chicken-sized but the color of stone. Darkmantles maintained no sort of relationship with either their mates or their offspring.
After a tenday or so, the eggs would hatch, and darkmantles would begin their lives as tiny black grubs, which appeared much like slugs. Darkmantle grubs were about an inch long and had eight eyespots, two in the front and three on each side. Grubs were herbivores, feeding on fungi, mosses, and lichen with toothed tongues called radulae.
After about seven days of life, a grub's radula would lengthen and split, and these prototentacles would then lengthen and split a second time. After a third splitting, the creature would have eight tentacles. Once its tentacles accounted for half of its body length, a darkmantle would begin to grow a shell from its back, composed of the minerals consumed during its time as a grub. After several months, the darkmantle would be an adult about two feet in length. They would usually cease growing at about four feet in length. A darkmantle's lifespan was about six years.
Darkmantles required sleep, and they also hibernated for several months at a time, hanging like stalactites during this time. Unless hibernating, an adult darkmantle could survive for about seven days between feedings. They consumed water from deep subterranean pools.
Some scholars believed that darkmantles were originally from the Shadowfell. Others believe them to have evolved from the piercer, another mollusk that hung from cave ceilings and disguised itself as stone.
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