Donaldson's Barnacle

"Named for Dr. Louis Donaldson, its discoverer and first victim, the air-barnacle (through a freak of convergent evolution) resembles an unnaturally large member of the terrestrial subclass of Cirripedia, which includes the common goose-neck barnacle. But while the mundane barnacle passively filters nutrients from shifting ocean waters, the xenomorphic dry-land variety takes an extremely active role in the capture of any lifeforms unfortunate enough to enter its habitat. They have been occasionally mistaken for stalactites and light fixtures, and the investigator who values his life should always perform a thorough advance survey of ceilings and before entering caverns and corridors."