Tardigrade (aka water bear or moss piglet); a moss-dwelling micro-animal, can survive extremes of temperature, pressure, radiation, and the vacuum of outer space and live. The name water bear comes from the way they walk, reminiscent of a bear's gait. The biggest adults may reach a body length of 1.5 mm (0.059 in), the smallest below 0.1 mm (Grain of Salt = 0.3mm. Newly hatched tardigrades may be smaller than 0.05 mm. They can live 10 years
From Wikipedia - The siphonophores, are an order of the Hydrozoa, a class of marine invertebrates belonging to the phylum Cnidaria. Although a siphonophore appears to be a single organism, each specimen is actually a colony composed of many individual animals. Some siphonophores superficially resemble jellyfish, like the dangerous Portuguese Man o' War (Physalia physalis). With a body length of 40–50 m, another species of siphonophore, Praya dubia, is one of the longest animals in the world.