The gastrotrich is a microscopic creature native to both marine and freshwater environments. It grows to a maximum of 3 mm in size and is flat, transparent and rather like a pineapple.

Intellectually, gastrotrichs appear to be on the simple side; two ganglia, each attached to a single nerve cord and connected by a commisure, are the whole of their think-box. However, they have been observed to display shockingly complex social behaviours, acting in a way that ought to be precluded by their limited mental capacities.

Gastrotrich spend their short three-day lifespans in herd-like schools of 40-50 members. They spend 9-12 hours of each day inactive, although not, strictly speaking, in a sleep-state. During this time, the gastrotrich layer themselves atop each other to form a sphere with the most juvenile of their number at its centre. The surface of this conglomerate sphere will then gently expand and contract, in a pulsing manner some say resembles the movements of certain species of Ctenophora. Although now believed to be a form of Batesian mimicry, earlier researchers were perplexed, one of them famously likening the behaviour to "some kind of noodly potluck".1 This is the origin of the expression "crowded as a gastrotrich potluck", still in use in anatomy labs across the Eastern United States (the site of most early gastrotrich research).

Most surprising of all, however, is an event that occurs only once every five years, or so the last six decades of observation has led scientists to believe. At such time, either on the evening of June 15 or the morning of June 16, depending on one's timezone, gastrotrichs will form 'fleets' consisting of nine- to ten-thousand specimens. How such primitive organisms locate each other, sometimes travelling most of their brief lives to do so, is a complete mystery, second only to the puzzle of how it is they know when to do it. Statistically speaking, only about one in six-hundred gastrotrichs will live during a quinquennial Fleet Day. During these Fleet Days, gastrotrichs do not gather in their usual sphere-states but rather collaborate to form larger and more complex arrangements and designs. The most common motif by far is a series of great arrows pointing to the bottom of the sea. In the case of freshwater gastrotrichs, these arrows will simply indicate the direction of the nearest ocean or sea; this phenomenon does not depend on the colony having had direct experience of such bodies of water and has even been observed in freshwater tanks in no way connected to the ocean.

Despite the advanced state of study in modern marine microbiology labs, the gastrotrich remains a perennial 'problem species'. Group behaviour may be partly innate, but even so it must still be stored within the animal mind — and scientists are at a loss as to where exactly the gastrotrich has found the room. Recent years have seen a renaissance in Gastrotrichology, and the emergence of several high-profile research labs devoted solely to the organism. The largest and best-funded of these is the Gastrotrich Language Project at MIT, a group whose mandate is establishing lines of communication with the gastrotrich by means of flavoured jelly arrays.

1Dr. Harold Cowper, American Gastrotrichology in its Infancy, New York: Cambridge University Press, 2005

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