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Wonderful Creatures: the tiny, predatory penis-worm that lies in wait in the sand

The seabed is really where it’s at in terms of animal diversity. Of the 35 known animal lineages, representatives of all but two are found here. In contrast, the huge numbers of species that inhabit tropical rainforests represent a mere 12 lineages.



One group of animals that illustrates the diversity of the seabed is the Priapulida, which also go by the unfortunate common name of “penis worms.” Only 20 species of priapulid are known today, a shadow of their diverse past, which extends back for well over 500 million years. Not commonly seen, the priapulids have attracted little attention from the zoology community as a whole.



This week’s animal, discovered in 1973, is perhaps the most interesting priapulid. Named after the leaders of an ancient Jewish rebel army, Maccabeus is a midget amongst its kind—just 1.4 to 2.8 mm and it lives in a tiny, gelatinous tube in the seabed. What’s really odd about this little animal is the way it catches its prey—smaller animals, such as microscopic crustaceans, etc. Much of the body of Maccabeus is concealed in its tube with the head end lying flush with the sea bed and its crown of spines poking up into the water—forming a trap to snare prey. When an unfortunate animal blunders into this trap, the spines close over to form a cage from which there is no escape. Trapped, the prey is sucked into Maccbeus’ mouth and eaten.



Although rarely seen by casual observers, priapulids can be very abundant in some places and densities of 85 adults and 58,000 larvae per square meter have been recorded. They even seem to thrive in anoxic sediments (depleted of oxygen) suffused with eggy, highly toxic hydrogen sulphide—a habitat that few other animals can tolerate. Not only can they be surprisingly abundant, but they, and other very poorly known animal lineages, once collectively known as “lesser lineages,” are fundamental to our understanding of animal evolution as a whole, yet we have only scratched the surface of their biology and ecology.





The tiny, tube-dwelling Maccabeus lies hidden in marine sediment with just the spines on its head-end poking above the surface to form a trap. Once sprung, the spines close over to make a cage that ensnares prey. Photo by: © Phil Miller.




Dr. Ross Piper is a zoologist and author and has recently presented on the BBC/Smithsonian TV production, Wild Burma: Nature’s Lost Kingdom, soon to be shown in the USA. You can read an interview with Ross Piper here: Animal Earth: exploring the hidden biodiversity of our planet.









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