Aphanostoma pisae: An interstitial Acoelomate Worm from the Liguric Sea.

Acoelomate Worms are microscopic  animals resembling Platyhelminths and formerly thought to be closely related to them. They share the same basic body-plan, with a flattened body comprising two layers of cells without separating tissue and a non-through gut, but recent genetic studies have suggested the groups are unrelated, having come up with the same simple bodies as a result of convergent evolution. However these studies have been unable to resolve the exact relationship between Acoelomate Worms and other animals, with suggestions that they might be the sister group to the Bilaterians (basically all animals except Sponges, Cnidarians and Ctenophores), a position which was formerly suggested for the Platyhelminths as a whole, or that they might be Deuterostomes, members of the group which includes Vertebrates and Echinoderms.Aceolomate Worms are predominantly marine animals, but have been studied very little away from the Baltic, so the full range of habitats they inhabit is probably not known.

In a paper published in the journal Zootaxa on 1 April 2015, Thomas Zauchner, Willi Salvenmoser and Bernhard Egger of the Institute of Zoology at the University of Innsbruck describe a new species of Acoelomate Worm from interstitial sands collected from the beach at Marina di Pisa in Italy, on the coast of the Liguric Sea (part of the Mediterranean).

The new species is placed in the genus Aphanostoma, and given the specific name pisae, in reference to the area where it was found. The worms are transparent and reach 400-700 μm in size on reaching maturity. They bred well in captivity, laying eggs which hatched after 46 hours, leading Zauchneret al. to suggest that they might make good animals for laboratory studies of the group.

Live differential interference contrast image of Aphanostoma pisae. Mature animal, anterior to the right. Scale bar is 100 μm.

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