This week, scientists reported the first evidence that one of the most ancient surviving animal lineages, placozoans, have sex. The finding, published in the Proceedings of the National Academy of Sciences, suggests placozoans could prove an excellent model organism for understanding metazoan evolution, co-author Ana Signorovitch at Yale University in New Haven, Conn., told The Scientist.

For instance, researchers could breed placozoans and chart their complete life cycle, then observe which development stages are shared between placozoans and sponges, Signorovitch noted. This exercise "could help answer questions such as what the relationships between the basal groups are," she explained.

Placozoans could also prove to be an essential model organism, Signorovitch added, since they are "easier than fruit flies" to culture in the lab, requiring only seawater, food such as red algae and light, and petri dishes kept at room temperature.

Since their discovery over a century ago, it...

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