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Hi,
Three weeks ago I saw a small black fly running on the wet algae washed ashore at the Baltic coast. I am sorry the pictures are bad quality, but I would like to show them nevertheless, because I have no idea where to place this fly. It has two strange "brushes" that meet at the abdomen tip, a structure I have not seen before. Help is greatly appreciated!
Thanks in advance, Sundew

This is the habitus:

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And here it is viewed from behind:

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Scathophagidae and Sepsidae are the families that come to mind first, and it doesn't match any Scathophagidae in the British key. One Sepsidae in the gallery has tufts on tergite 4 but it isn't a European species.

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Hi, this is a male Themira (Sepsidae).

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Many thanks, John and Stephane! Up to now I had known Themira females only, so this is a valuable enhancement of knowledge. I compared all species in the Sepsidnet (obviously, among other characters, shape and length of the brushes are decisive) and had also a look at the key by Pont & Meier (2002). Aside from the usual uncertainty there is a rather good conformity with T. putris (http://sepsidnet-...utris.html), so labeling the pictures "T. cf. putris" should not be too wrong ;).