(27) Diplosoma listerianum (H. Milne Edwards, 1841)

Status in U.K. – cryptogenic.

Diplosoma listerianum has been recorded at several monitoring programme sites, most years since 2012, most recently from scrape samples. It has also been recorded from renewable energy structures (Want et al. 2017). It is difficult to identify with certainty and is likely to have been present more widely but recorded as Didemnidae . A record from 2012 was listed as D. listerianum / spongiforme .

It is listed as non-native in the Mediterranean (Airoldi et al. 2015; López-Legentil and Legentil 2015) and as invasive in the Netherlands (Gittenberger 2007). Molecular studies by Pérez-Portela et al. (2013) identified cryptic species and evidence of anthropogenic introductions but did not determine the native range. The species should be considered cryptogenic in the U.K. Diplosoma spongiforme (Giard, 1872) is likewise also considered here as cryptogenic in Europe. Both D. spongiforme and D. listerianum were recorded from Orkney by Want et al. (2017) growing on marine renewable energy structures.

NMS voucher reference number: NMS.Z.2017.144.110.