Thyasiroidea (Mollusca: Bivalvia) from the mud volcanoes of the Gulf of Cadiz (NE Atlantic) Rodrigues, Clara F. Oliver, Graham Cunha, Marina R. Zootaxa 2008 1752 41 56 Jeffreys, 1881 Jeffreys 1881 [151,563,151,177] Bivalvia Thyasiridae Thyasira Animalia Lucinoida 9 50 Mollusca species tortuosa   Material examined. One live-collected specimen, TTR16 cruise, station AT 622Gr, Porto mud volcano, Gulf of Cadiz, 35º 33.773N, 09º 30.416W, 3902 m, 3 June 2006( DBUA00830.01).   Remarks.The only specimen examined is provisionally identified as  Thyasira tortuosaand has the characteristically compressed and anteriorly expanded outline noted by Payne and Allen (1991). The shell from Gulf of Cadiz ( 5.5 mm) is much larger than any of the shells described by these authors ( 3.2 mm) and comes from a greater depth: 3902mwhilst the maximum given by Payne & Allen (1991)was 2359 m. Dufour (2005)did not examine this species but the Gulf of Cadiz specimen has a Type2 gill with both demibranchs. The gills are rather thick and have the same appearance as the ones that exhibit strong bacterial symbiosis such as  T. flexuosa and  T. gouldi.