| Species |
Recipient region |
Date of the first record |
|
| Styela plicata | Greece / Eastern Mediterranean | 1968 |  |
| Styela plicata | Israel | 1955 | |
| Styela plicata | Italy / Adriatic Sea | 1953 - 1955 | |
| Styela plicata | Italy / Central Mediterranean | 1972 - 1982 | |
| Styela plicata | Italy / Western Mediterranean | 1822 - 1830 | |
| Styela plicata | Portugal / Azores | To 2010 | |
| Styela plicata | Portugal / Iberian Coastal | To 2009 | |
| Styela plicata | Portugal / Madeira | 1992 | |
| Styela plicata | Spain / Iberian Coastal | To 2016 | |
| Stylocheiron sp. | Romania | 1978 | |
| Stylochus flevensis | Netherlands | 1921 | |
| Stylonema alsidii | Australia / Bass strait | 1977 | |
| Stylonema cornu-cervi | Turkey / Black Sea | 2000 - 2009 | |
| Stypopodium schimperi | Greece / Central Mediterranean | 2008 | |
| Stypopodium schimperi | Greece / Eastern Mediterranean | 1994 | |
| Stypopodium schimperi | Israel | 1995 | |
| Stypopodium schimperi | Spain / Canary Islands | To 2002 | |
| Suberites massa | Netherlands | To 1989 | |
| Suberites massa | United Kingdom (Britain) / English Channel | | |
| Suberites massa | United Kingdom (Britain) / North Sea | To 2002 | |
| Sycon raphanus | USA / California Current | 2012 | |
| Sycon scaldiense | Netherlands | To 1975 | |
| Syllidia armata | Netherlands | 1943 | |
| Syllis gracilis | Netherlands | 1940 | |
| Syllis hyllebergi | France / Western Mediterranean | 2019 | |
| Syllis hyllebergi | Italy / Adriatic Sea | 2014 | |
| Syllis hyllebergi | Italy / Central Mediterranean | 2008 | |
| Syllis hyllebergi | Italy / Western Mediterranean | 2008 | |
| Syllis pectinans | Italy / Adriatic Sea | 2013 | |
| Syllis pectinans | Italy / Western Mediterranean | 2013 | |
| Syllis pectinans | Spain / Iberian Coastal | To 2017 | |
| Symphyocladia marchantioides | Italy / Western Mediterranean | 1984 | |
| Symphyocladia marchantioides | Portugal / Azores | 1971 | |
| Symphyocladia marchantioides | Portugal / Iberian Coastal | From 2003 | |
| Symphyocladiella dendroidea | France / Biscay Gulf | 2005 | |
| Symphyocladiella dendroidea | France / Celtic seas | 2018 | |
| Symphyocladiella dendroidea | France / English Channel | 2022 | |
| Symphyocladiella dendroidea | France / Western Mediterranean | 1995 | |
| Symplegma brakenhielmi | Greece / Eastern Mediterranean | 2015 | |
| Symplegma brakenhielmi | Israel | 1951 | |
| Symplegma brakenhielmi | Italy / Central Mediterranean | 2016 | |
| Symplegma brakenhielmi | Italy / Western Mediterranean | 2014 | |
| Symplegma brakenhielmi | Portugal / Madeira | From 2015 | |
| Synagrops japonicus | Italy / Western Mediterranean | 1987 | |
| Synanceia verrucosa | Israel | 2010 | |
| Synaptula reciprocans | Greece / Eastern Mediterranean | 1995 | |
| Synaptula reciprocans | Israel | 1971 | |
| Synchiropus sechellensis | Greece / Central Mediterranean | 2018 | |
| Synchiropus sechellensis | Greece / Eastern Mediterranean | 2014 | |
| Syngnathus acus | Turkey / Black Sea | 2000 - 2009 | |
