| Avagina glandulifera Westblad, 1953 | prior to 1945 | | parasite found in sea cucumber, sea urchins. Found in Spatangus purpureus. | |
| Convoluta convoluta (Abildgaard, 1806) | prior to 1905 | littoral | | |
| Plagiostomum girardi (Schmidt, 1857) | 1955 or earlier | | | |
| Acmostomum dioicum Metschnikoff, 1865 | 1949 | | | uncommon. |
| Trigonostomum penicillatum (Schmidt, 1857) | 5 July, 1949 | | | coll. SMNH by Westblad |
| Nannorhynchides herdlaensis (Karling, 1956) | 1956 or earlier | | | tide pools, Westblad. |
| Provortex affinis (Jensen, 1878) | 1913 or earlier | littoral | | |
| Syndesmis echinorum Francois, 1886 | 1913 or earlier | | | in sea urchins [Strongylocentrotus droebachensis (Müll.), S. lividus Brdt., Sphaerechinus granularis A.Ag., Echinus sphaera Müll., E. acutus Lam.] |
| Maehrenthalia agilis (Levinsen, 1879) | 1913 or earlier | | | |
| Byrsophlebs graffi Jensen, 1878 | 1913 or earlier | | | beach water. |
| Proxenetes flabellifer Jensen, 1878 | 1913 or earlier | | | beach water. |
| Promesostoma marmoratum marmoratum (Schultze, 1851) | 1913 or earlier | | | very active, in marine and brackish water. |
| Promesostoma marmoratum (Schultze, 1851) | 1913 or earlier | | | very active, in marine and brackish water. |
| Promesostoma ovoideum ovoideum Graff, 1905 | 1913 or earlier | | | |
| Promesostoma ovoideum purum Graff, 1905 | 1913 or earlier | | | |
| Promesostoma solea solea Graff, 1905 | 1913 or earlier | | | |
| Promesostoma lenticulatum (Schmidt, 1852) | 1913 or earlier | | | |
| Trigonostomum armatum (Jensen, 1878) | 1913 or earlier | 0-27 m | | found in Fucus at depths up to 27 m. |
| Trigonostomum penicillatum (Schmidt, 1857) | 1913 or earlier | | | |
| Acrorhynchus caledonicus (Claperede, 1861) | 1913 or earlier | 1-3 m | | in ebb tide pools, and litoral zone in large numbers. |
| Polycystis naegelii Kölliker, 1845 | 1913 or earlier | | | living among plants in the litoral zone. |
| Polycystis crocea (Fabricius, 1826) | 1913 or earlier | | | |
| Phonorhynchus helgolandicus (Metschnikow, 1865) | 1913 or earlier | | | |
| Plagiostomum ochroleucum Graff, 1882 | 1913 or earlier | | | |
| Plagiostomum sagitta (Uljanin, 1870) | 1913 or earlier | 6-9 m | | littoral. |
| Plagiostomum caudatum Levinsen, 1879 | 1882 or earlier | | | |
| Plagiostomum dioicum (Mecznikow, 1865) | 1913 or earlier | | | |
| Plagiostomum elongatum Gamble, 1893 | 1893 or earlier | | | littoral. |
| Plagiostomum siphonophorum (Schmidt, 1852) | 1913 or earlier | | | |
| Plagiostomum vittatum (Frey & Leuckart, 1847) | 1913 or earlier | | | |
| Plagiostomum koreni Jensen, 1878 | 1913 or earlier | | | |
| Vorticeros auriculatum (Müller, 1784) | 1913 or earlier | 0-35m | | littoral up to 35 m deep in Algen and Bryozoen. |
| Vorticeros luteum Hallez, 1879 | 1913 or earlier | 0-13 m | | Generally found among Ulven and Zosteren. Found a 13 m depth, with Bugula turbinata. |
| Pseudostomum quadrioculatum (Leuckart, 1847) | 1913 or earlier | | | |
| Pseudostomum inerme (Hallez, 1879) | 1893 or earlier | | | among algae. |
| Monoophorum striatum (Graff, 1878) | 1913 or earlier | 0-28 m | | among Ulven, Bryozoans. |
| Monoophorum elongatum Gamble, 1879 | 1879 or earlier | | | |
| Enterostomum fingalianum Claparede, 1861 | 1913 or earlier | 33-40 m | | |
| Allostoma austriacum (Graff, 1882) | 1913 or earlier | | | |
| Monocelis fusca Örsted, 1843 | 1913 or earlier | | | |
| Monocelis lineata (Müller, 1773) | 1913 or earlier | | | |
| Monocelis hamata Jensen, 1878 | 1893 or earlier | 21 m | | |
| Monocelis alba Levinsen, 1879 | 1913 or earlier | | | |
| Monocelis gamblei Graff, 1893 | 1861 or earlier | 36 m | | |
| Monocelis hirudo Levinsen, 1879 | 1913 or earlier | | | |
| Monocelis unipunctata (1) Fabricius, 1826 | 1913 or earlier | | | |
| Avagina glandulifera Westblad, 1953 | 1949 | | | Examining sea urchins at the Zoological Station at Plymouth, found specimen in Spatangus purpurens. |
| Anoplodium tubiferum Westblad, 1953 | 1949 | | | Examining Holothuria forskali at the Zoological Station at Plymouth, found this new species. |
| Umagilla forskalensis Wahl, 1909 | 1949 | | | Examining Holothuria forskali at the Zoological Station at Plymouth, found this species. |
| Marcusella atriovillosa Westblad, 1953 | Jul 3, 1948 | | | Examining sea urchins at the Zoological Station at Plymouth, found 5 specimens in the intestine of Spatangus purpureus along with Avagina incola. |
| Oligocladus sanguinolentus (Quatrefage, 1845) | 1893 or earlier | | | |
| Archilopsis spinosa (Jensen, 1878) | prior to 1989 | | | Collector Capstick. Date ?. |
| Triloborhynchus astropectinis Bashiruddin & Karling, 1970 | 1970 or earlier | | | found in Astropecten irregularis. |
| Procerodes plebeius (Schmidt, 1861) | 1989 or earlier | | | Mittelmeer, Schwarzes Meer, Ostatlantik (Plymouth, England). 'P. plebeia occurs in brackish water springs or in otherwise brackish habitats' (Sluys 1989b, p. 288) |
| Procerodes lobatus (Schmidt, 1862) | 1968 or earlier | | | Ausführliche Daten über Siedlungen in Sandstränden bei Plymouth (England) liefert. |
| Aphanostoma rhomboides Jensen, 1878 | 1905 or earlier | | | Kanal La Manche (Plymouth). |
| Macrostomum hystricinum Beklemischev, 1951 | 1953 or earlier | | | England, Plymouth u. Isle of Man in ausgesüsstem Wasser. |
| Rogneda anglica Karling, 1953 | 1953 or earlier | 10-36 m | loam | |
| Procerodes ireneae den Hartog, 1968 | 1968 or earlier | | | |
| Uteriporus vulgaris Bergendal, 1890 | 1968 or earlier | | | |