Species of Pollock (1998) are those that were reported as occurring between Cape Cod and Newfoundland (but not necessarily in the ocean waters surrounding Mount Desert Island). If they were not reported by Procter (1933), they need further examination and potential removal from this checklist. Please send corrections and updates to info@vfthomas.com. Photographs are welcome. Thank you.
| Class | Order | Family | Genus | Specific Epithet | authority | common name | Sources (full citations given after this table) |
| Hydrozoa | Anthoathecatae | Acaulidae | Acaulis | primarius | Stimpson | ? | Procter (1993, p. 117.), Pollock (1998) |
| Hydrozoa | Anthoathecatae | Bougainvilliidae | Aselomaris | michaeli | Berrill | ? | Pollock (1998) |
| Hydrozoa | Anthoathecatae | Bougainvilliidae | Bougainvillia | carolinensis | (McCrady) | ? | Procter (1993, p. 116.), Pollock (1998) |
| Hydrozoa | Anthoathecatae | Bougainvilliidae | Bougainvillia | superciliaris | (L. Agassiz) | ? | Pollock (1998) |
| Hydrozoa | Anthoathecatae | Bougainvilliidae | Garveia | franciscana | (Torrey) | rope grass | Pollock (1998) |
| Hydrozoa | Anthoathecatae | Corymorphidae | Corymorpha | pendula | L. Agassiz | nodding bouquet hydroid | Procter (1933, p. 117.), Pollock (1998) |
| Hydrozoa | Anthoathecatae | Corynidae | Sarsia | tubulosa | (M. Sars) | clapper hydroid | Pollock (1998) |
| Hydrozoa | Anthoathecatae | Hydractiniidae | Clava | multicornis | (Forsskål) | club hydroid | Procter (1933, p. 116. as Clava leptostyla), (Pollock, 1998) |
| Hydrozoa | Anthoathecatae | Oceanidae | Cordylophora | caspia | (Pallas) | freshwater hydroid | Pollock (1998) |
| Hydrozoa | Anthoathecatae | Oceanidae | Rhizogeton | fusiformis | L. Agassiz | freshwater hydroid | Pollock (1998) |
| Hydrozoa | Leptothecatae | Haleciidae | Halecium | articulosum | Clark | ? | Procter (1933, p. 119.) |
| Hydrozoa | Leptothecatae | Haleciidae | Halecium | halecinum | (L.) | herringbone hydroid | Procter (1933, p. 118.), Pollock (1998) |
| Hydrozoa | Leptothecatae | Haleciidae | Halecium | beanii | (Johnston) | ? | Procter (1933, p. 117.) |
| Hydrozoa | Leptothecatae | Haleciidae | Halecium | tenellum | Hincks | ? | Procter (1933, p. 119.) |
| Hydrozoa | Leptothecatae | Halopterididae | Halopteris | tenella | (Verrill) | ? | Pollock (1998, as Schizotricha tenella) |
| Hydrozoa | Anthoathecatae | Corynidae | Linvillea | agassizi | (McCrady) | ? | Procter (1933, p. 116., as Corynitis agassizii) |
| Hydrozoa | Anthoathecatae | Hydractiniidae | Hydractinia | polyclina | L. Agassiz | ? | Procter (1933, p. 116.) |
| Hydrozoa | Anthoathecatae | Eudendriidae | Eudendrium | album | Nutting | white stickhydroid | Procter (1933, p. 117.) |
| Hydrozoa | Anthoathecatae | Eudendriidae | Eudendrium | carneum | Clarke | red stickhydroid | Procter (1933, p. 117.) |
| Hydrozoa | Anthoathecatae | Eudendriidae | Eudendrium | dispar | L. Agassiz | ? | Procter (1933, p. 116.) |
| Hydrozoa | Anthoathecatae | Eudendriidae | Eudendrium | ramosum | L. | stickhydroid | Procter (1933, p. 116.) |
| Hydrozoa | Anthoathecatae | Tubulariidae | Ectopleura | crocea | L. Agassiz | ? | Procter (1933, p. 117., as Tubularia crocea) |
| Hydrozoa | Anthoathecatae | Tubulariidae | Ectopleura | larynx | (Ellis & Solander) | ringed tubularia | Procter (1933, p. 117., as Tubularia tenella) |
| Hydrozoa | Leptothecatae | Campanulariidae | Campanularia | amphora | (Agassiz) | ? | Procter (1933, p. 119.) |
| Hydrozoa | Leptothecatae | Campanulariidae | Campanularia | calceolifera | Hincks | ? | Procter (1933, p. 119.) |
| Hydrozoa | Leptothecatae | Campanulariidae | Campanularia | flexiosa | (Hincks) | ? | Procter (1933, p. 119., [as Campanularia flexuosa (Alder)?]) |
| Hydrozoa | Leptothecatae | Campanulariidae | Laomedea | neglecta | Alder | ? | Procter (1933, p. 119., as Campanularia fragilis) |
| Hydrozoa | Leptothecatae | Campanulariidae | Orthopyxis | integra | (MacGillivray) | ? | Procter (1933, p. 119., as Campanularia integra) |
| Hydrozoa | Leptothecatae | Campanulariidae | Campanularia | neglecta | (Alder) | ? | Procter (1933, p. 119.) |
| Hydrozoa | Leptothecatae | Campanulariidae | Campanularia | volubilis | (L.) | ? | Procter (1933, p. 119.) |
| Hydrozoa | Leptothecatae | Campanulariidae | Campanularia | caliculata | ? | ? | Procter (1933, p. 120., [as Orthopyxis caliculata (Hincks)?]) |
| Hydrozoa | Leptothecatae | Campanulariidae | Clytia | hemisphaerica | (L.) | ? | Procter (1933, p. 120., as Clytia bicophora) |
| Hydrozoa | Leptothecatae | Campanulariidae | Clytia | gracilis | (M. Sars) | ? | Procter (1933, p. 120., as Clytia cylindrical) |
| Hydrozoa | Leptothecatae | Campanulariidae | Obelia | longissima | (Pallas) | ? | Procter (1933, p. 120., as Obelia commissuralis) |
| Hydrozoa | Leptothecatae | Campanulariidae | Obelia | dichotoma | (L.) | sea thread hydroid | Procter (1933, p. 120., also as Obelia gracilis) |
| Hydrozoa | Leptothecatae | Campanulariidae | Obelia | geniculata | (L.) | knotted thread hydroid | Procter (1933, p. 120.) |
| Hydrozoa | Leptothecatae | Campanulariidae | Obelia | longissima | (Pallas) | ? | Procter (1933, p. 120.) |
| Hydrozoa | Leptothecatae | Campanulariidae | Gonothyraea | loveni | (Allman) | ? | Procter (1933, p. 121.) |
| Hydrozoa | Leptothecatae | Lafoeidae | Hebella | venusta | (Allman) | ? | Procter (1933, p. 121., as Hebella calcarata) |
| Hydrozoa | Leptothecatae | Phialellidae | Opercularella | lacerata | (Johnston) | ? | Procter (1933, p. 122.) |
| Hydrozoa | Leptothecatae | ? | Cuspidella | grandis | Hincks | ? | Procter (1933, p. 122.) |
| Hydrozoa | Leptothecatae | Calycellidae | Calycella | syringa | (L.) | creeping bell hydroid | Procter (1933, p. 122.) |
| Hydrozoa | Leptothecatae | Lovenellidae | Lovenella | grandis | Nutting | ? | Procter (1933, p. 123.) |
| Hydrozoa | Leptothecatae | Lafoeidae | Lafoea | dumosa | (Fleming) | ? | Procter (1933, p. 123.) |
| Hydrozoa | Leptothecatae | Lafoeidae | Filellum | serpens | (Hassall) | ? | Procter (1933, p. 123.) |
| Hydrozoa | Leptothecatae | Sertulariidae | Abietinaria | abietina | (L.) | sea fir | Procter (1933, p. 124.) |
| Hydrozoa | Leptothecatae | Sertulariidae | Diphasia | fallax | (Johnston) | ? | Procter (1933, p. 123.) |
| Hydrozoa | Leptothecatae | Sertulariidae | Diphasia | rosacea | (L.) | lily hydroid | Procter (1933, p. 123.) |
| Hydrozoa | Leptothecatae | Sertulariidae | Hydrallmania | falcata | (L.) | sickle hydroid | Procter (1933, p. 124.) |
| Hydrozoa | Leptothecatae | Sertulariidae | Sertularella | polyzonias | (L.) | great tooth hydroid | Procter (1933, p. 124.) |
| Hydrozoa | Leptothecatae | Sertulariidae | Sertularella | rugosa | (L.) | snail trefoil hydroid | Procter (1933, p. 124.) |
| Hydrozoa | Leptothecatae | Sertulariidae | Sertularella | tricuspidata | (Alder) | ? | Procter (1933, p. 124.) |
| Hydrozoa | Leptothecatae | Sertulariidae | Sertularia | pumila | (L.) | ? | Procter (1933, p. 123.) |
| Hydrozoa | Leptothecatae | Sertulariidae | Sertularia | argentea | (L.) | squirrel's tail hydroid | Procter (1933, p. 124., as Thuiaria argentea) |
| Hydrozoa | Leptothecatae | Sertulariidae | Sertularia | cupressina | L. | sea cypress hydroid | Procter (1933, p. 124., as Thuiaria cupressina) |
| Hydrozoa | Leptothecatae | Sertulariidae | Thuiaria | thuja | (L.) | bottlebrush hydroid | Procter (1933, p. 124.) |
| Staurozoa | Stauromedusae | Lucernariidae | Lucernaria | quadricornus | O. F. Müller | ? | Procter (1933, p. 125.) |
| Scyphozoa | Semaeostomeae | Cyaneidae | Cyanea | capillata | (L.) | lion's mane | Procter (1933, p. 125., as Cyanea artica) |
| Scyphozoa | Semaeostomeae | Ulmaridae | Aurelia | aurita | (L.) | moon jelly | Procter (1933, p. 125., as Aurenia aurita (flavidula)) |
| Anthozoa | Actiniaria | Actiniidae | Urticina | felina | (L.) | ? | Procter (1933, p. 126., as Tealia felina) |
| Anthozoa | Actiniaria | Metridiidae | Metridium | senile | (L.) | clonal plumose anemone | Procter (1933, p. 126.) |