Phaenomonas longissima, also known as the short-maned sand eel in St. Helena,Common names of Phaenomonas longissima at www.fishbase.org. is an eel in the family Ophichthidae (worm/snake eels).Phaenomonas longissima at www.fishbase.org. It was described by Jean Cadenat and Émile Marchal in 1963, originally under the genus Callechelys.Cadenat, J. and E. Marchal, 1963 (Oct.) Résultats des campagnes océanographiques de la Reine-Pokou aux îles Sainte-Hélène et Ascension. Bulletin de l'Institut Francais d'Afrique Noire (Sér A) Sciences Naturelles v. 25 (no. 4): 1235-1315, 51 unnumbered pls. It is a marine, tropical eel which is known from the Atlantic Ocean, including Ascension Island, St. Helena, Brazil, Senegal, Ghana, and Cape Verde. It dwells at a depth range of , and forms burrows in sand and mud sediments on the continental shelf. Males can reach a maximum total length of .
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