Laetinaevia marina is a frequent ascomycetous fungus that is widely distributed on the seashores of Scandinavia and Great Britain. It grows on fronds of Fucales (Phaeophyceae) that are washed ashore and lie decaying at the high tide mark or further up on the beach. It is one of the few described marine discomycetes. In the current generic concept it is regarded as a member of Naevioideae (Dermateaceae or Mollisiaceae), while it has previously been placed in the genus Orbilia (Orbiliaceae). We studied fresh collections, in live and dead state, to provide a morphological update on the species and to elucidate its systematic placement using molecular systematics. The hemiamyloid reaction of the apical ring, the absence of croziers, and the faintly refractive vacuolar bodies of the terminal cells of living paraphyses are reported here for the first time. A thin gel sheath surrounding the ascospores was confirmed to exist. Based on morphological characters, ribosomal RNA and protein coding gene sequences published for this species here for the first time, we show that L. marina is distinct from the genera and families it was previously placed in, and propose the new combination Calycina marina , despite its erumpent, sessile, pulvinate and rather immarginate apothecia. Furthermore, we present additional observations on the ecology, phenology, and distribution of the species.