Two new species of Heteromysini (Mysida, Mysidae) from the island of Madeira (NE Atlantic), with notes on Sea Anemone and Hermit Crab commensalisms in the genus Heteromysis S.I. Smith, 1873

Faunistic studies and a survey of anemone commensals in near-shore habitats at the Island of Madeira yielded two new species belonging to the genus Heteromysis: H. dardani commensal with the diogenid hermit crab, Dardanus calidus (Risso, 1827), and H. wirtzi with the sea anemone, Telmatactis cricoides (Duchassaing, 1850). Both species differ from previously known E. Atlantic species by a flagellate, modified seta on the inner distal corner of the antermular trunk. H. wirtzi shows more spines on the second to fourth male pleopods, and four spines on the endopods of the uropods compared to three spines in H. dardani. Morphological differences suggest that commensalism of Heteromysis species with hermit crabs has independently evolved in the (sub)tropical shelf areas of the Indo-Pacific, E. Pacific, and Atlantic oceans. The W. Atlantic anemone commensals belong to two morphologically distinct lines within the subgenus Olivemysis Bacescu, 1968, one of which shows close relationships to the two newly described E. Atlantic species. A key to the species of Heteromysis known from the E. Atlantic and the Mediterranean is given.