Seven new species of Macellomeniidae Salvini-Plawen, 1978 (Mollusca: Solenogastres) from the North Atlantic

ABSTRACT With only six described species, Macellomeniidae Salvini-Plawen, 1978 is a small monogeneric family within Solenogastres (Mollusca: Aplacophora). Species of Macellomeniidae can be identified by their unique claviform sclerite type, which consists of a proximal base plate and a distal acicular spine. Species of this family have been described from a wide depth range, 59–5430 m, from the Atlantic Ocean, Mediterranean Sea and Salish Sea (Pacific Ocean). Previous Macellomeniidae species descriptions have relied mostly on traditional morphological taxonomy, with molecular data available for only two of them. Here, we examined 17 specimens collected from the Northeast Atlantic during four expeditions of the Icelandic marine Animals: Genetics and Ecology (IceAGE) and Icelandic marine Animals meets Diversity along latitudinal gradients in the deep sea of the Atlantic Ocean (IceDivA) projects using both traditional morphological analysis and molecular species delimitation. This integrative approach revealed nine species in the waters around Iceland, including Macellomenia aciculata Scheltema, 1999, Macellomenia cf. palifera (Pruvot, 1890), and seven species new to science that we formally describe here; more than doubling the number of species in the family. This study highlights the unique hard part anatomy of this family, specifically the sclerites and radula, and their usefulness in the identification of these species. The description of these new species enriches our understanding of the biodiversity of Macellomeniidae and shows that the aplacophoran fauna in the Northeastern Atlantic is under-described. Thus, this work underscores the importance of taxonomic work to improve our understanding of both North Atlantic and overall solenogaster diversity. We also use molecular approaches to examine the ecological role of these animals in the deep sea, finding that they primarily feed on leptothecate and anthoathecate hydrozoans.