Barnich, Ruth; Dietrich, Anna; Hager, Tatjana; Fiege, Dieter. (2017). On the genera Malmgrenia McIntosh, 1874 and Pettibonesia Nemésio, 2006 in the Northeast Atlantic and Mediterranean Sea, with descriptions of two new species (Polychaeta: Polynoidae). Marine Biodiversity. [efirst, 12 pages].
Eleven species of Malmgrenia McIntosh, 1874 are currently recorded from the Northeast Atlantic and Mediterranean Sea. In eight of them, all long notochaetae have stout, entire tips [Malmgrenia andreapolis McIntosh, 1874; M. arenicolae (Saint-Joseph, 1888); M. castanea McIntosh, 1876; M. lilianae (Pettibone, 1993); M. ljungmani (Malmgren, 1867); M. lunulata (Delle Chiaje, 1830), M. mcintoshi Tebble & Chambers, 1982 and M. polypapillata (Barnich & Fiege, 2001)]. They differ by their elytral, parapodial and neurochaetal characters. Three additional species [Malmgrenia darbouxi (Pettibone, 1993), M. marphysae (McIntosh, 1876) and M. louiseae Jourde, Sampaio, Barnich, Bonifácio, Labrune, Quintino & Sauriau, 2015] can be separated from this group by their long notochaetae tapering to a fine, entire tip. Meanwhile, we found two new species in the area, Malmgrenia bicki sp. nov. and Malmgrenia thomsonae sp. nov., both with some long notochaetae showing a fine, bidentate tip (i.e. with subdistal tooth), but differing mainly by the shape of their supra-acicular process and middle neurochaetae. The presence of bidentate notochaetae first led to confusion with Pettibonesia furcosetosa (Loshamn, 1981), originally described as Malmgrenia as well. But in this species, some of the long notochaetae terminate in a fine furcate (i.e. distally split) tip. The discovery of the two new Malmgrenia species led us to re-assess the generic characters of the genera Malmgrenia and Pettibonesia Nemésio, 2006. As a result, we consider the presence of small cephalic peaks as a character of generic importance for Pettibonesia, especially since cephalic peaks are not found in any of the Malmgrenia species described for the area. The bidentate condition of some notochaetae suggests that the two new species could be assigned to Pettibonesia, but the fact that both new species lack cephalic peaks led us to assign them to Malmgrenia.