Description of a new genus and species of Chrysopetalidae (Annelida: Polychaeta) from the NE Atlantic, with some further records of related species Author Ravara, Ascensão Author Aguado, M. Teresa Author Rodrigues, Clara F. Author Génio, Luciana Author Cunha, Marina R. text European Journal of Taxonomy 2019 2019-07-26 539 1 21 journal article 26120 10.5852/ejt.2019.539 839397be-ec67-462e-9095-dd14ea81222f 3353542 17F463A6-5663-4E82-8FD4-759ACD25D2F2 Craseoschema Ravara & Aguado gen. nov. urn:lsid:zoobank.org:act: 28EA7F9D-30BF-408B-A133-2B2F38EA924E Type species Craseoschema thyasiricola gen. et sp. nov. , by present designation and monotypy. Diagnosis Body long, tapering posteriorly, arched dorsally and flattened ventrally. Prostomium short, with one pair of cirriform antennae with basal swelling and one pair of pad-like palps, without eyes. First segment fused with prostomium, with dorsal and ventral cirri, neuroacicula and neuropodial chaetae. Anterior parapodia with dorsal and ventral cirri and compound neurochaetae. Median and posterior parapodia subbiramous, with dorsal and ventral cirri, simple notochaetae and compound neurochaetae. All chaetae with modified tips. Pygidium cylindrical, without appendages. Etymology The genus name is a combination of the Greek words ‘ krasis ’, meaning ‘mixture’ or ‘combination’, and ‘ schema ’, meaning ‘characteristic’ or ‘figure’, in an allusion to the mixed characteristics from the symbiont and free-living forms. Remarks The subfamily Calamyzinae includes symbiont and free-living forms, the majority of which are associated with chemosynthetic environments. These forms have different morphological characteristics in a clear adaptation to their life style. The new genus is based on a specimen found inside a thyasirid bivalve and presents all the characteristics of a symbiont form (arched body, poorly developed notopodia with short dorsal cirri, neurochaetae with modified tips, absence of pygidial cirri), but also some characteristics of the free-living forms (presence of pad-like palps, notochaetae and compound neurochaetae). This particular combination of characteristics makes it different from all other genera within Calamyzinae except for a recently described new genus, Spathochaeta Jimi et al. , 2019 , found on the body surface of an octopus from the Kumano Sea, Japan ( Jimi et al. 2019 ). Spathochaeta and Craseoschema gen. nov. present a similar composition of characters: arched body, a pair of ventrally placed palps, notochaetae with modified tips, compound neurochaetae and pygidial cirri absent. However, they differ by the presence in Spathochaeta of a well-developed dorsal lobe in the notopodia and spinigerous neurochaetae, rather than falcigerous with modified tips. The genus Calamyzas , parasites of ampharetid polychaetes, also possesses compound neurochaetae but notochaetae are absent and the parapodia of the first chaetiger are reduced to a pair of ventral cirri. Craseoschema gen. nov. is similar to the freeliving genera ( Vigtorniella Kiseleva, 1996 , Boudemos Watson et al. , 2016 and Micospina Watson et al. , 2016 ) in the possession of notochaetae and compound neurochaetae, but differs in details of noto- and neurochaetal morphology and in lacking tentacular and anal cirri. The separation of Craseoschema gen. nov. from the other Calamyzinae is also evident in the phylogenetic analysis presented ( Fig. 2 ). Craseoschema gen. nov. is placed together with the symbiont forms of Calamyzinae in a monophyletic group, although this is not strongly supported ( Fig. 2 ).