Opheliidae Malmgren, 1867

Wiklund, Helena, Neal, Lenka, Glover, Adrian G., Drennan, Regan, Muriel Rabone, & Dahlgren, Thomas G., 2019, Abyssal fauna of polymetallic nodule exploration areas, eastern Clarion-Clipperton Zone, central Pacific Ocean: Annelida: Capitellidae, Opheliidae, Scalibregmatidae, and Travisiidae, ZooKeys 883, pp. 1-82 : 1

Opheliidae Malmgren, 1867

Notes.

Due to their simple morphology, there is much confusion in the taxonomic literature dealing with Opheliidae , and many species and genera are currently considered invalid (Read and Fauchald 2018c). Useful recent studies clarifying some of the confusion are Kongsrud et al. (2011) and Parapar et al. (2011) based on material collected from North-East Atlantic. It would appear that several previous descriptions were based on what are in fact different, if morphologically very similar, species. Characters such as the shape of the prostomium and associated palpode are often reported in descriptions and used to distinguish species, but the UKSR material showed that the shape in preserved specimens may be variable and the shape and size of the associated palpode can also vary with preservation. Additionally, the shape of the prostomium in live specimens can be of different shape to that observed in preserved specimens (L. Neal pers. obs.) and thus this character might not be useful. Mouth structures in opheliids are rarely observed and reported but considered important by some authors ( Tzetlin and Zhadan 2009). The number of chaetigers in a specimen has been deemed as a useful character by e.g. Kongsrud et al. (2011) and Blake (2000b). The chaetae of the opheliids are relatively uniform smooth capillaries of limited taxonomical importance. However, Sarda et al. (2009) reported the presence of hirsute capillaries in Ophelina margaleffi Sarda et al., 2009 observed under SEM. Opheliid branchiae are very fragile structures which are easily lost and thus their distribution and number can be difficult to observe. Kongsrud et al. (2011) illustrated the importance of examining a relatively large number of specimens in order to correctly establish the characters of these structures. The anal tube is also a very fragile structure that is easily lost, and true absence is difficult to distinguish from loss due to damage. Kongsrud et al. (2011) again illustrated the importance of examining a relatively large number of specimens in order to correctly establish the presence and form of this structure.

Unfortunately, the ABYSSLINE material provides very few specimens (often just one) per species, which complicates the morphological interpretation. Nevertheless, in combination with DNA data, we believe it is important to provide the currently best possible morphology, which can be amended as more and better-preserved examples become available in the future. As a result, only 8 out of 15 opheliid species found in the ABYSSLINE material are here formally described. Morphologically, the ABYSSLINE material can be assigned to two known genera, Ammotrypanella McIntosh, 1878 and Ophelina Örsted, 1843.