Kainonereis, Chamberlin, 1919

Conde-Vela, Víctor Manuel, Wu, Xuwen & Salazar-Vallejo, Sergio Ignacio, 2018, Elisesione imajimai Jimi & amp; Eibye-Jacobsen & amp; Salazar-Vallejo 2018, sp. nov., Zoological Studies (Zool. Stud.) 57 (6), pp. 1-24 : 21-22

Kainonereis as a distinct genus

All epitokes examined share the presence of dorsal discs in chaetigers 5-7. Because the dorsal discs have similar a form (structural criterion) and are at the same position along the body for all epitokes (positional criterion) ( Remane 1952:63-64, Williams and Ebach 2008:140), they are regarded as homologous, and because we assume that these similarities are due to a common ancestor, the dorsal discs are also regarded as homogenous ( Fitzhugh 2006:58); this reasoning was also applied for all the remaining structures discussed in this paper. This leads us to conclude that Kainonereis is a monophyletic group, diagnosed mainly by the presence of dorsal discs and other remarkable features such as truly articulated anterior cirri, dorsal lamellae of dorsal cirri, and notopodial ligules being clearly separated by a large prechaetal lobe.

The reason the currently defined Kainonereis species were regarded as belonging to other, closely related genera such as Nicon or Rullierinereis is because generic delineations were not clearly set off. First, finding a bare pharynx in N. polaris drove Hartman (1967:68) to include it in that genus. Pettibone (1971:4, 5, 8) considered the generic affinity of N. polaris as uncertain but she did not explain why, whereas de León-González and Trovant (2013:73) correctly pointed out the presence of elytriform dorsal cirri as a feature better resembling Kainonereis than Nicon . Second, in R. elytrocirra the presence of notopodial homogomph falcigers made Wu and Sun (1979:106) include their species in Rullierinereis , but later Sun and Yang (2004) regarded R. elytrocirra as belonging to Kainonereis based on the presence of elytriform dorsal cirri.

It might seem problematic to delineate separate nereidid genera on the basis of epitokes alone because of the complex body transformations involved. For reproductive patterns in Nereididae , after the compilation by Reish (1957, table 1), 9 out of 19 species undergo epitoky, and two others swarm, but their bodies are not modified, and these different reproductive patterns are present within the same genus. Clark (1977) showed that what has been regarded as a single species, turned out to include three different reproductive patterns, probably indicating they are different species as well. All species in Kainonereis undergo epitoky, but chances are that some undiscovered species might differ because this reproductive pattern cannot be generalized to the other species in the genus.