Paraonella sp. 1

Gunton, Laetitia M., Kupriyanova, Elena K., Alvestad, Tom, Avery, Lynda, Blake, James A., Biriukova, Olga, Boeggemann, Markus, Borisova, Polina, Budaeva, Nataliya, Burghardt, Ingo, Capa, Maria, Georgieva, Magdalena N., Glasby, Christopher J., Hsueh, Pan-Wen, Hutchings, Pat, Jimi, Naoto, Kongsrud, Jon A., Langeneck, Joachim, Meissner, Karin, Murray, Anna, Nikolic, Mark, Paxton, Hannelore, Ramos, Dino, Schulze, Anja, Sobczyk, Robert, Watson, Charlotte, Wiklund, Helena, Wilson, Robin S., Zhadan, Anna & Zhang, Jinghuai, 2021, Annelids of the eastern Australian abyss collected by the 2017 RV ' Investigator' voyage, ZooKeys 1020, pp. 1-198 : 1

Paraonella sp. 1 Fig. 19F

Diagnosis.

Complete specimen with 72 chaetigers, 0.3 mm maximum width, 8 mm total length. Prostomium oval, without apical organ, without eyes, two large nuchal organs, often with rusty pigmentation. Branchiae absent, notopodial post-chaetal lobes finger-like from chaetiger 1 to chaetiger 9, triangular, short afterwards, increasing in length for last 15 chaetigers. Pygidium rounded with three cirri approximately of the same length. Chaetae all capillaries. Methyl green staining: no pattern. The only complete specimen partially in a brittle, mucous tube.

Remarks.

The absence of modified chaetae and prostomial antenna allows the assignation of these specimens to the genus Paraonella Strelzov, 1973. Currently the genus includes eight species, three of which are abranchiate, namely Paraonella monilaris (Hartman & Fauchald, 1971), Paraonella myriamae (Laubier & Ramos, 1974) and Paraonella abranchiata Fauchald & Hancock, 1981. Both P. myriamae and P. abranchiata are characterised by triangular prostomium, and can be readily distinguished from Paraonella sp. 1; P. monilaris , instead, has a rounded prostomium and a similar pattern of notopodial lobes, and might be closer to this species, even though the structure of nuchal organs is not clear from the original drawings. However, P. monilaris has moniliform segments, with clear constrictions in between, while Paraonella sp. has less pronounced constrictions and shorter segments. Moreover, although the size of the specimens examined by Hartman and Fauchald (1971) is similar (<8 mm for 71 chaetigers), they are slenderer (0.23 mm vs. 0.27-0.35 mm maximum width). According to the original drawing, notopodial lobes are proportionally shorter in P. monilaris , but the pattern described by Hartman and Fauchald (1971) (lobes short, increasing until the eighth chaetiger, then shorter) is very similar to that observed in these specimens. Although the ecology of the two species is very similar and morphological features largely overlap, the difference between P. monilaris and Paraonella sp. is unclear as the original description of P. monilaris lacks detail.

Paraonella as currently described is most likely polyphyletic, including species close to Paradoneis Hartman, 1965 and to Paraonis Grube, 1873. The pattern of notopodial lobes observed in this species clearly resembles that occurring in Paradoneis , as in the majority of the known Paraonella species. However, there is the possibility that Paradoneis -like Paraonella also represent separate lineages that independently lost the modified notochaetae.

Records.

11 specimens. Suppl. material 1: ops. 33, 54 (AM).

Figures

Figure 19. Paraonidae A Aricidea sp., prostomium with median antennae B same, capillary with arista C Aricidea cf. simplex, dorsal view anterior (AM W. 52307) D same, ventral view anterior (AM W. 52307) E Levinsenia uncinata (AM W. 52320), methyl green stained dorsal view F Paraonella sp. 1 (AM W. 52310) G Paraonis cf. quadrilobata chaetae (AM W. 52307). Scale bars: 250 µm (A); 50 µm (B); 1 mm (C, D, E, F); 10 µm (G).