Ophelina ganae, Wiklund, Helena, Neal, Lenka, Glover, Adrian G., Drennan, Regan, Muriel Rabone, & Dahlgren, Thomas G., 2019

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

Ophelina ganae sp. nov. Fig. 12 A–I

Material examined.

NHM_245 NHMUK ANEA 2019.7140, coll. 16 Oct. 2013, 13°48.70N, 116°42.60W, 4076 m http://data.nhm.ac.uk/object/3a34b9cb-504b-48a3-a8e9-93077ec69520; NHM_248 NHMUK ANEA 2019.7141, coll. 16 Oct. 2013, 13°48.70N, 116°42.60W, 4076 m http://data.nhm.ac.uk/object/e67f7724-8c9f-4463-943e-7cda20441728; NHM_473 NHMUK ANEA 2019.7142, coll. 22 Oct. 2013, 13°43.597N, 116°40.20W, 4160 m http://data.nhm.ac.uk/object/79dcab18-936b-430e-b770-6aab60d285c5; NHM_598 (SEM) (paratype) NHMUK ANEA 2019.7143, coll. 17 Feb. 2015, 12°23.174N, 116°32.92W, 4202 m http://data.nhm.ac.uk/object/2fa20a59-8bb3-4ef8-b2e9-efccbe2c9414; NHM_708 NHMUK ANEA 2019.7144, coll. 20 Feb. 2015, 12°32.23N, 116°36.25W, 4425 m http://data.nhm.ac.uk/object/2077c6c6-0e3e-4dfa-97a0-16d6c386ff07; NHM_1098 NHMUK ANEA 2019.7145, coll. 26 Feb. 2015, 12°06.93N, 117°09.87W, 4100 m http://data.nhm.ac.uk/object/5661fb64-83a2-4e9a-b3c3-a8405705ed1a; NHM_1137 (holotype) NHMUK ANEA 2019.7146, coll. 26 Feb. 2015, 12°06.93N, 117°09.87W, 4100 m http://data.nhm.ac.uk/object/11616c16-bdb5-4813-9d17-7170bb62702b; NHM_1309 (paratype) (SEM) NHMUK ANEA 2019.7147, coll. 01 Mar. 2015, 12°15.44N, 117°18.13W, 4302 m http://data.nhm.ac.uk/object/1ff41b52-9801-4b2e-8e01-ea34597b708d.

Type locality.

Pacific Ocean, CCZ, 12°06.93N, 117°09.87W, depth 4100 m, in mud between polymetallic nodules.

Description.

Small species (4.5-8 mm long without anal tube), represented by eight specimens; all preserved specimens without anal tube (likely missing due to damage). Holotype is 7 mm long and 0.3 mm wide for 17 chaetigers. Paratypes 7-8 mm long and 0.33-0.35 mm wide for 17 chaetigers. Body cylindrical and smooth without distinct annulation. Preserved specimen yellow in ethanol ( Fig. 12A ); live specimens translucent ( Fig. 12B, G ). Ventral and lateral grooves distinct along whole length of body. Anterior and posterior-most chaetigers slightly shorter than mid-body chaetigers.

Prostomium elongate, conical with small acute terminal palpode ( Fig. 12C ). Eyes not observed. Nuchal organs rounded, laterally on posterior part of prostomium. Peristomium indistinct. Anterior prechaetigerous region of body with three elongated achaetous segments, detected upon observation of three lateral organs under SEM; lateral organs detected in all chaetigers under SEM ( Fig. 12D, E ). Parapodia rudimentary, biramous, embedded in lateral grooves; no distinct pre- or postschaetal lobes.

Chaetae all slender, smooth capillaries ( Fig. 12F ), appear in small numbers in both rami, often broken off entirely. Notochaetae mostly longer than neurochaetae, extremely short chaetae observed in most fasciles under SEM.

Branchiae absent. Anal tube not observed in preserved specimens (e.g. Fig. 12H ), but possibly captured in image of “live” specimen NHM_473 ( Fig. 12G ). Observed anal tube cylindrical, relatively short (only slightly longer than wide); with very long thin ventral cirrus attached subdistally on ventral side of anal funnel. Stained specimens without distinct pattern ( Fig. 12I ).

Genetic data.

GenBank MN217436-MN217442 for 16S, MN217503 for 18S and MN217521-MN217523 for COI. In our phylogenetic analyses, Ophelina ganae sp. nov. is sister to Ophelina cf. abranchiata (NHM_1769) and form a well-supported clade with this species and Ophelina cf. abranchiata (NHM_2017) together with at least two other abranchiate species ( Fig. 23 ).

Remarks.

Molecular analysis of the UKSR-collected material revealed presence of three distinct small abranchiate species that morphologically resemble Ophelina abranchiata . Given the taxonomic problems of this species, the challenge is not only to morphologically distinguish these species from each other, but also from O. abranchiata . Here, we restrict the definition of O. abranchiata to that provided by Kongsrud et al. (2011) based on re-description of holotype and material from the North Sea as consistently possessing 18 chaetigers only. Therefore, the new species is differentiated from O. abranchiata by possessing 17 chaetigers only in all observed specimens. Furthermore, the photograph of live specimen ( Fig. 12G ) suggests possible presence of much shorter anal tube compared to elongated anal tubes observed in O. abranchiata . This would represent another distinguishing character from the known species. We believe this structure to represent anal tube as it follows the chaetigerous regions of the body (i.e. the body is not interrupted immediately after the last chaetiger as it is common in O. abranchiata when the anal funnels are missing). There also appear to be very long thin cirrus attached subdistally on ventral side and such structure is present in anal tubes of Ophelina abranchiata . However, this conclusion is only tentative given the lack of anal tube in all preserved specimens of the newly described species and it is based on observation from the photograph only. See further discussion on specimens identified as Ophelina cf. abranchiata later in this text.

Ecology.

Found in polymetallic nodule province of the eastern CCZ.

Etymology.

Named in honor of Bin Qi Gan, member of the science party of the ABYSSLINE AB02 cruise onboard the RV Thomas G. Thompson.

Figures

Figure 12. Ophelina ganae sp. nov. A Lab image, whole specimen (holotype [specimen NHM _ 1137] B Live images, whole specimens (holotype [bottom], paratype NHM _ 598 [middle], paratype NHM _ 1309 [top]) C Lab image, detail of palpode (holotype) D SEM image, second chaetiger with lateral organ (paratype NHM _ 1309, lo = lateral organ) E SEM images, lateral organs, (a) pre-chaetigerous segment, (b) chaetiger 1, (c) chaetiger 2, (d) chaetiger 17 (last chaetiger) (paratype NHM _ 1309) F Lab image, detail of capillary chaetae (holotype) G Live image, with detail of potential anal funnel (specimen NHM _ 473, vc = potential ventral cirrus). H Lab image, detail of posterior (holotype) I Lab image, whole specimen (paratype NHM _ 598, stained). Morphological features in plates G, H have been outlined with a fine white or black line to improve clarity of those features. Scale bars: 1 mm (A); 100 μm (C); 20 μm (D); 5 μm (E); 50 μm (F); 100 μm (H); 1 mm (I).

Figure 23. Phylogenetic analysis of Opheliidae. 50 % majority rule tree from the Bayesian analyses using 18 S and 16 S, with posterior probability values on nodes. Twenty-nine taxa from GenBank were included, and Capitellidae and Echiura was chosen as outgroup following the annelid phylogeny of Weigert and Bleidorn (2016).