Ophelina cf. abranchiata sp. (NHM_2017)

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 cf. abranchiata sp. (NHM_2017) Fig. 19 A–F

Material examined.

NHM_2017 NHMUK ANEA 2019.7149, coll. 16 Mar. 2015, 12°03.03N, 117°24.28W, 4235 m http://data.nhm.ac.uk/object/9ebcd947-c53b-4616-81d4-da42afaeca03.

Description.

This species is represented by a single specimen, in reasonable condition, but anal tube is missing. Small species, 4 mm long and 0.35 mm wide; exact number of chaetigers difficult to establish, but at least 17 counted, although 18 may be present.

Body cylindrical and smooth without distinct annulation ( Fig. 19 A–C ). Preserved specimen yellow in ethanol; live specimen translucent, with yellow gut ( Fig. 19A ). 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. 19D, E ). Eyes not observed. Nuchal organs rounded, laterally on posterior part of prostomium. Peristomium indistinct. Anterior prechaetigerous region elongated, number of achaetous segments unknown (no SEM). Parapodia rudimentary, biramous, embedded in lateral grooves; no distinct pre- or postschaetal lobes.

Chaetae all slender, smooth capillaries ( Fig. 19F ), appear in small numbers in both rami, often broken off entirely. Notochaetae mostly longer than neurochaetae.

Branchiae absent. Anal tube not observed. Shirlastained specimens with wide, dark red, strongly stained stripe on the dorsum ( Fig. 19B, D ), not observed in species Ophelina ganae sp. nov. and Ophelina cf. abranchiata (NHM_1769).

Genetic data.

GenBank MN217434 for 16S. In our phylogenetic analyses, Ophelina cf. abranchiata sp. (NHM_2017) is part of a well-supported clade including Ophelina ganae sp. nov., Ophelina cf. abranchiata (NHM_1769) and at least two other abranchiate opheliid species ( Fig. 23 ).

Remarks.

Please refer to section "General comments on O phelina abranchiata and similar morphotypes" above and remarks for Ophelina ganae sp. nov.

Figures

Figure 19. Ophelina cf. abranchiata sp. NHM _ 2017 (specimen NHM _ 2017). A Live image, whole specimen B Lab image, whole specimen (stained,) C Lab image, whole specimen (faded stain) D Lab image, anterior (stained, arrow highlighting dark banding) E Lab image, detail of anterior F Lab image, detail of capillary chaetae. Scale bars: 1 mm (B, C); 100 μm (E, F).

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).