Ophelina cf. abranchiata (NHM_1769)

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 (NHM_1769) Fig. 18 A–E

Material examined.

NHM_1769 NHMUK ANEA 2019.7148, coll. 11 Mar. 2015, 12°10.43N, 117°11.57W, 4045 m http://data.nhm.ac.uk/object/8a2cbe4f-277d-4355-a34f-0b53c797bef0.

Description.

This species is represented by a single specimen, in reasonable condition, but anal tube is missing. Small species, 5.3 mm long and 0.3 mm wide; the exact number of chaetigers is difficult to establish, but at least 16 counted, although 17 may be present.

Body cylindrical and smooth without distinct annulation ( Fig. 18A, B ). Preserved specimen yellow in ethanol; live specimen translucent, with yellow gut ( Fig. 18A ). 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. 18C ). 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 postchaetal lobes.

Chaetae all slender, smooth capillaries ( Fig. 18D ), appear in small numbers in both rami, often broken off entirely. Notochaetae mostly longer than neurochaetae.

Branchiae absent. Anal tube not observed. Shirlastained specimens without distinct pattern ( Fig. 18E ).

Genetic data.

GenBank MN217433 for 16S, MN217501 for 18S and MN217520 for COI. In our phylogenetic analyses it is part of a well-supported clade with Ophelina ganae sp. nov., Ophelina cf. abranchiata (NHM_2017) and at least two other abranchiate opheliids ( Fig. 23 ).

Remarks.

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

Figures

Figure 18. Ophelina cf. abranchiata sp. NHM _ 1769 (specimen NHM _ 1769). A Live image, whole specimen B Lab image, whole specimen (very faded post-stain,) C Lab image, detail of prostomium and palpode D Lab image, detail of chaetae E Lab image, whole specimen (stained). Scale bars: 1 mm (B, E); 50 μm (C, D).

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).