Ophelina sp. (NHM_689)

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 sp. (NHM_689) Fig. 20 A–H

Material examined.

NHM_689 NHMUK ANEA 2019.7114, coll. 20 Feb. 2015, 12°32.23N, 116°36.25W, 4425 m http://data.nhm.ac.uk/object/6755d584-a20a-4ce5-a4f1-32ce0965128e.

Description.

This species is represented by a single specimen in poor condition, with anal tube and most of branchiae missing. Posteriorly incomplete specimen 4.7 mm long and 0.35 mm wide for at least 22 chaetigers (exact number of chaetigers is difficult to count in places). Body cylindrical and smooth without distinct annulation ( Fig. 20 A–C ). Ventral and lateral grooves distinct throughout body. Preserved specimen yellow in ethanol ( Fig. 20A ); live specimen translucent, pale brown gut ( Fig. 20C ). Chaetigers crowded in anterior part of the body and posterior part of the body (the last four chaetigers), elongated in the mid-section of the body.

Prostomium of preserved specimen conical, broad (only slightly longer than wide), anteriorly bluntly rounded (but prostomium appears damaged) ( Fig. 20D ). Proboscis extended, damaged, soft inflated sack-like structure observed.

Branchiae present, but many are likely missing. Branchiae observed in chaetigers 2-4 ( Fig. 20D, E ) and then in posterior region, where only one branchia remains attached on the fourth before the last chaetiger ( Fig. 20F ); no branchiae observed in mid-body region.

Parapodia distinct, biramous; embedded in lateral grooves ( Fig. 20G ). Chaetae are capillaries only ( Fig. 20H ); all very long but longest on chaetiger 1 where they are nearly twice the length of chaetae of subsequent chaetigers. Anal tube likely missing (damaged).

Genetic data.

GenBank MN217463 for 16S and MN217508 for 18S. COI was unsuccessful for this specimen, no identical GenBank matches for 16S or 18S. In our phylogenetic tree, Ophelina sp. (NHM_689) is sister to Ophelina cylindricaudata (Hansen, 1879) from the Atlantic (New England) ( Fig. 23 ).

Remarks.

Due to the condition of the single specimen representing this morphospecies, important diagnostic characters such as the structure of the anal tube and distribution of the branchiae cannot be determined. See Remarks under Ophelina sp. (NHM_1331) for more details.

Figures

Figure 20. Ophelina sp. NHM _ 689 (specimen NHM _ 689). A Lab image, whole specimen, lateral view (pre-stain) B Lab image, whole specimen, ventral view (faded stain, vg = ventral groove) C Live image, whole specimen D Lab image, damaged anterior (stained, br = branchiae, pr = prostomium) E Lab image, detail of anterior branchiae (br = branchiae) F Lab image, posterior branchiae (stained, br = branchiae) G Lab image, mid-body parapodia (stained, pp = parapodia) H Lab image, detail of capillary chaetae. Morphological features in plates B, D-G have been outlined with a fine white line to improve clarity of those features. Scale bars: 1 mm (A, B); 0.5 mm (D); 50 μm (E); 0.25 (F, H).

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).