Ophelina sp. (NHM_1331)

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_1331) Fig. 22 A–G

Material examined.

NHM_1331 NHMUK ANEA 2019.7115, coll. 01 Mar. 2015, 12°15.44N, 117°18.13W, 4302 m http://data.nhm.ac.uk/object/06d48d7f-7339-4cc5-8445-b51a980e4e0f.

Description.

This species is represented by a single complete specimen in relatively good condition. Specimen about 4.5 mm long and 0.5 mm wide for about 28 chaetigers. Body cylindrical and smooth with some annulation detectable ( Fig. 22 A–C ). Ventral and lateral grooves distinct throughout body. Preserved specimen yellow in ethanol; live specimen translucent, with yellow gut ( Fig. 22C ); everted nuchal organs with golden brown pigment ( Fig. 22 A–D ). 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) and anteriorly bluntly rounded; palpode not observed ( Fig. 22D, E ). Nuchal organs laterally on posterior part of prostomium, everted, round with golden brown pigment observable even in preserved specimen.

Branchiae present; with disjointed distribution, with three pairs on chaetigers 2-4 ( Fig. 22D, E ) and three pairs in posterior region on chaetigers 21-24 ( Fig. 22F, G ); branchiae in other chaetigers not observed, branchiae considered absent in the last four crowded chaetigers. All branchiae cirriform, of similar length.

Parapodia distinct, biramous; embedded in lateral grooves on chaetigers 1-24; no distinct pre- or postchaetal lobes. Chaetae are capillaries only; all very long but longest on chaetiger 1 where they are nearly twice the length of chaetae of subsequent chaetigers.

Anal tube attached, but not well preserved; cylindrical; appears distally asymmetrical with dorsal lobe overlapping the ventral lobe (but this may be an artefact of poor preservation) ( Fig. 22F, G ); cirrus not observed.

Genetic data.

GenBank MN217465 for 16S and MN217510 for 18S. COI was unsuccessful for this specimen, no identical GenBank matches for 16S or 18S. In our phylogenetic tree, Ophelina sp. (NHM_1331) is sister to " Ophelina sp. F14588" forming a clade with the taxa Ophelina cylindricaudata from the Atlantic (New England) and Ophelina sp. (NHM_689) ( Fig. 23 ).

Remarks.

Morphologically, Ophelina sp. (NHM_1331) is similar to Ophelina sp. (NHM_689) in having a broad prostomium and very long chaetae on chaetiger 1. Their branchiae appear to be arranged in a similar pattern (three pairs are present in chaetigers 2-5 and then few pairs present in posterior chaetigers). Nuchal organs are not everted in O. sp. (NHM_689). They may differ in number of chaetigers, although this is difficult to establish due to damage of O. sp. (NHM_689), anal tube has not been observed in O. sp. (NHM_689) (assumed missing) and cannot be compared.

Of known species of Ophelina , O. sp. (NHM_1331) is similar to a group with 28 chaetigers and four posterior parapodia crowded: O. cylindricaudata , O. breviata (Ehlers, 1913) and O. brattegardi Kongsrud et al., 2011.

The lack of branchiae in midbody has been described in some of these species, but for O. cylindricaudata this has been clarified as a mistake in the original description. Kongsrud et al. (2011) reported that branchiae in the mid-body region may be present in O. cylindricaudata but are often reduced in size and when they are lacking there is no consistent pattern. The absence of branchiae is considered “true” in Ophelina chaetifera ( Hartman 1965), described from the deep Atlantic (1330-5007 m) and O. brattegardi described from Iceland Sea (off East Greenland) in 1600 m depth. The UKSR species differs from both in having broad, anteriorly blunt prostomium. Ophelina chaetifera further differs in having only 26 chaetigers. However, with only single specimen available for examination, we cannot establish “true” branchial distribution in UKSR samples.

Figures

Figure 22. Ophelina sp. NHM _ 1331 (specimen NHM _ 1331). A Lab image, whole specimen, dorsal view (faded stain) B Lab image, whole specimen, lateral view (faded stain) C Live image, whole specimen D Lab image, anterior (faded stain, br = branchiae, no = nuchal organ) E Lab image, detail of anterior (br = branchiae, no = nuchal organ) F Lab image, posterior, anal funnel (br = branchiae) G Lab image, detail of posterior and anal funnel (br = branchiae). 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); 100 μm (E, G).

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).