Ophelina martinezarbizui, 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 martinezarbizui sp. nov. Figs 14 A–H , 15 A–E

Material examined.

NHM_681 (holotype) NHMUK ANEA 2019.7116, coll. 20 Feb. 2015, 12°32.23N, 116°36.25W, 4425 m http://data.nhm.ac.uk/object/0de17415-a8bf-4461-a663-dea9a3e6a2b9; NHM_718 NHMUK ANEA 2019.7117, coll. 20 Feb. 2015, 12°32.23N, 116°36.25W, 4425 m http://data.nhm.ac.uk/object/f6e2fa9b-a479-4e0d-aec6-57efff6987b2; NHM_883 NHMUK ANEA 2019.7118, coll. 20 Feb. 2015, 12°34.28N, 116°36.63W, 4198 m http://data.nhm.ac.uk/object/d9a3a3b3-c16e-4359-8eb0-f09deed98401; NHM_994 NHMUK ANEA 2019.7119, coll. 24 Feb. 2015, 12°08.02N, 117°17.52W, 4122 m http://data.nhm.ac.uk/object/4f6d2b7a-169f-46a9-8b3b-5d91a021aa34; NHM_1066 NHMUK ANEA 2019.7120, coll. 26 Feb. 2015, 12°06.93N, 117°09.87W, 4100 m http://data.nhm.ac.uk/object/972f9cb1-79d7-4296-a6d6-e04543c9105c; NHM_1766 (paratype) NHMUK ANEA 2019.7121, coll. 11 Mar. 2015, 12°10.43N, 117°11.57W, 4045 m http://data.nhm.ac.uk/object/dc754b1c-e66b-4a58-a93e-796ebfd32f6a; NHM_1870 NHMUK ANEA 2019.7122, coll. 13 Mar. 2015, 12°02.49N, 117°13.03W, 4094 m, http://data.nhm.ac.uk/object/b6247e8d-d155-4646-87d7-e5358ada5352; NHM_2088 (SEM specimen) NHMUK ANEA 2019.7123, coll. 20 Mar. 2015-03-20, 19°27.874N, 120°01.525W, 4026 m, http://data.nhm.ac.uk/object/7dd04f2c-435b-44b1-a85f-3b05dd3014d7; NHM_2092 NHMUK ANEA 2019.7124, coll. 20 Mar. 2015, 19°27.874N, 120°01.525W, 4026 m, http://data.nhm.ac.uk/object/1a095836-fa97-48b8-ad4c-07ed28356ecb; NHM_2102 NHMUK ANEA 2019.7125, coll. 20 Mar. 2015, 19°27.874N, 120°01.525W, 4026 m, http://data.nhm.ac.uk/object/93e91313-61a3-4cd7-8221-66bf20232f14; NHM_2116 (paratype) NHMUK ANEA 2019.7126, coll. 20 Mar. 2015, 19°27.874N, 120°01.525W, 4026 m, http://data.nhm.ac.uk/object/d439156e-657d-4dd5-8bb5-3531e150961e; NHM_2144 NHMUK ANEA 2019.7127, coll. 20 Mar. 2015, 19°27.874N, 120°01.525W, 4026 m, http://data.nhm.ac.uk/object/79767cab-eb56-4ef1-acd0-5067ec3736de; NHM_2149 NHMUK ANEA 2019.7128, coll. 20 Mar. 2015, 19°27.874N, 120°01.525W, 4026 m, http://data.nhm.ac.uk/object/1caa9eb3-3281-4ed6-8424-dfaebcf1e20b; NHM_2150 NHMUK ANEA 2019.7129, coll. 20 Mar. 2015, 19°27.874N, 120°01.525W, 4026 m, http://data.nhm.ac.uk/object/993f577c-ee86-4660-b2d9-af0146606f92.

Type locality.

Pacific Ocean, CCZ, 12°32.23N, 116°36.25W, depth 4425 m, in mud between polymetallic nodules.

Description.

This is a medium-sized species (8-14 mm long), represented by 14 specimens.

Body cylindrical, iridescent, some annulation detectable in first five to eight and last eight chaetigers, rest of body very smooth, no annulation detectable ( Fig. 14A ). Ventral and lateral grooves most distinct along the anterior half of the body, then less distinct. Preserved specimen yellow in ethanol ( Fig. 14B ); live specimens translucent, with orange gut ( Figs 14A , 15A ). Complete specimen with 31 chaetigers, first five to eight and last eight chaetigers crowded, chaetigers in between elongated, last six to eight chaetigers somewhat shifted ventrally.

Prostomium of all preserved specimens oval and broad (about as long as wide) and anteriorly bluntly rounded, somewhat truncated; bearing very distinct palpode, mostly short button-like sometimes distinctly bi-articulated with distal article oval in specimen NHM_2116 ( Figs 14C , 15B, C ). Similar form of prostomium (royal crown-shaped) can also be observed in live specimen NHM_2092 ( Fig. 14D ). Nuchal organs observed as slits laterally on posterior part of prostomium.

Branchiae present, with disjointed distribution in anterior and posterior chaetigers only, absent in mid-body chaetigers. Six very small (easily overlooked) branchial pairs observed consistently in chaetigers 2-7, with those on chaetigers 3-5 slightly longest. The number of attached posterior branchial pairs observed varied from one to eight pairs, with the most complete set observed in NHM_883 and NHM_1766, where eight pairs present in chaetigers 24-31 (the last chaetiger); first posterior pair small (1/2 the length of the subsequent pairs), others very long and robust in NHM_883, but all branchiae large in NHM_1766. All branchiae cirriform ( Figs 14 E–G , 15D ).

Parapodia distinct, biramous; well developed in anterior part of the body, then becoming smaller in subsequent chaetigers. Parapodia with short rounded dorsal cirrus present; provided with a tongue-shaped lobe bearing lateral organs (observable under SEM) ( Fig. 15E ). Parapodia embedded in distinct lateral grooves in chaetiger 1-13, then grooves becoming less distinct. Chaetae are capillaries ( Fig. 14H ); first seven chaetigers with numerous chaetae in bundles, chaetae getting longer in chaetigers 2-4, being longest in chaetigers 3-5, then becoming shorter to chaetiger 13; in the posterior half of the body chaetae few and short, often missing (broken off) entirely.

Anal tube best preserved in specimen NHM_1766; anal tube relatively short (about the length of two posterior chaetigers) and thick distally asymmetrical with dorsal margin slightly longer than ventral one; distally with several short cirri, particularly on dorsal margin ( Fig. 14A, G ) and ventral margin with robust, short and thick ventral cirrus ( Fig. 14A, G ).

Reproductive information.

Holotype ovigerous, with eggs of roughly 100 mm size clearly observed in mid through to posterior part of the body ( Fig. 14A ).

Morphological variation.

This species is represented by the greatest number of specimens (n = 13) of Opheliidae species found in UKSR material. The features observed consistently are: the "royal crown"-like shape of prostomium (even in live specimens, Fig. 14D ), 31 chaetigers, six pairs of tiny anterior branchiae in chaetigers 2-7. Number of attached posterior branchial pairs is variable as these are large and presumably more susceptible to damage, the exact number of posterior branchial pairs remains unknown, but the most complete observation was eight pairs in specimen NHM_883. The anal tube remains attached in all specimens, but the distal region is often damaged and ventral cirrus is often detached. The best-preserved anal tube has been observed in specimen NHM_1766 and can also be observed in the live image of the holotype.

Genetic data.

GenBank MN217444-MN217456 for 16S, MN217505 for 18S and MN217524-MN217531 for COI. This species is genetically identical or very similar to " Ophelina sp. 2" ( Janssen et al. 2015), with K2P values ranging from 0.0-0.006 between O. martinezarbizui sp. nov. and the already published sequences with accession numbers KJ736369-KJ736370 and KJ736372-KJ736377. In our phylogenetic analyses this species is sister to Ophelina meyerae sp. nov. ( Fig. 23 ).

Remarks.

This species superficially resembles Ammotrypanella species due to the presence of large branchiae in the posterior part of the body, but very small and easily overlooked branchiae are present in anterior chaetigers 2-7 in Ophelina martinezarbizui sp. nov. The presence of these very small branchiae easily distinguish this species from other Ophelina species encountered in UKSR-collected material, which are either abranchiate or branchiae are large (or at least easy to observe) in anterior chaetigers. Ophelina martinezarbizui sp. nov. represents a form with disjointed branchial distribution (see also comments under Ophelina sp. NHM_689 and NHM_1331), but it can be distinguished from these by the size of anterior branchiae, number of segments and form of anal funnel. Ophelina martinezarbizui sp. nov. also appears to have contrasting annulated and smooth body regions ( Figs 14 , 15 ).

Of the known Ophelina species, O. ammotrypanella Schüller, 2008 from the abyssal Southern Ocean shares the presence of small branchiae in anterior chaetigers and its " Ammotrypanella -like look" as the name suggests. However, in O. ammotrypanella the branchiae have a continuous distribution, being absent only in posterior quarter of the body.

Ecology.

Found in polymetallic nodule province of the eastern CCZ. This species is represented by 13 sequenced specimens, with potentially another 28 specimens available in material that has not been sequenced yet, making it the most abundant opheliid species in the UKSR samples.

Etymology.

Named in honor of Pedro Martinez Arbizu, member of the science party of the first ABYSSLINE cruise.

Figures

Figure 14. Ophelina martinezarbizui sp. nov. A Live images, whole specimen (center) with detail of anterior (left) and anal funnel (right) (holotype [specimen NHM _ 681], e = eggs, vc = enlarged ventral cirrus, c = cirri) B Lab image, whole specimen (holotype). C Lab image, detail of palpode (paratype NHM _ 2116) D Live image, prostomium, " royal crown " palpode (specimen NHM _ 2092) E Lab image, ventral posterior and branchiae (paratype NHM _ 1766, br = branchiae) F Lab image, lateral posterior and branchiae (paratype NHM _ 1766, br = branchiae) G Lab image, detail of anal funnel (paratype NHM _ 1766, vc = enlarged ventral cirri [folded over], c = cirri, br = branchiae H Lab image, detail of capillary chaetae (holotype). Morphological features in plates A, E, G have been outlined with a fine white or black line to improve clarity of those features. Scale bars: 1 mm (B, E, F); 100 μm (C, H).

Figure 15. Ophelina martinezarbizui sp. nov. (specimen NHM _ 2088). A Live image, whole specimen B SEM image, dorsal anterior C SEM image, lateral anterior D SEM image, dorsal posterior, br = branchiae) E SEM image, detail of mid-body lateral organ (lo = lateral organ). Scale bars: 300 μm (B, C, D); 40 μm (E).

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).