Ophelina curli, 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 curli sp. nov. Fig. 11 A–H

Material examined.

NHM_2112 (holotype) NHMUK ANEA 2019.7131, coll. 20 Mar. 2015, 19°27.874N, 120°01.525W, 4026 m, http://data.nhm.ac.uk/object/c1554f01-2324-4d8d-b775-dca42f5918e7.

Type locality.

Pacific Ocean, CCZ, 19°27.874N, 120°01.525W, depth 4026 m, in mud between polymetallic nodules.

Description.

This species is represented by a single specimen 30 mm long and 1 mm wide for 28 chaetigers.

Ventral and lateral grooves distinct along whole length of body. Colour in alcohol yellow to light tan ( Fig. 11A ); live specimen semi-translucent, with red gut ( Fig. 11B ). Body very smooth, iridescent, segmental furrows and annulations indistinct (best observed in the anterior-most chaetigers). First five chaetigers slightly crowded, the subsequent chaetigers elongated.

Prostomium conical (longer than wide), with distinct, tear-shaped terminal palpode ( Fig. 11C, D ). Eyes not observed. Nuchal organs observed as slits, laterally on posterior part of prostomium; without pigmentation. Proboscis fully everted; dorso-ventrally flattened multilobed structure with ventral groove ( Fig. 11E ).

Branchiae absent. Parapodia biramous, embedded in lateral grooves; parapodia small conical lobes, best observed on anterior seven chaetigers; no distinct pre- or postchaetal lobes observed ( Fig. 11F ).

Chaetae all slender, smooth capillaries ( Fig. 11G ), very few in both rami. Notochaetae mostly longer than neurochaetae.

Anal tube attached; narrow and smooth; no cirri observed ( Fig. 11H ). The proximal half cylindrical; distal half (in ventral view) as flattened sheath (if opened up), but observed with lateral margins curled up, ventrally slit; distal half (in lateral view) distinctly asymmetrical with dorsal margin longer than ventral one.

Genetic data.

GenBank MN217435 for 16S and MN217502 for 18S. COI was unsuccessful for this specimen, no identical GenBank matches for 16S or 18S. Ophelina curli sp. nov. is sister to Ophelina juhazi sp. nov. in our phylogenetic analyses ( Fig. 23 ).

Remarks.

Morphologically this species is very similar to Ophelina nematoides (Ehlers, 1913) and to UKSR Ophelina juhazi sp. nov. in being abranchiate and having 28-30 chaetigers. Two other abranchiate species that are morphologically similar to Ophelina abranchiata Støp-Bowitz, 1948 are also reported in this material, but these differ in having much smaller body size (4.5-8 mm) and having only 17 or 18 chaetigers.

Ehlers (1913) provided description (but no drawings) of O. nematoides (as Ammotrypane nematoides ) based on specimens from 2725 m depth in the Indian Ocean sector of the Southern Ocean (65°32'0"S, 85°30'0"E). Other reports from the Southern Ocean have been shallower ( Read and Fauchald 2019). Brief diagnosis based on translation of Ehlers (1913): "Specimen 30 mm long and 1 mm wide, with 30 chaetigers. Conical prostomium with palpode. No branchiae. Basal segment (= anal tube?) appears segmented in a brightened condition is a thick sheet, when stretched, of the length of the last two segments, the margins of which are curled against each other to form on the ventral surface the narrow entrance to a gutter emanating at the back. I did not see any attachments or papillae."

The main difference between O. nematoides and Ophelina curli sp. nov. is the number of chaetigers, 30 in the former versus 28 in the latter. The shape of anal tube appears to be similar, but without drawing or access to Ehlers’ type specimen, this structure cannot be meaningfully compared using Ehlers’ description alone.

The morphologically similar species Ophelina juhazi sp. nov. also found in the UKSR material can be distinguished by its smaller size, 17 mm compared to the 30 mm O. curli sp. nov., and the shape of anal tube, which in O. juhazi sp. nov. is cylindrical throughout, entire (no ventral slit), distally slightly narrowing and symmetrical.

Ecology.

Found in polymetallic nodule province of the eastern CCZ.

Etymology.

Named in honor of Cassidy Curl, Ordinary Seaman onboard RV Melville on the AB01 ABYSSLINE cruise in 2013.

Figures

Figure 11. Ophelina curli sp. nov. holotype (specimen NHM _ 2112). A Lab image, whole specimen (post-staining, very faded stain) B Live image, with detail of anterior C Lab image, anterior and proboscis, lateral view, stained D Lab image, detail of palpode E Lab image, anterior and proboscis, ventral view (stained, pb = proboscis) F Lab image, mid-body parapodium (stained, pp = parapodia) G Lab image, detail of capillary chaeta H Lab image, anal funnel. Scale bars: 1 mm (A, E); 100 μm (D, 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).