Anguillosyllis finnelli, Neal & Drennan & Wiklund & Stewart & Rabone & Dahlgren & Glover, 2025

Neal, Lenka, Drennan, Regan, Wiklund, Helena, Stewart, Eva C. D., Rabone, Muriel, Dahlgren, Thomas G. & Glover, Adrian G., 2025, New species of Anguillosyllis Day, 1963 (Annelida, Syllidae) from polymetallic nodule exploration areas, eastern Clarion-Clipperton Zone, central Pacific Ocean, European Journal of Taxonomy 1026, pp. 30-64 : 47-52

Anguillosyllis finnelli sp. nov.

urn:lsid:zoobank.org:act:

Figs 6B, 8–12

Diagnosis

Body with 11 chaetigers. Prostomium in two parts, with three short antennae. Palps elongated, free to the base. Parapodia with large conical dorsal lobes (flaps). Dorsal cirri absent in chaetiger 2. Heterogomph chaetae unidentate.

Etymology

The species name is dedicated to Cletus Finnell, Able Seaman on the RV Melville on the October 2013 cruise ‘ABYSSLINE AB01’.

Material examined

Holotype

PACIFIC OCEAN – Eastern Central Pacific , Clarion Clipperton Fracture Zone • 13.79335 ° N, 116.7030833° W; 4081 m depth; 11 Oct. 2013; A.G. Glover, H. Wiklund, T. Dahlgren and M. Georgieva leg.; USNEL Box Core; specimen GUID: 6d7ef8a1-9fa4-4eec-aca2-f68b1ace677b; field ID NHM_00093; GenBank COI gene: PV577530; 16S gene: PV579023; 18S gene: PV579030; NHMUK ANEA 2024.2720 .

Paratypes

PACIFIC OCEAN – Eastern Central Pacific , Clarion Clipperton Fracture Zone • 1 spec.; 10.33079203 ° N, 117.1940202° W; 4290.89 m depth; 1 Jun. 2021; H. Wiklund, R. Drennan, C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: c3b77851-d8d0-4a33-9f2b- 2a993391f41d; field ID; NHM_08730A; GenBank COI gene: PV577528; NHMUK ANEA 2024.2717 • 1 spec.; 10.35561637 ° N, 117.1686897° W; 4280 m depth; 11 Nov. 2020; H. Wiklund, R. Drennan, C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: 654e0cbb-ac72- 4aec-93b0-a24302d3e16c; field ID NHM_05880; GenBank COI gene: PV664495; NHMUK ANEA 2024.2713 .

Other material

PACIFIC OCEAN – Eastern Central Pacific , Clarion Clipperton Fracture Zone • 1 spec.; 12.36565642 ° N, 116.7520565° W; 4159.33 m depth; 10 Mar. 2020; A.G. Glover, H. Wiklund, G. Bribiesca Contreras and E. Simon Lledó leg.; USNEL Box Core; specimen GUID: 89b42808-8b28-431e-b4d1- 7c7b486289b7; field ID NHM_04733_ ECDS4 ; GenBank COI gene: PV577526; 16S gene: PV579021; NHMUK ANEA 2024.2714 • 1 spec.; 12.38927437 ° N, 116.6362959° W; 4179.39 m depth; 11 Mar. 2020; A.G. Glover, H. Wiklund, G. Bribiesca Contreras and E. Simon Lledó leg.; USNEL Box Core; specimen

GUID: c2db9a70-9ccb-4d7e-abbf-4bef0404844c; field ID NHM_04741_ ECDS4 ; GenBank 16S gene: PV579022; NHMUK ANEA 2024.2715 • 1 spec.; 10.35780083 ° N, 117.1593114° W; 4284 m depth; 13 Nov. 2020; H. Wiklund, R. Drennan , C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: 68b5e2d7-8061-4f19-adad-b577c49fb335; field ID NHM_08783_HW01; GenBank COI gene: PV577529; NHMUK ANEA 2024.2718 • 1 spec.; 10.33498329 ° N, 117.1741855° W; 4286 m depth; 6 Nov. 2020; H. Wiklund, R. Drennan , C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: 8a93a352-604b-420f-b328-930c84d540cf; field ID NHM_08789_HW05; GenBank COI gene: PV664496; NHMUK ANEA 2024.2719 • 1 spec.; 10.35561637 ° N, 117.1686897° W; 4280 m depth; 11 Nov. 2020; H. Wiklund, R. Drennan , C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: 04898df3-ab82-4b5d-8c82-7f0a5a396eac; field ID NHM_08801_HW03; GenBank COI gene: PV577527; NHMUK ANEA 2024.2716 • 1 spec.; 10.333014 ° N, 117.18551° W; 4281 m depth; 12 Feb. 2022; H. Wiklund, C. Boolukos, E. Stewart and A. Bessell leg.; USNEL Box Core; specimen GUID: 15c30fcb-cfdb-46c1-9066-f6eb52c4eb09; field ID NHM_10334_ CB3 ; GenBank COI gene: PV577532; NHMUK ANEA 2024.2722 • 1 spec.; 10.353342 ° N, 117.242837° W; 4296 m depth; 19 Nov. 2022; H. Wiklund, C. Boolukos, E. Stewart and A. Bessell leg.; USNEL Box Core; specimen GUID: 1cd18a15-4081-482f-b380-418cbe9a20e9; field ID NHM_10372_ CB06 ; GenBank COI gene: PV664497; NHMUK ANEA 2024.2723 • 1 spec.; 13.7309 ° N, 126.2041° W; 4704 m depth; 20 Feb. 2023; A.G. Glover, E. Stewart, G. Bribiesca Contreras and E. Simon Lledó leg.; USNEL Box Core; specimen GUID: f7d6faae-4c53-4fcd-a168-e55f53d3201c; field ID NHM_10602_GB01; GenBank COI gene: PV577531; NHMUK ANEA 2024.2721 .

Description

MEASUREMENTS AND APPEARANCE. Moderately sized species, up to 2 mm in length for 11 chaetigers ( Fig. 8A–B). Holotype NHMUK ANEA 2024.2720, now posteriorly incomplete due to tissue sampling for DNA, ~ 1.65 mm long and 0.25 mm wide for 7 chaetigers ( Fig. 9A, C); live specimen presented with complete body with 11 chaetigers ( Fig. 9A). Paratype NHMUK ANEA 2024.2717, now posteriorly incomplete with 9 chaetigers, 1.8 mm long and 0.3 mm wide at widest point ( Fig. 8B). Paratype NHMUK ANEA 2024.2713, SEM specimen on stub, posteriorly incomplete and damaged, ~ 1.55 mm long and 0.25 mm wide for 7 chaetigers ( Fig. 10A). Other specimens in variable condition, usually posteriorly incomplete due to fragmentation or tissue sampling for DNA, where complete body with 11 chaetigers. Body somewhat dorsoventrally flattened, tapering slightly from chaetiger 4 anteriorly. Live specimen semi-translucent, without pigmentation ( Fig. 9A); fixed specimen opaque, creamy white to pale yellow in ethanol ( Figs 8A–B, 9B).

PROSTOMIUM. Oval, wider than long; differentiation of median lobe visible even under light microscopy in holotype ( Fig. 9D); median lobe broadly pentagonal, anteriorly with two broad peaks ( Figs 6B, 9D). Eyes absent. Prostomium bearing three short, digitiform to club-shaped antennae and two palps ( Figs 9E– F, 10A–C). Antennae slightly shorter than the prostomium; median antenna club shaped ( Fig. 9E), slightly longer than lateral antennae, and inserted posterio-dorsally on the prostomium; lateral antennae digitiform ( Fig. 9F), inserted more anteriorly. Palps ~ 1.5 the length of prostomium, digitiform, thick and distally rounded, free to the base when fully extended ( Figs 9C, 10A–D); curled ventrally in holotype, obscuring their true shape ( Fig. 9A–B, D).

TENTACULAR SEGMENT. Achaetous, bearing two, very short, papilliform tentacular cirri,>⅓ the length of the antennae and inserted laterally ( Figs 9G, 10B). Pharyngeal tube extending to chaetiger 3, unarmed; proventricle spanning from chaetigers 3–5, barrel-shaped; number of muscle cell rows mostly obscured by body wall in preserved specimens, best observed in live specimen ( Fig. 9A).

PARAPODIA. Long, rectangular, and uniramous. Parapodia with distally rounded, large conical dorsal lobe ( Figs 10A–B, 11A) and two short papilliform lobes with anterior and posterior lobes of similar size ( Fig. 11B). Dorsal cirri missing, SEM shows presence of cirrophores on all chaetigers, except for chaetiger 2 where truly absent ( Fig. 10A–B). Ventral cirri conical, and short approximately half the length of the antennae, inserted midway to ⅔ along the length of the parapodia moving away from the body ( Fig. 11C). At least three acicula per parapodium, two with emergent tips. Each parapodium bearing dense bundles of numerous compound heterogomph chaetae ( Fig. 11A), with chaetal bundles becoming somewhat sparser posteriorly. Anterior falcigerous chaetae with denticulated shafts, denticles arranged in irregular horizontal rows ( Fig. 12A); other chaetae with smooth shafts and finely serrated, unidentate blades decreasing in length dorso-ventrally, ranging from elongate, slender spiniger-like to shorter falcigers ( Figs 11D–E, 12B–C). Blades of the longest spiniger-like chaetae ~ 170 µm, and shortest falcigers ~20 µ m. Tips of compound chaetae blunt, unidentate, at most gently hooked ( Fig. 12B–C).

PYGIDIUM. Damaged; pygidial appendages missing.

Genetic data

Specimens (n = 11) assigned to A. finnelli sp. nov. form a clade (Supp. file 3: Fig. S1, Supp. file 4: Fig. S2), with low intraspecific divergence across all sequences (maximum intraspecific p-distance/K2P distance 0.5/0.5% for 16S and 1.9/1.9% for COI). Sequences matched with high % identity (99–100%) in blastn search and by intraspecific distance (maximum p-distance/K2P 1.8/1.8%) to a COI sequence of an unidentified Anguillosyllis specimen (accession number: MK971075 ; ID: Anguillosyllis sp. 244_PB voucher 088-IOM-0246) ( Fig. 7) collected from the IOM contract area of the Eastern CCZ, published in Bonifácio et al. (2020). In combined analyses ( Fig. 7), this species is close to a polytomy consisting of Anguillosyllis villarae sp. nov. and GenBank sequences identified as Anguillosyllis sp. MTA_2011 from Costa Rica (accession numbers 18S: JF903571 ; 16S: JF903680 ; COI: JF903756 ) published in Aguado et al. (2012). However, minimum interspecific p-distance/K2P of 14.4/16% 16S, and 16.1/18.3% COI were observed between these species and A. finnelli , while in an alignment of nuclear 18S (1630 bp), A. finnelli differed by two and four mutations from A. villarae sp. nov and Anguillosyllis sp. MTA_2011 respectively.

Remarks

The new species belongs to the group of Anguillosyllis with 11 chaetigers, well-developed parapodial lobes and palps free to a large extent, although this character is difficult to establish when palps are curled up (Neal pers. obs.). Of the known species, Anguillosyllis truebloodi also shares such characters, and also the CCZ distribution (DOMES site, Wilson 2017). However, the new species can be easily distinguished by the true absence of dorsal cirri on chaetiger 2 as revealed by SEM ( Fig. 10B), which is present in A. truebloodi . Maciolek (2020) also reported palps as fused halfway to the base in A. truebloodi , whilst these are free to the base in the new species ( Fig. 10A, D), although from certain angles, particularly where bent, the palps may appear fused. Another similar species is Anguillosyllis palpata with type locality in the Drake Passage in relatively shallow depths of 384–494 m, which has since been widely reported worldwide, including abyssal depths ( Maciolek 2020). Morphological variation in specimens identified as A. palpata has been reported by Maciolek (2020), but in the absence of molecular data, species differentiation is difficult. The species newly reported here differs from A. palpata in the form of the chaetae, which are distinctly hooked in A. palpata , but not in the new species, in which they are at most gently hooked ( Figs 11D, 12B–C), absence of large postchaetal lobes and true absence of dorsal cirri on chaetiger 2 ( Fig. 10B).

Distribution

Eastern CCZ: NORI-D exploration area, depth ~ 4300 m; UK-1 exploration area, depth ~ 4200 m; OMCO site, depth ~ 4700 m. Also, IOM area ( Bonifácio et al. 2020).