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A new deep-sea species of spaghetti worms (Annelida, Terebellidae) from Walters Shoal, SE Indian Ocean

Published online by Cambridge University Press:  21 October 2026

Nicolas Lavesque Open the ORCID record for Nicolas Lavesque [Opens in a new window] ,
Pat Hutchings Open the ORCID record for Pat Hutchings [Opens in a new window]  and
Joao Nogueira Open the ORCID record for Joao Nogueira [Opens in a new window]
Nicolas Lavesque*
Affiliation:
CNRS, Bordeaux, INP, EPOC, UMR5805, CNRS, Arcachon, France
Pat Hutchings
Affiliation:
Australian Museum Research Institute, Australian Museum, Sydney, NSW, Australia
Joao Nogueira
Affiliation:
Departamento de Zoologia, Universidade de Sao Paulo Instituto de Biociencias, Sao Paulo, Brazil
*
Corresponding author: Nicolas Lavesque; Email: nicolas.lavesque@u-bordeaux.fr
Rights & Permissions [Opens in a new window]

Abstract

During an oceanographic campaign led by the Museum National d’Histoire Naturelle and the Institut de Recherche pour le Développement to explore the biodiversity of Walters Shoal Seamount in the Indian Ocean, a new species of Morgana was discovered. Until now, this genus was monotypic with the only known species described from shallow waters off São Paulo, south-eastern Brazil: M. bisetosa Nogueira & Amaral, 2001. This new deep-sea species, M. waltershoalensis sp. nov., is characterised by the absence of branchiae, the notopodia beginning from segment 4 and the neuropodia from the 6th, a great number of segments with notopodia (n = 53), and the presence of a pair of large nephridial papillae dorsally, on segment 3. This species differs from M. bisetosa by the absence of eyespots, the shape of both noto- and neurochaetae and by the presence of a large pair nephridial papillae on the third segment. Following this study, the boundaries of the genus have been modified, particularly with regard to the number of segments with notopodia, the presence of eyespots and the large papilla on segment 3.

Keywords

morphologynew speciespolychaeteseamounttaxonomyterebellid

Information

Type
Marine Record
Information
Journal of the Marine Biological Association of the United Kingdom , Volume 106 , 2026 , e74
Copyright
© The Author(s), 2026. Published by Cambridge University Press on behalf of Marine Biological Association of the United Kingdom.

ZooBank: urn:lsid:zoobank.org:pub:2920407C-9FFD-45A2-9865-9D97FAF64251.

Introduction

Seamounts are underwater mountains that rise from the ocean floor, usually originating from active or extinct volcanoes (Marsac et al., Reference Marsac, Galletti, Ternon, Romanov, Demarcq, Corbari, Bouchet, Roest, Jorry, Olu, Loncke, Roberts and Ménard2020). Due to their complex topography, hydrodynamic regimes, and localised upwelling of nutrient-rich waters, they are considered as biodiversity hotspots, hosting unique assemblages of benthic and pelagic species (Clark et al., Reference Clark, Rowden, Schlacher, Williams, Consalvey, Stocks, Rogers, O’Hara, White, Shank and Hall-Spencer2010; Rogers, Reference Rogers2018). These structures provide hard substrates for sessile organisms, create microhabitats for mobile fauna, and serve as stepping-stones for the dispersal of marine species (O’Hara et al., Reference O’Hara, Rowden and Williams2008; Clark et al., Reference Clark, Rowden, Schlacher, Williams, Consalvey, Stocks, Rogers, O’Hara, White, Shank and Hall-Spencer2010; Rogers, Reference Rogers2018; Mazzei et al., Reference Mazzei, Pinheiro, Simon, Moura, Macieira, Pimentel, Teixeira, Floeter, Ferreira, Ghisolfi, Francini-Filho, Quimbayo, Rocha, Gasparini and Joyeux2021). Seamounts are also recognised for their high levels of endemism, with many species exhibiting restricted geographic ranges (O’Hara et al., Reference O’Hara, Rowden and Williams2008; Pante et al., Reference Pante, France, Gey, Cruaud and Samadi2015). Their ecological importance is further emphasised by their vulnerability to anthropogenic threats, such as deep-sea fishing and mining, which can irreparably damage these fragile ecosystems (Clark et al., Reference Clark, Althaus, Schlacher, Williams, Bowden and Rowden2016; Marsac et al., Reference Marsac, Galletti, Ternon, Romanov, Demarcq, Corbari, Bouchet, Roest, Jorry, Olu, Loncke, Roberts and Ménard2020).

Discovered in 1962 by the South African vessel Natal, Walters Shoal Seamount is located in the southwest Indian Ocean, about 700 km south of Madagascar. This remote and large seamount rises from the Madagascar Ridge, with summit at 18 m below sea level (Marsac et al., Reference Marsac, Galletti, Ternon, Romanov, Demarcq, Corbari, Bouchet, Roest, Jorry, Olu, Loncke, Roberts and Ménard2020; Roberts et al., Reference Roberts, Ternon, Marsac, Noyon and Payne2020). Despite its ecological significance, Walters Shoal remains one of the least explored seamounts in the region and represents an exceptional field of study for biodiversity. Several expeditions, such as those of the research vessels (RV) Anton Bruun (1964) and the Vityaz (1988), led to the discovery of previously unknown species. But, with only 250 species recorded to date, most of which are small invertebrates (Marsac et al., Reference Marsac, Galletti, Ternon, Romanov, Demarcq, Corbari, Bouchet, Roest, Jorry, Olu, Loncke, Roberts and Ménard2020), Walters Shoal still hides an unsuspected biodiversity. Recent taxonomic studies confirm this potential and highlight the need to increase our knowledge of this biodiversity hotspot (Salazar-Vallejo, Reference Salazar-Vallejo2003; Groeneveld et al., Reference Groeneveld, Griffiths and van Dalsen2006; Mah, Reference Mah2018). The recent Walters Shoal MD208 expedition (2017), led by the Muséum National d’Histoire Naturelle (MNHN) and the Institut de Recherche pour le Développement (IRD), permitted the collection of numerous samples from both the shallow areas around the summit and along the deep-water slopes. Among these deep samples, two specimens of an abranchiate Terebellidae belonging to a new species were identified.

Terebellidae is a diverse family of marine polychaetes commonly known as ‘spaghetti worms’, due to their long and filiform grooved tentacles, used for selective deposit feeding (Lavesque et al., Reference Lavesque, Hutchings, Londoño-Mesa, Daffe, Nogueira, Nygren, Blanchet, Broudin, Dauvin, Droual, Gouillieux, Grall, Guyonnet, Houbin, Humbert, Janson, Jourde, Lamarque, Le Garrec, Pelaprat, Pézy, Sauriau and de Montaudouin2021; Hutchings et al., Reference Hutchings, Carrerette, Nogueira, Hourdez and Lavesque2021a). They are widely distributed across global oceans, from shallow waters to abyssal depths, and play key roles in sediment bioturbation and organic matter recycling (Hutchings et al., Reference Hutchings, Carrerette, Nogueira, Hourdez and Lavesque2021a). Among the Terebellidae sensu stricto, most of the species are characterised by the presence of one to three pairs of branchiae. Although most species of Terebellidae sensu stricto have branchiae, a few of them are abranchiate. Indeed, among the 388 valid species and 47 genera, only 40 species belonging to 14 genera do not have branchiae. Each of these genera is represented by only a few species, nine of them being monotypic (Hutchings et al., Reference Hutchings, Nogueira, Carrerette, Schmidt-Rhaesa, Beutel, Glaubrecht, Kristensen, Prendini, Purschke, Richter, Westheide and Leschen2021b). The absence of branchiae is a secondary loss, which apparently has occurred independently in several lineages of Terebellidae sensu stricto (McHugh, Reference McHugh1995; Nogueira et al., Reference Nogueira, Fitzhugh and Hutchings2013). Indeed, following Glasby et al. (Reference Glasby, Hutchings and Hall2004), the abranchiate terebellids do not form a clade, indicating that the branchial loss has occurred several times independently within the family. In abranchiate species, gas exchange occurs probably across the body wall (Hutchings et al., Reference Hutchings, Nogueira, Carrerette, Schmidt-Rhaesa, Beutel, Glaubrecht, Kristensen, Prendini, Purschke, Richter, Westheide and Leschen2021b).

This study aims to provide the description of a new species of abranchiate Terebellidae from Walters Slope, belonging to the genus Morgana Nogueira & Amaral, Reference Nogueira and Amaral2001.

Materials and methods

The benthic fauna of Walters Shoal Seamount was sampled in April–May 2017, through an MNHN/IRD expedition, managed in the frame of the Tropical Deep-Sea Benthos Program (https://campagnes.flotteoceanographique.fr/campagnes/17002700/fr/). The terebellids studied in this paper were sampled by a dredge on the RV Marion-Dufresne and fixed in 80% ethanol.

The two specimens were examined under a Nikon SMZ25 stereomicroscope and a Nikon Eclipse Ci microscope and photographed with a Nikon DS-Ri 2 digital camera. All plates were compiled using Adobe™ Creative Suite v.6 (including Photoshop and Illustrator).

One dehydrated specimen used for examination under scanning electron microscopy (SEM) was prepared by critical point drying, coated with gold, and examined and photographed with JEOL JSM 6480LA at Macquarie University, Sydney.

We have followed the terminology used by Nogueira et al. (Reference Nogueira, Hutchings and Fukuda2010) to describe the uncini.

Molecular analyses (COI and 16S genes) were performed using standard primers used for Terebellidae (16Sannf and 16SbrH for 16S gene; LCO1490 and HCO2198 for COI gene), but unfortunately no sequences could be obtained (Folmer et al., Reference Folmer, Black, Hoeh, Lutz and Vrijenhoek1994; Palumbi, Reference Palumbi, Hillis, Moritz and Mable1996; Sjölin et al., Reference Sjölin, Erseus and Kallersjo2005; Lavesque et al., Reference Lavesque, Bonifácio, Gouillieux, Daffe, Daramy and Hutchings2026).

Results

Systematics.

Family Terebellidae Johnston, Reference Johnston1846.

Genus Morgana Nogueira & Amaral, Reference Nogueira and Amaral2001.

Type species. Morgana bisetosa Nogueira & Amaral, Reference Nogueira and Amaral2001.

Diagnosis (emended from Nogueira and Amaral, Reference Nogueira and Amaral2001; Hutchings et al., Reference Hutchings, Nogueira, Carrerette, Schmidt-Rhaesa, Beutel, Glaubrecht, Kristensen, Prendini, Purschke, Richter, Westheide and Leschen2021b). Transverse prostomium attached to dorsal surface of upper lip; basal part as thick crest, eye spots present or absent, distal part shelf-like. Buccal tentacles all uniformly cylindrical. Peristomium restricted to lips; upper lip hood-like; swollen, cushion-like, and mid-ventral lower lip. Segment 1 expanded ventrally, with low mid-ventral lobe marginal to mouth; other lateral lobes on anterior segments absent. Anterior segments highly glandular ventrally, with discrete, smooth, rectangular to trapezoidal mid-ventral shields. Branchiae absent. Rectangular to trapezoidal notopodia beginning on segment 4, extending for 18–53 segments. Notochaetae distally serrated, at least on one row. Neuropodia beginning on segment 6, as low ridges throughout; neurochaetae as short-handled avicular uncini with high crest, in completely separated double rows, beak-to-beak arrangement, from segment 11 until posterior body. Nephridial and genital papillae present or absent. Pygidium smooth.

Remarks. We added herein variations that were not known for this genus, which was monotypic until now. With the description of this second species, the number of segments with notopodia is largely expanded, from 18–25 segments originally to 53 now; eyespots can be absent; and, finally, the large nephridial papillae present on segment 3, together with the nephridial/genital papillae on segments 4–12, are described for the first time.

Morgana waltershoalensis sp. nov

Figures 1–3.

Figure 1.

Morgana waltershoalensis sp. nov., holotype MNHN IA-2000-2139: (A) entire specimen, lateral view; (B) anterior end, dorsal view; (C) anterior end, lateral view; (D) anterior end, ventro-lateral view; (E) notochaetae, segment 10, bilimbate section; (F) notochaetae, segment 11; (G) uncinus, segment 13. Abbreviations: Bt, buccal tentacles; Ll, lower lip; Np, nephridial papilla; Ul, upper lip; Vl, ventral lobe; Vp, ventral pads. Numbers referring to segments.

A composite micrograph with even colour images labeled A to G, each with a scale bar.

Zoobank registration: urn:lsid:zoobank.org:act:B62AE961-B2D2-4EE7-942B-97F813EBC5CB.

Material examined. Holotype: MNHN IA-2000-2139, complete specimen, Indian Ocean, Madagascar Ridge, Walters Shoal, Sta CP4909, −32.75° S, 44.05° E, in sediment at a depth of 988 m, May 2017. Paratype: AM W.55319, incomplete specimen, same locality and date as for holotype, mounted for SEM.

Diagnosis. Eyespots, branchiae, and lateral lobes absent. Segment 1 expanded ventrally with low mid-ventral lobe. Rectangular ventral shields until segment 12. Notopodia on segments 4–53; bilimbate notochaetae with narrow wings and long whip-like serrated tip. Neuropodia from segment 6; uncini in double rows from segment 11. Large globular nephridial papilla on segment 3; nephridial/genital papillae short, globular, on segments 4–12.

Description (based on holotype and the paratype for SEM). Small species, holotype complete, 13.5 mm long, 1.6 mm wide. Body anteriorly inflated.

Prostomium at base of upper lip; eyespots absent; buccal tentacles long, deeply grooved, wrinkled. Upper lip wider than long, thick, hood-like (Figures 1D and 2B); lower lip wider than high, cushion-like (Figure 1D); pharyngeal organ hardly visible. Segment (SG) 1 conspicuous dorsally and laterally, expanded ventrally, with low mid-ventral lobe marginal to mouth (Figures 1D and 2A, B). Following segments well marked, lacking lateral lobes and branchiae (Figures 1A–C and 2A, C, E).

Figure 2.

Morgana waltershoalensis sp. nov., SEM paratype AM W.55319: (A) anterior end, lateral view; (B) anterior end, ventral view; (C) anterior end, dorsal view; (D) nephridial papilla, lateral view; (E) anterior segments, lateral view; (F) anterior segments, lateral view. Abbreviations: ; Np, nephridial papilla; P, prostomium; Ul, upper lip; Vl, ventral lobe; Vp, ventral pads. Numbers referring to segments; star indicates distal part of prostomium, white arrows genital papillae.

A composite micrograph with six grayscale SEM sub-images labeled A to E each with a scale bar.

Ventral shields as rectangular, narrow patches, until segment 12, then rectangular to squared, replaced posteriorly by deep mid-ventral groove (Figures 1D and 2B).

Notopodia from SG 4, almost to end of body, holotype with 53 pairs of notopodia in total of 63 segments; notopodia short, rounded (Figures 1A, C, D and 2A, C, E, F). Bilimbate notochaetae arranged in two rows, with distinctly narrow wings and long whip-like serrated tip, those of anterior row much shorter (Figures 1E, F and 3A, B).

Figure 3.

Morgana waltershoalensis sp. nov., SEM paratype AM W.55319: (A) notochaetae, segment 12; (B) notochaetae, segment 18; (C) uncini, segment 12; (D) uncini, segment 7.

A composite micrograph with four grayscale SEM sub-images labeled A to D, each with a scale bar.

Neuropodia from SG 6, as low ridges on anterior body, progressively narrower and more elevated from mid-body (Figures 1A, C,D and 2A, E,F); uncini in double rows from SG 11 (Figure 2B, F), rows partially intercalated, arranged in face to face; uncini higher than long, with dorsal button at halfway between base of main fang and tip of prow, base curved, heel sharp; crest with 3 rows of secondary teeth above main fang, dental formula MF: 3–4:6:12 (Figures 1G and 3C, D).

Large globular nephridial papilla on SG 3, situated more dorsally than level of notopodia of SG 4 (Figure 2A, C, D). Other nephridial/genital papillae short, globular, on SGs 4–12, between notopodia and neuropodia (Figure 2F).

Pygidium rounded, smooth.

Etymology. The species name refers to the type locality of this species.

Type locality. Indian Ocean, Madagascar Ridge, Walters Shoal slope.

Distribution. Known from type locality only.

Remarks. Until now, a single species, M. bisetosa (Nogueira & Amaral, Reference Nogueira and Amaral2001), is known in this genus. This species has been described from shallow-water substrates off São Paulo, southeastern Brazil, living on the underside of colonies of the stony coral Mussismilia hispida (Verrill, Reference Verrill1901). In contrast, M. waltershoalensis sp. nov. is described from the deep-water substrates of the Indian Ocean, on the slopes of Walters Shoal Seamount.

Specimens of M. waltershoalensis sp. nov. differ from those of M. bisetosa in several morphological characters. The number of segments with notopodia in members of M. bisetosa varies from 18 to 25, whereas it reaches 53 segments in M. waltershoalensis sp. nov. specimens. Eyespots seem to be absent in members of this latter species, while they are present in individuals of M. bisetosa. In regard to the shape of the uncini, specimens of M. waltershoalensis sp. nov. have only three rows of secondary teeth above main fang, while those of M. bisetosa have 6–8 rows of secondary teeth. The presence of a large pair of nephridial papillae on segment 3 in members of M. waltershoalensis sp. nov. is very distinctive; such large dorsolateral papillae are absent in representatives of M. bisetosa. Finally, the morphology of notochaetae also differs between members of these species. The specimens of M. waltershoalensis sp. nov. have only one type of notochaetae being narrowly winged, with long whip-like serrated tips. The members of M. bisetosa have two types of notochaetae, with the first type on the anterior row being alimbate with serrated tips, and the second type on the posterior row being long bilimbate chaetae, without serration.

Although only two specimens of M. waltershoalensis sp. nov. were collected during this study, we are confident that it is a new species given the differences in morphology and its habitat. In deep-sea environments, it is common practice to describe new species based on only one or two specimens. This is particularly true for Walters Shoal, which has remained almost unexplored (at least regarding polychaetes). Obtaining material from these environments is extremely costly, with no guarantee that further samples can be collected in the near future; this is why such an approach is widely accepted within the scientific community (Kupriyanova et al., Reference Kupriyanova, Criscione, Daffe, Hutchings, Lavesque, Murray, Paxton and Budaeva2026).

Acknowledgements

The authors would like to thank Sue Lindsay (Macquarie University, Sydney), who mounted the specimens for the SEM and took the images, and all people involved in the samplings and the cruise.

Author contributions

N.L.: conceptualisation of the study, morphological analyses, plates preparation, draft of the text. P.H.: co-authorship of the text and taxonomic advice. J.M.M.N.: co-authorship of the text, plates revision, and taxonomic advice.

Declaration of interest

The authors declare that they have no conflict of interest.

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article.

Ethics and approach

The authors declare that the work did not involve experiments with vertebrates. All applicable international, national, and institutional guidelines and permits were followed by the authors.

Funding statement

The MD208-Walters Shoal cruise (DOI: 10.17600/17002700) was funded by grant CZZ1890 of the French Global Environment Facility (‘Fonds Français pour l’Environnement Mondial’; FFEM) and was facilitated by the Institut Polaire IPEV, France. The MD208-Walters Shoal cruise was part of the FFEM-SWIO project on Areas Beyond National Jurisdiction (ABNJ) of the southwestern Indian Ocean, led by the International Union for Conservation of Nature (IUCN).

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Figure 0

Figure 1. Morgana waltershoalensis sp. nov., holotype MNHN IA-2000-2139: (A) entire specimen, lateral view; (B) anterior end, dorsal view; (C) anterior end, lateral view; (D) anterior end, ventro-lateral view; (E) notochaetae, segment 10, bilimbate section; (F) notochaetae, segment 11; (G) uncinus, segment 13. Abbreviations: Bt, buccal tentacles; Ll, lower lip; Np, nephridial papilla; Ul, upper lip; Vl, ventral lobe; Vp, ventral pads. Numbers referring to segments.

Figure 1

Figure 2. Morgana waltershoalensis sp. nov., SEM paratype AM W.55319: (A) anterior end, lateral view; (B) anterior end, ventral view; (C) anterior end, dorsal view; (D) nephridial papilla, lateral view; (E) anterior segments, lateral view; (F) anterior segments, lateral view. Abbreviations: ; Np, nephridial papilla; P, prostomium; Ul, upper lip; Vl, ventral lobe; Vp, ventral pads. Numbers referring to segments; star indicates distal part of prostomium, white arrows genital papillae.

Figure 2

Figure 3. Morgana waltershoalensis sp. nov., SEM paratype AM W.55319: (A) notochaetae, segment 12; (B) notochaetae, segment 18; (C) uncini, segment 12; (D) uncini, segment 7.