Meganerilla iensis, Worsaae, Gonzalez, Kerbl, Nielsen, Jorgensen, Armenteros, Iliffe & Martinez, 2025

Meganerilla iensis sp. nov.

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Figs 8–9 View Fig View Fig ; Table 5 View Table 5

Diagnosis

Meganerilla without a median antenna. Small body length, less than 450 µm. No eyes present. Short cirri in segment I. Parapodial cirri increasing in length posteriorly; glandular pigmentation in parapodial cirri of segments VI–VII and distally in pygidial cirri. Chaetae only lacking in segment I.

Etymology

Named after the type locality at ‘Ie Island’, and the Latin root ‘- ensis ’ (‘of’). The Japanese name for this new species is given here as ‘Sango-usamimi-gokai’ (meaning ‘Coral reef-rabbit ear-bristle worm’ in English).

Type material

Holotype

JAPAN • late juvenile; Ryukyu Islands, Okinawa Prefecture, Ie Island ; 26.72518° N, 127.83107° E; coarse coral sand at 13–15 meters depth; 3 Jun. 2019; Y. Fujita, M.J. Hansen, M.C. Allentoft-Larsen and K. Worsaae leg.; NHMD 1842018 mounted on SEM stub.

GoogleMaps

Representative DNA sequences

GenBank accession numbers PQ149840 (nuclear 18S rRNA), PQ149821 (nuclear 28S rRNA), PQ570590 (nuclear H3) and PQ421132 (mitochondrial COI) GoogleMaps ; from specimen with same collection data as holotype ( Table 1 View Table 1 ).

Description

Measurements are based on LM of holotype, counts and ciliation from SEM (no measurements from SEM pictures where the specimen seemingly shrank to about 60% of live length). Body about 405 µm long with nine segments ( Figs 8A View Fig , 9C View Fig ). Segment lengths of 43, 44, 40, 47, 47, 45, 54, 31, 27 µm. Trunk segments about 90 µm wide including parapodia, about 55 µm excluding parapodia. Segments II–VII similar in length and width, segments VIII and IX shorter and less wide, possibly because not fully grown ( Figs 8A–B View Fig , 9B View Fig ).

Prostomium round with straight palps, increasing slightly in width distally (pa, Figs 8C View Fig , 9A View Fig ). Palp 92 µm long and 29 µm wide. Prostomial lateral ciliary band next to palp insertion. Antennae and indicative scars thereof absent. Eyes absent. Nuchal organs laterally in groove between prostomium and segment I (no, Figs 8C View Fig , 9A, E View Fig ).

Cirri on segment I short, 13 µm long and with several cilia on and/or next to cirri ( Fig. 9F View Fig ). Lanceolate parapodial cirri on segments III–VIII, increasing in length and width posteriorly until segment VII (pc, Figs 8B, D View Fig , 9B–C View Fig ), maximum length 38 µm. Parapodial cirri on segments VI–VII with brown pigmented glands ( Fig. 8D View Fig ). Short pygidium with cylindrical pygidial cirrus, 73 µm long, and a shorter regenerating cirrus, 41 µm long (pyc, Figs 8A–B View Fig , 9B–C View Fig ). Pygidial cirri with brown pigmentation at distal tip.

Capillary chaetae in all trunk segments, increasing in length posteriorly until segment VIII, maximum 72 µm long. Maximum six chaetae in each parapodium of segments II–IX; many chaetae lost.

Prostomium with anterior and posterior fields of presumed sensory cilia and lateral rows of cilia next to palp insertion. Paired, densely ciliated nuchal organs on lateral border between prostomium and segment I (acf, lrc, pcf, Fig. 9A, C, E–F View Fig ). Palp with ventral longitudinal dense ciliary row from insertion to tip of palp, and lateral rows of small tufts of cilia (ct, sct, pcf, Fig 9F View Fig ). Segment I with paired dorsolateral transverse rows of ciliary tufts at level of parapodia. Following trunk segments with dorsal transverse continuous rows of cilia in all segments at level of parapodia (tdc, Fig. 9A–B View Fig ). Ventral ciliation consisting of i) densely ciliated mouth (mo, Fig. 9C, E View Fig ), ii) midventral longitudinal ciliary band extending from mouth to pygidium and iii) transverse ventral rows of cilia of up to 6 ciliary tufts in all segments at level of parapodia (tvc, vc, Fig. 9C View Fig ). Multiple single cilia scattered on dorsal, lateral, and ventral sides of body.

Reproduction unknown. Nephridia and gonoducts not investigated.

Distribution and habitat

Reef slope in front of and near Unnamed Cave, northern part of eastern reef of Ie Island, Okinawa Prefecture, Ryukyu Islands, Japan. Patches of coarse coral sand with shells and small coral fragments at 13–15 meters of depth between corals. Associated nerillids from the same locality include Nerillidium sp. 2 and Mesonerilla sp. 4 .

Molecular information

Meganerilla iensis sp. nov. nests within a fully supported clade of Meganerilla spp. , next to Meganerilla sp. 1 from Miyako Islands, Japan (with no morphological information available).

Pairwise comparison of Meganerilla iensis sp. nov. sequence similarity to other Meganerilla spp. : 18S rRNA – 99.77% similar to its sister taxon ( M. sp. 1) – 97.89–99.54% similar to the remaining Meganerilla spp. ; 28S rRNA – 99.80% similar to M. sp. 1 – 88.35–97.83% similar to the remaining Meganerilla spp. ; COI – 94.56% similar to M. sp. 1 – 94.07% similar to the remaining Meganerilla spp. ; H3 – 100% similarity M. sp. 1 – 90.52–96.27% similar to the remaining Meganerilla spp.

Remarks (see also Table 5 View Table 5 for Meganerilla spp. comparisons)

Like its five congeneric described relatives, M. iensis sp. nov. has nine segments, simple chaetae, lanceolate or leaf-shaped parapodial cirri (not found in Meganerilla bactericola ( Müller, Bernhard & Jouin-Toulmond, 2001)) and relatively large palps ( Boaden 1961; Magagnini 1966; Riser 1988; Müller et al. 2001; Westheide 2008; Worsaae et al. 2009; Worsaae 2021).

Meganerilla iensis sp. nov. is smaller in size compared to other species of Meganerilla ( Boaden 1961; Núñez et al. 1997; Worsaae et al. 2009); however, the holotype may not be fully grown. Meganerilla iensis does not possess any median antenna, as in M. cesari and M. bactericola , and lacks chaetae in the first segment but not in the following trunk segment. Moreover, M. iensis possesses apomorphic pigmented glands in the parapodial and pygidial cirri.

Meganerilla sp. 1 and M. iensis sp. nov. were collected from two Japanese islands about 350 km apart. Neither species was found in isolated caves, as Meganerilla sp. 1 was collected from subtidal sand at Irabu Island. The two taxa show a high molecular affinity (99.77% for 18S rRNA; 99.80% for 28S rRNA; 98.56% for COI; 100% for H3), but no morphological information is available for Meganerilla sp. 1 . Out of caution, they are so far treated as separate species mainly due to dissimilarities in COI. Additional morphological and molecular data are necessary to assess the taxonomic status of Meganerilla sp. 1 .