Cirrinerilla sulcipalpata, Worsaae, Gonzalez, Kerbl, Nielsen, Jorgensen, Armenteros, Iliffe & Martinez, 2025

Cirrinerilla sulcipalpata gen. et sp. nov.

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Figs 3–4 View Fig View Fig ; Table 3 View Table 3

Diagnosis

Cirrinerilla gen. nov. with very long antennae, up to ⅔ of body length. Palps ventrally densely ciliated and dorsally with longitudinal non-ciliated furrow. Eyes absent. Long cylindrical parapodial cirri of minimum half body length in segments II–VII, longest in segment V. Maximum 12 compound chaetae per parapodium. Dorsal and ventral transverse rows of ciliary tufts on each segment.

Etymology

‘Sulcipalpata’ refers to the dorsal, longitudinal furrow on each palp. The Japanese name for this new species is given here as ‘Iejima-doukutsu-usamimi-gokai’ (meaning ‘Ie Island-cave dwelling-rabbit ear-bristle worm’ in English).

Type material

Holotype

JAPAN • adult; Okinawa Prefecture, Ie Island, ‘Unnamed Cave’ (or sometimes called ‘ Sho-doukutsu’ ); 26.72518° N, 127.83107° E; 5–12 meters depth; 9 Jun. 2019; Y. Fujita, M.J. Hansen, M.C. Allentoft-Larsen and K. Worsaae leg.; NHMD 1842011 mounted on SEM stub.

GoogleMaps

Paratypes

JAPAN • 4 adults; same data as for holotype; 5–17 meters depth; 2–9 Jun. 2019; NHMD 1842012 and 1842013 as permanent whole mounts, NMHD 1842014 and 1842015 mounted on SEM stub GoogleMaps • 1 spec. examined with LM but lost during preparation for SEM; same data as for preceding GoogleMaps .

Representative DNA sequences

GenBank accession numbers PQ149834–PQ149835 (nuclear 18S rRNA), PQ149816–PQ149817 (nuclear 28S rRNA), PQ570584–PQ570585 (nuclear H3) and PQ421126–PQ421127 (mitochondrial COI); 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 of holotype; values for paratype are given in parentheses. Body about 525 µm long (500–685 µm, n = 5) with eight segments ( Figs 3A View Fig , 4A View Fig ). Segment I double length of following segment (n = 6); segment lengths of holotype 98, 53, 72, 70, 63, 53, 43, 28 µm, pygidium 24 µm long. Cigar-shaped body. Segment V widest, segments VII–VIII decreasing in length and width (n = 6). Maximum width of trunk segments, including parapodia, about 125 µm (115–180 µm, n = 3); about 90 µm excluding parapodia (90–125 µm, n = 3). Max length of parapodium segment I, 37 µm (35–45, n = 5); max length in segments II–VIII, 34 µm (37–48 µm, n = 5).

Prostomium carrying three antennae and two straight palps ( Fig. 3A, C, E View Fig ). Palps 117 µm long (121 µm, n = 2) and 18 µm in width (23 µm, n = 1) with heavy ventral ciliation and dorsal longitudinal furrow. Lateral antennae cylindrical with a length of about 400 µm, estimated relative to LM measure of total body length from dissection scope images of live holotype (la, Fig. 3E View Fig ). Scars from lateral and median antennae visible in fixed holotype (las, mas, Figs 3C View Fig , 4D View Fig ). Characteristics of median antenna unknown. Eyes absent. Elongated esophageal glands in segments II–IV, along foregut ( Fig. 3A View Fig ).

Parapodial cirri observed on live specimens on segments II–V and VII (cirri assumed lost in segment VI, absent on segment I (buccal segment) and VIII); increasing in length posteriorly until segment V. Cirri of segment V noticeably longest; maximum length of 310 µm estimated relative to LM measure of total body length from dissection scope images of live holotype (pc, Fig. 3E View Fig ). Parapodial cirri lost in fixed specimens. Pygidial cirri lost in all specimens; only regenerating bud of cirrus recorded (rpc, Fig. 3A View Fig ).

Compound chaetae in all segments. Up to ten chaetae in one bundle on each parapodium of segment I, pointing posteriorly, maximum 149 µm long (141 µm, n = 1). Segments II–VIII with up to 12 chaetae per parapodium (five-seven in each dorsal and ventral bundle, respectively; often broken or lost). Chaetae maximum 127 µm long (84–138 µm, n = 5) (cc, Fig. 4B, G View Fig ); shaft up to 96 µm long (52–111 µm, n = 5), blade up to 31 µm long (20–63 µm, n = 5), distal extension on shaft at joint 2 µm long (n = 1).

Prostomium with anterior and posterior fields of presumed sensory cilia and lateral rows of cilia extending from insertion of lateral antenna and more than halfway towards insertion of nearest palp (lrc, Fig. 4D View Fig ). Paired, densely ciliated nuchal organs on dorsolateral border between prostomium and segment I. Palps ventrally with longitudinal dense ciliary row from insertion point to tip of palps (pvc, Fig. 4D View Fig ), lined by ventrolateral row of ciliary tufts (each tuft with up to six cilia). Palps lost in most specimens during SEM and CLSM preparation. Segment I with paired dorsolateral transverse rows of each three ciliary tufts (each tuft with minimum four cilia) at the level of parapodia. Trunk segments each with dorsal transverse row of up to 20 ciliary tufts (with middorsal gap in segments III–V) on slightly elevated dorsal ridges at level of parapodia (tdc, Fig. 4B–C View Fig ). Ventral ciliation consisting of i) densely ciliated mouth, ii) midventral ciliary band and iii) continuous transverse rows of cilia in all segments at level of parapodia (vc, tvc, Fig. 4A, F View Fig ). Multiple single cilia scattered on dorsal, lateral, and ventral sides of body.

Three to ten blind ending enteronephridia extend from transition between mid- and hindgut, posteriorly along hindgut (ent, Fig. 3D View Fig ). Four pairs of segmental nephridia run laterally in segments III–VI, originating more dorsally and opening ventrolaterally (n3–n6, Fig. 3G View Fig ). Hermaphroditic. One pair of spermioducts opening in segment VII, and one pair of oviducts opening in segment VIII, both with an anterior ciliated ‘funnel’ and separate ventral openings ( Figs 3H View Fig , 4E View Fig ). Mature egg and many oocytes observed in a single specimen in segments IV–VI ( Fig. 3B View Fig ).

Distribution and habitat

‘Unnamed Cave (or ‘Sho-doukutsu’)’, northeastern reef of Ie Island, Okinawa Prefecture, Ryukyu Islands, Japan. Marine anchialine cave with entrance from the reef slope at 17 meters depth and main tube penetrating about 50 meters under land (see Osawa & Fujita 2019 for the description of the cave). Specimens collected at 5–17 meters depth from plankton tow and sediment samples from the main tube and the anchialine right hall of the cave. Associated nerillids from the cave include Leptonerilla sp. 3 , Mesonerilla gamaglandulata sp. nov. and Trochonerilla sp. 1 .

Molecular information

Cirrinerilla sulcipalpata gen. et sp. nov. is nested within a fully supported larger clade comprising the seven- to eight-segmented genera Trochonerilla , Micronerilla , and Aristonerilla ( Fig. 2 View Fig ). Within this clade, Cirrinerilla gen. nov. is sister group to Aristonerilla (PP/BS: 1/92), together with Micronerilla constituting a fully supported subclade, sister to Trochonerilla . The phylogenetic analyses ( Fig. 2 View Fig ) include two terminals of C. sulcipalpata found to represent identical haplotypes.

Pairwise comparison of C. sulcipalpata gen. et sp. nov. sequence similarity to phylogenetic closely related species: 18S rRNA – 100% intraspecific similarity between the two C. sulcipalpata sequences – 89.28–93.59% similar to its sister group ( Aristonerilla brevis ( Saphonov & Tzetlin, 1997) and A. sp. 1); 28S rRNA – 100% intraspecific similarity – 66.21–66.38% similar to its sister group; COI – 100% intraspecific similarity – 74.67–80.44% similar to its sister group; H3 – 100% intraspecific similarity – 96.65% similar to its sister group.

Remarks (see also Table 3 View Table 3 for genus comparisons)

Cirrinerilla sulcipalpata gen. et sp. nov. shows closest morphological and molecular similarity to species of Aristonerilla and Micronerilla , and to a lesser degree to species of Trochonerilla . Species of all four genera have less than nine segments, three antennae, relatively long parapodial cirri, and are of similar small size. However, Cirrinerilla sulcipalpata differs from all species of these closely related genera by being hermaphroditic, having a cigar-shaped body narrowing in width anteriorly and posteriorly, and by having significantly longer and straighter palps with a dorsal longitudinal furrow. Moreover, it differs from species of Trochonerilla by having compound rather than capillary chaetae and by lacking dense transverse segmental ciliary bands. It also differs from species of Aristonerilla by having eight rather than seven segments and from species of Micronerilla by having only single rather than double parapodial cirri on each parapodium as well as only a single rather than two pairs of spermioducts. Therefore, we choose to erect the new genus Cirrinerilla gen. nov., since a designation of the new species to Aristonerilla , Micronerilla or Trochonerilla would otherwise result in a considerable ambiguity of their diagnostic genus characters (e.g., reproductive mode, segment number, chaetal type), generally assumed to be constant within the genera of Nerillidae ( Jouin 1971; Tzetlin & Larionov 1988; Worsaae 2021; Worsaae et al. 2021a).

Additionally, Cirrinerilla sulcipalpata gen. et sp. nov. differs from the closely related species of Aristonerilla and Micronerilla by having longer and straight (rather than wrinkled) antennae, lacking eyes, and having relatively longer parapodial cirri, especially on segment V. Noticeably, A. brevis is reported to sometimes possess comparatively much longer parapodial cirri on segment VII ( Müller 2002).