Virchowia christophi Springer, Sato, Oguchi, Jimi, Miura & Aguado, 2025, sp. nov.

Virchowia christophi sp. nov. Aguado, Springer, Oguchi, Sato, Jimi & Miura Figs 4–10, Table 1 urn:lsid:zoobank.org:act: ACBF2731-315F-4BED-B31C-17EE83CD310C Material examined. Holotype (NSMT-Pol H-975) and two paratypes (NSMT-Pol P-976): Japan, Misaki: Arahaima Beach, Sagami Bay, Misaki, 35°09'34"N 139°36'40"E, 2–5 m, coll. Oguchi, 2022. Three paratypes (ZMUG 32498) and additional material (NSMT-Pol 113615): Japan, Misaki: Sagami Bay, Misaki Marine Biological Station, 35°09'36.1"N 139°36'40.1"E, 2–5 m, coll. Aguado & Oguchi 2019, Sato & Aguado 2024. Additional material (ZMUG 32500): Japan, Sugashima Island: Kamekobana, 34°28'40"N 136°53'00"E, 5 m, coll. Jimi, Tsuyuki & Ishibashi 2024. Comparative material. Virchowia pectinans (Hartmann-Schröder, 1983) (AM-W 41620): New South Wales: S. of Grasshopper Is., 2004. Description. Length between 8.7–12.8 mm for 37–39 segments, width 0.35–4 mm. Adult specimens with developing stolons. Body consists of prostomium, 13 segments, stolon head, 37–39 stolon segments (depending on the stolon’s developmental stage) and pygidium. Adult specimens without stolon consist of prostomium, 50 segments and pygidium. Body slender, tubular, ventrally flattened and thickest in segments 5–7 (Fig. 4A). Body and appendages contracted in fixed material (Fig. 4A), longer and slender in live specimens (Fig. 5A, B). Prostomium with four red eyes in trapezoidal arrangement. Nuchal epaulettes sand coloured in both live and fixed specimens, originating dorsally on prostomium (Figs 4A, 5B), bifurcated (Fig. 6A–C, E), and highly ciliated (7C). One band of cilia around the eyes (Fig. 7D). Median antenna thick (Fig. 4A), sand coloured, as long as three segments (Fig. 5A–B). Lateral antennae slim, sand coloured, length 2/3 of median antenna (Figs 4A, 5A–B). Palps ventrally located, basally fused to the prostomium, free distal ends (Fig. 6D). Peristomium fused with prostomium, not distinguishable. Dorsal tentacular cirri 2/3 length of median antenna, ventral pair long, thinner than dorsal pair (Figs 4A, 5A–B). Median antenna, lateral antennae, tentacular cirri cylindrical, distally pointed (Figs 4A, 5A–B, 6A–B, E). First dorsal cirri reaching chaetiger 3, longer than lateral antennae, fourth dorsal cirri as long as first pair (Figs. 4A, 5A–B). Second and third dorsal cirri smaller, as long as ventral tentacular cirri (Figs 4A, 5A–B). Ventral cirri fused to parapodia (Figs 4A, 7A). Dorsal cirri follow consistent pattern of alternation (pointing up: U; down: D): adult head, U, D, D, U, D, U, D, D, U, D, U, D, U, stolon head, D, U, D, U, D, U, D, D, D, U, D, U, D, U, D, D, U, U, D, D, D, U, D, D, U, U, D, D, D, U, D, D, U, D, D, U, D, stolon pygidium (Fig. 5A–B). Same alternation pattern in all specimens. No alternation in cirri placement (Fig. 8A). Upwards oriented dorsal cirri clavate, thick, sandy colouration, distally pointed (Figs 4A, 5A–B). Downwards oriented dorsal cirri short, slim, whitish, distally pointed (Figs 4A, 5A–B). Segments faintly secondarily annulated, more pronounced in anterior region (Figs 4A, 6A, 8B). All dorsal surface, dorsal cirri and antennae with glandular openings (Figs 8B, 9D, E). Bunch of cilia in antennae and first dorsal cirri (Figs 7A, B, 9A–D) and “star-shaped” filament extensions (Fig. 9B, F). Striking colour pattern (Figs 5, 6), consistent in all specimens, only slight deviations in the stolons. Colouration identical in both live and fixed specimens with no fading observed after five years of storage. Segment colours vary between sandy/beige and dark brown. Thin, dark brown bands mark the end/the beginning of each segment (Fig. 5A, B). Two dark-brown, rounded spots located laterally between segments 3/4; 8/9 and 12/13 of the adult holotype. Spots can vary in size; but placement is consistent in all specimens. Most segments with at least one line of small white refringent dots spanning across the width of the segment, some segments with up to four lines of white dots. Dotted lines may continue onto the downwards oriented dorsal cirri, but never onto the upwards oriented dorsal cirri. Most segments do not vary in colour within themselves, but the number of white dots per annulation may vary within a segment. Segments 10 and 11 of the adult holotype appear almost white and shining due to high number of white dots. Segments 4, 9 and 13 of the adult holotype appear dark brown. Parapodia with 7–10 chaetae (Fig. 10A). Parapodia rounded, bilobed (Fig. 10A). Chaetae bidentate, without blade serration (Figs 4B–C, 10B–D), and simple (shafts and blades fused, Figs 10 B, C), 1–2 most-ventral ones within the chaetae fascicle remain compound (Fig. 10D). Proximal tooth larger than distal one (Figs 4C, 10C, D). Chaetae from anterior and posterior-most segments with elongated distal teeth, especially the proximal one. No simple chaetae or bayonet chaetae present. Two pointed aciculae. Long and twice-sinuated pharynx reaching segments 1–3. Trepan provided with 25 unequal teeth, alternating 1 large and 1–2 small teeth, arranged in 1 ring (Fig. 4D). Proventricle cylindrical, occupying segments 3–6 (not clearly seen by transparency) in both live and fixed specimens. Pygidium with two small, opaque and cylindrical anal cirri (Fig. 5A–B, 6F). Reproduction. Schizogamy by anterior scissiparity. Developing stolon behind segment 13 (Fig. 5A–B). Stolon with four red eyes in trapezoidal arrangement, anterior pair larger (Fig. 5B). Median and lateral antennae developed, small, white opaque. Cirri, at this point of development (Figs 5A, B, 8C–D), with same colour and shape as anterior adult cirri. Pattern of alternation consistent across all stolon specimens. Pygidium with pair of small, rounded, white opaque anal cirri. Segment colours vary between sandy/beige and dark brown. Colouration pattern as described for the atoke specimens. Two dark-brown, rounded spots located laterally between segments 4/5; 8/9; 9/10; 10/11; 14/15; 15/16; 22/23; 30/31 of the stolon. Segments 6, 7, 13, 17, 18, 24–26, 29, 30 and 33–36 of the stolon appear almost white and shining due to high number of white dots. Segments 5, 8–11, 15, 16, 20, 24, 28 and 32 dark brown. Parapodia with 7–10 chaetae. Chaetae with slim shafts, no blade serration. Bayonet chaetae not seen. No notochaetae present at the described development stage. Habitat. Rocky shorelines, shallow waters 2–5 m deep, on algae and below rocks. Remarks. Virchowia christophi sp. nov. is characterized by the unique combination of bifurcated nuchal epaulettes, a striking colour pattern, the distinctly shaped chaetae (with long distal teeth and absence of serration on verge), and the alternation pattern of dorsal cirri in colour, shape and size. Its diagnostic characters fit well with those from the genus Virchowia (Nygren, 2004) (Table 1). The palps in Virchowia christophi sp. nov. are not completely fused to the prostomium. Virchowia branchiata Averincev, 1972, from the Antarctic, is the only other Autolytinae with nuchal epaulettes as bifurcated outgrowths (Nygren 2004). However, this species has chaetae with fine spinulation on verge, bayonet chaetae and less teeth on the trepan ring. Virchowia pectinans from Australia has a complex colour pattern, whose colours are similar to those of V. christophi sp. nov. (pers. obs. from AM fixed material). However, the colour pattern is different and it has chaetae with more curved distal teeth and long spinulation on verge. The number of trepan teeth and convolutions of the pharynx are also different to those of V. christophi sp. nov. In Japan, the only known species of the genus is V. japonica Imajima & Hartman, 1964, which was described from a single male stolon (Nygren 2004). This species possesses compound chaetae with serrations on the verge and includes bayonet chaetae. In contrast, V. christophi sp. nov. mostly has simple chaetae with shafts and fangs fully fused, (excepting those located most ventrally in the chaetiger), long distal teeth, serrations on the verge completely missing, and absence of bayonet chaetae. Additionally, V. japonica exhibits only DU-groups of alternating cirri, while the dorsal cirri alternation pattern in V. christophi sp. nov. is different. Regarding the shape of compound chaetae, V. spirifer Augener, 1913 is the only other species of Virchowia without serrations or spines along the cutting margin of the chaetae. Similarly, Imajimaea draculai also lacks blade serration along the blades of compound chaetae. However, V. christophi sp. nov. can be distinguished from V. spirifer and I. draculai, in addition to the bifurcated nuchal epaulettes, by its chaetae shape, trepan structure, absence of bayonet chaetae, and distinct dorsal cirri pattern. SEM images revealed glandular structures covering the entire body of V. christophi sp. nov. While similar structures have been observed in other syllids (San Martín & Aguado 2012; Jimi et al. 2024), their function remains unclear. Distribution. Misaki Sagami, Bay; Sugashima Island; Japan; NW Pacific. Etymology. This species is dedicated to Professor Dr. Christoph Bleidorn, for all his important contributions to systematics, and specifically to the phylogenetic relationships of Annelida.