Syllis pseudohyalina Samoilova, Simon, Martín & Martin, 2026, sp. nov.

Syllis pseudohyalina sp. nov. urn:lsid:zoobank.org:act: 394DF90F-E834-4853-AB6C-93CEF8AD5EC8 Figs 5–8 non Syllis (Typosyllis) variegata Grube, 1860 – Day 1967a: 248, fig. 12.3j–i. non Syllis variegata Grube, 1860 – Day 1960: 308, in part. — Sedick 2018: 137–138. Etymology The species name ‘ pseudohylalina ’ refers to the close similarity with the Mediterranean Syllis hyalina, by adding the prefix ‘ pseudo ’ coming from the Greek word ‘ pseudos ’ (ψεῦδος), meaning ‘false’ or ‘deceptive’, being commonly used to reflect something that resembles another thing but is not genuinely that thing. Type material Holotype SOUTH AFRICA • entire specimen; Mossel Bay; 34°11ʹ11ʺ S, 22°09ʹ38ʺ E; Apr.–Oct. 2015; Safiyya Sedick leg.; intertidal algal turf; fixed in 4% seawater formalin, preserved in 70% ethanol; SAM-A089289. Paratypes SOUTH AFRICA • 3 entire specimens, 1 regenerating posterior end, 1 lacking posterior region; same collection data as for holotype; SAM-A089290 • 2 specimens, prepared for light microscopy; same collection data as for holotype; CEAB AP 1001A • 2 specimens, prepared for SEM; same collection data as for holotype; CEAB AP 1001B. Other material examined SOUTH AFRICA • 3 incomplete specimens; West Coast Dredge, UCT Ecological Survey, station WCD19J; 33°5ʹ35.9988ʺ S, 17°54ʹ29.9982ʺ E; 29 Apr. 1959; fixed in 4% seawater formalin, preserved in 70% ethanol; SAM-MB-A069882 • 4 complete specimens, 5 incomplete specimens; West Coast Dredge, UCT Ecological Survey, station WCD8G; 34°9ʹ18ʺ S, 18°17ʹ30.0012ʺ E; 24 Mar. 1959; fixed in 4% seawater formalin, preserved in 70% ethanol; SAM-MB-A069870 • 1 incomplete specimen; Saldanha Bay, UCT Ecological Survey, station SB189M; 33°1.1”S, 18°0.3”E; 30 Apr. 1959; fixed in 4% seawater formalin, preserved in 70% ethanol; SAM-MB-A060274. Description Body long, 3.6 (3.1–7) mm long, 0.46 (0.35–0.5) mm wide, with 49 (33–74) chaetigers (Figs 5A, 7A). Prostomium small, usually with two pairs of eyes, anteriormost half size of posterior; figured specimen being aberrant in having right posterior eye divided in two (Fig. 5A–B). Palps triangular, as long as prostomium, fused at bases (Figs 5A–B, 7B–C). Median antenna with 24 articles, lateral ones with 16– 19 articles (Figs 5A–B, 7B–C). Dorsal tentacular cirri shorter than median antenna, longer than lateral, with 22 articles, ventral tentacular cirri with 14 articles (Figs 5B, 7A–C). Tentacular segment shorter than subsequent ones, partly covering posterior end of prostomium (Figs 5A–B, 7B). Nuchal organs not seen. Dorsal cirri thick, fusiform, distally tapering, similar in length, all along body, alternating long and short at midbody, longer ones slightly longer than body width, with 24 articles at chaetiger 1, 16 at chaetiger 2, 17 at chaetiger 3, 27 at chaetiger 4,12–13 (short), and 18–20 (long) at midbody chaetigers (Figs 5A, 7A–D). Parapodial lobes short, conical (Fig. 7C, F–G). Ventral cirri conical to pyriform in anterior segments, digitiform in mid- and posterior body, as long as parapodial lobes (Figs 6J– K, 7C–D). Compound chaetae with heterogomph shaft with few, short subdistal spines becoming thicker in midbody and posterior chaetigers; falciger blades bidentate, with subdistal teeth slightly smaller than distal one all along body, and few straight, thick marginal spines slightly longer at bases (Figs 6A–G, 8A–E). Anterior parapodia with nine compound chaetae, blades 27 µm (dorsal) and 22 µm (ventral) (Figs 6A–B, 7B–C, F, 8A). Midbody parapodia with 6–7 compound chaetae, blades 23 µm (dorsal), 20 µm (ventral) (Figs 6C–D, 7D, G, 8B–C). Posterior parapodia with 4–5 compound chaetae, blades 17.5–26.3 µm (dorsal), 12.5–14.2 µm (ventral), with some short blades markedly thinner than others (Figs 6E–G, 7E, 8D–E). Dorsal simple chaetae straight, bidentate, with teeth directed upwards, subdistal teeth slightly smaller than distal ones, with few short subdistal spines (Figs 6H, 8F), ventral simple chaetae curved, bidentate, with teeth directed laterally, both of similar size, with few short subdistal spines (Figs 6I, 8G). Four aciculae in anterior parapodia, one clearly thinner than others, with 90° bent tip, two straight with round, truncated end, and one with pointed oblique tip; two aciculae in midbody parapodia, thick, with pointed oblique tips, one clearly more oblique than other, both slightly protruding from acicular lobe; single acicula in posteriormost segments, with slightly inflated, oblique tips, slightly protruding from acicular lobes (Figs 6L–N, 7F). Pharynx short, red color, extending over 9–10 segments, with pharyngeal tooth located at opening, slightly posterior (Fig. 5B). Proventricle very long, extending along 11–12 segments, with 45 (42–51) muscular rows (Fig. 5A–B). Pygidium small; 2 anal cirri with 14–17 articles; pygidial appendix only one, digitiform (Figs 5A, D–E, 7E). Distribution South African coast. Western Cape Province: off southwestern and southern (Mossel Bay) coasts. Remarks Our specimens most closely resemble Syllis hyalina Grube, 1863, originally described from the Mediterranean (Grube 1863; San Martín 2003). Both species lack body color —despite some specimens of S. hyalina have been reported as having dark transversal bands in anterior segments (San Martín 2003)—, have only falcigerous bidentate chaetae with the subdistal teeth similar in shape and size to the distal, and have the posterior acicula slightly protruding from the acicular lobe, slightly inflated distally, and having an oblique tip. However, the Mediterranean S. hyalina is longer (21 vs 6–7 mm) and has more chaetigers (110 vs 74), robust palps longer than prostomium (triangular, shorter than prostomium), shorter antennae (median: 7–15 articles, lateral: 11–12 articles vs median: 24, lateral: 16–19), dorsal tentacular cirri as long as median antenna (shorter than median antenna), ventral cirri longer than parapodial lobes (as long as parapodial lobes), and the pharynx lacking color and being slightly longer than proventricle, which shows 33 muscular rows (reddish, shorter, with 42 muscular rows in our specimens). Our specimens also resemble Syllis armillaris (O.F. Müller, 1776) and Syllis malaquini Ribeiro, Ponz-Segrelles, Helm, Egger & Aguado, 2020 in overall body shape (Müller 1776; Ribeiro et al. 2020). However, S. armillaris differs in having the blades of the midbody compound chaetae with the distal tooth smaller and with short marginal spines (both teeth similar in size, marginal spines similar to anterior chaetae in our specimens). Moreover, S. malaquini shows a characteristic color pattern consisting of dark lines on the dorsum of each segment, including peristomium, and dark stain on the anterior region of prostomium (absent in our specimens) and dorsal simple chaetae with a distal notch (bidentate in our specimens) (Ribeiro et al. 2020). The specimens reported as Syllis (Typosyllis) hyalina in Day (1967a), despite being briefly described and illustrated, show marked differences with S. pseudohyalina sp. nov. (e.g., in having a very short proventricle), but also differ from the Mediterranean S. hyalina. Day (1967a) suggested that they might be juveniles of S. variegata, which is a Mediterranean species most likely absent in South Africa. Therefore, further sampling is required to clarify the taxonomic status of the specimens attributed to S. (T.) hyalina by Day (1967a). Day (1967a) cites Day (1953, 1960) as sources for his report of S. variegata. None of the material examined by Day (1953) was available, but we examined three of the 22 samples reported in Day (1960) as S. variegata. That paper, however, does not include a description of these specimens, which, upon examination, did not match the description of S. variegata in Day (1967a). Although smaller, our specimens, initially identified as S. variegata by Sedick (2018), more closely resemble this material (SAM MB-A060274; SAM MB-A069882; SAM MB-A069870) than the description in Day (1967a). Syllis variegata, as redescribed in San Martín (2003) and reported in Day (1967a), is much longer (15 mm and 40 mm long, respectively) than our South African specimens (6–7 mm), although the complete specimens collected by Day (1960) and examined here were all shorter than 40 mm long. However, the Mediterranean S. variegata and our specimens agree in having the midbody dorsal cirri as long as or shorter than body width, while these are longer than body width in Day’s (1967a) S. variegata. Furthermore, both the Mediterranean and Day’s (1967a) S. variegata have the anterior dorsal cirri longer than body width (similar or shorter in our specimens). Moreover, the Mediterranean S. variegata shows a characteristic reddish transversal ∞ pigmentation pattern in each anterior segment that progressively disappears in midbody and posterior segments (San Martín 2003), Day’s (1967a) specimens have a broken brown bar pattern (with three bars on each segment) also in anterior region and disappearing posteriorly, while our specimens and those we examined from Day (1960) lack pigmentation. This absence of pigmentation is unlikely due to fading, as specimens matching the description of S. variegata according to Day (1967a) are still strongly pigmented after being in 95% ethanol for a year (C. Simon, personal observation). The single acicula of posterior parapodia in the Mediterranean S. variegata has a straight pointed tip that clearly protrudes from the parapodial lobe (San Martín 2003), while our specimens show the single posterior acicula slightly protruding from the acicular lobe and having an oblique tip. Moreover, our specimens show slightly longer antennae (median: 24 articles, lateral: 16–18) than the Mediterranean (17–18 and 12–13, respectively) and Day’s (1967a) specimens (16 and 12, respectively), and the pharynx is shorter than the proventricle (extending through 9–10 segments) and shows a characteristic red color, while it is longer than the proventricle (extending through 11–12 segments