Thoracophelia foliformis Lee, Lee & Min 2024, sp. nov.

Thoracophelia foliformis Lee, Lee & Min, 2024 sp. nov. Materials Type status: Holotype. Occurrence: catalogNumber: NIBRIV 0000900976; individualCount: 1; lifeStage: adult; occurrenceID: FF9733A0-0010-58EA-BB06-AD28627CAD15; Taxon: scientificName: Thoracophelia foliformis; phylum: Annelida; class: Polychaeta; family: Opheliidae; genus: Thoracophelia; specificEpithet: foliformis; scientificNameAuthorship: Lee, Lee & Min; Location: country: South Korea; municipality: Boryeong-si; locality: Is. Hodo; verbatimLatitude: 36 ° 17 ’ 54 ” N; verbatimLongitude: 126 ° 15 ’ 58 ” E; Event: eventDate: 08-09 - 2021 Type status: Paratype. Occurrence: catalogNumber: NIBRIV 0000900977, 0910950–910952; individualCount: 18; lifeStage: adult; occurrenceID: 30FB9856-7E6A-571C-8474-A177E17B3759; Taxon: scientificName: Thoracophelia foliformis; phylum: Annelida; class: Polychaeta; family: Opheliidae; genus: Thoracophelia; specificEpithet: foliformis; scientificNameAuthorship: Lee, Lee & Min; Location: country: South Korea; municipality: Boryeong-si; locality: Is. Hodo; verbatimLatitude: 36 ° 17 ’ 54 ” N; verbatimLongitude: 126 ° 15 ’ 58 ” E; Event: eventDate: 08-09 - 2021 Type status: Paratype. Occurrence: catalogNumber: NIBRIV 0000910953; individualCount: 1; lifeStage: adult; occurrenceID: DEF1D918-59D7-5AC8-9BC3-C86B1BFC2C00; Taxon: scientificName: Thoracophelia foliformis; phylum: Annelida; class: Polychaeta; family: Opheliidae; genus: Thoracophelia; specificEpithet: foliformis; Location: country: South Korea; municipality: Taean-gun; locality: Malipo Beach; verbatimLatitude: 36 ° 47 ’ 16 ” N; verbatimLongitude: 126 ° 08 ’ 27 ” E; Event: eventDate: 29-03 - 2021; Record Level: institutionCode: NIBR Type status: Paratype. Occurrence: catalogNumber: NIBRIV 0000910954; individualCount: 1; lifeStage: adult; occurrenceID: 15E441E9-2197-5DB6-BA13-F74C062A5BA3; Taxon: scientificName: Thoracophelia foliformis; phylum: Annelida; class: Polychaeta; family: Opheliidae; genus: Thoracophelia; specificEpithet: foliformis; scientificNameAuthorship: Lee, Lee & Min; Location: country: South Korea; municipality: Wando-gun; locality: Is. Soando; verbatimLatitude: 34 ° 09 ’ 56 ” N; verbatimLongitude: 126 ° 39 ’ 28 ” E; Event: eventDate: 25-05 - 2021 Type status: Paratype. Occurrence: catalogNumber: NIBRIV 0000910955; individualCount: 1; lifeStage: adult; occurrenceID: 2F73D89A-D734-57BA-80F8-444D54780807; Taxon: scientificName: Thoracophelia foliformis; phylum: Annelida; class: Polychaeta; family: Opheliidae; genus: Thoracophelia; specificEpithet: foliformis; scientificNameAuthorship: Lee, Lee & Min; Location: country: South Korea; municipality: Sinan-gun; locality: Is. Imjado; verbatimLatitude: 35 ° 06 ’ 18 ” N; verbatimLongitude: 126 ° 04 ’ 10 ” E; Event: eventDate: 22-07 - 2021 Type status: Paratype. Occurrence: catalogNumber: NIBRIV 0000910956–910958; individualCount: 3; lifeStage: adult; occurrenceID: 30EFEDB9-3B6B-5AF9-BC6E-B9DFDAB7C843; Taxon: scientificName: Thoracophelia foliformis; phylum: Annelida; class: Polychaeta; family: Opheliidae; genus: Thoracophelia; specificEpithet: foliformis; scientificNameAuthorship: Lee, Lee & Min; Location: country: South Korea; municipality: Sinan-gun; locality: Is. Uido; verbatimLatitude: 34 ° 36 ’ 26 ” N; verbatimLongitude: 125 ° 49 ’ 38 ” E; Event: eventDate: 01-06 - 2022 Description Holotype complete with 38 chaetigers, 17.2 mm long, 1.6 mm wide in thoracic region and 1.3 mm wide in abdominal region. Paratypes with 37–38 chaetigers, 11.1–24.2 mm long, 1.3–2.0 mm wide. Live specimens reddish in colour and body wall transparent. The reddish colour gradually fades to yellow or cream after alcohol preservation, but can remain for a year in the case of formalin fixation. Body distinctly divided into three regions by weak constrictions; cephalic, thoracic, and abdominal regions (Fig. 2 A and Fig. 3 A). The cephalic region consisting of a pointed prostomium and two setigers. A pair of nuchal organs present in cephalic region dorsolaterally (Fig. 2 A and Fig. 3 E). Multilobulated proboscis eversible from mouth region (Fig. 3 B and E). The thoracic region inflated and consisting of eight chaetigers (Fig. 3 A and B). Each chaetiger with about five indistinct annulations. Chaetiger 10 with smooth lateral ridge (Fig. 2 A and Fig. 3 A). The abdominal region includes 17–18 chaetigers and pygidium (Fig. 3 A). Last 3–4 chaetigers decreasing in size (Fig. 2 A, Fig. 3 B and Fig. 4 H). Longitudinal mid-ventral groove extending from about chaetiger 10 to pygidium (Fig. 3 B). A pair of longitudinal lateral grooves present in the abdominal region, one on each side of body (Fig. 3 A and B). Body formula 13 a (abranchiate) + 15 b (branchiate) + 9–10 a (posterior abranchiate) = 37–38 chaetigers. Black rod-shaped spicules in coelom cavity corrugate or curve, with about 38–98 µm in length (Fig. 3 E). Branchiae pectinate, wrinkled, occurring from chaetigers 14 to 28 (Fig. 2 B, Fig. 3 C, D and Fig. 4 B and F). Branchiae with finger-shaped branchial filaments from the main stem; the well-developed ones bear up to 12–15 filaments. Each branchial filaments with cilia on dorsal and ventral side (Fig. 4 Fand I). Parapodia biramous, with rounded postchaetal lobes on each noto- and neuropodia (Fig. 4 G). Notopodial postchaetal lobes lower than neuropodial ones. Lateral organs present in between noto- and neuropodia, with a longitudinally arranged row of cilia (Fig. 4 G). Chaetae distally serrated in one side (Fig. 4 J and K). Chaetae distinctly longer in chaetigers 3–5 and posterior 3–4 chaetigers (Fig. 2 A). Pygidium with about 6–8 anal cirri on each lateral side and a foliaceous mid-ventral plate, flattened, wider basally and distally tapering (Fig. 2 C, Fig. 3 F and Fig. 4 H). Diagnosis Fifteen pairs of branchiae present on chaetiger 14–28. Branchiae pectinate, wrinkled and the well-developed ones bear 12–15 finger-shaped branchial filaments. Chaetiger 10 with a pair of smooth lateral ridge. Pygidium with a foliaceous mid-ventral plate and about 6–8 anal cirri on each lateral side. Etymology The new specific name derives from the foliaceous shape of the mid-ventral plate in the pygidium. The name is a combination of the Latin words folium (meaning ‘ leaf’) and formis (meaning ‘ shape’). Distribution The new species was collected from the upper intertidal zone, which consists of sand or muddy sand, in the Yellow Sea of South Korea (Fig. 1). Variation Although the number of branchial filaments in well-developed branchiae is variable (12–15), there was no variation in the number of pairs of branchiae (15 pairs) or the first branchiae-bearing chaetiger (chaetiger 14) amongst the specimens. Reproductive information Female adult specimens were observed in the present study. Oocytes present in coelom cavity, with about 0.1 mm diameter, visible through the transparent body wall (Fig. 3 C). Methyl green staining pattern (MGSP) Annulations of each segment have weak line-shaped stain and the stains are thicker at mid-dorsal abdominal region (Fig. 4 A, B and D). Several posteriormost segments and the mid-ventral plate of pygidium are intensely stained (Fig. 4 E). A deep and large circular patch present at the base of each branchiae anteriorly (Fig. 4 A and B). Prostomium with weak stain on lateral sides (Fig. 4 C). Genetics Sequences of mitochondrial COI, nuclear 18 S rDNA and 28 S rDNA were obtained from the three specimens of Thoracophelia foliformis sp. nov. The intraspecific variation in 28 S rDNA (849 bp) was 0.1 %; however, there was no intraspecific variation in COI (657 bp) or 18 S rDNA (1,684 bp). The interspecific variations between the new species and the congeners were 14.2–15.4 % in COI (654 bp), 0.2–0.3 % in 18 S rDNA (1,750 bp) and 3.6–4.2 % in 28 S rDNA (873 bp) (Table 1). Remarks Thoracophelia foliformis sp. nov. is the first Thoracophelia species described in the Yellow Sea. In possessing pectinate branchiae, Thoracophelia foliformis sp. nov. resembles Thoracophelia dillonensis (Hartman, 1938) from California and Thoracophelia ezoensis Okuda, 1936 from Japan. While most similar to T. dillonensis in having 15 pairs of branchiae, the new species is distinguished from T. dillonensis by the shape of its branchiae and pygidium. The new species has wrinkled branchiae with 12–15 filaments at best development and a foliaceous mid-ventral plate in the pygidium, whereas T. dillonensis has unwrinkled, smooth branchiae with 15–20 filaments at best development and two thick mid-ventral cirri instead of the plate. Thoracophelia ezoensis also differs from the new species as the former possesses 19 pairs of branchiae and a thick mid-ventral cirrus, whereas the latter has 15 pairs of branchiae and a foliaceous mid-ventral plate. Furthermore, the new species also differs from the two species, as the branchiae of the new species first appear on chaetiger 14, while those of the two species first appear on chaetiger 13. In Northeast Asia, six species have been reported and are clearly distinguished from the new species by the shape of the branchiae, except T. ezoensis mentioned above. Morphological differences amongst those species are mentioned in the identification keys below. New Korean name Yip-sa-gwi-Keun-yo-jeong-get-ji-reong-yi (잎사귀큰요정갯지렁이)