Thelepus japonicus Marenzeller, 1884

Lavesque, Nicolas, Londoño-Mesa, Mario H., Daffe, Guillemine & Hutchings, Pat, 2020, A revision of the French Telothelepodidae and Thelepodidae (Annelida Terebelliformia), with descriptions of three species and first European record of a non-indigenous species, Zootaxa 4810 (2), pp. 305-327 : 320-322

Thelepus japonicus Marenzeller, 1884

Figures 9–10

Thelepus japonicus Marenzeller, 1884: 208–209 , pl. II, fig.4.

Material examined: MNHN-IA- PNT 117, one specimen, complete, Northeast Atlantic Ocean , Arcachon Bay , Jacquets , 44°43’17”N 1°11’24”W, intertidal in oyster reefs, January 2018, some parapodia mounted for SEM. SMA_ ARC _ Thelepus _08, one specimen, complete, Northeast Atlantic Ocean, Arcachon Bay , Le Cla, 44°40’43”N 1°08’11”W, intertidal in oyster reefs, June 2017, some parapodia used for molecular analysis. AM W.53072, one specimen, complete, Northeast Atlantic Ocean, Arcachon Bay , Afrique Channel, 44°41’02”N 1°11’23”W, intertidal in oyster reefs, January 2019, some parapodia mounted for SEM and some used for molecular analysis. AM W.53073, one specimen, incomplete, Northeast Atlantic Ocean, Arcachon Bay , Jacquets, 44°43’17”N 1°11’24”W, intertidal in oyster reefs, January 2018. MNHN-IA- PNT 118, one specimen, complete, English Channel, Cotentin, Saint-Vaast-la-Hougue, 49°35’30”N 1°15’48”W, intertidal in oyster farms, April 2018, some parapodia mounted for SEM and some used for molecular analysis. AM W.53074, one specimen, complete, English Channel, Cotentin, Saint-Vaast-la-Hougue, 49°35’30”N 1°15’48”W, intertidal in oyster farms, April 2018, some parapodia used for molecular analysis. SMA-Arc-Thele-09, one specimen, incomplete, Northeast Atlantic Ocean, Arcachon Bay, Le Cla, 44°40’43”N 1°08’11”W, intertidal in oyster reefs, July 2017, some parapodia used for molecular analysis. SMA-Arc-Port02, one specimen, complete, Northeast Atlantic Ocean, Arcachon Bay, Harbour, 44°39’39”N 1°09’07”W, under pontoons, September 2017, some parapodia used for molecular analysis .

Comparative material: MNHN-IA- PNT 119, one specimen, complete, Northeast Pacific Ocean , Japan, Ago Bay, 34°18’00”N 136°50’44”E, November 2018. AM W.53075, one specimen, complete, Northeast Pacific Ocean , Japan, Ago Bay, 34°18’00”N 136°50’44”E, November 2018 , some parapodia mounted for SEM. SMA_JAP-Thele- 03, one specimen, complete, Northeast Pacific Ocean , Japan, Ago Bay, 34°18’00”N 136°50’44”E, November 2018 .

Description. Specimens about 67–150 mm long, 5.0– 6.5 mm wide.

Prostomium at base of upper lip; eyespots in thin and continuous dark band, with 2–3 irregular rows across posterior margin of basal part of prostomium ( Fig. 9C ); buccal tentacles long, reaching about SG24, deeply grooved ( Fig. 9 B–D). Peristomium continuing dorsally as narrow annulation; upper lip distinctly wider than long, not convoluted, hood-like ( Fig. 9D ); lower lip thick, surrounded by ventral crescent shape lobe originated from SG1 ( Fig. 9D ). SG1 short, more visible dorsally, except for ventral lobe.

Three pairs of branchiae, on SG2–4, with about 18–25 filaments on SG2, 11–13 on SG3 and 11–12 on SG4; filaments distally blunt, cylindrical, originating from glandular cushion-like structures, with large medial gap, the longest filaments about as long as body width at corresponding segments ( Fig. 9 A–C); branchial filaments arranged in two irregular rows; point of origin of filaments of SG2 and SG3 extending laterally beyond level of notopodia ( Fig. 9A ).

Ventral surface of anterior segments strongly glandular, corrugated on anteriormost segments, ventral shields absent ( Fig. 9D ); mid-ventral stripe beginning from about SG27, discrete. Notopodia from SG3, extending posteriorly to last segments; notopodia approximately rectangular, distally rounded, progressively shorter and more rounded from mid-body onwards; slightly bilobed, chaetae emerging between lobes ( Figs 9A ; 10A ). Two rows of falcate notochaetae, anterior row with twisted winged chaetae ( Fig. 10A ), posterior row with narrowly-winged notochaetae, with tapering tips; well-marked difference in length between rows ( Fig. 10A ).

Neuropodia from SG5, as long fleshy ridges on anterior body, progressively shorter and more raised from midbody segments onwards. Uncini with terminal dorsal button, with triangular rounded heel and very short knob-like prow, crest with two rows of secondary teeth, basal row with 2–3 teeth, second row with 1–2 larger teeth in-between teeth of basal row and minute denticles inserted laterally to them ( Fig. 10 B–D).

Short, spherical nephridial and genital papillae on SG4–7 ( Fig. 9A ), between notopodia and neuropodia (or corresponding position, on SG4). Pygidium crenulated.

Habitat. Oyster reefs or in oyster farms (this study).

Type locality. Pacific Ocean , Japan .

Distribution (based on literature). British Columbia ( Burd & Brinkhurst 1987), China ( Treadwell, 1936), Japan ( Marenzeller 1884; Kin et al. 2019), Korea ( Paik et al. 2007), Kuwait ( Al-Kandari et al. 2019), Bay of Biscay (Arcachon Bay), English Channel (Cotentin) (this study).

Remarks. The morphology of the French specimens closely matches the Japanese material, except for the upper lip, which is crenulated in the Japanese material. This may be a preservation artifact, with muscular relaxation of the lip. Among the French specimens observed, MNHN-IA- PNT 117 shows an asymmetry of the notopodia, with notopodia starting from SG3 on the right side and from SG2 on left side. This asymmetry could be related to the animal regenerating anterior segments after sustaining damage.

Molecular analyses also confirm that French specimens are the same as Japanese ones ( Figs 11 ; 12 ), with K2P distances comprised between 0.7% and 1.3% for COI. Sequence of T. japonicus deposited in Genbank (accession number: LC 455932 ) was obtained from a specimen collected in Japan (type locality) exactly from the same place ( Ago Bay ) as specimens used for morphological comparison in this study (N. Jimi, comm. pers.)

Figures

FIGURE 9. Thelepus japonicus AM W.53073 (A), SMA_Arc_Thele_08 (B–C), MNHN-IA- PNT 117 (D). A. Anterior end, lateral view; B. Anterior end, dorsal view; C. Anterior end, lateral view; D. Anterior part, ventral view. Br, branchiae; Bu, buccal tentacles; Ey, eyes; Np, nephridial papillae; Ll, lower lip; Ul, upper lip; Vl, ventral lobe. Numbers referring to segments.

FIGURE 10. Thelepus japonicus AM W.53072 (A–B), MNHN-IA- PNT 119 (C), MNHN-IA- PNT 117 (D). A. Notochaetae, CH8, SEM; B. Uncini, CH37, SEM; C. Uncini, CH12; D. Uncini, CH15. Arrow indicates dorsal button.

FIGURE 11. Majority-rule consensus tree of Thelepus species sequences obtained in this study and available on GenBank for COI gene. Asterisk indicates posterior probability> 80%. Sequence accession numbers refer to Table 1, text in red to specimens sequenced during this study.

FIGURE 12. Majority-rule consensus tree of Thelepus species sequences obtained in this study and available on GenBank for 16S gene. Asterisk indicates posterior probability> 80%. Sequence accession numbers refer to Table 1, text in red refers to specimens sequenced during this study.