Heteromastus filiformis (Claparède, 1864).

Port-Vendres, France.

(modified after Magalhães and Blake (in press)). Prostomium short to long, conical, eyespots present or absent. Thorax with 11 chaetigers. Chaetiger 1 biramous. Chaetigers 1–5 with only capillary chaetae, chaetigers 6–11 with long-shafted hooded hooks. Abdominal chaetigers with short-shafted hooded hooks. Branchiae present or absent on posterior abdomen. Genital pores presence on posterior thoracic chaetigers. Lateral organs distinct on thorax and indistinct on abdomen. Pygidium adorned with ventral caudal cirrus.

Holotype: MABIKNA00155558, sex uncertain, Cheongsando, 34°1.662'N, 127°4.272'E, subtidal, sandy mud bottom, 34 m depth, March 2016, coll. Man-Ki Jeong. Paratypes (two specimens): MABIKNA00155560, Yeosu, 34°41.569'N, 127°51.848'E, subtidal, sandy mud bottom, 15 m depth, June 2018; MABIK NA00155559, Jejudo, 33°16.699'N, 127°16.230'E, subtidal, sandy mud bottom, 54 m depth, April 2018. Additional 6 specimens from type locality on SEM stub.

Abdominal hooks with four rows of teeth, three teeth in basal row, three in second and third row, and four to six in superior row. Genital pores present in intersegmental furrows between chaetigers 7–8, 8–9, 9–10, and 10–11. Hemispheric notopodial lobes present on posterior abdominal segments.

Holotype entire, about 60 mm long, 0.9 mm wide for 98 chaetigers (terminal part missing). Paratypes range from 19–41 mm in length, 0.5–0.8 mm width for 41–95 chaetigers. Body thread-like, rounded dorsally, flattened ventrally, widest in anterior thoracic chaetigers, and tapering from abdomen to pygidium. Color brownish yellow in alcohol.

Prostomium conical, with short and hemispherical palpode; nuchal organs not seen, eyespots absent (Fig. 2A, B). Everted proboscis with numerous small papillae (Fig. 2A). Peristomium uni-annulated and slightly longer than first thoracic chaetiger (Fig. 2A, B).

Thorax with 11 chaetigers (Fig. 2A, B). Thoracic segments biannulated, with shallow intra- and intersegmental grooves (Fig. 2A, B). Anterior five thoracic segments slightly expanded (Fig. 2A, B). First chaetiger biramous, with three or four bi-limbated capillaries; chaetigers 2–5 with six to 14 capillaries per fascicle in both parapodia; chaetigers 6–11 with five to 12 long-shafted hooded hooks per fascicle (Fig. 2A, B, F); thoracic hooks with indistinct node on shaft and at least six teeth in three rows above the main fang (Fig. 2F). Notopodia located dorso-laterally, dorsally located in last few thoracic segments; neuropodia located in lateral positions (Fig. 2A, B). Lateral organs present between noto- and neuropodia of all thoracic chaetigers, nearer to notopodia in chaetigers 5–11; sometimes indistinct on first thoracic chaetigers (Fig. 2A). Genital pores present in intersegmental furrows of between chaetigers 7–8, 8–9, 9–10, and 10–11 (Fig. 2A).

Transition between thorax and abdomen distinguished by changes in ultrastructure of chaetae and shape of segment (Fig. 2A, B); abdominal segments multi-annulated, gradually longer posteriorly, with short-shafted hooded hooks in posterior parapodial lobes; thoracic chaetigers usually bi-annulated, wider than long, with long-shafted hooded hooks in center of segment (Fig. 2A, B).

Abdominal parapodial lobes located in posterior end of each segment, well separated from each other, and gradually developed posteriorly (Fig. 2A–D). Abdominal notopodia separated, mid-dorsal on anterior few segments, becoming dorsolateral in following abdominal region, with six to eight hooded hooks per fascicle, having dorso-posteriorly protruded and hemispheric lobes from chaetiger 90 to end of body (Figs 2A–D, 5B). Abdominal neuropodia well separated, with 10–12 hooded hooks per fascicle, having slightly protruded lobes in posterior abdomen; neuropodial lobes less developed than notopodial lobes (Figs 2C, D, 5B).

Hooded hooks with main fang extending slightly beyond hoods. Abdominal hooks with distinct node on shaft and four rows of small teeth above main fang; three teeth in basal row, three in second and third row, and four to six in superior row (Figs 2E, G, 5A). Pygidium with digitate anal cirrus (Figs 2D, 5B).

Figure 2. 

Heteromastus namhaensis sp. nov. A anterior end, left lateral view (holotype, NA00155558) B same, dorsal view C posterior abdominal segments, right lateral view (holotype, NA00155558) D posterior end, dorsal view (holotype, NA00155558) E abdominal short-shafted hook, frontal view. F thoracic long-shafted hook, lateral view G abdominal short-shafted hook, lateral view. Abbreviations: ac, anal cirrus; cc, capillary chaetae; Ch, chaetiger; gp, genital pore; hh, hooded hooks; lo, lateral organ; mf, main fang; neu, neuropod; no, notopod; per, peristomium; pro, prostomium; prob, proboscis; pyg, pygidium.

Prostomium, peristomium and thoracic chaetigers 1–2 not stained (Fig. 6A). Thoracic chaetigers 3–11 stained blue; chaetigers 3–8 stained dark blue; chaetigers 9–11 stained light blue; post-chaetal region of chaetiger 11 not stained (Fig. 6A). Abdominal region without any distinct staining pattern.

The species is named for its wide distribution in Namhae (=Korean name of southern sea of Korea).

Subtidal areas (15–54 m) near southern part of Korea (Fig. 1).

Heteromastus namhaensis was sampled from soft sediments in March of 2016 (10 ind./m²), April of 2018 (40 ind./m²), and June of 2018 (20 ind./m²). The most well-developed individual (having over 100 segments) was obtained in March and eggs in the coelom were 87–94 μm in diameter. Surface sediment of the station was mainly composed of sandy mud with fragmented shells. Leiochrides yokjidoensis Jeong, Wi & Suh, 2017 co-occurred in Jejudo of Korea (Jeong et al. 2017a; Fig. 1). The salinity range among sampling locations was about 31–32.5 PSU.

Heteromastus namhaensis resembles H. filiformis sensu Hutchings & Rainer, 1982 in the absence of distinct eyespots on prostomium, three teeth in basal row above the main fang of abdominal hooks, and the presence of posteriorly extended abdominal notopodial lobes (Table 2). However, they differ in the shape of notopodial lobes in posterior abdomen (hemispheric protrusion in H. namhaensis vs broadly-based and rounded lamellae in H. filiformis sensu Hutchings & Rainer, 1982), the different dental structure of abdominal hooks (Table 2). Heteromastus namhaensis is also easily distinguished from Korean former record of H. filiformis (Choi and Yoon 2016) by the presence of hemispheric abdominal parapodial lobes and the absence of eyespots in H. namhaensis. In particular, the hemispheric notopodial lobe of H. namhaensis is a unique feature in the genus.

Holotype: MABIKNA00155561, sex uncertain, Yeonggwang, 35°25.819'N, 126°25.482'E, intertidal, tidal mud-flat, 1 m depth, November 2017, coll. Man-Ki Jeong. Paratypes (2 specimens): MABIK NA00155562 and NA00155563, same information as holotype.

MABIK NA00155564, sex uncertain, Yeonggwang, 35°25.819'N, 126°25.482'E, intertidal, tidal mud-flat, 1 m depth, May 2015, coll. Man-Ki Jeong. Additional 16 specimens from type locality on SEM stub.

Abdominal hooks with four rows of teeth; three teeth in basal row, three in second row, four in third row, and two in superior row. Genital pores present in intersegmental furrows of between chaetigers 5–6, 6–7, 7–8, 8–9, 9–10, and 10–11. Posteriorly extended parapodial lobes absent on abdominal segments.

Holotype entire, about 26 mm long, 0.5 mm wide for 120 chaetigers. Paratypes range from 19–24 mm in length, 0.4–0.5 mm width for 75–110 chaetigers. Body thread-like, rounded dorsally, flattened ventrally, widest in anterior thoracic chaetigers, and tapering from abdomen to pygidium. Color yellowish white in alcohol.

Prostomium short, conical, with short and blunt palpode; nuchal organs not seen, eyespots absent (Fig. 3A, B). Everted proboscis with small hemispheric papillae (Fig. 3B). Peristomium weakly bi-annulated and subequal in length with chaetiger 1 (Fig. 3A, B).

Thorax with 11 chaetigers (Fig. 3A, B). Thoracic segments biannulated, with shallow intra- and intersegmental grooves (Fig. 3A, B). First chaetiger biramous, with three or four bi-limbated capillaries; chaetigers 2–5 with six or seven capillaries per fascicle in both parapodia; chaetigers 6–11 with six or seven long-shafted hooded hooks per fascicle (Fig. 3A, B, F); thoracic hooks with indistinct node on shaft and at least 10 small teeth in three rows above the main fang (Fig. 3F). Notopodia located in dorso-laterally, dorsally located in last few thoracic segments; neuropodia located in lateral positions (Fig. 3A, B). Lateral organs present between both parapodia of all thoracic chaetigers, nearer to notopodia in chaetigers three to 11 (Fig. 3B). Genital pores present in intersegmental furrows between chaetigers 5–6, 6–7, 7–8, 8–9, 9–10, and 10–11; sometimes indistinct between chaetigers 5–6 (Fig. 3B).

Transition between thorax and abdomen distinguished by changes in chaetation and shape of segment (Fig. 3A, B); abdominal segments multi-annulated, with short-shafted hooded hooks in posterior part of segment; thoracic chaetigers usually bi-annulated, with long-shafted hooded hooks in center of segment; last thoracic chaetiger usually shorter than first abdominal chaetiger (Fig. 3A, B).

Abdominal parapodial lobes well separated from each other, located in posterior end of each segment (Fig. 3A–C). Abdominal notopodia separated, mid-dorsal on anterior few segments, becoming dorsolateral in following abdominal region, with five or six hooded hooks per fascicle, not protruded in anterior abdominal region, and very weakly protruded above epidermis in mid-posterior abdomen; not extended over further segment (Figs 3A–D, 5D). Abdominal neuropodia separated, not protruded, with six to eight hooded hooks per fascicle; neuropodial lobes less developed than notopodial lobes (Figs 3A–C, 5D).

Hooded hooks with main fang extending slightly beyond hoods. Abdominal hooks with distinct node on shaft and four rows of small teeth above main fang; three teeth in basal row, three in second row, four in third row, and two in superior row (Figs 3E, G, 5C). Pygidium with digitate anal cirrus (Figs 3D, 5D).

Figure 3. 

Heteromastus gusipoensis sp. nov. A anterior end, dorsal view (holotype, NA00155561) B same, lateral view C posterior abdominal segments, left lateral view (holotype, NA00155561) D posterior end, dorsal view (holotype, NA00155561) E abdominal short-shafted hook, frontal view F thoracic long-shafted hook, lateral view G abdominal short-shafted hook, lateral view. Abbreviations: ac, anal cirrus; cc, capillary chaetae; Ch, chaetiger; gp, genital pore; hh, hooded hooks; lo, lateral organ; mf, main fang; neu, neuropod; no, notopod; per, peristomium; pro, prostomium; prob, proboscis; pyg, pygidium.

Prostomium, peristomium and thoracic chaetigers 1–2 not stained (Fig. 6B). Thoracic chaetigers 3–10 stained blue; blue speckles restrictively present on the median part of each segment; blue speckles sparse in chaetigers 3–4 (Fig. 6B). Abdominal region without any distinct staining pattern; parapodial lobes of chaetigers 12–13 slightly stained in blue but rapidly fades.

The new species is named for its limited distribution in Gusipo, Korea.

Intertidal area (0–1 m) near Gusipo, Korea.

Heteromastus gusipoensis was sampled in May of 2015 (9 ind./m²) and November of 2017 (71 ind./m²). Most well-developed individuals (having over 120 segments) were obtained in November. Surface sediment of the collecting station was mainly composed of fine sand and silt. Unidentified nereidid polychaetes co-occurred in the same location. The salinity of the sampling location was about 32.

Heteromastus gusipoensis closely resembles H. tohbaiensis Yabe & Mawatari 1998 in the chaetal arrangement and the absence of developed parapodial lobes in posterior abdomen (Table 2). However, they differ in the presence of eyespots on prostomium and distinct node on the shaft of thoracic hooks in H. tohbaiensis (Table 2; Yabe and Mawatari 1998). Moreover, they occur in different habitats and geographical areas. H. gusipoensis only occurs in the marine intertidal zone (salinity ca 32) of southwestern Korea, whereas H. tohbaiensis is only reported from the lacustrine habitat of northern Japan (Yabe and Mawatari 1998). Heteromastus gusipoensis is readily distinguished from the Korean former record, H. filiformis sensu Choi & Yoon, 2016, by the absence of prostomial eyespots and expanded abdominal parapodial lobes in H. gusipoensis.

Holotype: MABIKNA00155565, sex uncertain, Muan, 35°6.270'N, 126°20.093'E, intertidal, tidal mud-flat, 1 m depth, November 2017, coll. Man-Ki Jeong. Paratypes (2 specimens): MABIKNA00155566, sex uncertain, Anheung, 36°40.740'N, 126°9.121'E, intertidal, muddy sand beach, 1 m depth, April 2014, coll. Man-Ki Jeong; MABIK NA00155567, sex uncertain, Gwangyang, 34°55.940'N, 127°36.252'E, intertidal, tidal mud-flat, 1 m depth, November 2017, coll. Man-Ki Jeong.

MABIKNA00155568, sex uncertain, Seochun, 36°0.95'N, 126°39.79'E, intertidal, tidal mud-flat, 1 m depth, May 2015, coll. Man-Ki Jeong. Additional seven specimens from type locality on SEM stub.

Abdominal hooks with three rows of teeth; two teeth in basal row, three in second row, and four in superior row. Genital pores present in intersegmental furrows between chaetigers 7–8, 8–9, 9–10, and 10–11. Posteriorly extended and rounded thin parapodial lobes present on posterior abdominal segments.

Holotype entire, about 28 mm long, 0.5 mm wide for 115 chaetigers. Paratypes range from 36–51 mm in length, 0.6 mm width for 89–95 chaetigers. Body thread-like, rounded dorsally, flattened ventrally, widest in anterior thoracic chaetigers, and tapering from abdomen to pygidium. Color whitish yellow in alcohol.

Prostomium conical, with slender and relatively long palpode; nuchal organs not seen, eyespots usually not observed in preserved specimen (Fig. 4A), sub-epidermal eyespots observed in few preserved specimens from Anheung of Korea (Fig. 4B). Everted proboscis with numerous small papillae (Fig. 4A, B). Peristomium uniannulated and slightly longer than chaetiger 1 (Fig. 4A, B).

Thorax with 11 chaetigers (Fig. 4A, B). Thoracic segments biannulated, with shallow intra- and intersegmental grooves (Fig. 2A, B). Anterior five thoracic segments slightly expanded (Fig. 4A). First chaetiger biramous, with three or four bi-limbated capillaries; chaetigers 2–5 with five to eight capillaries per fascicle in both noto- and neuropodia; chaetigers 6–11 with six to 10 long-shafted hooded hooks per fascicle (Fig. 4A, B, F); thoracic hooks with indistinct node on shaft and at least eight small teeth in three or four rows above the main fang (Fig. 4F).

Notopodia located in dorso-laterally, dorsally located in last few thoracic segments; neuropodia located in lateral positions (Fig. 4A, B). Lateral organs present between noto- and neuropodia of all thoracic chaetigers, nearer to notopodia in chaetigers 5–11 (Fig. 4A). Genital pores present in intersegmental furrows of between chaetigers 7–8, 8–9, 9–10, and 10–11 (Fig. 4A).

Transition between thorax and abdomen distinguished by changes in shape of chaetae and segment (Fig. 4A); anterior abdominal segments multi-annulated, gradually longer posteriorly, with short-shafted hooded hooks placed posteriorly in segment; posterior thoracic chaetigers bi- or tri-anullated, with long-shafted hooded hooks in central part of segment; last thoracic chaetiger smaller than first abdominal chaetiger (Fig. 4A).

Abdominal parapodial lobes located in posterior end of each segment, well separated from each other, and gradually developed posteriorly (Fig. 4C, D). Abdominal notopodia separated, middorsal on anterior few segments, becoming dorsolateral in following abdominal region, with 5 or 6 short-shafted hooded hooks per fascicle, having posteriorly extended and rounded thin lobes from chaetiger 70–80 to end of body; expanded notopodial lobes overlap dorso-anterior part of further segment (Figs 4C, D, 5F). Abdominal neuropodia well separated, with 10–12 short-shafted hooded hooks per fascicle, having slightly protruded lobes in posterior abdomen; neuropodial lobes less developed than notopodial lobes (Figs 4C, D, 5F).

Hooded hooks with main fang extending slightly beyond hoods. Abdominal hooks with distinct node on shaft and three rows of small teeth above main fang; two teeth in basal row, three in second row, and four in superior row (Figs 4E, G, 5E). Pygidium with digitate anal cirrus (Fig. 4D).

Figure 4. 

Heteromastus koreanus sp. nov. A anterior end, lateral view (holotype, NA00155565) B same, dorsal view C posterior abdominal segments, left lateral view (holotype, NA00155565) D posterior end, left lateral view (holotype, NA00155565) E abdominal short-shafted hook, frontal view F thoracic long-shafted hook, lateral view G abdominal short-shafted hook, lateral view. Abbreviations: ac, anal cirrus; cc, capillary chaetae; Ch, chaetiger; gp, genital pore; hh, hooded hooks; lo, lateral organ; mf, main fang; neu, neuropod; no, notopod; per, peristomium; pro, prostomium; prob, proboscis; pyg, pygidium.

Prostomium, peristomium and thoracic chaetigers 1–5 not stained (Fig. 6C). Thoracic chaetigers 6–11 stained green (Fig. 6C). Abdominal region without distinct staining pattern; first two or three abdominal segments stained light green but rapidly fades; anal segment stained blue in well-developed specimens.

The new species is named for its wide distribution in coastal waters of Korea.

Intertidal areas (0–1 m) near Korea (Fig. 1).

Heteromastus koreanus was mainly sampled from Gwangyang in April of 2014 (35 ind./m²) and November of 2017 (470 ind./m²). Most well-developed individuals (having over 110 segments) were obtained from Muan and Gwangyang in November and coelomic eggs were 54–71 μm in diameter. Surface sediment of the collecting station was mainly composed of fine sand and silt. Unidentified cirratullid and nereidid polychaetes co-occurred in Gwangyang, Korea. The salinity range among sampling locations was about 15–33. Gwangyang is the only estuarine habitat. Other locations are situated in marine mud flats.

Heteromastus koreanus closely resembles former records of H. filiformis reported by Hutchings and Rainer (1982) and Choi and Yoon (2016) in the chaetal arrangement, the presence of posteriorly extended notopodial lobes in posterior abdomen, and the absence of the spine-like uncini and the distinct branchial structure (i.e. filamentous or digitiform) in posterior abdomen (Warren 1994; Blake 2000; Table 2). However, they differ in the dentition of abdominal short-shafted hooks (2/3/4 in H. koreanus vs 3–4/4–5/4–6 in H. filiformis sensu Hutchings & Rainer, 1982 vs three or four teeth in three rows in H. filiformis sensu Choi & Yoon, 2016), and the species-specific MGSP (Table 2). Additionally, H. filiformis occurs in the marine intertidal areas of Atlantic, Mediterranean, and America (Blake 2000) whereas H. koreanus of present study is collected mainly from the estuarine environment (salinity of 15–23) of Korea (Table 2). Heteromastus koreanus is also similar to H. tohbaiensis in the chaetal arrangement and presence of eyespots. However, they clearly differ in absence of distinct node on shaft of thoracic hooks and presence of expanded abdominal parapodial lobes in H. koreanus (Yabe 1998).

To verify the genetic divergence between examined specimens, partial sequences of mitochondrial (mtCOI) and nuclear (histone H3) genes were used. Intraspecific differences for mtCOI (MK032276–MK032284) and histone H3 (MK032285–MK032293) genes of each Korean species were very low (0–0.4%, Table 3). Based on mtCOI gene comparison, mean interspecific differences among these three new Korean species of the present study were distinct (16.0–18.9%, Table 3). All examined Korean Heteromastus species were well distinguished genetically from H. filiformis of China (13.3–19.6%, HZPLY183-12) and America (19.7–22.0%, MH235890). Based on histone H3 gene comparison, mean interspecific differences among the Korean Heteromastus species were 2.8–5.4% (Table 3). The known genetic difference for the mtCOI gene among capitellid species is 12.3–23.7% (Jeong et al. 2017b). In contrast, the published histone H3 gene difference between cryptic polychaetes is 2–9% (Glasby et al. 2013). Thus, genetic differences of these examined Heteromastus species (COI: 13.3–22.0%, H3: 2.8–5.4%) are significant at species level. Among all sequences of unidentified Heteromastus in Genbank database, sequences regarding two specimens from southern Japan (COI: LC208123–LC208124, H3: LC208100–LC208101) were genetically very close to H. koreanus of present study (COI gene difference: 2.1–3.3%, H3 gene difference: 0.9–1.3%). Among the described Heteromastus species from Japan, H. tohbaiensis resembles H. koreanus in the chaetal arrangement and presence of prostomial eyespots. However, they clearly differ in presence of distinct node on shaft of thoracic hooded hooks and absence of expanded abdominal parapodial lobes in H. tohbaiensis (Yabe 1998). Moreover, these two unidentified sequences (LC208123–LC208124) were originally reported from tidal mud flat and estuary near southern Japan, respectively (Tomioka et al. 2018). This distribution pattern is similar with those of H. koreanus (i.e. wide salinity range of 15–33) rather than H. tohbaiensis, which have been reported from lacustrine habitat of northern Japan. Despite the lack of morphological information regarding these Japanese specimens, the high similarity in genetic feature and inhabiting environment confirms the additional occurrence of H. koreanus in southern Japan.

Figure 5. 

Heteromastus namhaensis sp. nov. A abdominal hooded hook in lateral view B posterior end in dorsal view (holotype, NA00155558). Heteromastus gusipoensis sp. nov. C abdominal hooded hook in frontal view D posterior end in dorsal view (holotype, NA00155561). Heteromastus koreanus sp. nov. E abdominal hooded hook in frontal view F posterior end in dorsal view (holotype, NA00155565). Abbreviations: ac, anal cirrus; mf, main fang; neu, neuropod; no, notopod; pyg, pygidium.

Figure 6. 

Methylene green staining patterns of Korean three new species A anterior end of H. namhaensis sp. nov., lateral view (paratype, NA00155560) B anterior end of H. gusipoensis sp. nov., lateral view (using additional specimens from type locality) C anterior end of H. koreanus sp. nov., lateral view (NA00065689).