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Three new species of Heteromastus (Annelida, Capitellidae) from Korean waters, with genetic evidence based on two gene markers
expand article infoMan-Ki Jeong, Ho Young Soh, Hae-Lip Suh§
‡ Chonnam National University, Yeosu, South Korea
§ Chonnam National University, Gwangju , South Korea
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Abstract

Three undescribed species of Heteromastus Eisig, 1887 were collected from intertidal to sublittoral habitats in western and southern waters of Korea. Heteromastus namhaensis sp. nov. is distinguishable from other congeners by the presence of hemispheric notopodial lobes in the posterior abdomen. Heteromastus gusipoensis sp. nov. closely resembles H. tohbaiensis Yabe & Mawatari, 1998 in the absence of posteriorly extended abdominal notopodial lobes, but differs in the absence of eyespots on the prostomium and distinct node on the shaft of thoracic hooks in H. gusipoensis. Heteromastus koreanus sp. nov. is similar to H. filiformis sensu Hutchings & Rainer, 1982 in the shape of abdominal notopodia, but clearly differs in dentition of the abdominal hooks and methylene green staining pattern (MGSP). DNA sequences (mtCOI and histone H3) of these new Korean species were compared with all sequences of Heteromastus species available in the public database. Molecular results showed distinct genetic differences among these three new Korean species at species level. Comparison of mtCOI gene revealed significant genetic difference between H. filiformis and these Korean species. A comprehensive comparison between three Heteromastus species of present study and their closely related congeners is conducted based on morphological and genetic results.

Keywords

Genetic comparison, histone H3, morphology, mtCOI, new species

Introduction

The genus Heteromastus Eisig, 1887, which belongs to the family Capitellidae Grube, 1862, is commonly found from intertidal areas to shallow subtidal depths in a variety of sediment types, including fine and silty sand and mud (Blake 2000; Dean 2001). Feeding activity of Heteromastus plays an important role in the supply of overlying oxygenated water into anoxic muds below the redox potential discontinuity (Cadée 1979). Heteromastus is known as a biological indicator and opportunistic species in marine hypoxia condition (Cadée 1979). The genus Heteromastus was first designated by Eisig (1887) based on the description of H. filiformis Claparède, 1864 (as Capitella filiformis) from southern France. According to his diagnosis, Heteromastus is distinguished from other genera in the family by having 11 thoracic chaetigers, of which the first five only have capillaries. Green (2002) improved this generic definition by including the differences in the thoracic (long-shafted) and abdominal (short-shafted) hooks. However, the lack of good generic characteristics has led to taxonomic confusion in this genus (Blake 2000; Green 2002). For instance, although Heteromastus currently contains seven valid species (Read and Fauchald 2018), the chaetal arrangement of H. giganteus Zachs, 1933 does not match to the original generic definition (Zachs 1933). Among the recognized generic characteristics, the number of thoracic segments can be miscounted due to ambiguous boundaries among peristomium, thorax, and abdomen (Blake 2000). In addition, the thoracic chaetal arrangement varies depending on the degree of development (Fredette 1982).

Heteromastus filiformis (Claparède, 1864), the generic type species, is well known as a cosmopolitan species found in various types of the habitats and has been referred to in many ecological studies (Hutchings and Rainer 1982). Species-specific characters of this representative species have been controversial due to incomplete original description and the absence of the original type specimens from southern France, although Hutchings and Rainer (1982) have later designated the neotype from Egypt (Green 2002). In addition, the dental structure of abdominal hooks and the shape of posterior parapodial lobes of H. filiformis have been described differently in published records including the neotype (Blake 2000; Green 2002). In Korean waters, Choi and Yoon (2016) have reported that H. filiformis was the only species belonging to genus Heteromastus occurring in this region based on morphological features. They have suggested that Korean specimens have some minor differences with former records of H. filiformis in the morphology of abdominal hooks and methylene green staining pattern, although these characters have been used for identification of recorded species in family Capitellidae (Blake 2000; Green 2002; Jeong et al. 2017b). Recently, a combination of morphological and molecular analysis has been conducted to distinguish very close polychaete species and geographical populations (e.g. Glasby et al. 2013; Jeong et al. 2017b, 2018). The aim of the present study is to verify the taxonomic status of undescribed Heteromastus species inhabiting Korean waters based on morphological and molecular analysis using two different partial genes (mtCOI and histone H3) in comparison with their closest species in the genus.

Materials and methods

Morphological analysis

Samples were collected from eight stations of Korean sublittoral areas using a 0.05 m2 Van Veen grab (Fig. 1). Sediment samples were elutriated over a 0.5 mm sieve in a 30 L seawater container and organisms were transferred to a 1 L collecting jar containing 7% MgCl2 solution for anesthesia. Relaxed samples were fixed in a buffered solution of 10% formalin within one hour and then finally preserved in 95% ethanol. In the laboratory, Heteromastus specimens were sorted under a Zoom Stereomicroscope (SMZ745T, Nikon). Line drawings were performed using a differential interference contrast microscope (Eclipse Ci-L, Nikon) and a digital pen display (Cintiq 22HD, Wacom). Methyl green staining patterns (MGSP) and scanning electron microscopy (SEM) analyses were performed as delineated by Jeong et al. (2017b). The examined type materials were deposited in the collection of Marine Biodiversity Institute of Korea (MABIK) in Seocheon, Korea (Table 1).

Figure 1. 

Map of study area with main collecting locations indicated. Abbreviations (district names): AH, Anheung; CS, Cheongsando; GY, Gwangyang; JJ, Jejudo; MA, Muan; SC, Seochun; YG, Yeonggwang; YS, Yeosu.

A list of sampling localities, species name, sample type, voucher number, Genbank accession number, and references. AC: Accession number, BOLD: Barcode of life data system (http://www.boldsystems.org).

Species name Location Latitude / Longitude (DDM) Type Voucher number Accession number of Genbank References
Country District mtCOI Histone H3
H. namhaensis sp. nov. Korea Cheongsando 34°1.662'N, 127°4.272'E Holotype NA00155558 MK032276 MK032285 This study
Jejudo 33°16.699'N, 127°16.230’ E Paratype NA00155559 MK032277 MK032286
Yeosu 34°41.569'N, 127°51.848'E Paratype NA00155560 MK032278 MK032287
H. gusipoensis sp. nov. Yeonggwang 35°25.819'N, 126°25.482'E Holotype NA00155561
Paratype NA00155562 MK032279 MK032288
Paratype NA00155563 MK032280 MK032289
Non-type NA00155564 MK032281 MK032290
H. koreanus sp. nov. Muan 35°6.270'N, 126°20.093'E Holotype NA00155565
Anheung 36°40.740'N, 126°9.121'E Paratype NA00155566 MK032282 MK032291
Gwangyang 34°55.940'N, 127°36.252'E Paratype NA00155567 MK032283 MK032292
Seochun 36°0.95'N, 126°39.79'E Non-type NA00155568 MK032284 MK032293
H. filiformis China Bohai Sea 38°N, 120°E BIOUG03550-H04 HZPLY183-12 (AC of BOLD) BOLD (2019)
H. filiformis USA Maryland 38°52.428'N, 76°31.482'W USNM:IZ:1463490 MH235890 Unpublished

Molecular analysis

Genomic DNA was extracted from ethanol-preserved specimens. Specimens used for molecular analysis were partially dissected (ca 2 segments) in the middle part of the abdomen. To extract genomic DNA, 1.5 mL centrifuge tubes each containing 45 μL of 10% Chelex suspension (Bio-Rad Laboratories Inc.), 5 μL of Proteinase K (10 mg/ml, iNtRON Biotechnology, Inc.), and dissected tissues (ca 2 segments) were incubated at 56 ℃ for 3–12 hours. Extracted genomic DNA was used as a template to amplify the target region. Polymerase chain reaction (PCR) was performed on a MasterCycler PCR thermal cycler (Eppendorf Co.). The primer pair for mtCOI was LCO1490 and HCO2198 (Folmer et al. 1994). For histone H3, it was H3F and H3R (Colgan et al. 1998). PCR mixtures contained 17 μL of deionized water, 1 μL of each primer (10 μM), 1 μL of DNA template and PCR premix (20 μL, BiONEER Co.). The temperature profile was as follows: 94 °C/180 s–(94 °C/30 s–46 °C/30 s–72 °C/60 s) * 40 cycles–72 °C/480 s for mtCOI and 94 °C/180 s–(94 °C/45 s–50 °C/60 s–72 °C/60 s) * 35 cycles–72 °C/420 s for histone H3. Purification and sequencing of obtained PCR products were performed at Macrogen Inc. facilities (Seoul, Korea). Forward and reverse sequences were edited using Chromas software version 2.3 (Technelysium Pty Ltd). Partial sequences of the mtCOI and histone H3 genes were aligned with the available sequences obtained from GenBank (http://www.ncbi.nlm.nih.gov/Genbank) and BOLDSYSTEMS (http://www.boldsystems.org/) using the Molecular Evolutionary Genetics Analysis (MEGA) software version 7.0 (Kumar et al. 2016). Table 1 summarizes information for all sequences used in the analyses. These aligned sequences were used as data sets to generate genetic distance using Kimura’s two-parameter (K2P) model (Kimura 1980). Based on K2P distances, intraspecific genetic differences within the Korean specimens and the interspecific genetic differences among the closest taxa were calculated.

Results

Systematics

Family Capitellidae Grube, 1862

Heteromastus Eisig, 1887

Type species

Heteromastus filiformis (Claparède, 1864).

Type locality

Port-Vendres, France.

Generic diagnosis

(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.

Heteromastus namhaensis sp. nov.

Figures 2A–G, 5A, B, 6A

Material examined

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.

Diagnosis

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.

Description

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.

Methyl green staining pattern

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.

Etymology

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

Distribution

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

Ecology

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.

Remarks

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.

Morphological comparison between Heteromastus species of this study and their closely related species. A: absent; P: present; Ch: chaetiger.

Species Eyespots Dental structure of abdominal hooks Notopodial lobes in posterior abdomen Methyl green staining pattern Habitat (locality)
H. namhaensis sp. nov. A 4 rows (3/3/3/4–6) Hemispheric notopodial lobes dorso-posteriorly extended Ch 3–11 blue, abdomen not stained Subtidal, 36 m, sandy mud with shell fragments (Korea)
H. gusipoensis sp. nov. A 4 rows (3/3/4/2) Not extended Ch 3–10 with blue speckles, median part of each segment stained densely Intertidal, 0–1 m, sandy mud (Korea)
H. koreanus sp. nov. P 3 rows (2/3/4) Rounded notopodial lobes posteriorly extended Ch 6–11 green, Ch 11 dark, abdomen not stained Intertidal, estuarine, 0–1 m, sandy mud (Korea)
H. filiformis sensu Hutchings & Rainer, 1982 A 3 rows (3–4/4–5/4–6) Broadly-based and rounded notopodial lobes posteriorly extended Unknown Intertidal (Mediterranean)
H. filiformis sensu Choi & Yoon, 2016 P 3–4 teeth in 3 rows Rounded notopodial lobes posteriorly extended Ch 1 & Ch 3–11 Intertidal (Korea)
H. tohbaiensis Yabe & Mawatari, 1998 P Variable (>11) Not extended Unknown Lake, low salinity, fine mud (Japan)

Heteromastus gusipoensis sp. nov.

Figures 3A–G, 5C, D, 6B

Material examined

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.

Additional material examined

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.

Diagnosis

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.

Description

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.

Methyl green staining pattern

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.

Etymology

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

Distribution

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

Ecology

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.

Remarks

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.

Heteromastus koreanus sp. nov.

Figures 4A–G, 5E, F, 6C

Material examined

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.

Additional material examined

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.

Diagnosis

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.

Description

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.

Methyl green staining pattern

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.

Etymology

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

Distribution

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

Ecology

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.

Remarks

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).

Molecular comparisons

To verify the genetic divergence between examined specimens, partial sequences of mitochondrial (mtCOI) and nuclear (histone H3) genes were used. Intraspecific differences for mtCOI (MK032276MK032284) and histone H3 (MK032285MK032293) 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: LC208123LC208124, H3: LC208100LC208101) 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 (LC208123LC208124) 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).

Mean genetic distances between examined Heteromastus species based on K2P distance. Bold numbers represent the mean intraspecific genetic distance of each species.

mtCOI 1 2 3 4 5
1. H. namhaensis sp. nov.(Korea) 0.003
2. H. gusipoensis sp. nov. (Korea) 0.184 0.001
3. H. koreanus sp. nov. (Korea) 0.189 0.160 0.004
4. H. filiformis (China) 0.133 0.196 0.182
5. H. filiformis (USA) 0.218 0.220 0.197 0.194
histone H3 1 2 3
1. H. namhaensis sp. nov. (Korea) 0.002
2. H. gusipoensis sp. nov. (Korea) 0.054 0.000
3. H. koreanus sp. nov. (Korea) 0.048 0.028 0.000

Key to species of Heteromastus

1 Thorax with 11 chaetigers; first chaetiger biramous; capillary chaetae only present on chaetigers 1–6 H. giganteus Zach, 1933
Thorax with 11 chaetigers; first chaetiger biramous; capillary chaetae only present on chaetigers 1–5 2
2 Thoracic hooded hooks with distinct node on shaft H. tohbaienesis Yabe & Mawatari, 1998
Thoracic hooded hooks without distinct node on shaft 3
3 Abdominal hooks with node located posterior to middle of shaft H. similis Southern, 1921
Abdominal hooks with node located anterior to middle of shaft 4
4 Posterior abdominal segment with conspicuously projecting uncinial spines H. caudatus (Hartman, 1976)
Posterior abdominal segment without conspicuously projecting uncinial spines 5
5 Posterior abdomen with multiple filamentous branchiae H. filobranchus Berkeley & Berkeley, 1932
Posterior abdomen without multiple filamentous branchiae 6
6 Posterior abdomen with hemispheric and dorsally protruded notopodial lobes H. namhaensis sp. nov.
Posterior abdomen with thin notopodial lobes 7
7 Notopodial lobes on posterior abdomen not extended over following segment H. gusipoensis sp. nov.
Notopodial lobes on posterior abdomen overlap dorso-anterior part of following segment 8
8 Abdominal hooded hooks with at least 9 teeth above main fang; 2 distinct teeth in basal row H. koreanus sp. nov.
Abdominal hooded hooks with at least 11–15 teeth above main fang; 3 or 4 distinct teeth in basal row H. filiformis sensu Hutchings & Rainer, 1982
9 Hooded hooks with 7–8 teeth above main fang; 3 or 4 distinct teeth in basal row H. hutchingsae Green, 2002

Acknowledgements

We thank the anonymous reviewer and the editor who made constructive and invaluable suggestions and comments. This research was a part of the project titled “Research center for fishery resource management based on the information and communication technology” (2019), funded by the Ministry of Oceans and Fisheries, Korea.

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