Heteromastus koreanus, Jeong, Man-Ki, Soh, Ho Young & Suh, Hae-Lip, 2019

Jeong, Man-Ki, Soh, Ho Young & Suh, Hae-Lip, 2019, Three new species of Heteromastus (Annelida, Capitellidae) from Korean waters, with genetic evidence based on two gene markers, ZooKeys 869, pp. 1-18 : 1

publication ID	https://dx.doi.org/10.3897/zookeys.869.34380
publication LSID	lsid:zoobank.org:pub:50D49A54-A386-4738-AE1F-393B77EC652C
persistent identifier	https://treatment.plazi.org/id/C70CE167-A93A-45B1-AD5F-45DD159511C7
taxon LSID	lsid:zoobank.org:act:C70CE167-A93A-45B1-AD5F-45DD159511C7
treatment provided by	ZooKeys by Pensoft
scientific name	Heteromastus koreanus
status	sp. nov.

Treatment

Heteromastus koreanus sp. nov. Figures 4 A–G View Figure 4 , 5E, F View Figure 5 , 6C View Figure 6

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 View Figure 4 ), sub-epidermal eyespots observed in few preserved specimens from Anheung of Korea ( Fig. 4B View Figure 4 ). Everted proboscis with numerous small papillae ( Fig. 4A, B View Figure 4 ). Peristomium uniannulated and slightly longer than chaetiger 1 ( Fig. 4A, B View Figure 4 ).

Thorax with 11 chaetigers ( Fig. 4A, B View Figure 4 ). Thoracic segments biannulated, with shallow intra- and intersegmental grooves ( Fig. 2A, B View Figure 2 ). Anterior five thoracic segments slightly expanded ( Fig. 4A View Figure 4 ). 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 View Figure 4 ); thoracic hooks with indistinct node on shaft and at least eight small teeth in three or four rows above the main fang ( Fig. 4F View Figure 4 ).

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

Transition between thorax and abdomen distinguished by changes in shape of chaetae and segment ( Fig. 4A View Figure 4 ); 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 View Figure 4 ).

Abdominal parapodial lobes located in posterior end of each segment, well separated from each other, and gradually developed posteriorly ( Fig. 4C, D View Figure 4 ). 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 View Figure 4 , 5F View Figure 5 ). 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 View Figure 4 , 5F View Figure 5 ).

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 View Figure 4 , 5E View Figure 5 ). Pygidium with digitate anal cirrus ( Fig. 4D View Figure 4 ).

Methyl green staining pattern.

Prostomium, peristomium and thoracic chaetigers 1-5 not stained ( Fig. 6C View Figure 6 ). Thoracic chaetigers 6-11 stained green ( Fig. 6C View Figure 6 ). 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 View Figure 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 (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.