Notomastus koreanus, Jeong, Man-Ki, Soh, Ho Young, Wi, Jin Hee & Suh, Hae-Lip, 2018

Jeong, Man-Ki, Soh, Ho Young, Wi, Jin Hee & Suh, Hae-Lip, 2018, A new Notomastus (Annelida, Capitellidae) species from Korean waters, with genetic comparison based on three gene markers, ZooKeys 754, pp. 141-155 : 144-148

Notomastus koreanus sp. n. Figs 2 A–D, 3 A–G

Materials examined.

Holotype: MABIKNA00066337, sex uncertain, Busan, 35°6.33'N, 129°3.31'E (DDM), subtidal, sandy mud bottom, 16 m depth, October 2011, collected by Byoung-Mi Choi. Paratypes: MABIKNA00146048, MABIKNA00146049, sex uncertain, Yeosu, 34°39.03'N, 127°40.86'E, subtidal, sandy mud bottom, 20 m depth, October 2017, collected by Man-Ki Jeong; MABIKNA00066329, sex uncertain, Busan, 35°5.83'N, 129°2.42'E subtidal, sandy mud bottom, 15 m depth, October 2011, collected by Byoung-Mi Choi; MABIKNA00066396, sex uncertain, Pohang, 36°3.09'N, 129°23.55'E, subtidal, sandy mud bottom, 12 m depth, January 2012, collected by Byoung-Mi Choi; MABIKNA00066311, sex uncertain, Geoje, 34°54.17'N, 128°36.98'E, subtidal, sandy mud bottom, 10 m depth, January 2012, collected by Byoung-Mi Choi.

Additional materials examined.

MABIKNA00115263, sex uncertain, Busan, 35°4.7'N, 128°55.4'E, subtidal, sandy mud bottom, 14 m depth, January 2012, collected by Byoung-Mi Choi; MABIKNA00066302, sex uncertain, Hwaseong, 37°8.95'N, 126°35.39'E, subtidal, sandy mud bottom, 20 m depth, September 2011, collected by Byoung-Mi Choi; MABIKNA00066303, MABIKNA00115303, sex uncertain, Seosan, 37°2.03'N, 126°23.94'E subtidal, sandy mud bottom, 15 m depth, September 2011, collected by Byoung-Mi Choi; MABIKNA00066385, sex uncertain, Pohang, 36°1.31'N, 129°25.16'E subtidal, sandy mud bottom, 12 m depth, November 2010, collected by Byoung-Mi Choi; MABIKNA00115314, sex uncertain, Wando, 34°22.12'N, 127°0.79'E, subtidal, sandy mud bottom, 10 m depth, September 2011, collected by Byoung-Mi Choi. Additional 3 specimens from type locality on SEM stub.

Diagnosis.

Thorax with achaetigerous peristomium and 11 chaetigers. Anterior 5 thoracic segments tessellated. First chaetiger without neuropodia. Chaetigers 1-11 with capillary chaetae only. Abdominal chaetigers with hooded hooks only. Lateral organs not protruded above surface, narrow and oval shape, present along body. Genital pores present in intersegmental furrows between chaetigers 7-8, 8-9, 9-10, and 10-11. Parapo dial lobes in anterior to moderate abdominal region not protruded. Posteriorly extended parapodial lobes present on posterior abdominal segments. Pygidium without anal cirri.

Description.

Holotype entire, about 80 mm long, 1.2 mm wide for 280 chaetigers. Paratype material ranges from 31-87 mm in length, 0.7-1.3 mm width with 30-270 chaetigers. Body elongate, rounded dorsally, flattened ventrally, widest in anterior thoracic chaetigers, with ventral white line in abdominal region. Color in alcohol whitish yellow.

Prostomium conical, with short and rounded palpode; nuchal organs not seen, eyespots absent (Figs 2A, 3A, D). Proboscis everted, with numerous hemispherical papillae (Figs 2A, 3D). Peristomium achaetous, weakly biannulated, slightly longer than first chaetiger (Figs 2A, 3D).

Thorax with 12 segments including achaetous peristomium and 11 chaetigers (Figs 2 A–B, 3B). Thoracic segments biannulated with intra- and inter-segmental furrows (Figs 2 A–B, 3A). Anterior thoracic segments tessellated; peristomium and chaetigers 1-2 tessellated, chaetigers 3-4 slightly tessellated; remaining segments smooth (Figs 2 A–B, 3D). First chaetiger with only notopodia having 12 capillaries per fascicle; remaining thoracic chaetigers with 40-60 bilimbate capillaries per fascicle in both parapodia (Figs 2 A–B, 3 D–E). Thoracic parapodia reduced, located in intra-segmental furrows (Figs 2 A–B, 3D); notopodia dorso-laterally on first chaetiger and middorsally on following chaetigers (Fig. 2B); neuropodia ventrolaterally on whole chaetigers. (Figs 2A, 3 A–B). Lateral organs not protruded above surface, narrow and oval shape, present along body, situated in furrow between notopodia and neuropodia, less distinct in posterior abdominal region (Figs 2 A–B, 3 A–D); position of lateral organs slightly nearer to neuropodium in chaetigers 1-3, nearer to notopodium in following chaetigers (Figs 2A, 3A, D). Genital pores present in intersegmental furrows of between chaetigers 7-8, 8-9, 9-10, and 10-11 (Figs 2A, 3 A–B).

Transition between thorax and abdomen distinguished by changes in shape of chaeta and segment (Figs 2 A–B, 3 A–B); last thoracic chaetiger bi-annulated, with capillaries only, slightly thinner than first abdominal chaetiger; anterior abdominal segments multi-annulated, with better developed neuropodial lobes than thoracic ones, having hooded hooks only (Figs 2 A–B, 3B). Parapodia in anterior to mid abdominal region not protruded, well separated (Figs 2 A–B, 3 A–B). Notopodial lobes not protruded in anterior abdomen, middorsal on anterior few segments, becoming dorsolateral in following abdominal region, with 6-15 hooded hooks only per fascicle, having posteriorly extended and semicircular lamella from chaetiger 160 to end of body (Figs 2 A–C, 3 A–C). Neuropodial lobes having 15-30 hooded hooks per fascicle, well separated and weakly protruded in anterior abdomen, more protruded and almost fused ventrally in posterior abdomen, partially fused to notopodial lobes in posterior end (Figs 2A, C, 3 A–C); dorsal tips of neuropodial lobes do not protruded above surface, extended below lateral organs in anterior to mid abdominal region (Figs 2A, C, 3B).

Hooded hooks with main fang extending slightly beyond hoods; hood slightly flared. Main fang of hooded hooks with 3 rows of small teeth; 5 in basal row, 6-8 in second row, and at least 6 in superior row (Fig. 3 F–G).

Digitiform branchiae not observed in abdomen; each notopodial lobe with posteriorly extended semicircular lamella in posterior abdomen (Figs 2C, 3C). Pygidium simple, without anal cirri (Fig. 2D).

Methyl green staining pattern.

Anterior thoracic segments (peristomium and chaetigers 1-6) not stained. Posterior thoracic segments (chaetigers 7-10 or 11) stained (Fig. 3A); chaetiger 10 and dorsum of chaetiger 7 more deeply stained with blue (Fig. 3A). Anterior few abdominal chaetigers temporary stained with green; fading within 10 minutes (Fig. 3A). Ventral side of abdominal segments having pair of longitudinal green bands. Individual-specific variations observed; sometimes chaetigers 5-6 and chaetiger 11 weakly stained with blue, posterior edge of each abdominal segment stained with blue in large specimens (Fig. 3C).

Etymology.

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

Distribution.

The subtidal areas (10-20 m) near Korea (Fig. 1). The subtidal habitat (ca. 20 m) of Bohai Sea, China (see details in Discussion).

Ecology.

Notomastus koreanus sp. n. was sampled from soft sediments throughout the year. Most well-developed individuals (having over 250 segments) were obtained between October and January. The sediment of the collecting stations was mainly composed of sandy mud with shell fragments. Leiochrides yokjidoensis Jeong, Wi & Suh, 2017 and an undescribed Heteromastus Eisig, 1887 species co-occurred in southern stations of this study.

Remarks.

Notomastus koreanus sp. n. is distinguished from other species of the genus by the morphological combination of absence of distinct eyes and first neuropodia, last thoracic chaetigers with only capillary chaetae, presence of genital pores between chaetigers 7-11, non-protruded lateral organs and neuropodial lobes in anterior abdomen, and posteriorly extended parapodial lobes in posterior abdomen. The new Korean Notomastus species closely resembles N. torquatus Hutchings & Rainer, 1979 in the chaetal arrangement, the absence of developed neuropodial lobes in anterior abdomen, and the presence of posteriorly extended parapodial lobes in the posterior abdomen (Table 2). However, they differ in the presence of eyes on posterior prostomium (eyespots vs. absence) and the location of genital pores (between chaetigers 3 or 5-10 vs. 7-11, Table 2). Additionally, N. torquatus is regarded as an endemic species of Australia and has a much wider thorax (4 mm vs. 1.3 mm) than comparable specimens of N. koreanus sp. n., which have 280 segments when fully developed ( Doyle 1991, Hutchings and Rainer 1979). Notomastus hemipodus Hartman, 1945 and N. tenuis Moore, 1909 are also similar to N. koreanus sp. n. in the chaetal arrangement and the absence of protruded neuropodial lobes in anterior abdomen, but clearly differ in the details of the eyes, the genital/lateral organs, and the MGSP (Table 2). Moreover, they have the unique features of the indistinct palpode and the bilobed notopodial lobes, respectively.

Genetic comparison with the published sequences of Notomastus species.

To confirm the genetic distances among the new species and its closely related species, we used the partial sequences of mitochondrial (mtCOI and 16S rRNA) and nuclear (histone H3) genes. In all genetic comparisons, the intraspecific differences among the Korean specimens were negligible (0-0.1%, Table 3). The mean interspecific differences for mitochondrial COI (50.9%) and 16S rRNA (43.2%) genes were much higher than the mean interspecific difference for the nuclear histone H3 gene (7.6%). In the mtCOI gene comparison, the mean genetic difference between N. koreanus sp. n. and N. profondus (Eisig, 1887) of Portugal (KR916899) was substantial (51.2%, Table 3). In the interspecific comparison for the 16S rRNA gene, N. koreanus sp. n. was well distinguished from N. hemipodus (38.1%, HM746714) of Canada and N. latericeus (47.3%, AY340469) of Sweden (Table 3). In the histone H3 gene comparison, N. koreanus sp. n. genetically differed from N. torquatus (3.7%, AF185258) of Australia, N. latericeus (7.0%, DQ779747) of Sweden, and N. hemipodus (9.3%, HM746759) of Canada (Table 3). Previously known genetic difference of the mtCOI and the 16S rRNA genes among the capitellid species is generally about 18-20% ( Jeong et al. 2017b, Silva et al. 2016). In contrast, the histone H3 gene difference between cryptic nereidid polychaetes is around 2-9% ( Glasby et al. 2013). Thus, the genetic differences between N. koreanus sp. n. and its closely related species (COI: 51.2%, 16S: 38.1-47.3%, H3: 3.7-9.3%) is significant at the species level revealing the speciation among them. On the other hand, the mtCOI gene sequence of the Chinese specimen (BIOUG03550-A09, Table 1) is genetically matched with N. koreanus sp. n. (0.007 in K2P distance, Table 3), although it has been reported as N. latericeus on BOLD (www.barcodinglife.org) database ( BOLD Systems 2017). Notomastus latericeus was originally described from Norwegian waters, and it is easily discriminated from our new species in terms of morphology (Table 2). The published histone H3 and 16S rRNA sequences of N. latericeus from Swedish waters are clearly distinguished from the sequences of N. koreanus sp. n. by the significant genetic difference (Table 3). Thus, the mtCOI sequence of the Chinese specimen on the BOLD database is regarded as a misidentification at the species level and confirms the additional occurrence of our new species in the Bohai Sea of northeastern China.