Siphonaria acmaeoides Pilsbry, 1894: Pilsbry 1894: 16; Pilsbry 1895: 6, pl. 6, figs. 19–22; Lee 1956: 79; Hirase 1941: 94, pl. 121, fig. 15; Kuroda and Habe 1952: 86 (cited from Jenkins and Köhler 2024); Azuma 1960: 62 (cited from Jenkins and Köhler (2024)); Baker 1964: 159 (cited from Jenkins and Köhler (2024)); Christiaens 1980b: 466; White and Dayrat 2012: 60 [checklist]; Jenkins and Köhler 2024: 114, 115, figs. 43A–D, M, N, 44A–C.

Siphonaria (Patellopsis) acmaeoides: Hubendick 1945: 70, fig. 19 (cited from Jenkins and Köhler (2024)); Hubendick 1946: 30, pl. 6, figs. 12–15; Habe and Kikuchi 1960: 64 (cited from Jenkins and Köhler (2024)); Kira 1962: 201, pl. 69, fig. 9a, b (misspelled as 'Patellops'; cited from Jenkins and Köhler (2024)).

Siphonaria zebra: Kuroda and Habe 1952: 86 (non Siphonaria zebra Reeve, 1856) (cited from Jenkins and Köhler (2024)).

Planesiphon acmaeoides: Kuroda et al. 1971: 484, pl. 64, fig. 8; Choe 1992: 749, pl. 126, fig. 224.

Siphonaria (Mouretus) acmaeoides: Christiaens 1980a: 79, 80.

Siphonaria (Planesiphon) acmaeoides: Inaba 1983: 149 (cited from Jenkins and Köhler (2024)); Je 1989: 29 [checklist]; Higo et al. 1999: 402, G4976 [checklist]; Okutani 2000: 815, pl. 405, fig. 7; Cheng et al. 2005: 8, fig. 1e–g; Noseworthy et al. 2007: 90 [checklist]; Okutani 2017: 1101, pl. 403, fig. 7.

Measurements: Shell length [SL] 11.32–17.58 mm, Shell width [SW] 9.42–14.87 mm, Shell height [SH] 2.63–6.73 mm.

Shell (Fig. 2a, b) solid, oval, small to medium in size (in examined specimens, SL 11.32–17.58 mm), medium-high in height (about 2/7 on its length). Exterior colour generally greyish-brown or yellowish-brown with dark brown irregular maculations. Shell surface with 14–17 wide, light-cream or white-coloured primary ribs, unevenly spaced, sometimes discontinuous from apex to outer shell margin in juvenile. Interspaces between primary ribs filled with 1–7 thin secondary ribs. Apex white, glossy, spiral in counterclockwise direction (Fig. 2bC), often eroded due to shell growth, positioned in posterior one-third of shell, biased towards left. Shell margin weakly undulated. Anterior slope slightly convex, posterior slope short, nearly straight. Siphonal groove indistinct on outer shell surface. Interior colour dark brown, reddish-brown, with light cream bands near margin, reddish-brown or pale at centre.

Radula (Fig. 3a, b) dentition formulae 27:1:27 (in specimens measuring SL 16.23 mm, SW 11.88 mm, SH 4.80 mm). Each transverse row with narrow central rachidian tooth flanked by symmetrical half rows with lateral teeth, decreasing in size outwards. Rachidian tooth (Fig. 3a) short, approximately one-third length of lateral tooth, with sharply-pointed cusp. Innermost lateral teeth (first 7 lateral teeth), each tooth consisting of mesocone without ectocone; mesocone with bicuspid (Fig. 3a). Middle lateral teeth (following 5 lateral teeth), each tooth consisting of mesocone and ectocone; mesocone with bicuspid to blunt towards the outer margins; ectocone sharply pointed. Outermost lateral teeth (remaining 12 lateral teeth) consisting of endocone, ectocone and mesocone; mesocone subquadrate-shaped; endocone and ectocone short, sharply pointed (Fig. 3b).

Korea, Japan and Taiwan.

Type locality: Japan; Boshiu island (Boso Peninsula).

Habitat: On rocky substrate in high intertidal zones, typically in shallow pools (Fig. 2aA).

The Korean S. acmaeoides corresponds well with Pilsbry (1894)'s original description. The external shell morphology is characterised by wide, low primary ribs with fine secondary ribs in the interspaces, a glossy spiral apex coiling counterclockwise and a weakly undulated shell margin. Christiaens (1980a) described a new subspecies, S. acmaeoides paulae Christiaens, 1980, from Hong Kong, distinguishing it by its finer, thinner, more elliptical, lighter-coloured shell. This subspecies was also noted to lack a marked central area and exhibit a more bulging siphon compared to S. acmaeoides reported from Japan. However, Jenkins and Köhler (2024) later synonymised S. a. paulae with the S. acmaeoides, citing the morphological similarity of the shell. Based on our examination of the Korean specimens (Fig. 2b), we did not observe the light-coloured shell characteristics described in S. a. paulae by Christiaens (1980a). Further morphological and molecular analyses for S. a. paulae sampled from Hong Kong are necessary to confirm the taxonomic validity of this subspecies. In addition, S. acmaeoides has repeatedly been noted for its similarity in shell and radula morphology to S. zelandica Quoy and Gaimard, 1833 which is distributed in Australia (Hubendick 1946, Dayrat et al. 2014, Jenkins and Köhler 2024). Both species share the following morphological characteristics: a homostrophic apex, broad primary ribs with fine secondary ribs and an innermost lateral tooth in the radula with a mesocone that lacks ectocone and endocone (Quoy and Gaimard 1833, Pilsbry 1894, Jenkins 1983, Jenkins and Köhler 2024). Hubendick (1946) reported the radula formula of S. acmaeoides as 26:1:26, noting the absence of an ectocone on the lateral teeth. In this study, we observed a similar pattern of radula characters, with a radula formula of 27:1:27, also lacking an ectocone on the lateral teeth. This can be generally included within the documented range of intraspecific variation for the genus Siphonaria (e.g. in S. lessonii Blaninville, 1827, the radula formula varies from 13:1:13 to 76:1:76; Hubendick (1946), Güller et al. (2016)). In shell morphology, S. acmaeoides is distinguished by having its less prominent, almost flat radial ribs and a more indistinct siphonal groove, whereas S. zelandica is characterised by relatively finer and dual radial ribs within the siphonal groove. In our phylogenetic tree, the two species form a sister clade with 95% bootstrap support (Fig. 4). The uncorrected p-distances between S. acmaeoides and S. zelandica range from 5.71 to 6.51%, while S. sirius, the next closest related species shows a significantly higher genetic divergence (27.94%) (Table 2). Thus, a taxonomic re-assessment of the two species is necessary to confirm their taxonomic validity.

Patella japonica Donovan 1824: pl. 79; Kuroda et al. 1971: 483, pl. 64, fig. 7; White and Dayrat 2012: 64 [checklist].

? Siphonaria radiata: Adams and Reeve 1850: 69, pl. 13, fig. 2.

? Siphonria radians: Adams and Adams 1855: 271; Hubendick 1946: 43.

Siphonaria cochleariformis: Reeve 1856: pl. 6, fig. 28; Hubendick 1946: 43, pl. 2, figs. 33–35; Kuroda et al. 1971: 483, pl. 64, fig. 7.

Siphonaria japonica: Hanley 1858: 152 [checklist]; Pilsbry 1920: 141; Abe 1940: 59 (cited from Jenkins and Köhler (2024)); Hirase 1941: 94, pl. 121, fig. 12; Kuroda 1941: 137; Hubendick 1945: 27, fig. 34, 36, 39, 41 (cited from Jenkins and Köhler (2024)); Kuroda and Habe 1952: 86 (cited from Jenkins and Köhler (2024)); Lee 1956: 79; Kuroda 1960: 43 (cited from Jenkins and Köhler (2024)); Habe and Kikuchi 1960: 64 (cited from Jenkins and Köhler 2024); Shikama 1964: 6 (cited from Jenkins and Köhler (2024)); Berry 1977: 197, fig. 19 (cited from Jenkins and Köhler (2024)); Lee and Chao 2003: 35, pl. 6, fig. 173; Qi 2004: 198, pl. 108, fig. E; Dayrat et al. 2014: 266, fig. 3B; Jenkins and Köhler 2024: 31–34, figs. 13A–L, Q–S, 15B–E.

Siphonaria alterniplicata: Grabau and King 1928: 237, pl. 11, fig. 117; Hubendick 1946: 62; White and Dayrat 2012: 60 [checklist]; Coan et al. 2015: 221, fig. 38A, B.

Siphonaria (Sacculosiphonaria) japonica: Hubendick 1946: 42, pl. 2, figs. 29–32; Kira 1962: 201, pl. 69, fig. 8a, b (cited from Jenkins and Köhler (2024)); Habe 1971: 15, pl. 4, fig. 16 (cited from Jenkins and Köhler (2024)); Yoo 1976: 89, pl. 19, figs. 1–4; Christiaens 1980a: 79; Christiaens 1980b: 466, 467; Je 1989: 89 [checklist]; Fukuda et al. 1992: 76, pl. 23, fig. 360a, b (cited from Jenkins and Köhler (2024)); Kwon et al. 1993: 334, fig. 61-1; Okutani 2000: 815, pl. 405, fig. 6; Kwon 2001: 191, fig. 723; Hamamura 2004: 115; Min et al. 2004: 335, fig. 1056; Noseworthy et al. 2007: 90 [checklist]; Okutani 2017: 1101, pl. 403, fig. 6.

Sacculosiphonaria japonica: Kuroda et al. 1971: 483, pl. 64, fig. 7; Trew 1983: 9 (cited from Jenkins and Köhler (2024)); Choe 1992: 747, 748, pl. 125, fig. 222.

Siphonaria (Mastosiphon) sirius: Yoo 1976: 89, pl. 19, fig. 5 (non Siphonaria sirius Pilsbry 1894).

Siphonaria acmaeoides: Kwon et al. 1993: 335, fig. 61-3 (non-Siphonaria acmaeoides Pilsbry 1894).

Siphonaria (Planesiphon) acmaeoides: Kwon 2001: 191, fig. 724; Min et al. 2004: 337, fig. 1057 (non-Siphonaria acmaeoides in Pilsbry (1894)).

Siphonaria japonica tall form: Yokogawa et al. 2010: fig. 1A.

Measurements: SL 10.5–15.45 mm, SW 7.5–12.24 mm, SH 2.81–4.7 mm.

Shell (Fig. 2c) thin, oval, small size (in examined specimens, SL 10.5–15.45 mm), medium-high in height (2/7 of its length). Exterior colour greyish-brown. Shell surface with 17–23 thin, yellowish white-coloured primary radial ribs. Interspaces between radial ribs sometimes with 1–2 secondary ribs. Apex eroded, located centrally in posterior one-third of shell. Shell margin weakly undulated. Anterior slope slightly convex, posterior slope shorter, nearly straight. Siphonal groove weakly prominent with two radial ribs on outer shell surface. Interior colour reddish-brown.

Radula (Fig. 3c, d) dentition formulae 29:1:29 (in specimens measuring SL 10.54 mm, SW 7.47 mm, SH 2.81 mm). Each transverse row with narrow central rachidian tooth flanked by symmetrical half rows with lateral teeth, decreasing in size outwards. Rachidian tooth (Fig. 3c) short, -approximately one-third length of lateral tooth, with sharply pointed cusp. Innermost lateral teeth (first 17 lateral teeth), each tooth consisting of mesocone and ectocone; mesocone with bicuspid or unicuspid (Fig. 3c); ectocone shorter, pointed. Outermost lateral teeth (remaining 12 lateral teeth) consisting of endocone, ectocone and mesocone; mesocone paddle-shaped, not angled; endocone and ectocone short, sharply pointed (Fig. 3d).

Korea, China, Japan and Taiwan.

Type locality: Japan.

Habitat: On rocky substrate in low to high intertidal zones (Fig. 2cE).

Jenkins and Köhler (2024) designated a neotype for S. japonica due to the absence of the original type specimens and provided a detailed description of the shell morphology, reproductive system and morphological features of spermatophore. The shell morphology of the Korean S. japonica specimens match es well both by Donovan (1824)'s original description and the observations by Jenkins and Köhler (2024). Nevertheless, moderate variations in the number of ribs were observed in this study, with the number of primary ribs ranging from 17 to 23 and secondary ribs ranging from 1 to 2. These ranges differ from those reported by Jenkins and Köhler (2024), which included up to 20 primary ribs and 2 to 3 secondary ribs. In addition, Jenkins and Köhler (2024) considered the shell images of Figs. 1 and 4 of S. japonica described by Yoo (1976) to likely represent misidentification, without providing detailed information on their interpretation. Upon re-examination of the Figs. 1 and 4, we observed that the specimens show characteristics consistent with S. japonica, including 20–25 primary ribs with secondary rib interstices (though the exact number is ambiguous) and two primary ribs on the siphonal groove. Based on our integrated analyses of the morphology (including the number of radial ribs on the shell surface) and molecular sequence data, we have concluded that all the shell images in Yoo (1976), including Figs. 1 and 4, represent within the normal range of shell variations typically observed in S. japonica. In radula morphology, Hubendick (1946) provided a brief sketch of radula characters, based on only two specimens in his description of S. japonica. He provided a radula formula ranging from 32:1:32 to 40:1:40 and noted the presence of an ectocone on the innermost lateral teeth. Our examination of the Korean specimens revealed a radula formula of 29:1:29, which differs from those reported in Hubendick (1946), while the presence of an ectocone on the innermost lateral teeth was consistent with his findings. These observations suggest that the radula formula can vary within the same species.

S. japonica is commonly found in intertidal zones along the Korean coast, often occurring alongside S. acmaeoides and S. sirius (Fig. 2aA, Fig. 2dG). Their wide range of distribution and variations in shell morphology can lead to confusion in identification, resulting in past misidentifications in Korean illustrations as S. sirius (Yoo 1976) and S. acmaeoides (Kwon et al. 1993, Kwon 2001, Min et al. 2004). However, this species can be distinguished from other sympatric Siphonaria species by its thinner, regularly spaced primary ribs, siphonal groove with two radial ribs, undulated margin and dark brown-coloured interior (Fig. 2cF). Yokogawa et al. (2010) described two types from S. japonica, based on the combination of morphological, molecula, and ecological data, as the “tall form” and the “short form”. The tall form is characterised by weak radial ribs over the shell margin and alternating sized (thick and thin) radial ribs, while the short form has projected radial ribs over the shell margin and generally thick radial ribs. The Korean S. japonica morphologically matches the “tall form”. A comprehensive analysis of shell morphological data, coupled with molecular sequence information from broader sampling of this species, is required to confirm whether the “short form” of S. japonica is also distributed along the Korean sea coast, as previously reported in Japan (Yokogawa et al. 2010). Our phylogenetic tree indicates that S. japonica is positioned basal amongst selected Siphonariidae species in the north-western Pacific, with 99% bootstrap support value (Fig. 4). This species exhibits relatively high sequence divergence from other Siphonaria species, ranging from 28.89% (S. zelandica) to 33.81% (S. subatra) (Table 2).

Siphonaria (Siphonaria) javanica: Lee and Min 2002: 146 [checklist]; Min et al. 2004: 334, fig. 1054.

Siphonaria javanica: Noseworthy et al. 2007: 90 [checklist].

Japan (Okinawa island), Malaysia, Palau, Indonesia and northeast Australia.

Type locality: Indonesia; Java Island.

This species was initially included by Lee and Min (2002) in their checklist. Later, Min et al. (2004) described the shell characters of this species as having a large shell size (SL 20 mm, SW 18 mm, SH 9 mm) and white primary ribs with 2–3 thin secondary ribs in the interspaces. However, the shell characters in their description do not align with the original description of S. javanica provided by Lamarck (1819) or the subsequent studies by Morrison (1972) and Jenkins and Köhler (2024). The original description of S. javanica is brief, noting that the species possesses ‘white radiating ribs and crenated margin’ (translation from Latin). Morrison (1972) further noted that S. javanica was readily distinguished from other congeneric species by its high conical shell with buttress-like strong white radial ribs. Jenkins and Köhler (2024) provided a further detailed description of S. javanica by designating a lectotype and refined its taxonomy by clarifying its diagnostic characteristics. Their study also emphasised that S. javanica possesses well-developed primary ribs that extend beyond the shell margin, resulting in a coarsely undulated shell margin. This contrasts with the shell image provided by Min et al. (2004), which depicts the species with a smooth shell margin. Given the restricted distribution range of S. javanica to Indonesia and Timor-Leste, as clarified by the recent revision in Jenkins and Köhler (2024), Morrison (1972) and the discordance between the shell description of Korean “S. javanica” samples and both the original and subsequent descriptions, it is likely that the previously reported Korean specimens of “S. javanica” are likely misidentifications of S. japonica. Further studies with broader taxon sampling are necessary to resolve this taxonomic issue.

Siphonaria laciniosa: Kwon et al. 1993: 335, fig. 61-4.

Siphonaria (Siphonaria) laciniosa: Kwon 2001: 191, fig. 721.

Siphonaria (Mestosiphon) laciniosa: Lee and Min 2002 [checklist]: 146, fig. 268; Min et al. 2004: 336, fig. 1059; Noseworthy et al. 2007: 90 [checklist].

Persian Gulf, Red Sea, Samaoan Islands, Tonga, Fiji (Morrison 1972).

Type locality: India.

Kwon et al. (1993) first reported the occurrence of this species in Korea, noting its high shell height (SL 20 mm, SW 18 mm, SH 9.4 mm), with approximately 50 radial ribs and a pointed apex. Subsequent literature described this species as having less pronounced radial ribs, with white spots along the inner shell margin (Kwon 2001, Min et al. 2004), which are shell features also commonly observed in some individuals of S. japonica. Jenkins and Köhler (2024) recently designated S. laciniosa as a “nomen dubium”, highlighting the “utter confusion” in its original description and subsequent literature. Jenkins and Köhler (2024) noted that many type specimens attributed to S. laciniosa are either lost or represent mixed lots. Given the substantial taxonomic confusion regarding the validity of S. laciniosa and the morphological overlap between Korean specimens previously identified as S. laciniosa (Kwon et al. 1993, Kwon 2001, Min et al. 2004) and S. japonica (as observed in this study), it is likely that the earlier records of S. laciniosa in Korea represent misidentifications of S. japonica. As a result, we excluded S. laciniosa from the list of Korean Siphonaria species.

Siphonaria rucuana: Kwon et al. 1993: 335, fig. 61-5.

Siphonaria (Siphonaria) rucuana: Kwon 2001: 191, fig. 722; Lee and Min 2002: 146 [checklist]; Min et al. 2004: 335, fig. 1055; Noseworthy et al. 2007: 90 [checklist].

Japan (Okinawa Island).

Type locality: Japan; Ryukyu island (Okinawa Island).

Kwon et al. (1993) first reported this species in Korea, based on shell morphology, describing it as having a flatly convex shell with a brown apex curving posteriorly and brown intervals with secondary ribs. However, in contrast to this description, Pilsbry (1904) described S. rucuana as having a steeply conic shell with a glossy brown-coloured apex curving posteriorly and dusky-coloured intervals without secondary ribs. These characteristics are consistent with the recent revision of Jenkins and Köhler (2024). Yokogawa et al. (2010) divided S. japonica into two shell forms—“tall form” and “short form” — based on an integrative analysis of their morphology, habitat ecology and allelic frequencies. Compared to these two shell forms of S. japonica, the specimens previously described as S. rucuana in Korean waters (Kwon et al. 1993, Kwon 2001, Min et al. 2004) do not accord with the Pilsbry (1904)'s original description and morphological characters described in the recent revisional study (Jenkins and Köhler 2024). A re-evaluation of prior records of S. rucuana in Korea suggests that the specimens described in Kwon et al. (1993) correspond to the “tall form” of S. japonica, representing the original S. japonica. On the other hand, the other two reports (Kwon 2001, Min et al. 2004) are assumed to correspond to the “short form” of S. japonica discovered first by Yokogawa et al. (2010) in Japan. In addition to these morphological aspects, S. rucuana is known to have a limited geographic distribution, being reported exclusively from Okinawa Island, a subtropical region of Japan (Pilsbry 1904, Oyama et al. 1954, Okutani 2000, Okutani 2017). Given this restricted geographic distribution range and the morphological discrepancies observed in the Korean nominal records of “S. rucuana”, it is likely that these previous records in the Korean malacofauna result from misidentifications.

Siphonaria sirius Pilsbry 1894: 9, 10; Pilsbry 1895: 5, 6, pl. 6, figs. 23–28; Hirase 1941: 94, pl. 121, fig. 16; Hubendick 1945: 29 (cited from Jenkins and Köhler (2024)); Kuroda and Habe 1952: 86 (cited from Jenkins and Köhler (2024)); Azuma 1960: 62 (cited from Jenkins and Köhler (2024)); Kuroda 1960: 43 (cited from Jenkins and Köhler (2024)); Baker 1964: 159 (cited from Jenkins and Köhler (2024)); Shikama 1964: 6 (cited from Jenkins and Köhler (2024)); Habe and Igarashi 1967: 28 (cited from Jenkins and Köhler (2024)); Inaba 1983: 145 (cited from Jenkins and Köhler (2024)); Trew 1983: 7 (cited from Jenkins and Köhler (2024)); Je 1989: 29 [checklist]; Morton and Morton 1983: 298, pl. 1K (cited from Jenkins and Köhler (2024)); Hylleberg and Kilburn 2003, 2003: 133; White and Dayrat 2012: 68 [checklist]; Dayrat et al. 2014: 269, fig. 5H; Jenkins and Köhler 2024: 115–118, figs. 43E, F, O, P, 44D, E.

Siphonaria (Siphonaria) sirius: Hubendick 1946: 50, 51, pl. 3, figs. 24–27.

Siphonaria (Mestosiphon) sirius: Habe and Kikuchi 1960: 60 (cited from Jenkins and Köhler (2024)); Kira 1962: 200, 201, text-fig, pl. 69, fig. 12a, b (cited from Jenkins and Köhler (2024)); Habe 1971: 15, pl. 4, fig. 12 (cited from Jenkins and Köhler (2024)).

Anthosiphonaria sirius: Kuroda et al. 1971: 483, 484, fig. 9; Inaba 1983: 145 (cited from) ; Je 1989: 29 [checklist]; Choe 1992: 748, 749, pl. 126, fig. 223; Fukuda et al. 1992: 76, pl. 23, fig. 361a, b (cited from Jenkins and Köhler (2024)).

Siphonaria laciniosa forma sirius: Christiaens 1980a: 79.

Siphonaria laciniosa: Springsteen and Leobrera 1986: 285, pl. 81, fig. 19 (non Siphonaria laciniosa (Linneaus, 1758); cited from Jenkins and Köhler (2024)).

Siphonaria subatra: Je 1989: 29 [checklist].

Siphonacmea oblongata: Je 1989: 29 [checklist].

Siphonaria (Anthosiphonaria) sirius: Kwon et al. 1993: 334, fig. 61-2; Higo et al. 1999: 402, G4977 [checklist]; Kwon 2001: 191, fig. 725; Min et al. 2004: 336, fig. 1058; Okutani 2000: 815, pl. 405, fig. 5; Noseworthy et al. 2007: 90 [checklist]; Okutani 2017: 1101, pl. 403. fig. 5.

Measurements: SL 11.23–19.63 mm, SW 9.09–15.62 mm, SH 2.87–4.93 mm.

Shell (Fig. 2d) solid, oval, small to medium in size (in examined specimens, SL 11.23–19.63 mm), low in height (about 1/4 of its length). Exterior colour greyish-brown or blackish-brown. Shell surface with 5­–11 strong, white-coloured primary radial ribs. Interspaces between the primary radial ribs with 1­–8 thinner secondary ribs, coloured white, sometimes same as shell colour. Apex often eroded, located central of the shell. Shell margin prominently undulated by primary ribs. Anterior slope slightly convex, posterior slope nearly straight. Siphonal groove protruded with one radial rib on outer shell surface. Interior colour reddish-brown to black with white bands, sometimes white or pale-coloured at centre.

Radula (Fig. 3e, f) dentition formulae 34:1:34 (in specimens measuring SL 14.69 mm, SW 11.80 mm, SH 3.89 mm). Each transverse row with narrow central rachidian tooth flanked by symmetrical half rows with lateral teeth, decreasing in size outwards. Rachidian tooth (Fig. 3e) short, approximately one-third length of lateral tooth, bud-shaped, middle widest, tapering gently towards the top with sharply-pointed cusp. Innermost lateral teeth (first 15 lateral teeth), each tooth consisting of mesocone and ectocone; mesocone bicuspid, with U-shaped cleft; ectocone shorter, sharp (Fig. 3e). Outermost lateral teeth (remaining 19 lateral teeth) with short and sharply-pointed endocone, ectocone and mesocone; mesocone subquadrate (Fig. 3f).

Korea, China, Japan, Philippines, Singapore, Indonesia (Sumatra Island) and Vietnam.

Type locality: Japan; Sagami, Kashiurazaki, Boshiu (Boso Peninsula).

Habitat: On rocky substrate in middle to low intertidal zones (Fig. 2dG).

This species is clearly distinguished from other Korean sympatric species (S. acmaeoides and S. japonica) by its flat shell, remarkably extended white radial ribs, siphonal groove with a single radial rib and pale-coloured inner centre (Fig. 2d). It closely resembles S. atra Quoy and Gaimard, 1833, by having a flat shell and strongly stretched radial ribs. Christiaens (1980a) noted that S. sirius represents one of the three forms of S. laciniosa (Linnaeus, 1758); (S. laciniosa forma sirius, S. laciniosa forma atra (representing S. atra Quoy and Gaimard, 1833) and S. laciniosa forma subatra (representing S. subatra Pilsbry, 1904). He reported no differences in niche selection between S. atra and S. sirius, both of which inhabit highly exposed rocky substrates in the low tidal zone at Ping Chau, Hong Kong. However, the two species differ in colouration and the number of ribs in the siphonal groove. While S. atra has a dusky brown shell with radial ribs of the same colour (sometimes paler than the interspaces) and a siphonal groove with two radial ribs, S. sirius is characterised by a black or dark brown-coloured shell with solid white radial ribs and a siphonal groove with only one radial rib. In the radula formula, as mentioned in the cases of S. acmaeoides and S. japonica, Siphonaria species exhibits high levels of intraspecific variation. Similarly, the radula formulae of S. sirius reported in previous studies showed considerable variation depending on the authority, ranging from 40:1:40 (Hubendick 1946) to 34:1:34 (Christiaens 1980a). The radula formula (34:1:34) observed in this study is consistent with the finding of Christiaens (1980a). The phylogenetic tree shows that S. sirius forms a sister group with S. atra and S. subatra receiving 99% bootstrap value (Fig. 4). The p-distances within S. sirius species range from 0.16% to 0.79%, while this species shows high sequence divergence from other congeneric species ranging from 22.38% (S. atra) to 31.90% (S. japonica) (Table 2).