Shell minute (2.5±0.26 mm in width, 2.2±0.15 mm in length), ovato-conica. Whorls 4-5, spire low, body whorl rather ventricose (Fig. 2). Suture distinct. Every whorl is striated by about 9-10 distinct spiral ribs and the distance between the spiral ribs is not uniform. Reddish-brown spiral ribs contrasting with iridescent interspaces; lines on ribs occasionally broken by white spots, with crater‐like pitted microsculpture on protoconch. Aperture ovate, outer lip thin, with small notches, inner lip simple and slightly convex. Umbilicus circular deep. Basal surface flat, with 9-10 circular spiral ribs.

Figure 2.  

Lirularia iridescens Schrenck, 1863.

Yellow Sea of China; Japan Sea, South Kurile Islands.

L. iridescens was recorded by Kantor and Sysoev (2006). Okutani (2017) described and illustrated in detail L. iridescens. In this study, the species was re-described, based on the SEM. Crater‐like pitted microsculptures on the protoconch were first discovered here. At present, there are very few morphological studies on this genus Lirularia. Many studies have shown that L. iridescens are phytal gastropods inhabiting seaweeds (Toyohara et al. 1999, Agatsuma et al. 2005).

Shell small (8.5±0.34 mm in height, 4.5±0.18 mm in width), ovate-conica, thin, fragile, translucent, whorls about 8, less inflated, spire high, body whorl inflated (Fig. 3). Suture shallow. Shell surface smooth, varices on whorls here and there. Yellowish-brown in colour, with red-brown fine spiral striae and irregularly red-brown longitudinal striae and with thin periostracum. The aperture wide and large, outer lip thin, simple, columella concave, without umbilicus.

Figure 3.  

Alaba picta A. Adams, 1861.

From Liaoning to Shandong coasts of China; Japan; Australia.

Alaba picta with obvious morphological variance in colour, aperture, shell length and sculpture (Liu 2013). Diala vitrea G. B. Sowerby, 1915 is the name given to a phenotype lacking a colour-pattern (Okutani 2017). Diala picta A. Adams, is the original name of A. picta, which is from the Shandong coast of China (Adams 1861).

Shell minute (4.3±0.76 mm in length, 1.2±0.26 mm in width), conical, depressed or auricular (Fig. 4). Whorls 4, inflated. Spire low; body whorl large, sudden expansion of width, slightly tilted. Shell thin, smooth, except for weak growth lines, with tawny periostracum. Keel round the body whorl, with grooved suture. Aperture large, pyriform, oblique, with angulate periphery on the underside of the outer lip, inner lip thick. Umbilicus open. Protoconch usually eroded.

Figure 4.  

Lacuna carinifera (A. Adams, 1853).

China, Japan.

Stenotis lois (Yen, 1936) is very similar to Lacuna carinifera (A. Adams, 1853), but the aperture is wider, with angulate periphery on the underside of the outer lip, the umbilicus more open. This study thinks Stenotis lois (Yen, 1936) is the larva of Lacuna carinifera (A. Adams, 1853) and is a synonym.

Shell minute (2.5±0.18 mm in length, 1.3±0.09 mm in width), elongate conical, solid (Fig. 5). Whorls about 5, with high spire, periphery weakly angulate in immature individuals, round when matured. Suture distinct. Shell glossy and smooth, colour uniformly reddish-brown in northern localities. Protoconch with several pits on the surface. Aperture small, peristome simple, rounded-ovate, outer lip thin, the columellar and parietal margins somewhat thickened. No umbilicus.

Figure 5.  

Barleeia angustata (Pilsbry, 1901).

China, Japan, Australia.

The species originally belonged to Rissoidae. Rissoina dunedini Grabau & S. G. King, 1928 and Rissoina nelsoni Grabau & S. G. King, 1928 were the synonyms of this species (Zhang et al. 2016). There are shell colour variations, lightly coloured forms with distinct brown spiral bands in warm waters.

Shell minute (1.2±0.42 mm in width, 1.8±0.13 mm in length), conic to ovate-conic, dark brown, smooth or with weak axial microsculptures and rather solid, periphery weak convex to angled (Fig. 6). Whorls 4, suture prominent and deep. Protoconch dome-shaped, smooth, with a diameter of about 300 μm, some sediment attached to it, with several pits on the surface. Apical angle around 45°. Aperture oval with a simple peristome, the posterior of outer lip in contact with the body whorls. Operculum, not a canal; inner lip attaching to the previous whorl, but not contacted with outer lip, not umbilicate and anterior canal; outer lip thin, anterior prosocline.

Figure 6.  

Barleeia sp.

China

Barleeia sp. very similar to Barleeia angustata (Pilsbry, 1901), but the aperture is open.

Shell minute (3.0±0.22 mm in length, 1.6±0.14 mm in width), elongate conical, stout (Fig. 7). Whorls 5, inflated, with deeply impressed suture. Whorls increasing gradually in size. Surface of shell glossy dark brown at apical and yellowish-brown at abapical part, sculptured with many fine spiral lirae and fine growth lines. Periphery of body whorl rounded, base of whorl gradually curved. Protoconch is small, depressed dome-shape. Aperture oval and weakly angled both up and down, peristome somewhat thickened and broad down region, outer lip rounded. Umbilicus narrow and very shallow.

Figure 7.  

Iravadia (Fluviocingula) elegantula A. Adams, 1861.

Korea, China, Japan.

The Iravadia includes the subgenera Fluviocingula Kuroda & Habe, 1954, Pseudomerelina Ponder, 1984 and Pseudonoba O. Boettger, 1902. The original description from the species Onoba elegantula A. Adams, 1861. At present, the Iravadia elegantula (A. Adams, 1861) has been accepted as Fluviocingula elegantula (A. Adams, 1861).

Shell minute (2.1±0.14 mm in length, 1.5±0.07 mm in width), ovate-conic, rather thick, dorso-ventrically compressed, with rounded to angled inflation of last whorl (Fig. 8). Up to 5 whorls including protoconch, with less convex whorls and sutures moderately deep. Surface smooth, yellowish-brown, sculpture not dotted lines, but continuous spiral grooves. The aperture abruptly descending, contracted and near circular; peristome continuous, showing a weak triangular area above; outer lip round with marked grooves. Operculum ovate, yellowish, translucent, with very weak angulation aligning with posterior apex of aperture; exterior surface with central paucispiral nucleus close to the inner lip. Protoconch dome-shaped, smooth, 1-3/4-2 whorls; some pits in the first whorl.

Figure 8.  

Stenothyra glabra A. Adams, 1861.

Yellow Sea and Bohai Sea of China, Korea and Japan.

The type locality of Stenothyra glabra A. Adams, 1861 is “estuary of the Pei-ho, North China”, which is on the coast of the Bohai Sea. One of the localities in this study, Yellow River Estuary, is adjacent to the type locality. Moreover, the shells exhibit remarkable similarity in terms of size, shape, and microsculpture when compared to the descriptions provided by Adams (1861), Yen (1939), Yen (1942), and Kantor and Sysoev (2006), although the available photograph of the holotype is lacking (Agatsuma et al. 2005). We believe that specimens collected in this study belong to common species from the coasts of the Yellow Sea and Bohai Sea in China and are conspecific with the type material.

Shell minute (2.2±0.36 mm in length, 1.5±0.08 mm in width), globose-conic, solid (Fig. 9). Whorls 5, spire low, each whorl weakly convex in spire, body whorl large and more convex, with impressed suture. Surface smooth, with many fine axial growth threads, yellowish, with 2 brown bands on body whorl. Aperture large, simple, ovate, columellar lip of aperture pale brown, but inner lip dark purplish-brown. Early whorls of teleoconch without spiral ribs.

Figure 9.  

Assiminea estuarina Habe, 1946.

China, Japan.

The genus Assiminea H. & A. Adams, 1865 is cosmopolitan, but most of them are from the Indo-pacific Region. A. estuarina is rarely found in China. The shell of this species is similar to A. hiradoensis Habe, 1942, but there are some differences between them. Each whorl of A. estuarina is more convex than A. hiradoensis. The height of the spire of A. hiradoensis is higher.

Shell minute (4.5±0.41 mm in length, 2.4±0.11 mm in width), elongate conical (Fig. 10). Whorls about 6, slightly convex, with elevated spire, deeply sutured. Shell surface reddish-brown, sculptured with many spiral ribs and strong axial ribs; axials tend to weaken on body whorls in populations in temperate waters. Aperture simple, ovate, outer lip thin, without varix, the upper part of outer lip slightly angular. Apex generally not strongly tilted in species with paucispiral protoconch. No umbilicus.

Figure 10.  

Alvania concinna A. Adams, 1861.

China, Japan and Korea.

The trait of the genus Alvania Risso, 1826 is that the teleoconch is ovate-conic to elongate-conic, with clathrate sculpture or spiral sculpture (Adams 1850). The changes of morphological characteristics and surface colour are relatively large, the synonym Hydrobia plicosa E. A. Smith, 1875 is a northern form of this species (Okutani 2017).

Shell minute (1.3±0.19 mm in length, 3.1±0.16 mm in width), depressed conical, round pie, solid (Fig. 11). Whorls about 5, spire very low, body whorl large, the spiral layers are almost in the same plane, whorl periphery appears markedly truncate with a deep concave sulcus between the two peripheral keels. Suture distinct, grooved. Surface sculptured with thick spiral cords and many strong axial ribs, white or covered with yellow crust, thin sculpture lines on the sides of the whorl. Protoconch smooth. Aperture thickened, ovate, declining. Umbilicus deep.

Figure 11.  

Pseudoliotia pulchella (Dunker, 1860).

China, Japan.

Pseudoliotia Tate, 1898 is characterised by a depressed conical shell with strong axial and spiral ribs on its surface. P. pulchella is similar to P. astericus, but much larger, lower in shell height and with relatively weak axial ribs.

Shell minute (3.0±0.28 mm in length, 2.4±0.09 mm in width), depressed conical, thick, stout; outline domed (Fig. 12). Whorls 3, whorls almost flat-sided or rounded or slightly shouldered; body whorl large with sharply angulate periphery; teleoconch whorls usually smooth, with spiral microstriae. Base flat to slightly rounded, with about 4 spiral ribs. Dark brown with irregular white spots. Suture impressed; peripheral keel prominent, often a projecting flange, rarely slightly undulating. Umbilicus usually narrow; columella narrow, curved at base. Protoconch usually eroded. Aperture ovate, outer lip thin and bottom angular, inner lip slightly thick and the upper part not connected with outer lip.

Figure 12.  

Peasiella habei D. Reid & Mak,1998.

China, Korea, Taiwan, Japan.

This species is variable in conspicuous features of the shell including colour, spire profile and sculpture, but consistent characteristics are the row of dark spots above the periphery, which extend on to the pale peripheral keel, the darker and often black spire whorls and the prominent keel at the periphery.

Shell minute (2.5±0.15 mm in length, 0.9±0.08 mm in width), cylindrical to fusiform, thick, solid, with fine and indistinct spiral grooves (Fig. 13). Surface white, smooth, slightly corroded. Whorls about 3, spire small, body whorl was slightly constricted on the upper part. Shoulder acutely angulated. Protoconch prominently projecting. Suture oblique. Columella stout, with a fold above.

Figure 13.  

Acteocina fusiformis A. Adams, 1850.

Bohai Sea in China, Japan, South African.

Shell cylindrical or fusiform, spire conspicuous, apex papillated, suture channelled, columella callous, with a single fold in the genus Acteocina Gray, 1847 (Adams 1850). The division of the genus Acteocina is problematic in systematics. Okutani (2017) divided it into the family Cylichnidae, but it was divided into Tornatinidae in WoRMS.

Shell minute (3.0±0.34 mm in length, 1.3±0.11 mm in width), pyriform, thin, white, polished (Fig. 14). Apex narrowly perforated with rounded margin. The upper end of the body spiral shrinking and the lower end expanding, covered with spiral grooves overall, axial grooves distinct on upper extremity. Columella with fold. Outer lip thin.

Figure 14.  

Pyrunculus tokyoensis Habe, 1950.

China and Japan.

P. tokyoensis is similar to P. phiala, but differs from P. phiala in having distinct spiral grooves overall.

Shell minute (3.2±0.27 mm in height, 1.5±0.34 mm in width), oval conical, moderately thick, translucently milky-white, solid (Fig. 15). Whorls about 5, each spiral slightly convex, the height of the body whorl is larger than spire. Surface covered with yellowish-brown periostracum. Suture distinct, grooved. Growth lines coarse and flexuous. Aperture ovate. Columella with a weak fold. Outer lip margin with a shallow posterior sinus.

Figure 15.  

Brachystomia bipyramidata (Nomura, 1936).

North of China, Japan.

The genus Brachystomia Monterosato, 1884 is very similar to Odostomia spp. in shell characters, but differs in the protoconch turning down on the teleoconch apex, attaching to other molluscs when alive (Okutani 2017).

Shell minute (5.0±0.12 mm in height, 2.3±0.03 mm in width), conical, milky-white, moderately thick, solid (Fig. 16). Whorls about 6, each whorl nearly flat-sided, shoulder of each whorl feebly angulate. Sutures distinct, grooved. Protoconch immersed in first teleoconch whorl, rotated right. Umbilicus narrowly opened. Aperture simple, long-ovate, columella with fold, outer lip thin, curved.

Figure 16.  

Odostomia subangulata A. Adams, 1860.

North of China, Japan.

Megastomia tenera (A. Adams, 1860) very similar to Odostomia subangulata A. Adams, 1860 in shell characters, but differs in having palatal ridges in the inner lip.

Shell minute (3.8±0.13 mm in height, 1.0±0.21 mm in width), towered, moderately solid, white (Fig. 17). Whorls about 10, each whorl with convex sides. Sutures constricted. Axial ribs oblique and straight, terminating at periphery. Interspaces of axial ribs twice as wide as ribs, the axial rib of the upper whorl is aligned with the interspace of the lower whorl. Aperture simple, upper of the outer lip with angular, columella with no folds, basal lip circle. The apex of the protoconch is composed of two parts of different sizes.

Figure 17.  

Turbonilla osyuensus Nomura, 1936.

Bohai Sea of China, Japan.

Chemnitzia osyuensis (Nomura, 1936) is the type specimen and a synonym. Very similar to T. gracilenta, but differs in the protoconch rotated right (Higo and Goto 1993).

Shell minute (1.5±0.12 mm in height, 0.88±0.06 mm in width), elongate oval, thin, vitreous, fragile, translucent (Fig. 18). Whorls about 4, each whorl rather convex, spire about 25% of shell height. With deep sutures. Surface almost smooth, the axial growth lines of body whorl shrinking at base. Protoconch smooth, low. Aperture simple, ovate. With narrow umbilicus.

Figure 18.  

Rissoella elatior (Golikov, Gulbin & Sirenko, 1987).

China, Japan, Russia.

The shell characteristics of the genus Rissoella are thin; vitreous and soft parts can be seen through it. As some species are similar in morphology, many species are misidentified or undescribed. In this study, our sampled material agrees with the original description of this species (Golikov et al. 1987), as well as the study from Siaden et al. (2019).

Shell small (2.7±0.15 mm in length, 1.9±0.11 mm in height), elongate-ovate, thin, fragile (Fig. 19). Surface purplish-red, ornamented with concentric growth striae. Umbo prominent, situated slightly behind the mid-point of the dorsal margin. Break located near posterior margin. Hinge plate very strong, with one cardinal socket, with one anterior lateral cardinal tooth and two posterior lateral cardinal teeth of different sizes in right valve.

Figure 19.  

Lasaea undulata (A. A. Gould, 1861).

Yellow Bay (Shandong Province) of China, Japan.

Lasaea consists of small pelecypod species, the largest of which attains a size of about 8 mm in length; adult specimens of the smaller species are about 2 mm long. In general, these shells are quadrangular in outline; they are equivalved, but inequilateral, the anterior end being the longer (Keen 1938). Most, if not all, species of Lasaea are nestlers, finding shelter in dead barnacle tests and amongst the holdfasts of seaweeds. It is cosmopolitan, but only L. undulata is found in China.

Shell minute (1.1±0.17 mm in length, 1.0±0.22 mm in height), triangular-ovate, inflated, equivalved (Fig. 20). Umbo prominent, almost situated at the middle of the dorsal margin. Anterior and posterior ends round. Surface smooth and yellowish, ornamented by densely-spaced co-marginal lamellae. Hinge plate with one anterior and one posterior cardinal tooth in the left valve and one cardinal tooth in the right ligament external parivincular, with small resilium.

Figure 20.  

Alveinus ojianus (Yokoyama, 1927).

Yellow Sea and Bohai Sea of China, southern Japan.

Spaniodon Reuss, 1867 was considered a senior synonym of Alveinus Conrad, 1865, containing only Alveinus miliaceus (Issel, 1869) and Alveinus ojianus (Yokoyama, 1927) in WoRMS. A. miliaceus is very similar to A. ojianus in shell characters, but differs in the cardinal tooth. The cardinal teeth bifurcate into two lamellae (Conrad 1865).

Shell minute (2.3±0.02 mm in length, 1.5±0.04 mm in height), elongate squarish, thin, moderately inflated (Fig. 21). Antero-posterior margin round, anterior narrower and shorter than posterior; posterior hardly oblique, sides weakly angulated at upper part. Umbo corroded, situated in front of dorsal margin. Surface with 33 radial riblets of various prominence and strong concentric ribs near the umbo; covered with lamellate epidermis at interstices; inner surface margin is toothed. With a depression at the ventral margin. Cardinal plate with 3 teeth on anterior arc and 4 on posterior arc.

Figure 21.  

Bentharca sp.

Bohai Sea of China.

This species is very similar to Bentharca spp. in shell characters including radial riblets and is covered with lamellate epidermis at interstices, cardinal plate and umbo.