Assiminea estuarina Habe, 1946

Li, Ya-fang, Xu, Run-lin & Online, Published, 2013, Brackish water snails from Qi’ao-Dan’gan Island in the Pearl River estuary, China, Turkish Journal of Zoology 37 (4), pp. 449-457 : 450-455

Assiminea estuarina Habe, 1946

Materials and locality: Specimens (SH × SW: 4–4.5 × 3.1– 3.5 mm), TR, SK, SA, and SC.

Brief description: Shell ( Figure 2 ) small, moderately thick and solid, colored yellow-green to yellow-orange and with 4 rather distinct, darker, reddish brown spiral bands (the last whorl with 2 bands and the other 2 wide bands around the last 2 sutures). Shell consists of 5–5½ whorls, each whorl smooth and polished except for irregular microscopic spiral threads and weak growth lines. Shoulder, periphery of each whorl is not angled and each whorl has rounded bottom. Aperture ovate; peristome incomplete; outer lip sharp; inner lip broad, not thick and expanded; columellar lip continued from inner lip, slightly thick, expanded. Umbilicus narrow, half covered.

Operculum: Ovate, thin, and corneous, with fewer spirals and the nucleus off to one side.

Radula ( Figure 3 ): Central with 3 pairs of basals and a cutting edge formula of 2-1-2. Lateral with a denticle formula of 2-1-2. Inner marginal long, moderately narrow and with 6 denticles, 2 of them smaller. Outer marginal bearing 9 fine denticles.

Remarks: This species is a new finding for China. It was first reported as a new species in Wakayama-ken, Japan, by Habe (1946). The shell, operculum, and radula features of Assiminea estuarina in the present study agreed with the description given by Habe in 1946 except for the irregular microscopic spiral threads on the shell. The shell and radula of this species were similar to those of Assiminea septentrionalis Habe 1942 , but there were some differences between them. The periphery of the body whorl of A. septentrionalis is a little angled and has a wider aperture (Habe, 1942); each whorl of A. estuarina is not angled. This species lives in the same type of habitat in Japan and China (in brackish water of estuaries). In the present study, they were collected from 4 sites (TR, SK, SA, and SC), which are all located in the intertidal zone, and are all intermittently flooded by the tide.

Genus: Sphaerassiminea Habe 1942

Sphaerassiminea brevicula (Pfeiffer, 1855)

Materials and locality: Specimens (SH × SW: 5–9 × 4–7 mm), TR, SA, and SC.

Brief description: Shell ( Figure 4 ) globes, thick and colored an opaque bright brick-red or yellowish-tan; 6 to 7 well-rounded whorls. Suture sharp, smooth, minutely indented, below which is a wide, rounded, moderately raised, lighter-colored, spiral cord. The cord is bounded

LI and XU / Turk J Zool below by a weak, spiral, indented, or incised channel of varying width, which may or may not be further scratched by oblique threads. Below the channel, the body whorl may have 1, 2, or 3 finer, sharply incised spiral lines. Columellar pillar whitish, strong, arched, rounded, entirely or partially covering the chink-like umbilicus.

Operculum: Corneous, thin, transparent-tan, elongate and with the nucleus far off to one side.

Radula ( Figure 5 ): Central radular tooth, with a cutting edge formula of 2-1-2, a pair of lateral cusps, sides with slight cusp-like swellings, which are probably not basals. Lateral teeth with 7–8 cusps, the formula of 2-1-4(5), and with 2 small detached accessory plates. Inner marginal strong, elongate, with 5 to 7 well-developed cusps. Outer marginal with 3 to 5 cusps and a wide, very thin, flaring flap.

Remarks: This is a common, widely dispersed species in Southeast Asia. The general distribution is from the coasts of India and Sri Lanka and eastward through Southeast Asia, Indonesia, and then northward through the Philippines to southern China and Taiwan. The central radular of this study was consistent with the description by Abbott (1958), but the other teeth were more similar to those reported by Habe (1942). The differences in the radula of S. brevicula indicated that much more work was required to determine the variation and taxonomic limits of this species. Concerning the habitat of this species, there were several views. Abbott (1958) collected this species from a habitat located in an estuary covered alternately by salt water and freshwater. Leith, cited by Abbott (1958), presumed through an experiment that it preferred freshwater habitats and could not tolerate brackish or salt water. Pace (1973) stated that Van Benthem Jutting collected this species from the estuaries and mangrove swamps in Java. In the present study, this species was collected from 3 sites; they were all located in estuarine

LI and XU / Turk J Zool areas. The TR site is located in the intertidal zone of a brackish tidal river, and the other 2 sites ( SA and SC) are mangrove swamps.

Genus: Taiwanassiminea Kuroda & Habe, 1950

Taiwanassiminea sp.

Materials and locality: Specimens (SH × SW: 4.9–6 × 3.0– 3.5 mm), SK, SA, and SC.

Brief description: Shell ( Figure 6 ) conically elongate, moderately thick, colored a uniform chocolate-brown; 6 to 7 whorls, moderately rounded. Suture sharp, finely indented and smooth, and bordered below by a fairly strong, quite distinct, raised spiral thread. Body whorl with a distinct umbilical thread. Umbilicus a slit-like, small chink.

Operculum: Corneous, thin, transparent-tan, ovalelongate and with the nucleus far off to one side.

Radula ( Figure 7): Central radular tooth, with a cutting edge formula of 2-1-2, lacking basal cusps. Lateral teeth with a denticle formula of 2-1-3, and with a single, long accessory plate. Inner marginal strong, elongate, narrow, and with 6 well-developed cusps. Outer marginal with about 20 fine denticles.

Remarks: The shell and radula of this species were similar to those of Taiwanassiminea hayasii Habe, 1942 and Assiminea crassitesa O. Boettger 1893 . T. hayasii is the type species, but the shapes of tentacles and penis were distinctly different from those of T. hayasii and A. crassitesa . The penis of T. hayasii shows a “knot” formed by 2 strong constrictions and a pear-shaped bulb in the proximal portion (Pace, 1973). The penis of A. crassitesa is long, swollen, and laterally flattened at the basal half, and becomes tubular and narrow distally where, at the tip, there is a slight swelling ( Abbott, 1958). The penis of this species is long and narrow, without a knot or swollen part at the end. Pace (1973) reported that T. hayasii was collected in and out of the water on the banks of a river. Little is known about the habits of A. crassitesa except that it seems to prefer dark, shady areas in brackish water regions. In this study, the specimens of this species were collected from SK, SA, and SC wetlands. These areas are dark, shady areas with brackish water regions.

Family Potamididae H. & A. Adams, 1854

Genus Cerithidea Swainson, 1840

Cerithidea sinensis Philippi, 1848

Materials and locality: Specimens (SH × SW: 13 × 4 mm), SK and SC.

Brief description: Shell ( Figure 8 ) turreted, elongate, thin, colored brownish with tan base, comprising about 12 inflated whorls. Each whorl has distinct axial riblets that incline with a slight angle to the right. The base of each whorl has 2 thick spiral brown bands. Aperture ovate, with small anterior groove.

Operculum: Corneous, thin, circular, and multispiral with central nucleus.

Radula ( Figure 9 ): Central radular teeth, with a cutting edge formula of 3-1-3, lacking basal cusps. Lateral teeth with a denticle formula of 1-1-3, and with long, tapering lateral projection inserting onto basal radular membrane. Inner marginal teeth long, with 2 broad, nearly fused. Outer marginal with 6 small pointed cusps and a narrow, flaring flap.

Remarks: In this study, the habits and the length of this species were different from the domestic reports (Zhang et al., 2008). According to previous reports in China, they were generally found in the temperate zones, where the salinity and temperature are lower. However, the sampling sites are located in tropical zones with different salinity and temperature conditions compared with former reports. David G. Reid had seen some specimens from Hong Kong and N Vietnam, and so its habitat may extend into the tropical region (private conversation on 7 November 2011). There may be more than one species involved— the shells are not very distinctive in this genus. This will require further study at the molecular level.

Family Thiaridae Gill, 1871

Genus Melanoides Oliver, 1804

Melanoides tuberculata (Müller, 1774)

Materials and locality: Specimens (SH × SW: 14–19 × 4.5–6 mm), AL, SK, and SA.

Brief description: Shell ( Figure 10 ) with vertical ribs and spiral threads, which confer a nodular appearance; spiral sculpture and transverse ribs are about equally prominent on the early formed whorls.

Radula ( Figure 11 ): The central teeth in the 6 radulae examined (each from a different locality) had 3 (rarely 4) well-developed cusps on either side of the median cusp, and a pair of lateral cusps. Thus, the number of cusps on the central tooth overlaps that in Thiara scabra (Müller, 1774) . Lateral with a denticle formula of 3-1-2.

Remarks: The teeth and shell of M. tuberculata are consistent with the description by Brown and Gallagher (1985). Pace (1973) reported that the central tooth of this species had 9 superior cusps (4:1:4). M. tuberculata apparently is the most widespread freshwater mollusk; it has been reported from many types of freshwater habitats, including streams, ponds, lakes, and rice paddies. However, Jutting pointed out this species does not even avoid hot springs (temp. 35 °C) or iodine springs, and it has been found at elevations up to 1600 m (Pace, 1973). It is not surprising then that these snails are so widely distributed even outside their natural range. In this study, they were collected from 3 sites, 2 of which were mangrove wetlands located in the intertidal zone and are intermittent flooded by the tide; the other one was an artificial brackish lake that was almost completely closed off by controlling the amount of water entering through the gate. Due to the wide distribution, the shell shapes are variable; sometimes whorls are nearly smooth with only fine incised spiral lines.

Family Ellobiidae Pfeiffer, 1854

Genus Laemodonta Phlippi, 1846

Laemodonta punctigera (H. & A. Adams, 1853)

Materials and locality: Specimens (SH × SW: 4.5–6.4 × 3.2–4.0 mm), AL, SK, SA, and SC.

Brief description: Shell ( Figure 12 ) with (usually) 3 brown bands (usually) on the body whorl, and spiral rows of comparatively large pits, and a lack of subsutural sulci. The spire is obtusely dome-shaped, the umbilicus closed. Aperture with the typical 3 folds and with 2 palatal teeth.

Remarks: This species is extralimitally known from almost all countries bordering the Indian Ocean and South China Sea, India, Burma, Thailand, Malaya, Indonesia, South China, Philippines, and S Vietnam ( Brandt, 1974). The first recording of this species in China was from Hong Kong’s intertidal zone.

Family Iravadiidae Thiele, 1928

Genus Iravadia Blanford, 1867

Subgenus: Iravadia s.s

Iravadia (Iravadia) ornata Blanford, 1867

Materials and locality: Specimens (SH × SW: 5–5.5 × 2.5–3.0 mm), AL, TR, SK, and SC.

Brief description: Shell ( Figure 13 ) ovate elongate-conic, nonumbilicate, with strong spiral cords. Aperture oval, subangled posteriorly and anteriorly, peristome

LI and XU / Turk J Zool thick; outer lip with heavy varix. Protoconch is consistent with the genus. Animal grayish with large pigment dots on head and back and small black pigment dots dusted over the whole body with exception of the sole; the long tentacles carry 5–6 black pigment rings. Penis similar to that of Iravadia ornata from Australia illustrated by Ponder (1984).

Operculum: With nucleus midway on columellar edge. Two low radial folds emerge from nucleus and cross about two-thirds of inner surface of operculum.

Radula ( Figure 14): The radula with a broad and low, trapezoidal rhachis that carries 4–6 small cusps on either side of the larger middle cusp on the cutting edge. The basal corners are shaped like broad wings. There is a small basal cusp in the bay formed by the wings and the sides of the central process. Lateral teeth with 2(-3)-1-3, marginals with 12–14 cusps.

Remarks: Ponder (1984) collected this species under stones in the lower littoral, in an estuarine situation, but it is not associated with extant mangroves. In this study, the sampling sites were located in the western part of the Pearl River estuary. They were taken from 4 sites; 2 sites had a habitat similar to that described by Ponder, but the other 2 sites were dominated by mangrove trees. Brandt (1974) reported that the species lives in brackish water, in the drainages of mud-flats, in mangrove swamps, and in the estuarine area of rivers. That was consistent with the findings of the present study. The first report of this species in China was from Hong Kong.

Genus Iravadia Blanford,1867

Subgenus: Fairbankia Stoliczka, 1868

Iravadia (Fairbankia) cochinchinensis Bavey & Dautzenberg, 1910

Materials and locality: Specimens (SH × SW: 8.2–11 × 3.2–4.1 mm), SK, SA, and SC.

Brief description: Shell ( Figure 15 ) elongate-conic, with strong, brown periderm; with fine spiral lines that carry ciliae; with 8–10 moderately convex whorls; the embryonic shell is missing. Aperture relatively small; nonumbilicate. The foot is straight in front and rounded behind. The long tentacles carry 3–4 black pigment rings.

The penis and operculum: Similar to those of I. bombayana illustrated by Ponder (1984).

Radula ( Figure 16 ): Central teeth with 17 cusps on the cutting edge, without basal cusps. Laterals with the formula (2-3)-1-(5-6), marginal teeth with 15–16 cusps.

Remarks: This species is a new finding in China. It is differentiated from the type species I. bombayana by its larger size and coarser spiral lines; otherwise, there were no noteworthy differences between these 2 species ( Brandt, 1974). According to description by Brandt (1974), this species is distributed in S Vietnam, Thailand, and Malaya. They were collected from 3 sites dominated by mangrove trees in the present study.

Figures

Figure 2. Assiminea estuarina. A. front view B. back view. Scale bar = 1 mm.

Figure 3. Assiminea estuarina. Radular teeth.

Figure 4. Sphaerassiminea brevicula. A. front view B. back view. Scale bar = 1 mm.

Figure 5. Sphaerassiminea brevicula. Radular teeth.

Figure 6. Taiwanassiminea sp. A. front view B. back view. Scale bar = 1 mm.

Figure 8. Cerithidea sinensis. Scale bar = 1 mm.

Figure 9. Cerithidea sinensis. Radular teeth.

Figure 10. Melanoides tuberculata. Scale bar = 1 mm.

Figure 11. Melanoides tuberculata. Radular teeth.

Figure 12. Laemodonta punctigera. Scale bar = 1 mm.

Figure 13. Iravadia ornata. Scale bar = 1 mm.

Figure 15. I. (Fairbankia) cochinchinensis. Scale bar = 1 mm.

Figure 16. I. (Fairbankia) cochinchinensis. Radular teeth.