Korean mud

Bullacta exarata, common name the Korean mud snail,[6 ] is a species of a sea snail or bubble snail, a marine gastropod mollusc in the family Haminoeidae, the bubble snails.

Bullacta exarata is a commercially important mollusc which is used as a food item in eastern China.[7 ]

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Contents
[hide] *1 Taxonomy
 * 2 Distribution
 * 3 Description
 * 4 Ecology
 * 5 Human use
 * 6 References
 * 7 Further reading
 * }

[edit] Taxonomy
Bullacta exarata is the only species in the genus Bullacta. cf.[4 ]

Bullacta is the type genus of the family Bullactidae Thiele, 1926, as shown in the taxonomy of the Gastropoda by Bouchet & Rocroi (2005).[8 ]

Based on phylogenetic genetic analysis by Malaquias (2010),[1 ] Bullacta exarata should be placed in the family Haminoeidae.[1 ]

[edit] Distribution
Bullacta exarata is endemic to coastlines of the South and East China Seas from Hainan to the Bohai Sea in north-eastern China,[1 ] [9 ] the western coast and south coast of Korea[1 ] and Japan.[10 ] An ecotype of this snail introduced from further south has became invasive in Laizhou Bay, with population densities of over 160 snails per square meter.[11 ]

[edit] Description
The shell is bullate, fairly thick, white, spirally striate, with a well developed periostracum.[3 ] There is no spire and no umbilicus.[3 ] The columella is smooth and simple.[3 ] The aperture extends for the whole length of the shell, and is narrower above than below.[3 ] The apertural lip extends upwards beyond the apex of the shell.[3 ]

The height of the shell is 8 mm and the width of the shell is 6 mm.<sup class="reference" id="cite_ref-11">[12 ]

The animal cannot withdraw itself into the shell, which contains the visceral hump only.<sup class="reference" id="cite_ref-Annandale_1924_2-6">[3 ] The cephalic disc is large and slipper-shaped, feebly emarginate on the dorsal surface behind and with a narrow free margin.<sup class="reference" id="cite_ref-Annandale_1924_2-7">[3 ]

The cephalic disc, which is rounded in front, occupies about half of the whole bulk in a contracted state.<sup class="reference" id="cite_ref-Annandale_1924_2-8">[3 ] The edge of the mantle is smooth, without processes of any kind.<sup class="reference" id="cite_ref-Annandale_1924_2-9">[3 ] It, the edge of the mantle (which is slightly retroverted over that of the shell), the foot and the epipodia are (in alcohol) of a pale green colour.<sup class="reference" id="cite_ref-Annandale_1924_2-10">[3 ] The greater part of the mantle, however, under the shell is colourless and transparent.<sup class="reference" id="cite_ref-Annandale_1924_2-11">[3 ] The foot is short, truncate before and behind, and with the epipodia (in much contracted specimens) apparently not well developed.<sup class="reference" id="cite_ref-Annandale_1924_2-12">[3 ] The eyes are minute and quite invisible on the surface.<sup class="reference" id="cite_ref-Annandale_1924_2-13">[3 ] The eyespots are deeply sunk in the tissues.<sup class="reference" id="cite_ref-Annandale_1924_2-14">[3 ] The gill, which is situated far back on the right side, is large and consists of a considerable number of fleshly lobes.<sup class="reference" id="cite_ref-Annandale_1924_2-15">[3 ] Drawing of one row of teeth in the radula of Bullacta exarata. C - central tooth, L - lateral tooth, 1-12 - marginal teeth.Digestive system: The mouth is a minute tranverse slit in the front of the cephalic disc.<sup class="reference" id="cite_ref-Annandale_1924_2-16">[3 ] The jawss are large, but imperfectly cornified.<sup class="reference" id="cite_ref-Annandale_1924_2-17">[3 ] The jaws are angular and minutely, irregularly serrate.<sup class="reference" id="cite_ref-Annandale_1924_2-18">[3 ] They are composed of numerous minute prismatic rods.<sup class="reference" id="cite_ref-Annandale_1924_2-19">[3 ] On the margin many of these rods are transverse and project slightly, forming a minute serration.<sup class="reference" id="cite_ref-Annandale_1924_2-20">[3 ] The radular sack is small.<sup class="reference" id="cite_ref-Annandale_1924_2-21">[3 ] The radula has the formula 12.1.1.1.12.<sup class="reference" id="cite_ref-Annandale_1924_2-22">[3 ] The central tooth is a simple flat triangular plate.<sup class="reference" id="cite_ref-Annandale_1924_2-23">[3 ] The single lateral tooth is well differentiated from the marginal teeth, from which it is separated by a considerable space, and points in the opposite direction.<sup class="reference" id="cite_ref-Annandale_1924_2-24">[3 ] The marginal teeth are slender, elongate, curved rod-like bodies somewhat expanded at the base.<sup class="reference" id="cite_ref-Annandale_1924_2-25">[3 ] They decrease in size gradually from the second or third marginal, which is slightly larger than the first, outwards.<sup class="reference" id="cite_ref-Annandale_1924_2-26">[3 ]

There is a long, narrow, thin-walled oesophagus with a single coil; before entering the muscular gizzard it is considerably dilated.<sup class="reference" id="cite_ref-Annandale_1924_2-27">[3 ] A longitudinal strand of muscular tissue runs up its dorsal surface for a short distance from the gizzard.<sup class="reference" id="cite_ref-Annandale_1924_2-28">[3 ] The gizzard is large and it contains three horn-shaped, transversely ridged chitinous plates arranged in a triangle.<sup class="reference" id="cite_ref-Annandale_1924_2-29">[3 ] It is maintained in position by a stout transverse muscle on either side, the proximal end of the muscle being fixed to a constriction in the outer wall of the gizzard.<sup class="reference" id="cite_ref-Annandale_1924_2-30">[3 ] The gizzard contains three large, stout chitinous bodies, which are smooth and heart-shaped at their base on its external surface.<sup class="reference" id="cite_ref-Annandale_1924_2-31">[3 ] Internally they are convex, curved and tapering, with stout, somewhat serrate reversed V-shaped transverse ridges.<sup class="reference" id="cite_ref-Annandale_1924_2-32">[3 ] The intestine after leaving the gizzard bears three small, almost spherical, diverticula, one behind the base of each of the chitinous plates.<sup class="reference" id="cite_ref-Annandale_1924_2-33">[3 ] The wall of the intestine is thin and its structure simple; it has a single closely adpressed bend.<sup class="reference" id="cite_ref-Annandale_1924_2-34">[3 ] Drawing of penis-sack of Bullacta exarata.Drawing of penis extracted from the sack.Drawing of stylet extracted from the penis.Reproductive system: The male intromittent organ is provided with an elongate chitinous stylet.<sup class="reference" id="cite_ref-Annandale_1924_2-35">[3 ] The penis is enclosed in an oval sack.<sup class="reference" id="cite_ref-Annandale_1924_2-36">[3 ] When extracted therefrom it is an almost cylindrical organ with two coils, or constrictions, in its course, bluntly pointed at the apex and much contracted proximally.<sup class="reference" id="cite_ref-Annandale_1924_2-37">[3 ] Its walls are highly muscular, but all the muscles are longitudinal and there is no circular muscular bulb.<sup class="reference" id="cite_ref-Annandale_1924_2-38">[3 ] Its outstanding feature is the presence of a long, slender, sharply pointed, scimitar-shaped, black, horny stylet with a saddle-shaped base which is sometimes prolonged into a long, sharply pointed spur.<sup class="reference" id="cite_ref-Annandale_1924_2-39">[3 ] In some individuals, however, the spur is completely absent.<sup class="reference" id="cite_ref-Annandale_1924_2-40">[3 ]

The female genitalia include a well-developed uterus but no spermatheca.<sup class="reference" id="cite_ref-Annandale_1924_2-41">[3 ] The hermaphrodite gland is small in immature specimen.<sup class="reference" id="cite_ref-Annandale_1924_2-42">[3 ]

Nervous system: The central nervous system closely resembles that of Atys cylindrica.<sup class="reference" id="cite_ref-Annandale_1924_2-43">[3 ]

[edit] Ecology
The habitat for this species includes intertidal flats, including the supratidal zone and subtidal zone.<sup class="reference" id="cite_ref-Ye_2001_Analysis_9-1">[10 ]

Bullacta exarata is a hermaphroditic species.<sup class="reference" id="cite_ref-Du_2010_10-1">[11 ]

Its life cycle has been extensively studied: Bullacta exarata feeds on diatoms.<sup class="reference" id="cite_ref-Malaquias_2010_0-5">[1 ] It is an important consumer in the tidal flat ecosystem.<sup class="reference" id="cite_ref-Ye_2001_Analysis_9-2">[10 ]
 * Vitellogenesis (Ying & Yang, 2001)<sup class="reference" id="cite_ref-12">[13 ]
 * Oogenesis (Ying, 2002)<sup class="reference" id="cite_ref-13">[14 ]
 * Spermatogenesis (Ying et al., 2002)<sup class="reference" id="cite_ref-14">[15 ]
 * Reproductive system (Ying et al., 2002)<sup class="reference" id="cite_ref-15">[16 ]
 * Spermatozoa (Ying et al., 2004)<sup class="reference" id="cite_ref-Ying_2004_6-1">[7 ]

Bacteria identified in the digestive system of Bullacta exarata include the genera Photobacterium, Bacillus, Pseudomonas, Vibrio, some genera from the family Enterobacteriaceae and others.<sup class="reference" id="cite_ref-Wang_2002_16-0">[17 ]

According to the measurement of hygienic indicator bacteria Escherichia coli in 2001, the meat of Bullacta exarata meets national standards (3 cells of Escherichia coli in one gram of fresh meat) in Shanghai province and in most of Zhejiang province.<sup class="reference" id="cite_ref-UNEP_2005_17-0">[18 ]

Heavy metals in the tissues of Bullacta exarata from the Yangtze Estuary were measured by Lu et al. in 2001.<sup class="reference" id="cite_ref-18">[19 ] In Shanghai, the coast is seriously polluted<sup class="reference" id="cite_ref-UNEP_2005_17-1">[18 ] and measured pollutants in the meat of Bullacta exarata were in 2003 as follows:
 * 20.70 mg of petroleum hydrocarbons in one kg of wet weight (exceeds grade I of biological standard)<sup class="reference" id="cite_ref-UNEP_2005_17-2">[18 ]
 * 13.10 mg of zinc in one kg of wet weight<sup class="reference" id="cite_ref-UNEP_2005_17-3">[18 ]
 * 33.60 mg of copper in one kg of wet weight (exceeds grade II of biological standard)<sup class="reference" id="cite_ref-UNEP_2005_17-4">[18 ]

[edit] Human use
Bullacta exarata is a commercially important mollusc in eastern China.<sup class="reference" id="cite_ref-Ying_2004_6-2">[7 ] Common names in Mandarin Chinese include Tutie (Chinese: 吐铁; pinyin: Tǔtiě) and Niluo (Chinese: 泥螺; pinyin: Níluó).<sup class="reference" id="cite_ref-20">[21 ] It is exported as a food source to Hong Kong, Macau, Taiwan and to Southeast Asia.<sup class="reference" id="cite_ref-21">[22 ]

Mass mortalities of Bullacta exarata in Zhejiang in 1995 caused economic losses.<sup class="reference" id="cite_ref-Wang_2002_16-1">[17 ] The species is being cultivated in mariculture, especially in Zhejiang Province, where there was a cultivated area of 8,000 ha in 1999.<sup class="reference" id="cite_ref-Wang_2002_16-2">[17 ]

For example Bullact

a exarata was the main farming species at the farming area of about 10 100 mu (6.73266 km2) in the Cixi City, with an estimated annual output of 15 million RMB.<sup class="reference" id="cite_ref-22">[23 ]

Bullacta exarata has high nutrition value.<sup class="reference" id="cite_ref-Ye_2001_Analysis_9-3">[10 ] There is high amount of omega-3 fatty acids in the canned meat of Bullacta exarata (there is 600 mg of eicosapentaenoic acid in 100 g of meat).<sup class="reference" id="cite_ref-Siriamornpun_2006_19-2">[20 ]