Ark shells: mollusca (Mollusca) bivalve (Bivalvia) teeth (Taxodonta) ark family (Arcidae) ark shells belong to the marine economy shellfish. Distributed in the western Pacific Ocean, Japan, Korea, China coast. In China, from the Yalu River in the north to Guangxi in the south are distributed, Laizhou Bay, Bohai Bay, Liaodong Bay, Haizhou Bay and other shallow water resources are particularly rich.
Characteristics The shell of Arca inflata is firm, thick and wide, and both shells are convex; the left shell is slightly larger than the right shell. The ventral margin of the shell is rounded at the front end and slightly extended at the back end, which is long ovoid in shape. There are about 32 slightly convex and dense radial ribs on the shell surface, with square nodules on the ribs, which are more obvious on the left shell. The shell surface is covered with a layer of brown downy epidermis, which is the reason for the name of ark shell.
Biological characteristics Arca inflata lives in the sandy and muddy substrate in the shallow sea at a depth of less than 20 meters, with a depth of 2-10 meters more; it is also often distributed in the lower intertidal zone. They are shallow, and generally deepen with the growth of individuals, with the depth ranging from 3 to 10 centimeters. It is preferable to live in the inner bay where there is a moderate amount of freshwater inflow, and the salinity is generally between 21 and 28.8, and the water temperature varies between 0 and 32℃, so it is a species with wide temperature and wide salinity. It feeds on organic phytoplankton debris.
The cockles are dioecious, with a sex ratio of 1:1. The gonads of 2-year-old shells begin to mature. Female gonads are reddish-orange, while males are milky-white, which is more obvious at maturity. Breeding period is mostly in July to September; the water temperature is 25 to 27 ℃ for the bloom, salinity to 23.5 to 28.8 is suitable. Shell length of 3.5 to 4.0 centimeters of 3, 4-year-old shells can be oviposited 2.5 to 3 million grains at a time. Mature eggs are round. The diameter of the egg is 62～73 microns. The spermatozoa are tiny, with a total length of only 40 micrometers. During reproduction, sperm and eggs are discharged at the same time, fertilized in the water. 2 days shell formation, after more than 10 days the shell grows to 300 microns or so, from the planktonic life into the attachment life, secretion of filaments attached to the gravel, shells, macroalgae underwater and can cut off the filaments for prostrate activities, and then secretion of filaments to be attached to another. The shell length of a few millimeters of young shells still have filaments attached to other things. The growth rate of ark shells is related to the temperature, salinity and bait of the living water, and the fastest growth is at the age of 1, with an annual growth of 2.3 centimeters; at the age of 2, the shell length is 3.7 centimeters; at the age of 3, the shell length is 4.6 centimeters; and at the age of 4 or above, the growth is slow. The life span is up to 10 years.
Production Arkshells can be harvested almost all the year round except for the freezing and hot season. The main use of motorized fishing boats trawling operation. However, if trawling is carried out continuously for a long time, the substrate of the mudflat in the distribution area will be seriously damaged, which will affect the attachment and life of arkshells. Artificial culture of arkshells has also begun.
The meat of arkshell is fat, and can be dried in the sun in addition to being boiled and eaten fresh, and the shells can be used as raw materials for calcium carbide and cement, and can be crushed and used as feed for poultry and livestock.