Sexual reproduction - the unique point of the species

Many people think that the claw is like asexual worm by breaking up to multiply new individuals, but in fact it has a continuation of two asexual and sexual methods.

These days, people in coastal provinces such as Hai Duong, Thai Binh and Thanh Hoa are hunting nests - animals that bring high economic value with VND 100 million per day. However, the number of reefs is decreasing, because they are picky of their living environment and the farming is not easy.

The clam has the scientific name Tylorrhynchus heterochaetus , is an invertebrate, belonging to the polychaete class, many places are called earthen dragons . There are many views on the distribution of the ridge, but the majority of scientists believe that they are often concentrated in brackish waters of Vietnam's coastal estuaries.

According to a research work on the ridge by author Nguyen Quang Chuong (Center for Monitoring - Research Institute for Aquaculture No. 1), the main breeding season of the ridge is May 6 (the year of the circus) and October-November. (spring season). From January to June, due to the rising tide at night, the reef migrates to reproduce at night. When migrating they do not float to the surface but sink 20-30cm from the bottom. In addition, the spawning spawns scattered throughout the months of the year.

Experts say that the number of reefs is decreasing due to being fully exploited in the breeding season to serve the needs of people.(Photo: Ngoc Thanh).

The migration of the ridge is affected by turbidity and salinity in the tide. Evidence is that in the two months of November and December - when the salinity in the water is highest, it is also the time when the spawning spawns the most quantity. Therefore, the exploitation output of this two months is very large.

In the project "On some biological characteristics and reproductive season of the species in the northern coastal region of Vietnam" (1999), the author Pham Dinh Trong discovered that the lunar calendar appeared 6 lunar months in the year including 4 , 5, 9, 10, 11, 12 (equivalent to May, June, October, 11, 12 and January of the solar calendar). The author also mentioned three factors related to the appearance of the ridge are weather, tide and light.

The form of reproduction is the unique point of the claw. Many people think that the claw as well as those in the house of asexual worms by breaking up to multiply new individuals, but the reality in the reef has the continuation of two asexual and sexual methods.

Dr. Le Hung Anh (Institute of Ecology and Biological Resources) said that in order to create a surface flock in the breeding season, the mother cut her body into sexual individuals. These individuals quickly regenerate their heads, tails and are filled with sexual products, in which females contain eggs, males contain sperm.

While the mother reborn her tail and stayed in the bottom, sexual individuals with stout bodies filled with sexual products would come from the bottom of the river, rice fields, sedge swamps and emerge into herds. They both swim and twist themselves to release eggs and sperm into the water environment. After releasing all sexual products, the individual will die.

However, when they have just surfaced, people have been collected for food or waiting for hunting by shrimps, crabs, fish and waterfowl. However when a spawning individual is hunted, the cuts on the body, egg or sperm still escape into the water environment to proliferate the next generation.

The blade has long been a nutritious dish and has a high price of more than half a million VND per kilogram.

After fertilizing eggs with sperm quickly develop through larval stages that characterize the earthworm as Trocophora. After some metamorphosis, the Trocophora larvae turned into Metatrocophora , then Nectochaeta and eventually became adult worms with the same body composition as the mother. Thanks to active feeding, larvae can accumulate fat in their bodies so they don't sink. When the body is fully developed like mature individuals, the fat gradually disappears, the body weight increases and they sink to the bottom and settle at the bottom.

When floating on the water, the viewer will see the color of the fringe different between the male and the male. Females are light yellow, 60-90mm long, 5-8mm wide; males are blue, about 60mm long, 3-5mm wide.

The blade has long been a nutritious dish and has a high price of more than half a million VND per kilogram. Scientists said that the number of species is decreasing, because the demand for this species is increasing, so in the breeding season they are fully exploited. In addition, the use of chemicals and pesticides in agricultural production has reduced resources in recent years.