The so-called freshwater crab, as the name suggests, refers to crabs that live in freshwater streams. Their entire life history is almost spent in the freshwater environment, fertilized eggs in the development process without going through the planktonic larval stage and directly develop into juvenile crabs, which to a certain extent limits the ability of freshwater crabs to spread offspring, so many freshwater crabs are often limited to scattered small areas, forming a local endemic species.
China is the country with the richest variety of freshwater crabs in the world, with as many as 311 species, far more than the 101 species in Thailand and Colombia. The province with the largest number of freshwater crab species in China is Yunnan, and 50 species of 16 genera have been recorded. In natural waters, freshwater crabs are a key species in the freshwater large invertebrate taxa, and are also indicator organisms of the aquatic ecological environment, but there are relatively few literature related to the classification of freshwater crab systems in China.
This article aims to summarize and classify freshwater crabs in China and introduce common species, without further ado, let's get to the point.
<h1 class= "pgc-h-arrow-right" > First of all, it is necessary to first clarify the difference between freshwater crabs and marine crabs</h1>
Speaking of freshwater crabs, many people first think of the Chinese velvet crab, and the most representative brand is the Hairy Crab of Yangcheng Lake. However, the Chinese downcreed crab is not a freshwater crab in the strict sense (narrow sense), it grows and fattens in freshwater rivers, but the spawning and hatching is done offshore, belonging to the intermediate species that transition from seawater to freshwater. In terms of taxonomy, the Chinese river crab belongs to the square crab family, and in China, the freshwater crab in the strict sense refers to the taxa of the quasi-land crab family (bonded crab family) and the brook crab family.
From the appearance, the back of the freshwater crab is similar to the round, such as the Huaxi crab, while the marine crab is mostly similar to the fusiform, such as the three-wart pike crab. Most marine crabs are very bright in color, and the color difference between different species is very large, while the body color of freshwater crabs is generally close to blue-gray, which has a lot to do with their living environment.
In order to adapt to their respective environments, marine crabs and freshwater crabs have evolved different adaptive characteristics, the most obvious manifestation of which is in the legs. Freshwater crabs have sharp legs that are suitable for crawling on land, and most typical seawater crabs have their last pair of stepping feet specialized into paddle-shaped feet (also called swimming feet), but there are exceptions, and some seawater crabs that are not good at swimming also have needle-shaped limbs, such as Alaskan king crabs, deep-sea spider crabs, etc. Therefore, the characteristics of the foot are only for reference and cannot be used as the final basis for judgment.
< h1 class= "pgc-h-arrow-right" > the external morphological structure of crabs</h1>
Both marine crabs and freshwater crabs belong to the order Decapods, which is also the largest order in the subphylum Crustaceans, containing more than 9,000 species of shrimp and crabs. The body structure of the crab can be divided into cephalothorax and abdomen, divided into 5 pairs of appendages, of which the first appendage is specialized as a claw, which is used to attack prey and eat, the 2nd to 4th appendages are step feet, which are the main motor organs, and the 5th appendage is often specialized into paddles, which is an important indicator to judge its swimming ability.
Some friends may think of Xun Zi's "persuasion" in the "crab six kneeling and two claws" a sentence, "six kneeling" plus "two claws" is eight appendages, but in fact crabs have ten appendages, is there any misunderstanding?
Some scholars believe that the "six" in the ancient text is actually a mistake of "eight", and some people believe that the ancient text is not written wrongly, of which "kneeling" should be understood as the 2nd-4th step foot, and does not include the 5th pair of paddle-shaped feet, which also reflects the meticulous observation of Xunzi. For this issue, we also welcome you to continue to discuss it in the comment area!
1. The back of the cephalothorax of the crab is covered with cephalothorax, and the shape varies from species to species. The center of the forehead has the first and second pairs of antennae, and the outer side is a compound eye with a stalk. The mouthparts consist of 1 pair of large jaws, 2 pairs of small jaws and 3 pairs of jaw feet.
2. There are 5 pairs of pectoral feet on both sides of the cephalothorax. The abdomen is degenerate, flattened, and zigzagging on the ventral surface of the cephalothorax. The abdomen of the male is narrow and long, mostly triangular, with only the first two pairs of appendages deformed into a joint; the female abdomen is broad, with 1 pair of double-branched appendages in the 2nd to 5th segments, densely covered with bristles, which are used to hold eggs.
▲The above pictures are female and male Chinese velvet crabs. The distinction between male and female crabs on the ventral surface of the body is clear at a glance, and will not be repeated here.
<h1 class = "pgc-h-arrow-right" > the quasi-native crab family (contains only 1 genus, 28 species, or 9% of the total).</h1>
▼ A common species of the quasi-land crab family
Gecarcinucidae Rathbun was also known as the corset crab family before, and later changed its name to the quasi-land crab family with the continuous discovery of new species, representing the Species of Chinese Corset Crab.
As the name suggests, the width of the middle section of the abdomen of the corset crab is narrower than before and after, much like the ancients wearing a corset Hanfu form, the abdomen has a total of 7 sections, negative upwards, from top to bottom, from the 5th section to become narrow and wide, the 6th section is the corset section, and the 7th section is tongue-shaped.
<h1 class = "pgc-h-arrow-right" > brook crab family (containing 283 species in 44 genera, 91% of the total).</h1>
The following is a brief introduction to the common types.
01 Genus Qingxi crab (type species: Qingxi crab)
There are 4 species of Qingxi crab in the world, and there is 1 species in China, that is, The Qingxi crab of Lashi, which is mainly distributed in Taiwan, the treasure island of China. According to Professor Dai Aiyun's record in 1999, there are two kinds of Qingxi crabs in China, namely La's Qingxi crab (found in 1914) and Guangdong Qingxi crab (discovered in 1999). However, after that, some experts and scholars conducted a comparative study of the specimens of Guangdong Qingxi crab and Lashi Qingxi crab, and found that there was no significant difference in morphology between the two, which speculated that the Guangdong Qingxi crab found in 1999 was likely to come from Taiwan, and the two were most likely the same species.
02 Yuexi crab genus (type species: Zhuhai Yuexi crab)
There are 4 species of Yuexi crab in China, all of which are distributed in Guangdong Province, and Zhuhai Yuexi crab is a new model species discovered by Ahyong and Shih in 2017.
03 South China Sea Creek Crab Genus (Type Species: South Sea Creek Crab, Taiwan)
There are a total of 16 species of Nanhai creek crabs in China, most of which are named after the place names of the species first discovered, and the common ones are Guangdong Nanhai creek crab, Taiwan Nanhai creek crab, Fujian Nanhai creek crab, Hong Kong Nanhai creek crab, Wenzhou Nanhai creek crab. Among them, there are morphological differences in the same species of Guangdong Nanhaixi crab, and the identification of this species must not only refer to morphological indicators, but also accurately determine according to 16S rDNA sequence analysis.
Guangdong Nanhai creek crab
For example, in 1997, China's biologists found two kinds of South China Sea Creek Crab in Guangdong Heping, named Heping South Sea Creek Crab and Pinghe South Sea Creek Crab, when experts set it as two different species according to morphological differences, and later after 16S rDNA sequence analysis, it was shown that these two samples should be the same species, and the morphological differences were only adaptive characteristics formed in different environments.
04 Genus Huaxi crab (type species: Potamon davidi Rathbum 1904)
Huaxi crab
There are 85 species of Huaxi crabs in China, basically distributed near the Yangtze River Basin, Huaxi crabs are also the most abundant species diversity of endemic freshwater crabs in China, accounting for 27.3% of the total number of freshwater crabs. The traditional classification of Huaxi crab is based on the structure of the cephalothorax, the large claw, and the two lobes of the terminal section of G1. In 2016, Shih et al. found that there were obvious defects in the original classification method of Huaxi crab species, such as spoon-fingered Huaxi crab and concave-fingered Huaxi crab, although the first appendage of male crabs met the standard characteristics given, but the G1 segments of these two crabs were rectangular and watercress-shaped, respectively, which were significantly different from the cylindrical shape of other crabs.
At present, the species identification of Huaxi crab has risen to the level of mitochondrial genes and nuclear genes. At present, there are still omissions in the classification of Huaxi crab in the revised "Zoological Records of China", and it is urgent to adopt more advanced identification technology to further supplement and improve.
05 Ze crab (model species: Geothelphusa obtusipes stimpson 1858)
There are 37 species of crabs in China, accounting for 11.9% of the total number of freshwater crab species, and the number of species is second only to the genus Huaxi crab. Ze crab is mainly distributed in Taiwan Province, China, and is also found in the main island of Japan and the Ryukyu Islands abroad, and the main species are Dunzuzawa crab and Korean Ze crab.
There is also such a small story about the Korean-style Ze crab. According to reports, the Mingxing National Zoological Collection in Munich, Germany, has two specimens of Korean-style crabs from China, one of which was collected by Hans Sauter in 1906, and he recorded the location of the collection as "Yentempo, China", but after inquiring that Yentmpo is not a place name from the mainland, but is located in Kaohsiung City, Taiwan. Later, it was identified that this specimen was more like the Pingtung Ze crab (rather than the Korean Ze crab).
Korean-style crab
The collection point for the label record of another specimen is Qingdao, Shandong, but only one freshwater brook crab is produced in the Qingdao area of Shandong, that is, the plain Huaxi crab, so it is speculated that it is caused by the wrong label placement. Based on the current sampling survey, it can be preliminarily concluded that: .
06 Oriental Brook Crab (Type Species: Potamon Smithianum Kemp, 1923)
Oriental creek crab body bloated, also known as fat brook crab, there are 3 species in China, widely distributed in Yunnan, Guangxi, Sichuan and other provinces, northeast Thailand, southern Vietnam is also distributed.
07 Hainan Creek Crab (Type Species: Oriental Hainan Creek Crab)
The Oriental Hainan Creek Crab is different from the Oriental Creek Crab and the South China Sea Creek Crab above, and its head and thoracic carapace are swollen and large, and the back is raised front and back, and the division is not obvious. The two large jaws of the Oriental Hainan Creek Crab are asymmetrical, with blunt, slightly raised lobes on the back of the forehead, preferring to inhabit stream caves or mountain stream stones.
08 Genus Sino-Indian Brook Crab (Type Species: Potamon villosum Yeo &Ng, 1998)
The genus is distributed in the southwestern border of China, more distributed on the northeast border with India, and is also distributed in Southeast Asian countries such as Myanmar, Thailand, and Laos.
▲▲Incense temple in the Indian creek crab
▲▲Deng's Sino-Indian creek crab
▲▲Chin-style Chinese-Indian creek crab
09 Weixi crab genus (type species: Shanwei weixi crab)
There is only one kind of micro-creek crab in China, namely the Shanwei micro-creek crab, distributed in Guangdong, which is a new species officially named in 2014.
10 Qianguixi crab genus (type species: whipless Guixi crab)
Qianguixi crab
The genus was named in 2018 by the research team of Nanchang University, and the article about the discovery of this species was published in Biodiversity And Conservation, the specific name is, interested friends can consult it for themselves.
<h1 class="pgc-h-arrow-right" > how to solve the problem of freshwater crab feeding? </h1>
There are many species of freshwater crabs with special behaviors or body colors, which can be raised as ornamental crabs. The rearing of freshwater crabs is relatively simple and is mainly divided into the following points:
1. Preparation of breeding utensils and materials.
"If you want to do a good job, you must first use it", freshwater crabs have a high degree of adaptability to their living environment. Some prefer to inhabit the gravel grains, some like to hide under the bark leaves, some like to stay under the mossy boulders, in the breeding to fully respect the original living environment of freshwater crabs, try to create a similar environment.
Different crabs are suitable for different materials
For example, leopard point crabs raised in deep water environments are best raised in deep fish tanks. If it is a crab that lives in shallow water, such as the new inner stream crab and the South China Sea creek crab, the water level control should not be too high, so that it is convenient for crabs to breathe, and it is best to add stones, wooden stakes, coconut shells and other coverings in the tank.
2. Clean water quality
The water quality of mountain streams is mostly refreshing and clean, and some can even be drunk directly, so most freshwater crabs prefer clean water quality. If there is no condition, tap water can also be used as a water source, but be sure to remove the remaining chlorine before starting to raise crabs.
After a period of breeding, if the water quality deteriorates, it is necessary to replace the new water body in time. Stones, wooden stakes and other ornaments put into the water should also be cleaned, and conditionally disinfected before being put into the tank. In addition, calcium should be replenished to the water in time every once in a while to facilitate the smooth dehulling of freshwater crabs.
3. Freshwater crabs should not be polycultured as much as possible
The environment in the crab tank is relatively cramped, the living space of freshwater crabs is limited, coupled with a strong sense of territory and aggressive personality, so the vast majority of freshwater crabs are not suitable for polyculture with other types of crabs, and even some crabs and species are unbearable.
Error demonstration
Two crabs fight each other, and the smaller crabs take the initiative to remove their appendages if they feel threatened. Immature crabs also have the opportunity to re-grow appendages, but need to consume a lot of energy as a price, mature freshwater crabs once they lose their appendages are unlikely to grow again, which will greatly affect their survival chances and ornamental effects. Therefore, freshwater crabs should not be polycultured as much as possible.
4. If you want to see the feeding behavior of freshwater crabs, you can try feeding different baits
Like fish, freshwater crabs are out-and-out opportunists, and herbivorous freshwater crabs are not strictly vegetarians and will actively prey when meat is served. Nanning neixi crabs are good at catching insects, Nanhai creek crabs will catch small fish, and Longxi crabs like to eat algae, but they will not refuse organic detritus and bread worms. So if you want to observe more interesting feeding behaviors, try feeding with different baits such as red worms, bread crumbs, earthworms, grasshoppers, shrimp, and harvest worms, which may have unexpected results.
<h1 class="pgc-h-arrow-right" > the geographical distribution and research significance of freshwater brook crabs in China</h1>
The current survey results show that there are freshwater crabs in 24 provinces, municipalities, autonomous regions and municipalities directly under the Central Government in China, but there are still a large number of freshwater crabs that have not been found (the unknown species are expected to account for more than 60%). In China, Yunnan has the largest number of freshwater crab species, with 16 genera reported, a total of 50 species, followed by Guangxi, with 13 genera, a total of 37 species, Fujian and Jiangxi have 34 species and 33 species, respectively.
In general, Freshwater Crabs in China are mainly distributed in the provinces south of the Yangtze River Basin, while the number and number of freshwater crab species in the areas north of the Yangtze River are very small. The natural distribution of freshwater crabs has not been found in areas with cold environments, such as Tibet, Qinghai, Xinjiang, Ningxia, Liaoning, Heilongjiang, inner Mongolia, etc., mainly because freshwater crabs prefer wet, warm and dark stream environments.
Freshwater crabs live in a secluded environment, their habitat is highly fragmented, and they are not easy to detect. In 2017, the scientific research team found a new kind of Hell Creek Crab in the sinkhole in Anlong County, Guizhou, and in the same year, two new species were found in Lingyun County and Leye County, Guangxi, namely Clark Chinese Creek Crab and Dashiwei Chinese Creek Crab. Experts estimate that the number of freshwater crab species in China is likely to exceed 400 species, and more new freshwater crab species and even new genera are expected to be found in the underground caves, mountain streams and streams in the southwest region, as well as inaccessible Hengduan mountainous areas in the future.
The discovery of freshwater crabs is of great significance to improving the existing crustacean classification system, and some freshwater crabs also have certain ornamental value and edible value, and are expected to be developed into artificial breeds with local characteristics, so freshwater crabs have great market application potential in the future.
The above content refers to a large number of literature, but omissions are inevitable, please criticize and correct netizens! #Creek Crab # #Aquatic Product # #Crab # #我要上头条 #