The original intention of this article is to know more about crabs, so that long-distance travel can catch catch and catch supplies, to achieve survival in the wild; cooking at home is handy, making people eat fingers; out of the meeting can smell the incense and get off the horse, bowen strong memorization without knowing half-understanding.
Become a museum traveler
And through this article, after many years of confusion, we have obtained correct knowledge, such as:
What are the types of crabs?
Are there many wild crabs?
How to catch it?
Why are hairy crabs so famous?
Is the river crab cooked or steamed?
How to eat the crab clean?
……
This article is nearly 30,000 words, the above three articles are examining the crab structure, various crabs, hairy crabs, the pictures come from museums, research websites and search engines, most of which have been carefully modified by myself to achieve scientific research purposes, if there is infringement, please inform.
Graphic descriptions should be accurate and concise
First, understand crabs with a scientific attitude
Crabs, crabs, including all crabs, are taxonomically a lower order, scientifically known as Brachyura.
Various crab species
1. Classification of crabs
Since the advent of clade taxonomy Cladistics in 1960 and the development of evolutionary biology Evolutionary Biology, the traditional taxonomy has undergone many changes, taking the Chinese river crab as an example, according to WoRMS in April 2019, the highest domain to the lowest genus species classification is as follows:
Chinese river crab
Animal kingdom Animalia
-Arthropoda Phylum Arthropoda
--Crustacea
--- Soft Armor General Order Multicrustacea
---- Soft-nailed Maracostraca
----- eucalyptus subclass Eumalaccostraca
------ Eucarida, the head of the real shrimp
------- Decapoda
-------- egg-hugging suborder Pleocyemata
--------- brachyura, the lower order of the short-tailed
---------- Crab Pie Eubrachyura
----------- chest aperiostemato Thoracotremata
------------ crab family Grapsoidea
------------- Varunidae of the family Varunidae
-------------- subfamily Varuninae
--------------- genus Eriocheir
---------------- Chinese river crab Eriocheir sinensis
Arthropods are the most species in the animal kingdom, it is said that more than 750,000 species of insects have been named by humans, there are currently 58,008 species verified and accepted by WoRMS, and there are 4 subphylums that are still alive, a total of 17 orders, such as insects, arachnids, crustaceans, etc.; their common features are segmented limbs, and the main component of exoskeletons is chitin.
Various arthropods
Crustaceans, also known as soft beetles, including true soft beetles, leaf shrimp, skimmed shrimp a total of 3 subclasses, 32870 species, is the crustacean subphylum the largest number of species, and the true soft beetle suborder is divided into real shrimp, proto shrimp, cystic shrimp 3 general orders, of which the true shrimp is further divided into decapods and krill orders 2 orders. The main features of the carapacea include the body is generally divided into 21 segments, fixed or located on the rod compound eye, etc.
Decapods are the most familiar to humans, and various lobsters and crabs are members of this order; in 2009, it was estimated that there were 2,700 genera, about 15,000 species, and in 2019 WoRMS recognized 13,444 species. According to the different gill structures, this order is divided into the suborder Oviduct and the suborder Phyllonorycter. Important features of the decanter order include: the body is divided into cephalothorax and abdomen; there are eight pairs of thoracic limbs, the first three pairs are called jaw feet, and the last five pairs are called step feet, that is, full feet.
The Australian part is full of order
Egg-hugging suborder, also known as the suborder Epidermomorph, has a total of 11 suborders, such as short-tailed, hetero-tailed, claw-less, proto-shrimp, true shrimp, crayfish, carved shrimp, nail shrimp, sheath shrimp, and scorpion shrimp; their most important features are: after fertilization, the eggs are stained on the female gastropods before hatching, so they are called egg-hugging; most of this suborder is edible, and it is a type of crustacean of the greatest economic significance, of which the short-tailed suborder is crabs in the popular sense.
Short-tailed order, relative to the shrimp these long-tailed animals, the tail beetle of the crab has evolved into the abdomen, short enough to no longer be seen, so called short tail; there are 5871 species in the world, the number listed by the wiki is 93 families 6793 species, China has about 800 species; according to different regions, it is divided into sea crabs, river crabs, lake crabs, etc., among them, relative to sea crabs, other crabs are commonly known as land crabs, that is, freshwater crabs, about 1300 species. There were many sects before the order Brachycephalus, after 2016, according to genetic comparison, it was uniformly divided into limb hole sect and crab sect, and there were only 5 general families under the limb hole school, and the crab school was divided into heteroporous subpopulation and thoracic subporain according to different reproductive hole positions, of which the heteroporous subporain contained 30 general families, while the thoracic subfamily only had 4 general families of square crab, sand crab, bean crab, and hidden crab; the square crab family was further divided into bow crab, ground crab, square crab, carved square crab, strange square crab, oblique crab, phaset crab, Percnidae, Leptograpsodidae et al. 9 families.
Schematic diagram of the classification of Chinese river crab
The bow crab family contains 6 subfamily, of which the bow crab subfamily is divided into 20 genera, and there is a genus of river crab in these 20 genera, which is divided into 4 species according to the different lateral teeth, one of which is called the Chinese river crab.
The latest WoRMS determines that there are 4 species of river crabs:
E.japonica De Haan, 1835
E.sinensis H. Milne Edwards,1853
E.hepuensis Dai, 1991
E. ogasawaraensis Komai, Yamasaki, Kobayashi, Yamamoto & Watanabe, 2006 (less common)
The newest genus of river crabs eliminates two species of river crabs, narrow-fronted and straight-fronted
Many encyclopedia books or popular science magazines still use the previous and even pre-60s divisions, such as the special curated column of the October 2018 issue of "Museum", which mentions real crabs, which are divided into six major families according to the previous ones: pike crab family, square crab family, sand crab family, fan crab family, stream crab family and corset crab family.
Another example is "Chinese Zoology", "Chinese Marine Crab", "Chinese River Crab Biology", etc., using the division of the decanter order into swimming suborders and reptile suborders before 1960, many of which are very loose descriptions, such as the three-warty pike crab, whose forehead features are recorded as 2 frontal teeth, and my actual observation is not so, it is very doubtful, fortunately, the Ministry of Agriculture of the People's Republic of China issued a national standard on September 29, 2006, the authoritative definition is "the frontal margin has 2 -6 small teeth, generally 4" Another example is the subfamily Varuninae H. Milne Edwards, 1853 written as Varuninae Alcock, 1900, the subfamily Varuninae of the bow crab subfamily Varuninae as the square crab family Grapsidae, and so on.
There are more articles on the Internet that are misused, misused, and misused, and I will not count them here. It is not that WoRMS or EOL is correct, in fact, the classification of crustaceans has always been very chaotic, with the advancement of technology, the concept is updated, it will certainly be reclassified in the future, but now, WoRMS has concentrated the world's most serious and authoritative biologists, through molecular genetics and the study of sperm structure, etc., to change our usual plausible cognition.
2. The evolution of crabs
About 3.5 billion years ago, life began to appear in the oceans. According to scientific measurements, at least 5 billion species have existed on the earth, and some scholars even believe that more than 1 trillion species, of which 99% have been extinct.
Fossils of crustaceans are few, with the earliest appearance of hard-shelled organisms dating back to the Cambrian Period, 540 million years ago. The ancestors of most modern animals were born during the Cambrian explosion of life, including sites such as the Burgess Shale in Canada and the Chengjiang Fossil Site in Yunnan Province. Some people on the Internet believe that the living fossil horseshoe crab hòu, which began to appear 500 million years ago, has to shed its shell 16 times in a lifetime, and is the ancestor of all crustaceans, in fact, the horseshoe crab belongs to the limb orthopere of the arthropod phylum, and can only be said to be relatives of crustaceans at best.
Chengjiang Hat Tianshan Fossil Land
The oldest crab fossils were found in Argentina, archaeologically identified as the Jurassic period 150 million years ago; more Cretaceous crab fossils have been found, suggesting that crabs also began to migrate around the world as the continents drifted and the bony fish radiated. Fossils closer to the crab family are the general family of crabs under the subphyllae of the limb-hole crab family, which is dated to the Daning period 65 million years ago, the first stage of the Paleocene, the non-avian dinosaurs of this period have become extinct, and most terrestrial animals have begun to show a miniaturization trend.
Jurassic crab fossils from Argentina
5.3 million years ago, in the Eocene, Spain began to appear pike crab fossils, Haikou Museum has a large-eyed crab fossil of the sand crab family, beijing natural museum also has several pieces of burr crab fossils, it is said that Tanzania also found freshwater crab fossils, and the bow crab family under the river crab family has not yet had any fossils. However, some scholars believe that by 1 million years ago, the shape of river crabs was fixed as we see them now, and at the same time, in order to survive, they also changed from vegetarian to omnivorous.
Portunus catalaunicus - Anoia, Catalonia, Spain
Around Taihu Lake, the Majiabang ruins 7,000 years ago, the Songze ruins 6,000 years ago, and the Liangzhu ruins 5,000 years ago, among the Neolithic cultural relics excavated, the crab bones in the clay kettle and the crab shells thrown after eating have been found one after another, proving that the ancestors of Taihu Lake had long had the habit of eating crabs; in addition, there are sites such as the Jiangxi Wannian Immortal Cave and the Guangxi Dalongtan Carp Mouth, which have unearthed crab remains. However, it was not until the pre-Qin Dynasty more than 2,000 years ago that there began to be written records detailing the expression of hairy crabs.
3. The structure of the crab
Most crabs have a flat back and a flat abdomen, and the body consists of a cephalothorax, abdomen, and appendages.
Cephalothorax shell is called cephalothorax, also known as dorsal carapace, the shape varies from species to species, the surface is uneven, divided into several areas, these areas correspond to the liver, stomach, heart, intestine, gills and other internal organs one by one; the edge includes the frontal edge, the eye edge, the anterior lateral edge, the posterior margin and the posterior edge; the bottom shell is composed of 7 symmetrical abdominal carapaces, of which the 1st-3 sections are usually healed together, commonly known as crab belly, and the middle is the inguinal groove. The cephalothorax and abdominal carapace are the bones of crabs, also called exoskeletons; the dermis of exoskeletons contains astaxanthin that is not afraid of high temperatures, so most crabs look red when cooked.
The back of the crab
Different crabs have different hearts, for example river crabs are generally hexagonal. The circulatory system of the crab first presses the blood out of the heart, flows through the whole body through several arteries, supplies nutrients and oxygen to the tissues, and absorbs the carbon dioxide and metabolites into venous blood, and then enters the gill blood vessels through the chest sinus, exchanges gas with the oxygen dissolved in the water, and the venous blood becomes back into the arterial blood, and then flows into the heart cavity to the heart, so that the cycle is repeated to complete the breathing process. The gills are the respiratory organs of the crab, with a total of 6 pairs on both sides, divided into gill axes and gill leaves, juxtaposed with each other, shaped like eyebrows, grayish white, while the land crab adapts to land life, the gill cavity is enlarged, the function is like a lung, and the morphology changes.
Schematic diagram of crab gill breathing
Above the heart is the stomach, most of which are triangular cone-shaped, dividing the cardia stomach and the pyloric stomach. The cardia stomach is a capsule, the inner wall has calcium teeth and comb bone formation chewer, also known as gastric grinding, the function is to store and grind food, so the sac often has dead fish rotten shrimp, duckweed algae; the pylorus is connected to the midgut and extends to the hind intestine of the abdomen, the end of the hind intestine is the anus, and the opening is in the 7th section of the abdomen.
Crab stomach
The male crab has two milky white sperm nests, located on both sides of the stomach, there is a vas deferens under the sperm nest, the front end of the vas deferens is thin, the posterior end is large, it is a sperm reservoir vesicle, the posterior seminal vesicle is the paragonads, secreting a milky white viscous substance; after the ejaculatory duct and the paragonads converge, the 8th section of the chest generates a penis, about 0.5 cm long, and the opening is the reproductive hole; the sperm nest, vas deferens, paragonads and ejaculatory ducts are white paste. Female reproductive organs include the ovaries and fallopian tubes, the ovaries are H-shaped, when ripe, they are sauce purple, commonly known as "red paste"; the ovaries have a pair of very short fallopian tubes, and the end of the fallopian tubes is attached to a nanocentrosceros, and the opening is the reproductive foramen, located in the 6th thoracic segment.
reproductive system
Liver pancreas, commonly known as crab yellow, is an important digestive gland of crab, the left and right lobes are composed of many fine branches of blind tubes, there is a pair of liver tubes into the midgut, transporting digestive juices to help digest food; healthy liver and pancreas are orange.
Schematic diagram of liver and pancreas
The abdomen, most of the crab's abdomen degenerates and folds below the cephalothorax, commonly known as the umbilicus, with a total of 7 segments, the first 3 segments are somewhat healed together. In the crab stage, the crab navel is pointed, long striped, after growing up, the male abdomen becomes narrower, in an isosceles triangle, called the pointed umbilicus, while the female abdomen becomes wider, almost semicircular, commonly known as the umbilicus, but there are also several crabs, whether male or female, crab umbilicus is the same.
The belly of the crab
The appendages are distributed in the head, chest and abdomen, and have different functions in different positions, and different functions and different forms, but they are composed of the original limbs, the inner limbs and the outer limbs; like the shrimp, except for the first cephalic segment, there is no appendage, but a pair of compound eyes with a handle, and other body segments have a pair of appendages.
There are 2 pairs of head appendages, namely the first and second antennae, the first antennae are bilimb, very short, with a balancer inside, the second antennae are single-limb type, which is also very short, and there are water holes below the base, that is, urine excretion holes; both pairs of antennae have tactile and olfactory functions. The compound eye on the outside of the second antennae, with a viewing angle of up to 180°, has a regenerative function, but if both the eyeball and the eye handle are damaged, only one antennae can grow in the eye socket, not a new eye.
head
The mouthparts in the mouth, from the inside to the outside, are the large jaws, the first and second small jaws, and the first, second, and third jaw feet, in which the large jaws are used to tear food. The shape of the mouth frame is one of the main bases for crab classification.
There are five pairs of appendages on both sides of the chest, also known as pectoral feet, of which the first pair is particularly strong, with predatory, digging, defensive functions, called claws, above the base is a water hole, generally male cray feet are larger than females; the last four pairs are called step feet, with crawling, swimming, digging functions. The thorax foot is divided into the bottom segment, basal segment, seat segment, long segment, wrist segment, palm segment (anterior segment), and knuckles from the proximal body to the end; the thorax and foot have regenerative functions, and the foot also has the ability to distinguish taste.
Step foot with claw foot
Abdominal appendages, male crabs have 2 pairs, single limb type, located on the 1st and 2nd abdominal segments, tubular and stick-shaped, has evolved into a joint, also called reproductive limbs, used to transport sperm pods during mating; female crabs have 4 pairs, bilimb type, located on the 2nd to 5th abdominal segment, the inner limbs are densely covered with thin and long bristles, about 30-40 rows, used to hold eggs, and the bristles of the outer limbs are thick and short, playing a role in protecting the egg population. The appendages of the abdomen are also one of the important bases for classification.
Abdominal appendages
Crabs have very sensitive ganglia, and when humans or other creatures get close to 9 meters, they all hide. In addition, the bristles of river crabs also have a tactile function.
Crabs in different places have evolved different body structures, some run fast, such as the horn-eyed sand crab, the fastest speed of 2 meters per second, and some will climb, such as the folded crab, the tail foot with a hook, can firmly nail the body to the tree, and some will swim, such as saw-edge frogs, the procession speed reaches more than 1 meter per second.
A pike crab swimming on its tail foot
4. The growth of crabs
From the perspective of developmental biology, the life of crabs is divided into five stages of embryonic development, larval development, adult development, gonadal development and mating and spawning, and the specific growth process is summarized as follows: fertilized eggs - flea larvae - big-eyed larvae - juvenile crabs - adult crabs; different species of growth stages are different, such as river crabs, in addition to experiencing fertilized eggs, flea larvae, big-eyed larvae (crab seedlings), as well as baby crabs (bean crabs), juvenile crabs (buckle crabs), yellow crabs (June yellow), green crabs (adult crabs) and brood crabs and a total of eight stages.
5 growth stages of crabs
The crabs have different mating styles, most of them in missionary positions, which last from a few minutes to several days. After mating, the female crab soon lays eggs, and fertilizes with the sperm of the seminal vesicle, and then releases the fertilized egg, holding it with the bristles of the abdominal limbs until it hatches the larvae; the number of eggs held by different crab species varies greatly, from tens to millions, such as stream crabs are generally thousands, river crabs are millions, and can be produced 2 to 3 times.
The number of eggs held varies significantly
The newly hatched larvae are very small, usually only 2 to 3 mm, and the appearance is completely different from that of adult crabs, tiny and transparent, or with bone spurs, like water fleas, so it is called flea larvae. They follow the waves and feed on microorganisms; the flea larvae molt many times, such as the river crab, which generally 5 times, and gradually increase in size to become large-eyed larvae.
Pike crab flea larvae
The big-eyed larvae are shaped like spiders, have a small tail, have a certain ability to swim and climb, and feed on plankton; at this time, the big-eyed larvae are more like crabs, but the abdomen is larger and does not fold under the chest. After several molts, the big-eyed larvae gradually translucent, the tail begins to contract under the chest, and after the last molt, it becomes a juvenile crab.
Barracuda crab big-eyed larvae
Morphologically developed juvenile crabs, in addition to the splicer will change, the shape has been fixed, after which the molting shell is called the growing molting shell, and the mating period molting shell is called the reproductive molting shell, which is also the last molting shell. The molting shell of the larval body is also called the developmental metamorphosis molting shell, because with each molting, the morphological structure of the crab will change until it is perfected.
A spider crab is molting its shell
How many times does a crab molt in its shell in its lifetime? Different crab species, places, and periods will produce different numbers, which cannot be determined. The carapace is a lifeless hard structure that cannot expand with the growth of the body, so crabs must molt after a period of time, and at the same time molt off the attachments and parasites on the carapace through molting, so the molting shell is of great significance for the survival and growth of crabs. There are articles on the Internet in order to boast about the "soft shell crab", but even the idiom of reborn and reborn, saying that the crab not only sheds the exoskeleton, but also leaves the stomach, gills, the skin of the intestine and the 3 tooth plates of the stomach grinding in the old shell, which I once believed to be true.
Some crabs also undergo a migratory process, such as wild river crabs, which undergo two migrations from birth to death:
The first is the bait migration of juveniles, that is, the river-tracing migration. After the fertilized eggs have developed into juvenile crabs, they begin to travel to freshwater areas, encounter rivers or lakes with abundant bait, and burrow or retreat for about 18 months.
The second is reproductive migration after maturity, that is, the migration of descending rivers. In late autumn and early winter, the gonads of river crabs mature and begin to migrate to the offshore areas to breed and lay eggs, because river crabs must maintain osmotic balance when ovulating, otherwise they will cause edema and death due to different pressures, which is the source of "autumn wind, crab feet itch".
Schematic diagram of Chinese river crab migration
But there are also 1300 species of freshwater crabs, do not need to go to the beach to breed, because they have evolved a pattern of direct development in the egg, that is, do not go through the larval stage of metamorphosis development, but develop into juvenile crabs and then leave the mother crab, juvenile crabs are much larger than the larvae, and therefore, freshwater crab offspring are not many, and some species are even endangered.
The hatched baby crabs are still protected by the mother crab under her belly
Crabs in the natural environment are generally plant-feeding, such as seaweed, duckweed, manjiang red, water hyacinth, goldfish algae and other aquatic plants, sometimes also eat microorganisms, insects, etc., depending on the species, but the vast majority of crabs especially like to eat carrion; eat different foods, crab paste will also show different colors, with algae as the main food, crab paste is generally green, mainly microbial food, crab paste will be yellow. The image below shows a drop of seawater magnified 25 times and you can see that the surrounding crabs are full of food.
David Littschwager《One Dip of the Hand Net》
5. The distribution of crabs
More than 80% of crabs live in the sea or part of their life history is related to the marine environment, such as square crabs and sand crabs living in the tidal zone, frog crabs, steamed crabs and pike crabs living in the offshore sea, spider crabs living in the deep sea; a very small number such as drifting crabs live on wood or other floating objects, and bean crabs, cotton crabs, Guan Gong crabs, etc. live in symbiosis with other animal camps.
The sediment bottom crabs in Taiwan are distributed vertically
It should be pointed out that river crab is an important fishery crop in China, and the naturally grown river crab is divided into several populations of Liaohe River, Yellow River, Yangtze River, Oujiang River and Minjiang River from north to south, while farmed crabs are represented by the Liaohe River system and the Yangtze River system, which has the highest yield in Panjin City, Liaoning Province, and the Yangtze River system is the most famous in Suzhou, in addition, Xinjiang, Qinghai, and Inner Mongolia also have many lakes that have successfully raised river crabs, and even the development of large cities can also open "river crab apartments".
The distribution of crabs will be specific to which one, described in the next article.