Crab (páng xiè) is a crustacean, belonging to a decapod mollusk. Its body is protected by a hard shell and it breathes through its gills. Taxonomically, it is the same kind of animal as shrimp, lobster and hermit crab.
Most kinds of crabs live in the ocean or offshore areas, and some live in fresh water or land. Common crabs are Portunus trituberculatus, Portunus trituberculatus, Eriocheir sinensis and Eriocheir sinensis (Eriocheir sinensis, Eriocheir sinensis and Eriocheir sinensis).
Crab's body is divided into head, chest and abdomen. The head, chest and back are covered with head and breastplate, and the shape varies from species to species. There are 1 and 2 pairs of antennae in the center of the forehead, and compound eyes with stalks on the outside. The mouthparts include 1 pair of big jaws, 2 pairs of small jaws and 3 pairs of jaws.
There are five pairs of chest feet on both sides of the head breastplate. The abdomen degenerates, flattens and bends on the ventral surface of the head and chest. The male abdomen is long and narrow, mostly triangular, and only the first two pairs of appendages are deformed into connectors; The female has a broad abdomen, and there are 1 pairs of double-branched appendages in the 2nd to 5th sections, which are densely covered with bristles for holding eggs.
Most crabs are marine, with the most species in tropical shallow waters. A small number of crabs grow and breed completely in fresh water, and most of them live under rocks in mountain streams.
Methods of learning new words
1, make a study plan: set a certain number of new words to learn every day and stick to the plan. You can make a study plan according to your own time and ability, and gradually increase the difficulty and quantity of study.
2. Sorting: Sorting the learned new words according to different classifications, such as radicals, glyphs, phonology, etc. This can help memory and induction and improve the learning effect.
3. Read and write more: While learning new words, it is very important to read and write more. Through repeated reading and writing, we can deepen our understanding and memory of new words and improve our literacy.
4. Making a memory card: Write new words on the card, including font, pinyin, interpretation and other information. For easy memory and consolidation, you can use this word to write examples or words on the back of the card.