Whales, dolphins, turtles and seals also live in water. Why are they not fish? Are they like fish in shape and structure? Big brother, big sister, tell me. Simple.

Well, do you want something simple or specific?

Let's talk briefly first, so as to make it easy for everyone to see: whales, dolphins and seals are viviparous mammals and advanced vertebrates. After a woman is pregnant, she gives birth to a baby in her stomach, regenerates, and needs to breastfeed for a while. Moreover, like terrestrial mammals, they have skin fur (less hair than terrestrial mammals), constant body temperature and developed physiological structure. For example, they breathe with lungs, and their hearts and brains are developed. After training, they can even perform performances to help humans complete some specific tasks.

Fish are generally oviparous, ovoviviparous and viviparous are rare. Belonging to lower vertebrates, the body temperature is not constant, and the physiological structure is relatively primitive and low-level. For example, they breathe with their gills, and the brain is more used as a conditioned reflex. Fish's memory can last about 5 seconds. . .

Morphological structure. . . Um ... They are streamlined and adapt to aquatic life. . .

You are so cute. . There are turtles. . .

Tortoise: They belong to reptiles. They are higher than fish and amphibians (frogs) and lower than birds and mammals. Breathe with the lungs, the temperature is not constant, and the eggs are laid.

More specifically:

Fish: A variable-temperature vertebrate that lives in water all its life. It breathes through gills and uses fins to assist its balance and movement, which is the lowest among vertebrates. Its morphological structure is not only related to systematic development, but also reflects its adaptability to water environment.

The skin of fish includes epidermis and dermis. The epidermis consists of several layers of living cells, in which mucus cells are distributed to reduce friction and protect the body. Zhu Xing is the product of keratinization of local epidermal cells, which is related to reproductive activities. The poison glands and luminous bodies of some fish are derivatives of epidermis.

The heart of fish generally consists of sinus, auricle, ventricle and conus arteriosus.

Fish scales are divided into shield scales, hard scales and bone scales. The scales of cartilaginous fish are called shield scales. Hard scales and bony scales are usually produced by dermis. The fish scales are arranged horizontally, which is convenient for the fish to move and protect. Many fast-swimming hermit fish often lose their scales or disappear.

Fish are generally hermaphroditic, and gonads are usually paired. Cartilaginous fish are generally fertilized in vivo, viviparous, viviparous or oviparous, and most bony fish are fertilized in vitro. The eggs of freshwater fish are heavy or floating, while marine fish are floating. The sexual maturity of fish is closely related to species, nutrition, water temperature and light, and is regulated by gonadotropins. After a certain period of time, the fertilized eggs hatch and the larvae emerge from the membrane.

Mammals: A class of vertebrates. Known as the beast. Body hair; Constant body temperature; Viviparous (single hole exception) and lactation; The left and right ventricles of the heart are completely separated, and the left ventricle pumps blood to all parts of the body through the left arterial arch; The skull is enlarged and the brain volume is enlarged, which is the highest existence of life on earth at present. Their or our advanced nature is as follows: the brain is highly developed; Constant temperature and viviparous lactation.

Is it specific enough? You can give it to me ~ ~