Vermicelli biology

Main features of Platycladus orientalis:

1, flat, bilateral symmetry.

From radial symmetry to bilateral symmetry is the evolution of animal system, which differentiates animal body into front and rear ends, left and right sides and dorsal surfaces.

The functions of various parts of the body are different:

Head: Nerves and sensory organs converge to the front head.

Back: it has a protective effect.

Ventral surface: it undertakes the functions of exercise and food intake.

Biological significance of bilateral symmetry;

It is divided into front and rear ends, left and right sides and dorsal ventral surfaces.

The functions of various parts of the body are different:

The action is changed from non-directional to directional, and the induction is more accurate, fast and effective.

Wider adaptability

Landing is an important condition for aquatic development.

2. It has mesoderm.

The significance of mesoderm appearance:

A. Mesoderm is the material basis of animal body and organ system structure, and most body structures are differentiated from mesoderm, which provides the necessary foundation for the development of animal body structure and the complexity and integrity of physiology.

B, promote the development of motor function.

Metabolic function is enhanced.

In oblate animals, it is partially differentiated into parenchyma and muscle tissue.

3. The organ system began to be constructed.

(1) Skin muscle sac: The epidermis and muscles of animals cling together to form a saccular body wall, which is called skin muscle sac.

There are some rods perpendicular to the body surface scattered in epithelial cells, which are formed by rod cells in the material and then stored in epidermal cells. When the planarian meets the enemy's injury or strong stimulation, a large number of rod-shaped bodies are discharged from the cells, and the rod-shaped bodies meet water outside to form mucus. Worms surround their bodies with mucus or attack their enemies with mucus, so rods have the ability to defend and attack. Some people think that the rod-shaped body has some evolutionary relationship with the stinging cells of coelenterates.

(2) Incomplete digestive system: mouth, pharynx, intestine, no anus.

(three) with the original renal tubular excretion system:

Primary renal duct: Primary excretory duct, one end of which is blind and the other end is open (excretory orifice).

The protorenal duct is formed by ectoderm on both sides of the body and has drainage holes running through the body. The protonephric duct of oblate animals is composed of many branches of excretory duct, and the end of each branch is composed of flame cells.

(4) It has a trapezoidal nervous system, which is more concentrated than coelenterates.

A pair of cranial nerve segments, several longitudinal nerves and transverse nerves; Sensory organs: eye point, auricular process, balance capsule.

Auricular process: rich in tactile receptors, taste receptors and sense of flow.

4. Reproductive characteristics: mostly hermaphroditic, complicated reproductive organs, fixed gonads, reproductive ducts and accessory glands, mating behavior and in vivo fertilization.

5. The individual development of marine life has gone through the stage of Muller larva.

Direct development: the development mode in which an animal larva hatches from an egg or is produced by its mother and grows into an adult without metamorphosis. Larvae and adult have roughly the same morphology and lifestyle.

Indirect development: The development mode in which an animal larva can grow into an adult only after it is hatched from an egg or given birth by its mother. The morphology and living habits of larvae and adults are obviously different.