Segmentation refers to the phenomenon of a series of similar segments arranged along the longitudinal axis of the body in animals. Each segment is called a segment.

Tonglu section

Idiosyncratic stanzas

1. The segmentation phenomenon that began with annelids is an important symbol in the evolution of invertebrates.

2. Isotactic segmentation means that except for the head, the shape and structure of the rest of the body segments are basically the same, making movement more flexible. It is also the beginning of physiological division of labor and provides a basis for the further differentiation and development of the animal body.

3. The emergence of heterorhythmic segmentation makes it possible for the animal body to develop to a higher level and gradually differentiate into parts such as head, thorax, and abdomen.

Protostomes (Annelids)

Deuterostome

1. The wall of the digestive tract has a muscle layer, and the body cavity contains organ systems such as nerves, circulation, excretion, and reproduction. The complexity of the structure promotes the improvement of various physiological functions.

2. The muscles of the digestive tract enhance peristalsis and improve digestion capacity

3. The improvement of the circulation system promotes the transportation of materials

definition

effect

Blood does not always flow in blood vessels during circulation, which is called open circulation

kidney mouth

thin renal duct

excretory duct

Kidney hole group

A winding tube with openings at both ends. One end is a funnel-shaped nephrostomy composed of multiple ciliated cells, which opens into the body cavity of the anterior body segment; the other end is a renal pore or excretory pore, which opens into the body cavity on the ventral surface of the body segment. surface

Has a distinct head composed of preoral lobe and periorbital segment

Nereis

Most polychaetes are dioecious, with relatively primitive reproductive systems, without fixed gonads and reproductive ducts. Gonads only appear during the reproductive season, and there is no reproductive zone.

Leech

Hermaphroditic, cross-fertilization, reproductive zone after sexual maturity

Mainly terrestrial and aquatic, most live in fresh water, and a few live in sea water. The head is not obvious, the senses are not developed, there are no warts, the setae are directly attached to the body wall, there is a reproductive belt, hermaphrodites, direct development

earthworm