Basic characteristics of Cirrhostoma:

The body is eel-shaped, divided into three parts, trunk and tail. The body length varies greatly with different species, from less than 20mm to as long as 1m (adult). Parasitic or semi-parasitic life, with large fish or turtles as the host.

Primitive characteristics of Cirrhostoma:

1. There is no real upper and lower jaw;

2. There are no paired appendages (only odd fins without lateral fin);

3. There are no real teeth, only horny teeth formed by epidermis;

4. The spinal cord is retained for life, and only the embryonic spine appears;

5. The skull is incomplete and has no top;

6. Less muscle differentiation, maintaining the original muscle node arrangement;

7. The brain is underdeveloped, and there is only one (blind eel) or two (lamprey) in the inner ear.

Specialization characteristics of Cirrhostoma;

1. Mouth funnel with adsorption that cannot be opened and closed;

2. The olfactory sac is single, which is opened on the midline of the head through a single nostril;

3. The gill is located in a special branchial sac, which is attached with gill filaments originating from endoderm, so it is round-mouthed

Also known as cystgills.

Morphological characteristics of lamprey;

1. Shape

The body is eel-shaped, and the tail is flat. The body is divided into three parts, the trunk and the tail. There is no lateral fin, only odd fins. The eyes have no eyelids, are covered by a transparent membrane, have a funnel, have a single nostril, and have seven round gill slits (hence the name lamprey). There is an anus at the junction of trunk and tail, followed by a small papilla (cloacal sinus), on which the cloacal hole is opened.

2. Skin

Epidermis: It consists of multiple layers of epithelial cells with many single-celled glands.

Dermal: connective tissue (including collagen fibers and elastic fibers) arranged regularly. There are star-shaped pigment cells in the dermis. Shallow grooves with lateral ducts on the head and trunk are opened on the skin.

Skin derivatives: only the mouth funnel and tongue end have horny teeth derived from epidermis.

3. Bones

Only cartilage and connective tissue, no hard bone.

The notochord remains for life and remains the main supporting structure of the body. There is a thick notochord sheath around the notochord, which also surrounds the spinal cord upwards.

On the back of the notochord, there are two pairs of tiny cartilage arcs in each segment, which is the beginning of the embryonic spine. A skull has appeared to protect the brain and sensory organs, but there is only one cartilage base plate, and the top of the skull has not yet formed.

There are also a series of special cartilage supporting the mouth funnel and tongue and gill cages supporting the gill sac.

4. Muscle

The muscles of lamprey are very primitive, basically similar to amphioxus. Body wall muscle has little differentiation and consists of a series of primitive sarcomere, and the shape of sarcomere is inverted W-shaped. Visceral muscles are mainly annular muscles in branchial sac and complex muscles in mouth funnel and tongue related to absorption and feeding.

5. Digestive system

Digestive tract: mouth, pharynx, esophagus, intestine (straight tube, undifferentiated).

Digestive gland: independent liver, gallbladder and bile duct in larvae, but not in adults. There is no independent pancreas, but there are pancreatic cell groups scattered at the junction of intestinal wall, intestine and esophagus.

6. Respiratory system

The pharynx is divided into two tubes, the back of which is the esophagus, the ventral surface is the respiratory tube (with a membrane at the entrance), and the rear end is the blind end. There are seven internal gill holes on the left and right sides of the tube, each communicating with a gill sac. The wall of the sac has gill filaments evolved from endoderm, and there are abundant capillaries on the gill filaments, where gas exchange occurs. Each branchial sac has an external branchial hole communicating with the outside world. Adult water flows in and out through the external gill holes.

7. Circulation system

Heart: an atrium, a ventricle, a venous sinus, no conus arteriosus.

Arteries: Ventricle sends out 1 abdominal aorta-8 pairs of inlet branchial artery-8 pairs of outlet branchial artery-dorsal artery root (a carotid artery sends forward to the head and merges backward into 1 dorsal artery-to all parts of the body).

Vena: the anterior main vein (1 pair) and the posterior main vein (1 pair) * * * join the common main vein and then pour into the venous sinus. There is hepatic portal vein.

8. Nervous system

The brain has been divided into five parts: the brain, the diencephalon, the midbrain, the cerebellum and the medulla oblongata, but they are primitive and arranged in one plane in turn. Cranial nerve 10 pair.

9. Sensory organs

Olfactory organ: there is only one external nostril, which opens in the center of the back of the head. The external nostril leads to a circular olfactory sac.

Hearing organs: only the inner ear, with two semicircular canals (blind eel has only one semicircular canal), and the oval sac and spherical sac have not been clearly differentiated.

Visual organs: the cornea is underdeveloped, without ciliary body, iris and eyelids, and without eye glands. Visual adjustment mainly depends on the contraction of corneal muscle.

Lateral line: There are vertical shallow grooves on both sides of the head and trunk of lamprey, and there are sensory cell groups in the grooves, which are connected by nerves, called lateral line.

10. Clonal system

Lamprey is hermaphroditic. Mature eggs and sperm break through the gonad wall and fall into the body cavity, enter the cloacal sinus through the abdominal hole, and then leave the body through the cloacal hole. The eggs are fertilized in vitro in water.

1 1. Life history and development

Seven lampreys live in rivers or oceans. From June to July every year, adult eels flock to the riverbed with coarse gravel and clear water to breed. During the spawning period of 2-3 days, they mate for many times to lay eggs, and the number of eggs can reach14,000-2,000. The young eels were once mistaken for a protozoan and named as-Sarcocephalus. Their feeding and independent lifestyle are similar to Wenchang. It takes 3-7 years to metamorphose into an adult, and then it reaches sexual maturity after several months of parasitic or semi-parasitic life. Only reproduce once in your life.