Sea squirts, also known as pineapples in the sea, are named after their appearance resembling pineapples. Coastal areas of Shandong Province in China are commonly known as sea milk.
R&D
Chordata is a representative animal of Chordata subfamily. Adults are usually fixed on rocks or the bottom of ships. An oval bag with a water inlet at the top and a water outlet at the lower side. Water carries food and oxygen from the inlet hole into a large cystic pharynx, and the pharyngeal wall is penetrated by many gill slits. Branchial fissure does not open directly in vitro, but opens in the peribranchial cavity. Water flows into the gill cavity and then is discharged from the body through the water outlet. The tiny food in the water is bound into food balls by the mucus secreted by the inner column on the ventral side of the pharyngeal wall. Depending on the oscillation of cilia around branchial cleft, the water flows directionally, and the food mass is transported backwards with the water flow and enters the intestine. Although adults have branchial cleft, they have no notochord and dorsal neural tube.
Although this animal was described by Aristotle more than 2000 years ago, it has long been classified as an invertebrate. It was not until the19th century that Russian embryologist levski (A. O.Ko валевский) studied the embryonic development of ascidians and correctly clarified that its taxonomic status should belong to lower chordates similar to amphioxus. The larva of sea squirt is an animal that looks like a tadpole and swims freely in the water. The tail has a typical notochord, and the pharyngeal wall has a hollow dorsal nerve canal and branchial fissure, which has the main characteristics of chordates. This free living state of larvae can only last for a few hours or even a day, that is, they sink to the bottom of the water, are fixed on the objects in the water by the attachment process at the front end, and begin to retrograde metamorphosis: the spinal cord disappears with the retraction of the tail, and the neural tube degenerates into ganglion; With the enlargement of pharynx, the number of branchial cleft increases greatly; The digestive tube is bent into a U-shaped tube, so that the orifice and anus are upward; In vitro, a thick capsule with protective effect is produced, forming an adult ascidian [1].
The open circulation of ascidian blood is a special reversible blood circulation direction, that is, the contraction of the heart is periodic and intermittent, and the direction of blood changes periodically. Blood vessels flow in both directions regardless of arteries and veins, which is unique in the animal kingdom.
morphological character
Some sea squirts are shaped like eggplant, others like flowers, and they are shaped like teapots. If you touch the sea squirt with your fingers, it will shoot a strong current from the outlet hole, and then it will fall softly from its original standing state, so it is an animal. Newborn sea squirts are very much like tadpoles, with eyes and brain bubbles, a well-developed tail, a spinal cord in the center, a nerve tube on the back of the spinal cord leading straight to the front of the body, and paired gill slits in the throat. Small sea squirts can swim freely in the sea.