Subphylum Caudal Chordates of the phylum Chordates

The phylum Chordates is divided into three subphyla, namely the caudal chordate subphylum, the cephalic chordate subphylum, and the vertebrate subphylum. The phylum Chordates is the highest phylum of the animal kingdom and the most successfully developed of the phylum. Their common feature is the presence of the notochord, dorsal neural canal, and gill fissure throughout or at some point during their ontogeny.

The subphylum Vertebrates is the most numerous, most complex and most evolutionary group in the animal kingdom, with very different morphological structures and very different lifestyles.

Caudal chordates are the lowest chordates, and are evolutionarily related to higher chordates, both of which may have evolved from a common ancestor of free-living protocephalic animals similar to sea squirt larvals.

The body structure of cephalochordates is relatively simple, but the typical structure of chordates already exists, and the three major structures survive for life. According to the morphological rise and fall of Xiangxiao, chordates evolved from a primitive headless companion with left and right asymmetry, no gill cavity, few gill clefts, and free life.

First, the morphological characteristics are different.

1. Chordates.

A rod-like structure located between the digestive tract and the neural tube with a supportive function, all chordates have a notochord in the embryonic stage, but are either retained for life later in life (subphylum caudal chordates, subphylum cephalic chordates), or degenerate and replaced by the vertebral column (vertebral column).

2. Subphylum Vertebrates.

A distinct head is present, the central nervous system is tubular and the anterior end expands into the brain, which differentiates posteriorly into the spinal cord of the withered sun. Most digging notochords are found only in the early stages of development (with the exception of Rotundus, Cartilaginous Fishes, and Bony Fishes) and are later replaced by a spine connected by a single vertebrae.

Second, the habits of life are different.

1. Chordates.

The adult body of the stalk sea squirt is oblong and the juvenile shape resembles that of a tadpole. The base is attached to the bottom of the sea or to objects submerged by seawater, and at the other end there are two holes not far apart: the top one is the water inlet hole, which passes through the digestive tube and has a cribriform border membrane in the middle, which is used to filter out coarse objects, allowing only water and small food to enter the digestive tract.

2. Subphylum Vertebrates.

Primary aquatic animals respire with gills, secondary aquatic and terrestrial animals only have gill slits at the embryonic stage, and adults breathe with lungs. With the exception of the round mouth, they all have upper and lower jaws.

The circulatory system is more perfect, and the heart can contract, promote blood circulation, and help improve physiological functions. Replacing simple renal ducts with complex kidneys improves excretory function, and a large amount of waste products produced by metabolism can be excreted more efficiently.

Third, the subordinate things are not different in the chain.

1. Chordates.

It includes the subphylum Caudal Chordate, the Subphylum Cephalic Chordate, and the Subphylum Vertebrates.

2. Subphylum Vertebrates.

This subphylum includes Rotunds, Cartilaginous Fishes, Bony Fishes, Amphibians, Reptiles, Birds, and Mammals.