Ecdysozoa - Branchiozoa
Eukaryotic domain
Animalia
Eumetazoa Subkingdom
EcdysozoaGeneral phylum
Priapulida
Priapulida (scientific name: Priapulida) is a phylum in the animal kingdom. It is a small group of marine benthic animals. They are mostly distributed in cold seas near the poles and live in mud, shallow seas or tubes. Although the body has body rings, it is not segmented. Only more than 20 species are known to exist. Their closest relatives are the phylum Kinorhynchus, and these two phyla are collectively called Scalidophora.
The Latin name of this phylum comes from Priapus, the god of fertility in Greek mythology, because some species of this phylum resemble the penis of male Homo sapiens in appearance.
1. Appearance
is small or medium in size, ranging from 5 mm to 20 cm at maximum. The body is cylindrical and divided into snout, trunk and tail. The snout can be turned over and has 25 columns of spines. There are body rings on the surface of the trunk, but it is not segmented. circular muscles are arranged in separate rings, making the body surface appear a ring; the longitudinal muscles are arranged in bundles in the snout area, showing a ridge shape; the well-developed muscles enable it to drill holes in the mud and move. It mainly feeds on polychaetes and small crustaceans. When feeding, it turns its pharynx out and uses the spines around the mouth and pharynx to tear the prey. Dioecious. It is widely distributed and often lives benthic in soft ocean bottom camps. It is mostly distributed in cold seas near the poles, ranging from shallow seas to deep seas. It lives in mud or in tubes. It has been classified as a pseudocoelomate in the past, but after it was discovered in 1961 that it had a coelomic membrane, it was classified as a true coelomate and became an independent phylum. Only more than 10 species have been reported. According to the research results of electron microscope observation, it was found that the previously observed coelomial membrane with cell nucleus structure was actually wrong. This membrane was the membrane of non- cell structure secreted by the body wall muscles, and the observed nucleus was not on the structure of this membrane. Accordingly, the branchial drag animals were corrected to belong to pseudocoelomates. 18 species have been discovered. Such as the gill dragworm Priapulus.
2. Body wall structure
body wall structure is similar to annelid , but the epidermal layer sheds as it grows. Epidermal cells protrude outward to form papillae or tumors on the body surface. The circular muscles are arranged in separate rings, giving the body the appearance of a body ring. The longitudinal muscles are arranged in bundles in the snout area and appear ridge-like. The well-developed muscles allow it to drill holes in the mud and sand.
3. In vivo structure
There is a developed body cavity in the body, with a very thin body cavity membrane, and surrounds the internal organs to form mesenteries (mesenteries), which contain amoebocytes and blood cells containing earthworm hemoglobin . Gill drag animals are carnivorous and feed mainly on polychaetes and small crustaceans. When feeding, the pharynx is turned out and the prey is torn open with the spines around the mouth and pharynx. There are well-developed muscles on the periphery of the pharynx to control the expansion and contraction of the pharynx. Behind the pharynx are the intestines, rectum, and finally the anus opening at the end of the trunk. There is a nerve ring at the front end of the pharynx, followed by a nerve cord , close to the epidermal cells. The mastoid processes of the snout and trunk have sensory functions. Its excretory organs are closely connected with the reproductive organs, forming a pair of renal reproductive organs (urogenital organs), located on both sides of the intestine. In its center is a protonephric duct, with piles of solenocytes connected to one side of the protonephric duct and the gonads on the other side. The protonephric duct can discharge the metabolite and germ cells, and its end is the renal genital pore (urogenital pore).
4. Growth and reproduction
Gill drag animals are all dioecious. The release of sperm stimulates the female to lay eggs. The eggs are fertilized in vitro, cleavage by radiation, and hatch into a small posterior gastrula. After developing into a larvae, the trunk is surrounded by the cuticle to form an armor-like shape, similar to the rotifer . The larvae stage molts multiple times and metamorphoses into adults, which also molt. These characteristics are similar to those of pseudocoelomates, so their taxonomic status is still controversial. Perhaps we can draw a firm conclusion only after we have a better understanding of its embryology .
5. Living habits
may be an important animal component in coastal environments such as anaerobic mudflats, hypersaline or brackish waters. Living in this habitat may avoid competition with other metazoans.It swallows small polychaete ringworms, crustaceans, and other trolling animals in the mud with its snout.
Gill drag animals are marine benthic animals. Most of them live in cold seas near the poles, ranging from shallow seas to deep seas. They live freely and mainly inhabit muddy sediments.
6. Distribution
Only 18 species of gill-drag animals have been recorded, all of which live in the mud and sand of shallow seas and deep seas, from intertidal zones to thousands of meters deep sea. Most of the larger species live in cold waters; some smaller species (such as Tubiluchus) are widely distributed, including in tropical oceans. Branchial drag animals are important members of the benthos (benthos) of the Middle Cambrian marine oceans. Eleven fossil species have been described, which were the dominant invertebrates in the Cambrian oceans. The species has not changed much from its Cambrian ancestors.
7. Subordinates
Palaeoscolecida
Archaeopriapulida
Priapulimorpha
Priapulimorphida
Sea Insect Gill Halicrytomorpha
Seticoronaria
Seticoronarida
8. Species
"Ottoia" is also nicknamed "penis" by Americans "worm" (so named because it looks like a penis) is the most famous gill-trailer. The body length ranges from 8 cm to 40 cm, making it a relatively large group of spiny animals. All are extinct today, and the fossil period is in the middle to late Cambrian period.
Otozoa tridentata is a new species of Otozoa with three odontoid processes in the pharyngeal teeth discovered by British scientists through detailed morphological studies of fossil pharyngeal teeth. O. tricuspida is a new species of O. tricuspida and was named O. tricuspida. In a latest study, British scientists discovered through detailed morphological studies of fossil pharyngeal teeth that O. prolifica should actually contain at least two species. The difference between them is that one of them has multiple odontoid processes on the pharyngeal teeth, while the newly discovered species has three odontoid processes on the pharyngeal teeth. The discovery of this new species of Otozoa suggests that the diversity of branchial drag animals may have been higher during the Cambrian era than previously estimated. Because the chitinous pharyngeal teeth and rostral processes of branchial drag bugs are easy to form microfossils, further study of these microfossils may give scientists a new understanding of the diversity of branch drag animals during the Cambrian period.
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