Sipuncula It is a phylum belonging to the animalia kingdom that is made up of non-segmented round worms. Its members are known by the name of "peanut worms." It was first described in 1814, by the English naturalist Constantine Rafinesque.
Many of the animals that belong to this phylum are a mystery to science, since they are mainly found on the seabed and their observation and study in their natural habitat is quite difficult for this reason.
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The taxonomic classification of the sipuncúlids is the following:
- Domain: Eucarya.
- Animalia Kingdom.
- Phylum: Sipuncula.
These worms are made up of eukaryotic cells, with their genetic material (DNA) enclosed within the cell nucleus. They are also multicellular because they are made up of cells specialized in various functions..
Likewise, it presents bilateral symmetry, so that, if an imaginary line is drawn through the median plane of this animal, two halves are exactly equal to each other..
Likewise, these animals are triblastic, since three germ layers appear in their embryonic development: ectoderm, mesoderm and endoderm. From them each tissue of the animal develops.
Its type of reproduction is sexual and its embryonic development is indirect with the formation of a larva.
Its essential characteristic is given by the presence of tentacles around the mouth.
Sipunculi are round-type worms, which have varying lengths, ranging from a few millimeters to about 500mm..
These types of worms do not have a segmented body and most of it is made up of muscle tissue. They have a cephalic end, with the mouth as the main organ and a posterior end.
Due to the fact that throughout their life they are mainly buried in the seabed, the body of the animal has a “U” shape. One of its most representative characteristics is the so-called "introvert", which is a retractable structure that can be propelled outward or retracted into the animal. At the extreme of this introvert lies the mouth.
Parallel to the esophagus of the animal are the retractor muscles of the introvert. Its function is to make the introvert stretch out of the animal or hide inside it..
The mouth, which is the entrance opening to the rudimentary digestive system of the animal, is surrounded by tentacles. In addition, it is possible to find in the introvert a kind of extensions like hooks or spines, which are believed to play a role in the feeding process of the animal..
The wall of this animal is made up of several layers. First of all, a cuticle that is quite thick and performs protective functions; the epidermis which is of the glandular type; muscle layers (circular and longitudinal) and an inner dermis.
It is important to note that this dermis has extensions called cilia and is also completely surrounding the coelom..
Internally it presents a cavity, the coelom. This is large and is filled with a fluid whose function is to transport nutrients and oxygen throughout the body..
It is important to note that the sipunculi do not have a circulatory system or a respiratory system..
It is the most developed system that the sipunculi present. Your front door is the animal's mouth.
A digestive tube that consists of the esophagus, and an intestine that has a contoured shape, which ends in the anus, which opens on one side of the animal, emerges from the mouth..
The digestive system is shaped like a "U".
The nervous system is quite rudimentary. It is made up of a ventral nerve cord, as well as a cerebral ganglion that is located above the esophagus. In the rest of the body of the animal there is no presence of any other nervous ganglion.
Likewise, at the level of the cephalic portion of the animal there are a series of photoreceptors known as ocelli, which are primitive and only allow it to perceive certain flashes of light from its surrounding environment..
Likewise, very close to the introvert there are abundant sensory cells that allow the animal to orient itself and explore the environment that surrounds it..
Sipunculi are dioecious organisms. This means that they have separate sexes. There are female individuals and male individuals.
The gonads are very close to the retractor muscles of the introvert, specifically at the base of these.
As with annelids, with which the sipunculi have a certain resemblance, the excretory system is made up of metanephridiums, which open to the outside through an opening called the nephridiopore..
These organisms are heterotrophic, but they do not feed on other living beings; that is, they are not predators.
The favorite food of the sipunculi is represented by suspension particles that they can capture thanks to the action of their tentacles.
Likewise, there are species that have digging habits, so they feed on sediments..
The digestion of the ingested particles is extracellular and takes place inside the intestine. Subsequently the nutrients are absorbed and finally the waste released through the anus.
The type of respiration of the sipunculi is cutaneous because these organisms do not have a respiratory system with specialized organs.
In cutaneous respiration, gas exchange occurs directly through the animal's skin, which must be highly vascular and also moist. The latter is not a drawback, since sipunculi are found in aquatic habitats..
Gases are transported through simple diffusion, following a concentration gradient. Oxygen is transported to the inside of the animal, while carbon dioxide is released to the outside..
The most frequent type of reproduction in these organisms is sexual, which involves the fusion of gametes. Fertilization is external.
In general, once the gametes are produced, they mature in the coelom. When they are mature they are released abroad. Outside the body of the worm are the female and male gametes, fertilization occurs.
The development is indirect, since a trochophore larva is formed as a result of fertilization. This larva is shaped like a top or spinning top and has a series of extensions or apical hairs at its upper end. It also has several lines of cilia around its body.
This larva undergoes a series of transformations until it forms an adult individual.
The phylum sipuncula comprises two classes: sipunculidea and phascolosomatidea.
Animals belonging to this class inhabit the seabed, although some may also occupy snail shells. Likewise, one of its distinctive elements is that they have tentacles around the mouth.
This class includes two orders: sipunculiformes and golfingiiformes.
It encompasses animals that have tentacles only above the mouth, not around it. In addition, its hooks are organized into regular rings. This class is made up of two orders: aspidosiphoniformes and phascolosomatiformes..
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