Entoprocts . Tiny invertebrate animals , mostly marine and sessile, very similar to the Bryozoa , a group in which they were included before it was found that they lack a true coelom. They are organisms with a great power of regeneration, measuring less than 5 mm and resembling hydroid polyps ; their body is divided into a calyx , which houses the internal organs, and a peduncle , which they use as a fixing structure. The calyx bears a crown of retractable tentacles that circumscribe an area called the vestibule, where the mouth and anus open .
They are filter feddiatom algae and protozoa . The digestive system occupies most of the visceral mass and is folded in a U-shape, the excretory system is protonephridial and they lack a circulatory system. Mostly dioecious (separate sexes), there are a few hermaphroditic forms . They reproduce sexually , although they sometimes multiply by budding ( asexual reproduction ). The loxosomatids are marine and solitary, the pedicelinids , marine and colonial; and the urnatelids , colonial and freshwater .
Summary
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- 1 Habitat and Diversity
- 2 Morphology
- 3 Physiology
- 4 Evolution
- 5 Sources
Habitat and Diversity
Entoprocts have only 150 described species, of which only one lives in fresh water; all the others live in the sea. Most of these animals live attached to shells , rocks , algae and even other animals, such as crabs , shrimps , hydrozoans , polychaetes , sipunculids and sponges . Some species have a solitary life, but it is more common for them to form large colonies.
Morphology
Entoprocts are morphologically very similar to bryozoans but, unlike these, entoprocts are considered pseudocoelomates and are therefore classified in separate phyla. The pseudocoelom is filled with gelatinous cells . These small animals have a cup-shaped body. The upper part is called the calyx ; it contains the internal organs, and the stem serves as a support. At first glance they could be confused with hydrozoan cnidarians or bryozoans, but you can easily identify them because neither of these two groups can fold their tentacles , as entoprocts do.
Entoprocts
In the colony of entoprocts there is a stolon or creeping stem that branches to form individual nuclei. View of the ventral surface of an entoproct. Contrary to what one might imagine when seeing them, the stem does not represent the posterior part of the body, but rather an extension of the animal ‘s back ; therefore, the calyx is the ventral surface. The rim of the calyx has six to thirty-six tentacles , which are nothing more than extensions of the body wall and surround the vestibule. On one side of the vestibule is the mouth and on the other, the anus.
Physiology
The muscles of the entoproclos are limited to longitudinal pounds in the tentacles and in the stem. This helps them to contract their tentacles when they feel some danger or when the water is very dirty, and to move their whole body like a pendulum. On the tentacles, the entoprocts have a large number of cilia that move to form a current of water that enters the vestibule between the tentacles and exits above them. Some of the cilia of the tentaclesThey have specialized in trapping protoctists and other organic particles that they feed on and that are part of the plankton. Then, like a highway made of cilia and mucus, the food particles are transported to the mouth .
Evolution
Due to the large number of similarities between the loriciferans, the priapulids, the quinorhynxes and the nematomorphs, some specialists place them in a single phylum. However, as long as there is no hard evidence, it is better to treat them as separate blades. Loriciferans resemble quinorhynchus in that they have an oral cone with stylets that can be stored inside the body. Also some tardigrades , (a phylum that we will see later), have this type of mouth, but it is only a phenomenon of convergence, that is, by having similar habits, the appearance of similar structures is favored, but the organisms are not related . The larvae of the nematomorphs resemble those of the loricifera .by ventral spines. If at some point it is confirmed that the glands of the fingers are adhesive, then they could have the same origin as the glands that the quinorhynchus have along their bodies or, more likely, to the glands that the priapulids and rotifers have in their fingers . hollow, at the end of the body. However, the truth is that almost everything about the biology of the loricifera is unknown and, as long as this continues, it is difficult to establish the relationships of this group.
