Lophophores. The lophophorates are a grouping of three phyla of dubious phylogenetic position: Phoronids , Brachiopods , and Bryozoans . The members of these groups are related to the deuterostomes and their structure is trimetameric, that is, the body is divided into an anterior prosome, a middle mesosoma and a posterior metasoma. Each of these regions has an independent coelomic cavity: procoel, mesocoel, and metacoel, respectively. The coelom is possibly enterocoelous. In addition, Lophophorates have a U-shaped digestive tract, are poorly cephalized and, above all, are characterized by the presence of a rapical tentacle organ called a lophophore.
They have exoskeletons: tubes, shells or habitats that secrete. They are benthic, sedentary or sessile animals. Altogether, there are about 5,400 current species. All of them are aquatic, and most are marine, except for a few freshwater Bryozoans.
The phylogenetic position of the Lophophorates, both individually and as a whole, is controversial due to the mixture of protostomes and deuterostomes that they present.
Summary
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- 1 General characteristics
- 2 Classification of lophophores
- 3 See also
- 4 Sources
General characteristics
- Possession of a tentacled organ, the lophophore(from lophos, crest, and phoreus, possessor), which they use to capture food and as a respiratory organ, which surrounds the mouth but not the anus; they contain an extension of the coelom, and the thin ciliated walls of the tentacles are not only an efficient feeding system, but also function as a respiratory surface for gas exchange between the water and the coelomic fluid.
- The coelomis formed by enterocelia.
- The adult mouth is not derived from the embryonic blastopore(except in phoronids).
- A trimeric organization, that is, the body divided into three regions, prosoma, mesosoma , and metasoma , each with an independent and usually paired coelomic cavity , procoel , mesocoel, and metacoel, respectively.
- U-shaped digestive tube.
- They have total and radial segmentation of the eggs and lack a head.
- They develop from larvaeassimilable to a dipléurula of echinoderms (or a trochophore of polychaetes, according to the authors).
Classification of lophophores
Three large groups of lophophores have been identified: phoronids, ectoprocts, and brachiopods. These groups are considered “living fossils”, since, when compared with their fossil forms, it is observed that they have barely undergone modifications.
- Foronídeos: The foronídeos are marine animals that occupy the bottoms of very shallow waters. Only 10 species have been identified, all sessile. They live in tubes of solid structure that they build themselves. The only part that shows is the plume of tentacles that can be retracted in situations of danger to the animal.
- Ectoprocts: Ectoprocts are colonial animals that inhabit both marine and fresh waters, but always at very shallow depths. They are tiny, barely reaching 0.5 m.
But when forming colonies, by sexual reproduction , they give the sensation of complex and large structures.
- Brachiopods: Brachiopods are marine animals that occupy shallow waters. Although its name mentions the existence of arms and feet, it actually refers to the lophophore.
One of the most remarkable characteristics of this group is the existence of two shells that cover the body of the animal and that are synthesized by its own walls. They resemble molluscs but have notable differences.
