Echiura. Group of worm -like marine animals that live in mud, sand . The female, similar to a pear or carrot .
Summary
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- 1 Description
- 1 He lives
- 2 Etymology
- 3 Biological characteristics
- 4 Grouped into three genres
- 5 Body Section
- 6 Development
- 7 Taxonomy
- 2 Sources
Description
A class of coelomate protostome worms from the phylum Annelids , although for years they were considered an independent phylum. They measure between 3 and 25 cm long.
Habitat
They are marine, living in sand , mud or rock fissures . About 150 current species are known ; the oldest fossil echiuroid dates from the Late Carboniferous .
Etymology
The equiuroids or equiuros (Echiura, from the Greek echinos, ” thorn ” and ourá, “tail”).
biological characteristics
In them, the female, similar to a pear or carrot , has a long, retractable proboscis , with a ventral mouth and a terminal anus . Her body has 3 cell layers and she has a true coelom. While the female actively feeds on small animals and organic sediments , the male is small and parasitizes the female.
They lack segmentation. Interior of the tube ciliated, the cilia drag the food to the mouth. Digestive tube longer than the body, folded into convolutions. Body with bands of silks similar to those of annelids .
Echiurida bonellidae, (another genus)
There are excretory rectal glands . The tube (sometimes hypertrophied) and the body are differentiated. Mouth in ventral position.
The circulatory system with a dorsal and a ventral vessel , gas exchange takes place in the tube.
Nervous system with esophageal collar. The sexual products accumulate in the urns where they mature and from where they exit through the gonopores.
grouped into three genera
- Bonellia viridis.
- Echiurus Echiurus
- Thalassema thalassemun.
body section
- Protective cuticle.
- Epidermis.
- Two muscle layers.
- Coelomic cavity separated in plane of symmetry by mesentery.
Developing
It presents traces of mesodermal metamerization that disappears when it becomes an adult. It develops from a trochophore larva with two metatrochas. Great growth of the episphere that will give rise to the tube .
taxonomy
They have been treated as an independent phylum, given their anatomical peculiarities. Today they tend to be considered a group of annelids , despite lacking body segmentation in the adult state; Phylogenetic analyzes based on DNA sequencing place the Echiuroids within the Annelids.
