Nemertina is a worm, a ribbon-like type. Creatures of this category do not have external organs of touch. However, they are able to obtain food in a rather original way - by “shooting” at the prey with an abundance of mucus, which is secreted by a long proboscis, which goes deep into the creature's body.
What way of life are the animals represented? What does nemerthine (worm) look like? Photos and descriptions of such reptiles will be discussed later in the article.
History of the discovery of the Nemerthins
For the first time, the existence of the nemerthins was learned through the discovery made by the scientist G. Barleyz. In 1758, a researcher discovered a worm of the present type in sea waters, described its morphological structure and even created an image of an animal.
Encyclopedic knowledge of the Nemerthins in the 19th century expanded significantly. Many zoologists have brought into science new, interesting information about these unique animals that live mainly on the seabed. Making discoveries in the presented field became possible thanks to the advent of technical means for working in depth. During this period, the very definition of "nemertina" was proposed.
The study of nemerthins was actively engaged in by the Soviet zoologist N. A. Livanov. In 1955, he proved that these animals are a transitional branch between flat and ribbon-shaped worms. Prior to this, such creatures were classified as annelids - annelids.
Appearance
A typical representative of nemerthins has a body elongated in the anteroposterior direction, somewhat flattened in the dorsal and abdominal regions. The body length of individual representatives varies from several millimeters to tens of meters. However, measuring the actual magnitude of nemerthins is complicated by the fact that these creatures are able to stretch like leeches.
Nemertina is a worm whose body is divided into the trunk and head sections. The border between these areas is the cervical sulcus. The head of the animal contains a mouth opening. The trunk does not have pronounced external organs. Only small gonads are secreted on the sides of the body. At the back of the worm is a clearly visible anal opening.
The skin of nemerthins is capable of producing a significant amount of mucus. Therefore, most worms of this type look unattractive to predators. Numerous marine individuals have a bright color, which is a warning signal about the danger to potential enemies in their natural habitat. At the same time, there are enough representatives of nemerthins of whitish tones. Some of them have translucent integuments through which the internal organs are visible.
Nutrition
Nemerthine is a worm that has an elongated tubular-type mouth opening. Inside the oral apparatus contains a special proboscis, which folds deep into the body cavity and is located above the internal organs when the animal is resting. During the hunt, this plastic tube unfolds and is ejected by the worm in the direction of the victim under the influence of hydraulic pressure. Extraction is covered with sticky, thick and corrosive mucus.
How does nemertin eat? A worm can swallow an entire immobilized victim or divide it into parts. Some animals of the present type envelop prey in a cocoon of mucus, leaving it in stock.
Internal structure
Nemerthine is a worm that does not have a body cavity as such. All gaps between the internal organs are filled with a connective tissue - the parenchyma. The insides are represented by the posterior, middle and anterior intestine.
Nemerthins have the most developed circulatory system among all ribbon-like worms. As for the respiratory system, such animals do not have them. Saturation of cells with oxygen occurs through its passage through the skin.
The nervous system is built on the principle of orthogon. In other words, nerve cells form specific fibers, which collect in nerve trunks.
Classes
The following classes of nemerthins are distinguished:
- Anopla - the so-called unarmed worms. A distinctive feature of creatures of this class is the absence of a proboscis in the oral cavity. Food is captured through an opening in the abdominal region. A striking representative of this class is a giant marine nemerthine called Lineus Longissimus, whose body length can reach up to 30 meters with a width of not more than one centimeter.
- The Nemertina worm, an Enopla class, has a proboscis in the front of the body. The latter is thrown out, hitting the victim with several stilettos and wrapping it with thick mucus. Representatives of this class differ mainly in modest sizes.
Lifestyle
Most worms that are classified as nemerthins are bottom-living marine animals. However, quite a lot of species of freshwater creatures of this type are known. There are also isolated land representatives of nemerthins.
Nemertina is a worm that leads a predatory lifestyle. Some animals of this type do not hunt on their own, but are scavengers. Nemerthins are also known that parasitize in the mantle cavity of marine mollusks. Currently, there is a detailed description of the order of 1,200 species of these worms.