The house of echinoderms is coral. marine invertebrates

Starfish, sea urchins, brittle stars, holothurians (sea cucumbers) belong to the type of echinoderms. Echinoderms existed already 520 million years ago. Fossil forms of echinoderms reached 20 meters in length! About 6 thousand species have survived to our time. Echinoderms live in the seas and oceans, and inhabit them to the greatest depths. Starfish were found at a depth of 7.5 kilometers!

Characteristic features of this type are ray symmetry, and the number of rays is usually a multiple of 5, as well as an amazing water-vascular (ambulacral) system, which nature has not endowed with anyone except echinoderms. Their body is pierced by channels filled with sea ​​water. From the outside this sea ​​water not reported. By distilling water inside their body, echinoderms control the movement of special legs with suction cups and tentacles, they can move and capture food. Such a “hydraulic” way of movement is not very fast (usually about 10 m / h), but, apparently, this speed is quite enough for echinoderms.

After all, for example, starfish hunt mainly for mollusks, which, as you know, are also not fast walkers. True, sometimes they grab stars and live fish. The fish can swim away, dragging a star on itself, but this will not hurt the predator - it will digest the victim on the go. And the method of digesting large prey in starfish is very original - the star turns its stomach out of its mouth and covers it with fish or puts it into the shell of the prey through the gap. So it digests, right in the sea water.

Ofiura grabs her sponge.

Sea stars.

The largest of the sea stars (from the family breezingid) has a span of tentacles over 130 cm. The heaviest starfish weigh up to 6 kg. by the most dangerous pests people count starfish eating coral. For example, one starfish - the crown of thorns, lives in the Pacific and Indian Oceans, can destroy up to 400 sq. see corals. And what remains of coral after the invasion of hundreds of thousands of starfish?

Coral reefs are the traditional habitat of many species of echinoderms. All young individuals of the five-pointed star are males, which, growing up, turn into females! But a multi-beam star is a purely dioecious creature, like most echinoderms. The oldest fossil echinoderms sea ​​lilies- lived in Cambrian period, were sedentary creatures in which the mouth opening opened upwards. Feeding on small organisms and food particles floating in the water column, they led approximately the same lifestyle as modern sea lilies.

Echinoderms reached the greatest diversity in the Ordovician and Silurian: the number known to science their fossil species exceeds 20 thousand. AT Cretaceous, 300 million years ago, crinoids dominated the marine life. Sedentary, fragile and delicate, at first glance, echinoderm crinoids may seem like easy prey for potential predators, but they prefer to stay away from them.

Echinoderm crinoids of coral reefs

Most crinoids accumulate poisonous substances or repellents that repel enemies in their tissues. It is no wonder that in the midst of their fan-shaped petals many small creatures find shelter - from crabs and shrimps to small fish that feed on the remnants of the owner's meal. One sea lily serves as a refuge for a couple of dozen "lodgers".

Reaching a diameter of 60 cm, the multi-beamed starfish, nicknamed the "crown of thorns", feeds on polyps of stony corals, causing terrible devastation in coral reefs. During the period mass reproduction Australians bred these starfish and released predatory snails on the reefs - one of the few natural enemies"crown of thorns". The expanded side of the calyx with a mouth opening is turned upwards, and pinnately branched rays up to 30 cm long depart from it.

The supporting skeleton of each beam consists of separate vertebrae - brachial plates, interconnected by movable muscles. The number of rays ranges from 5 to 200, but in most species it does not exceed 10-20. Sea lilies are typical filter feeders. A special groove runs along the beam with all its branches, seated with two rows of ambulacral legs.

The mucus secreted by the glandular cells of the grooves envelops small organisms and organic particles passing by, which the animal feeds on. Ambulacral legs perform only grasping, respiratory and tactile functions.

Many echinoderm sea lilies, primarily deep-sea species, live sedentary, attached to the substrate with a stem up to 2 meters long (in some fossil species, the stem length reached 20 meters). Free-living sea lilies do not have a stem - they swim or crawl along the bottom with the help of their rays or are temporarily attached to the substrate by jointed roots (cirrs) located at the bottom of the calyx.

Almost all sea lilies feed at night, and during the day they hide under stones and in niches among reefs. Today, over 500 species of sea lilies are known. Most of them look the same as their distant ancestors 300 million years ago, and the largest living sea lily reaches 90 cm in diameter.

The body of a starfish consists of a central disk and 5-20 more or less pronounced radially diverging rays. The mouth opening is on the underside of the body. The internal skeleton is formed by movably connected calcareous plates, bearing on their surface skin gills, spikes, tubercles, needles, and special grasping organs - pedicellaria, which are modified needles. The main function of pedicellaria is to clean the skin from dirt.

Let's watch the video - fish, echinoderm sea lilies and stars:

Echinoderms are represented on reefs by stemless sea lilies - comatulids, holothurians, sea urchins, brittle stars and starfish. These main groups reach a significant species diversity in reef biotopes with the manifestation of endemism in their communities in areas of individual and especially isolated reef systems, such as the reefs of the Red Sea or the Caribbean (Clark, 1976). More than 1000 species of echinoderms live on the Indo-Pacific reefs, about 150 species live on the reefs of the Western Atlantic, and there are only 8 species common to these two large zoogeographic regions. Such isolation of the echinoderm faunas of these regions is similar to the isolation of the faunas of the corals living in them. The endemism of the echinoderm fauna in certain areas is expressed, in particular, in the fact that out of 1027 species inhabiting the Indo-Pacific reefs, there are only 57 species inhabiting this region from end to end. On average, within individual reef systems, there are usually from 20 to 150 species of echinoderms. So, the number of their species in the Red Sea is 48, in the Caribbean - about 100, on the reefs of the Philippines - about 190, in the area of ​​the B. barrier reef - about 160 (Marsh, Marashall, 1983).

The groups of echinoderms listed above, excluding sea stars, form rather dense communities and monospecific populations on reefs and especially in shallow zones of the lagoon, flat and outer slope, being essential element free-living macrobetos. Their functional role as a component of the reef ecosystem is also great. They occupy all major trophic niches. Among them there are filter feeders (brittle stars, sea lilies), detritophages and ground beetles (brittle stars, sea cucumbers), phytophages (sea urchins) and predators (starfish, as well as partly hedgehogs and brittle stars).

Echinoderms play an essential role in the regeneration of biogens (Webb et al., 1977) and exert a significant influence on the processes of reef genesis. They have a massive calcareous skeleton that makes up up to 90% of their body weight. Their skeletal elements serve as an important source of carbonate material. Eating coral periphyton and spat macrophytes by sea urchins and stars has a significant impact on the formation of coral communities, as well as eating corals themselves by stars and urchins, especially the star Acanthaster. Holothorn-eaters, passing huge masses of coral sand through their intestines, significantly affect the formation of bottom sediments and the production processes occurring in them. Finally, echinoderms serve as a food source for many mollusks and fish, and holothurians are one of the main objects of fishing on reefs.

We currently have enough complete information in the composition and structure of communities of reef echinoderms, on the feeding and reproduction of some of their groups (Endean, 1957; Clark and Taylor, 1971; Clark, 1974; 1976; Marsh, 1974; Lisddell, 1982; Yamaguci and Lucas, 1984). Information about their quantitative distribution is very fragmentary. Estimating the population density of most dominant species of hedgehogs, brittle stars, sea lilies, and stars is difficult because these predominantly nocturnal animals hide in shelters of the rock flat during the day and are difficult to count. Therefore, reliable quantitative data are available only for holothurians (Bakus, 1968).

Invertebrates are animals that lack an axial skeleton. Lots of the most beautiful inhabitants seas - corals, sea anemones, crustaceans are invertebrates, and a large part of fans of this species buy an aquarium because of them. Invertebrates are much more sensitive to water quality than fish, which means that more sophisticated equipment. It is important to remember that copper-based fish treatments are detrimental to most invertebrates.

corals

The most famous among the invertebrates are the inhabitants of tropical seas and oceans, striking with their bright colors and bizarre shapes. The body of most corals contains symbiotic organisms - zooxanthellae, which often determine the color of the coral. Zooxanthellae are unicellular algae that are synthesized for coral organic compounds and oxygen, so the right type of lighting is of great importance for keeping corals in aquariums. The skeleton of corals can be composed of both calcium and other horn-like structures. To build it, various types of corals need many trace elements, such as strontium, magnesium, iodine, etc. The key to successful content is knowledge and constant monitoring of the presence of trace elements. Corals are colonial organisms, each individual element of which is called a polyp and is associated with others.

Madrepore corals

They have a calcium skeleton and are reef-building corals. Over millions of years of existence, stony corals have done a lot of work on the appearance of the old Earth. The most sensitive aquarium organisms requiring perfect quality and chemical composition water. Therefore, by the time the stony corals are placed in the aquarium, the environment in the latter must be absolutely stable. In addition, this type of coral does not accept neighborhoods with a large number of fish. Individual polyps in different types can vary in size from 1-2 mm to 20 cm in diameter. Madrepore corals have chemical means of protection (“burn”) and can wage real “wars” among themselves, therefore, when settling in an aquarium, it is worthwhile to calculate in advance the availability of free space between corals, taking into account their future growth.

tubular corals

There are different colors, polyps are small - up to 1.5 cm, and in the colony are interconnected, forming large swaying surfaces. Some, such as the tubipora, have a honeycomb-like tubular skeleton that they can retract into when threatened. Other species have no skeleton at all.

soft corals

The skeleton is represented by separate internal spines, due to which these corals can significantly change their volume depending on the conditions. As a rule, they are strongly branched and look like small underwater trees. Different species have a different dependence on light, but light-loving species are easier to keep in aquariums, since they do not need additional live food.

Most suitable "for beginners" corals. They have a dense structure and consist of small polyps that can "retract" or "stretch". At good conditions content and a sufficient amount of essential micronutrients can increase in size very quickly.

horn corals

As well as soft corals, they are popular because of their relative unpretentiousness, fast growth and spectacular appearance.

Anemones (anemones)

Unlike corals, they consist of only one polyp, do not have a rigid skeleton and are filled with water. Interesting due to the large "choice" of colors and sizes, as well as various kinds"burning" tentacles, with which you need to be especially careful. Anemones are excellent eaters of captured food, and many of them live in symbiosis with clown fish. The latter feed, clean and protect “their” sea anemones, in return receiving an underwater “home” protected from predators. It should be noted that sea anemones can actively move around the aquarium, causing inconvenience to other invertebrates. It is especially necessary to carefully monitor the location of the pumps in the aquarium - there are frequent cases when the anemone was "sucked" into the pumps and "grind" into fine dust.

Disc anemones and zooanthids

They usually live large groups, breed well in captivity and are not too whimsical.

Crustaceans

In nature, there are about 40 thousand species of crustaceans, but only relatively few are suitable for keeping in an aquarium. Shellfish are chosen not only for unusual shape and color, but also for their "sanitary" features - they usually dispose of leftover food. All crustaceans molt regularly, shedding their outer skeleton (shell), and the empty shell is so impressively similar to a living crustacean that some mistake this moment for the death of the animal. Large crustaceans can lead a predatory lifestyle and be dangerous to small fish. On the other hand, many small shrimp and hermit crabs will be useful even in a reef tank.

Echinoderms

Echinoderms include such well-known inhabitants of the sea as starfish, sea urchins, as well as lesser-known ones - brittle stars, sea cucumbers and sea lilies. Many of the starfish are predators and can harm or eat corals. Many starfish are excellent at regenerating, that is, restoring own body even with significant damage. So, for some of them, a new starfish grows over time from each “torn off” ray. In turn, many of the other popular class of echinoderms are sea ​​urchins- feed on fouling and algae, although some do not disdain and coral polyps. Depending on the species, their needles can have different lengths and shapes. It should be remembered that the injections of some hedgehogs - for example, diatoms - are extremely painful, while other representatives are completely poisonous. But sea cucumbers are named so because they really resemble large cucumbers in shape, with tentacles at one end of the body that filter food. When keeping sea cucumbers, you need to pay attention to the fact that in the event of a danger, some species emit toxic substances into the water, which in a confined space of an aquarium is detrimental to all its inhabitants.

shellfish

It is very numerous (about 120 thousand species) and diverse group animals. Many bivalve mollusks are well suited for keeping in an aquarium, the Tridacna species being the most popular. Bivalve mollusks feed on water filtration, in addition, the bodies of many of them, like corals, contain zooxanthellae. gastropods, as a rule, are not very popular, because in addition to vegetation, they can harm corals by eating them. But with live stones, as a rule, medium-sized species that eat fouling and - which is very useful for aquarium environment- decay products. Cephalopods, such as cuttlefish and octopuses, also belong to molluscs. The content of the latter is also possible in marine aquariums, but rather complicated by the peculiarities of their nutrition - cuttlefish and octopuses can destroy all living organisms in the aquarium, so they need a separate microcosm.

Worms

Among all the diversity of terrestrial worms, aquarium interest is mainly represented by sitting polychaete worms. They typically live in tubes of slime or a horn-like substance from which protrude a corolla of brightly colored tentacles. With them, the worm filters the water and receives food. Representatives of other groups of worms can also be observed in aquariums - on live stones and in the ground. Often they are complementary and natural food for fish.

Echinodermata, a type of marine invertebrate. Appeared in the early Cambrian, by the end of the Paleozoic reached a great diversity. Sizes from a few millimeters to 1 m (rarely more - in modern species) and up to 20 m in some fossil crinoids. The body shape is varied: star-shaped, disc-shaped, spherical, heart-shaped, cup-shaped, worm-shaped or resembling a flower. About 10,000 fossil species and about 6,300 modern ones are known. Of the 20 known classes, 5 subtypes have survived to the present: crinozoans (sessile forms oriented with their mouth up, with the only class crinoids), echinoses (combines sea urchins and holothurians) and asterozoans (includes starfish and brittle stars). According to another classification, representatives of the last 2 subtypes are combined into a subtype of Eleutherose.

All modern echinoderms are characterized by the presence of an ambulacral system and five-ray symmetry; the latter extends in many cases to the outlines of the body, the arrangement of individual organs (the nervous and circulatory systems), and the details of the skeleton. Deviations from five-ray symmetry in modern echinoderms (for example, in holothurians) are a secondary phenomenon; at the same time, early Paleozoic homalazoans were initially devoid of radial symmetry.

In most modern species, the mouth is in the center of the body (on the oral side) and the anus is at the opposite pole (on the aboral side). The intestine is poorly differentiated, has the form of a long narrow tube, spirally twisting clockwise, or saccular; in some groups it is secondarily blindly closed. There are no digestive glands. Circulatory system consists of a perioral annular vessel and radial canals, devoid of their own walls, extending from it - a system of lacunae. There is no gas exchange in this system; it serves to deliver nutrients from the intestines to all parts of the body. Weak blood movement occurs due to the pulsation of the heart - a plexus of blood vessels surrounded by epithelial-muscular tissues. The function of the respiratory organs is performed by ambulacral legs, the back of the intestine and other formations. The excretion products are removed by coelomocytes, ambulacral legs and through thin-walled areas of the body.

The nervous system is primitive, without a pronounced brain center. It consists of 3 rings, from each of which 5 radial nerves depart, which do not have direct contacts with each other. Thus, we can talk about the presence of echinoderms, as it were, three nervous systems. In accordance with this, ectoneural (dominant, predominantly sensory, located on the oral side in the integumentary epithelium), hyponeural (controlling the motility of skeletal muscles, cells connective tissue and located in the middle layer) and aboral (controls motor function, prevails in sea lilies, poorly developed in other echinoderms) systems. Echinoderms are dioecious (rarely hermaphrodites). The ducts of the genital glands open outwards. Fertilization is mainly external. A floating larva from bilaterally symmetrical in the course of metamorphosis is transformed into a radially symmetrical adult animal.

Lit .: Beklemishev VN Fundamentals of comparative anatomy of invertebrates. M., 1964. T. 1-2; Invertebrates: a new generalized approach. M., 1992.

S. V. Rozhnov, A. V. Chesunov.