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Once upon a time, the seas abounded with relatives of starfish and sea urchins - sea lilies. There are very few of them left these days.

These creatures received their romantic name for their resemblance to flowers, but in fact, sea lilies have nothing to do with plants. Crinoids (or Crinoidea) are a class of echinoderms related to sea ​​urchins and starfish. Like all echinoderms, crinoids have a five-ray symmetry of the body, more characteristic of plants (usually animals are characterized by bilateral symmetry).

Like all echinoderms, crinoids have a hard, calcareous skeleton with openings from which flexible, tubular arms emerge. The water-vascular system allows the animal to pump fluid through the body and control its arms, which it uses to catch food particles from the water, transporting them to the mouth located in the center. Some "mobile" echinoderms (such as starfish) have arms that allow them to move slowly along the seabed, but many creatures of this type simply "hang out" in the sea. The latter include most modern crinoids. Only some species, like their ancestors, lead a sedentary lifestyle. The rest spend at least part of their lives floating freely.

Successful evolution

The first crinoids appeared in the Ordovician, approximately 460 million years ago. Scientists do not know exactly how they interacted with other echinoderms, because at that time several separate groups organisms, like crinoids, spent their lives attached to a solid surface. However, in the Ordovician there was sudden increase and the number of species and abundance of sea lilies. They remained widespread throughout the Paleozoic until the end Permian period(252 million years ago). In some places, the lilies were so numerous that their calcareous plates turned into thick layers of sedimentary rock.

After this, crinoids suffered catastrophic losses along with other animals in a major extinction event. Only a small number of subclass species have survived Articulata, which was characterized by more flexible arms. At the beginning of the Triassic, the revival of crinoids began - completely new species appeared that occupied their former evolutionary niches, as well as places vacated after the death of some closely related animals. However, the sea lilies were never returned past glory. Modern crinoids are rare and noticeably different from their ancestors.

Pentacrinites

This genus of crinoids was widespread approximately 190 million years ago. Their fossils are often found along the famous Jurassic Coast in, as well as in other parts of our planet. Animals of this genus formed colonies with individual stems reaching 2 m in length. Probably, like all sea lilies, Pentacrinites reproduced as larvae. They floated in the water until they attached themselves to a suitable substrate and began to reproduce. As the tree became saturated with water and sank deeper into the water, stem growth accelerated - thus the sea lily's calyx remained in the surface, food-rich layers of water.

The stem segments of crinoids resemble thick cylinders. If you drill holes in them, you will get beads. According to legend, St. Cuthbert, revered in England, used rosaries made from sea lilies. They are considered fairy money. Such fossils are also called St. Boniface coins.

There are no holes on the lower part of the sea lily's body. Its intestines are shaped like a horseshoe, and its anus, from which waste products are removed, is located on the same side as its mouth.

a brief description of

Latin name: Crinoidea.
Name: sea lilies.
Period: 460 million years ago - our time.
Type: echinoderms.
Fossil type: calcareous blades.
The main differences: a cup-shaped body, branching rays (arms), a stem or movable processes.
Size: stem length - up to 5 m, diameter of the “head” - about 35 cm.
Habitat: tropical seas.
Locations of finds: found everywhere.

Any beauty is dangerous and insidious, psychologists say. Who-who, ah marine biologists agree with them. Imagine a creature that has no blood...

It's full of surprises. Some of them, together with corals and algae, form unique underwater gardens. Sea lilies are bottom animals, and not plants, as it seems at first glance. They belong to the echinoderms.

Where do sea lilies live?

Their class has a fairly extensive distribution area. There are practically no places in the world's oceans where they are not found. There are about 700 species of feather stars. In Russia there are only 5 species of them.

Sea lilies have inhabited all the oceans. Depth doesn't matter to them. They feel equally good everywhere. And yet, the bulk of these animals prefer to settle in warm ocean waters with thickets of coral reefs located at shallow depths (up to 200 meters).

Types of sea lilies

The sea lily class is represented by two varieties of feather stars - stalked and stalkless. All individuals, regardless of their species, are attached to all kinds of objects located under water. Stalked crinoids, having secured their stems to something, remain in this position forever. The area of ​​their life activity is limited by the length of the stalk on which they swing.

Stemless lilies, having lost their support, found more freedom actions. They, having detached themselves from the substrate, are able to cover small distances. Animals swim using rays that work like fins. However, each feather-star deprived of a stalk in the process of development does not bypass the attached stalked stage. This feature and the reproduction of crinoids of both species brings them closer to each other.

Biological description

The name of this class of animals has Greek roots. Crinoidea translates as “lily-like.” Indeed, in individuals belonging to this class, freaky bodies like lush flower. The resemblance to flowers is enhanced by the colorful body coloring of the feather stars. When you see a beautiful creature in the ocean, you just want to take a photo of it. Sea lilies are a delightful decoration of underwater gardens, created by a brilliant designer - nature itself.

Crinoids have a cup-shaped body with a mouth cavity in the center. Branching rays (arms) and a corolla rise upward from the calyx. In stalked crinoids, a stalk is attached to the bottom of the calyx, growing up to one meter in length. The stalk with supporting lateral appendages (cirrhi) is attached to the ground. Stemless lilies have only movable cirri, the ends of which are equipped with either denticles or “claws”. Thanks to them, stemless individuals cling to the ground.

Featherstars became the only echinoderms that managed to retain the body orientation characteristic of their ancestors. Their dorsal side touches the ground, and the surface that is equipped with the oral cavity is turned upward. The structure of their bodies is based on five-ray radial symmetry. The body is formed by five rays, capable of being dismembered many times and forming 10-200 “false arms”. The rays are equipped with multiple lateral branches (pinnules).

Thanks to the blossoming corolla, a kind of network is formed that traps plankton and detritus. Rays framing inner side, equipped with mucociliary grooves, which are reduced to the oral cavity. The food caught in them moves towards the mouth. The calyx along the edge from the side of the conical eminence is equipped with an anus.

Calcareous segments contribute to the formation of the external skeleton. It is formed by two parts: the endoskeleton of the rays and the stalk. These bottom animals have an ambulacral, nervous and reproductive system (which determines the reproduction of crinoids). Branches of all designated systems penetrate into the cavity of the rays and stalk.

Crinoids differ from their fellows not only in the orientation characteristic of the dorso-abdominal center line, permeating the bodies of all individuals, but also external configurations. The components of the ambulacral system in feather stars are simplified. For example, it did not include ampoules designed to control the legs. Madrepore plates were also not found in individuals.

Reproduction

Let's figure out what kind of reproduction occurs in sea lilies. These echinoderms are dioecious animals. Reproductive products enter those pinnules that are located closer to the calyx. The male, as a rule, is the first to spray sperm from the pinnules, using special holes.

His behavior leads to stimulation of a female that does not have any reproductive ducts. Her kicknules simply burst and eggs fall out of them. Fertilization of the eggs occurs directly in the water, after which they turn into a barrel-shaped doliolaria larva. This is how sea lilies reproduce.

Development of doliolaria

After 2-3 days, doliolaria settles on the ground. Its front tip is fixed on the substrate, any solid objects, and even on similar individuals.

Having lost her eyelashes, she becomes motionless.

The pentacrinus stage is expressed by the fact that a five-ray structure gradually appears on the calyx. The stalk grows, lengthening, rays develop, and the attached disk enlarges. Doliolaria begins to resemble a tiny feather-star swaying on a stem. Its size varies in the range of 0.4-1 cm. Cold arctic waters encourage the larvae to develop up to 5 cm in length. Over time, the doliolaria lengthens, differentiates into a stalk and a calyx, where it subsequently forms. This ends the cystoid stage of larval development.

Differences in group development

If the reproduction of crinoids and the development of larvae are absolutely the same, then after the completion of the pentacrinus stage, further maturation proceeds differently in both groups of crinoids. Stem-shaped individuals, confined to one place, acquire new stalk segments. Their lengthening stem becomes like a stack of coins (after all, individual vertebrae are strung on top of each other).

The vertebrae have a movable joint that is provided by muscles. The center of the stem is pierced by a canal where nerves lie and other organs are hidden. Cirri are located in two ways: either along the entire stem or at its base.

The individual acquires an incredible resemblance to a flower, which, in fact, is demonstrated by multiple gorgeous photos. Modern sea lilies have stems of different lengths, usually limited to 75-90 cm. And in fossil forms, the length of the stems reached 21 meters. The feather stars of antiquity were real giants.

Stemless lilies develop differently. After a month and a half, the calyx, having independently broken off from the stem, begins to float freely. The stalk dies over time.

Sea lilies are echinoderms. In the photo, sea lilies look like underwater plants.

These unusual creations nature got its name thanks to the unusual appearance, which really resembles a pinnately branched lily flower.

Structure and description of sea lily

The body of the echinoderm underwater inhabitant has a central cone-shaped part, called the “cup” and radially extending tentacles in the form of “arms”, covered with lateral branches - pinnules.

Crinoids are perhaps the only modern echinoderms that have retained the body orientation characteristic of their ancestors: the mouth part faces upward, and the dorsal side of the animal is attached to the ground. A jointed stem extends from the calyx of the stalked lily, performing the function of attachment. Bunches of shoots - cirrhus - diverge from the stem; their purpose is the same as that of the main stem. The tips of the cirri have denticles, or “claws,” with which the lily can firmly attach to the substrate.

Like all echinoderms with a radial pentaradial structure, the crinoids have five arms, but they are capable of dividing, giving from ten to two hundred “false arms” with a large number of lateral pinnules, forming a dense “net”.

The mouth opening is also surrounded by tentacles with mucous eyelash-shaped grooves, through which captured food particles are transported to the mouth opening. The latter is located in the center of the “abdominal” surface of the cup, and next to it is the anus.

Nutrition of sea lilies

The feeding method of sea lilies allows them to be classified as sestonophages - aquatic animals that feed on a suspension of detritus particles, microorganisms and small plankton (seston). In addition, sea lilies are able to filter water, trapping food particles.

Sea lilies, which do not have a stem, detach from the substrate and move along the bottom. Sometimes they even float up, actively moving their “arms”.

The planktonic larvae of crinoids are called vitellaria.

Once metamorphosis is complete, the larvae develop into miniature stalked animals that closely resemble adult crinoids. In stemless individuals, as they grow, the stem gradually disappears.

About 625 species of these marine animals are known to exist. most of which are found in tropical waters or at great depths.

Lifestyle of sea lilies

Stalked sea lilies, of which there are about 80 species, lead a sessile life. They can be found at a depth of 200 - 9700 m.

Much more stemless lilies have been discovered - 540 species. These animals are inhabitants of the shallow waters of tropical seas, so their coloring here is brighter and more variegated than the deep-sea representatives.

More than half of the species of stemless crinoids known to us live at depths of less than 200 m.

Interest of sea lilies for humans

Fossils of crinoid segments called trochytes, as well as stars and disks with a hole in the center, have long attracted human attention. ABOUT space communications polygonal segments in the shape of stars with heavenly bodies The British were the first to say so. There are opinions that gear-shaped trochites were considered “parts of alien machines” that aliens created hundreds of millions of years ago.

Attached echinoderms, leading a permanently sessile lifestyle, or can sometimes break away from the substrate on which they sit and swim freely, moving their rays like fins.

OVERVIEW OF THE CLASS

External structure. The body of the sea lily consists of a calyx and long branched five rays, or arms, extending upward from it. From the lower end of the calyx extends either a more or less long stalk (stalked sea lines), or numerous antennae or cirri, serving to attach the lily to the substrate. The rays of the lilies branch at the very base, and thus, as if ten rays extend from the cup. Like the arms of brittle stars, they are made up of a number of segments consisting of skeletal vertebrae, movably connected to each other, and can therefore bend quite well. Lateral branches - pinnules - are usually attached to each segment alternately, either on the right or on the left side.

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1 - mouth, 2 - anus on the tubercle, 3 - ambulacral grooves

In the center of the upper surface of the calyx there is a mouth opening, from which five ambulacral grooves, or grooves lined with cilia, extend further onto the rays and extending from them. inner surface. The ambulacral legs, or tentacles, are located in these grooves. On the upper surface of the cup there is also a special tubercle on which the anus is located.

Ambulacral system. The ambulacral system consists of the perioral ring canal and five radial canals extending from it, running under the ambulacral grooves and correspondingly branching along the rays. Branches extend from these channels into pinnules and ambulacral legs, or tentacles, which serve in the lily for capturing food, touching and breathing.

In lilies, the ambulacral system communicates somewhat differently than in other echinoderms. external environment. Five or more stony canals extend from the annular canal, which open into the body cavity with their free ends. The body cavity communicates with the external environment through numerous water pores that penetrate the upper surface of the calyx.