The unpredictable world of marine animals, it is full of surprises. Some of them, together with corals and algae form unique underwater gardens. Sea lilies are bottom animals, not plants, as it seems at first glance. They are echinoderms.
Where do sea lilies live?
Their class has a fairly wide distribution area. In the oceans there are practically no places where sea lilies are not found . There are about 700 species of feather stars. Only 5 of their varieties live in Russian sea waters .
Sea lilies inhabited all the oceans. Depth is not important for them. They are equally good everywhere. Nevertheless, the bulk of these animals prefers to settle in warm oceanic waters with thickets of coral reefs located at shallow depths (up to 200 meters).
Types of Sea Lilies
The class of sea lilies is represented by two varieties of feather stars - stalked and stemless. All individuals, regardless of their species, are attached to all kinds of objects under water. The stalked crinoids, having fixed themselves with the stalk for something, will always remain in this position. The zone of their life is limited by the length of the stem on which they swing.
Stemless lilies, having lost their support, gained greater freedom of action. They, breaking away from the substrate, are able to overcome insignificant distances. Animals swim due to rays working like fins. However, each feather-star-free stalk during development does not pass the attached stalk stage. This feature and the reproduction of sea lilies of both species brings them together.
Biological description
The name of this class of animals has Greek roots. Crinoidea (Crinoidea) is translated as "similar to lilies." Indeed, individuals belonging to this class have bizarre bodies that look like a lush flower. The similarity with flowers increases the colorful coloring of the body of feather stars. Seeing a beautiful creature in the ocean, I just want to take his photo. Sea lilies are a delightful decoration of underwater gardens, on the creation of which a brilliant designer worked - nature itself.
Crinoids have a cup-shaped body with a mouth in the center. Branching rays (arms) and a nimbus rise upward from the calyx. In stalked crinoids, a stalk is attached to the bottom of the calyx, growing to one meter in length. A stalk with bearing side appendages (cirres) is attached to the ground. Dotless lilies have only movable cirs, the ends of which are equipped with either cloves or “claws”. Thanks to them, tableless individuals cling to the ground.
Feather stars were the only echinoderms that managed to maintain the body orientation characteristic of their ancestors. With their dorsal side, they cling to the ground, and the surface that is equipped with the oral cavity is turned up. The basis of the structure of their bodies laid five-radial radial symmetry. The body is formed by five rays, capable of being repeatedly divided and form 10-200 “false hands”. The rays are equipped with multiple lateral branches (pinnulas).
Thanks to the corolla, a peculiar network forms, trapping plankton and detritus. The rays framing the inner side are equipped with mucous-ciliary grooves, which are reduced to the oral cavity. The food that gets into them moves to the mouth. The calyx along the edge of the conical elevation is equipped with an anus.
The formation of the external skeleton is promoted by calcareous joints. It is formed by two parts: the endoskeleton of the rays and the stalk. These bottom animals have an ambulacral, nervous and reproductive (causing the reproduction of sea lilies) system. Branches of all designated systems penetrate into the cavity of the rays and the stalk.
The crinoids differ from their counterparts not only in the orientation characteristic of the dorsal-abdominal axial line penetrating the bodies of all individuals, but also in their 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. No madrepor plates were found in individuals.
Breeding
We will deal with what kind of reproduction of sea lilies. These echinoderms belong to dioecious animals. Sex products fall into those kicks that are located closer to the cup. The male, as a rule, is the first to eject sperm from the kick, using special holes.
His behavior leads to stimulation of a female who does not have any genital ducts. Her kicks just burst, and eggs fall out of them. Fertilization of eggs takes place directly in the water, after which they turn into a barrel-shaped larva of the lobar. This is the reproduction of sea lilies.
Development of lobar
After 2-3 days, the lobar is seated on the ground. Its front tip is fixed on the substrate, any solid objects, and even on similar individuals.
Having lost her cilia, she becomes motionless.
The pentacrinus stage is expressed by the fact that a five-beam structure gradually appears on the cup. The stalk grows, lengthening, rays develop, the attached disk increases. The dololaria begins to resemble a tiny feather-star swaying on a stalk. Its size varies in the range of 0.4-1 cm. Cold Arctic waters cause the larvae to develop up to 5 cm in length. Over time, the lobar is elongated, differentiated into the stalk and calyx, where the oral cavity subsequently forms . On this, the cystoid stage of larval development ends.
Differences in Group Development
If the reproduction of sea lilies and the development of larvae are exactly the same, then after the pentacrinus stage is completed in both groups of crinoids, further maturation proceeds differently. Stalked individuals, chained to one place, are overgrown with new segments of the stalk. Their elongated stalk becomes like a stack of coins (after all, individual vertebrae are strung on each other).
The vertebrae have a movable joint that provides the muscles. The center of the stem is pierced by a channel where nerves run and other organs hide. Cirs are arranged in two ways: either throughout the stalk, or at its base.
The individual acquires an incredible similarity to a flower, which, in fact, is demonstrated by multiple gorgeous photos. Sea lilies of our time have stems of different lengths, usually it is limited to 75-90 cm. And in fossil forms, the length of the stems reached 21 meters. 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, sets free swimming. The stalk dies over time.