Sea spiders in the black sea. Sea spider. Population of marble crabs

Sea spiders, they are spider crabs, they are also marble crabs, live in the Mediterranean, Black Sea and Atlantic Ocean, near the coast of Morocco and France. They are found on the Crimean peninsula and the coast of the Caucasus, at shallow depths with a rocky or rocky bottom.

Sea spiders are members of the Grapsidae family. These crabs are called "spiders" because of their long, dark legs, and they got the name "marble" because of the characteristic pattern on the shell.

Description of the sea spider

The spider crab is small and agile, measuring only 38 millimeters long and 43 millimeters wide. The shell is square and flat. The anterior margin between the eyes is especially wide and straight, with 3 sharp teeth on each side. The upper part of the shell can be overgrown with small crustaceans called balanus, as well as algae.

The skeleton is external, breathing is carried out with the help of gills. On the left claw there are small teeth that are tightly closed together. The right claw is larger than the left, the teeth are bent, and a gap is obtained between them. Outwardly, the right claw resembles tongs. The marble crab belongs to the ten-legged crustaceans, has 10 long, strong paws, covered with hairs. The color of the shell is from brown-greenish to brown-violet. The shell is decorated with a wavy pattern, reminiscent of marble.

Spider crab lifestyle

Sea spiders live in the coastal zone, they stay at the very edge of the water and can even leave the water at a distance of up to 5 meters. This is the only Black Sea crab that can run out of the water. In the sea, they can live at a depth of up to 10 meters.

Marble crabs tolerate drying well and love to bask on rocks in the sun. Spider crabs build their own homes. The crab chooses a stone and begins to climb under it, throwing sand grains out from under the stone with its claws, and the crab hides in the resulting niche. Having accumulated supplies, and having eaten well, the sea spider hides in a safe haven.

Sea spiders feed on plant and animal remains, plankton, mollusks and polychaetes. They climb onto the stones protruding from the water and clean their surface. In case of any danger, the crab instantly hides in any crevice, and if there is none, it throws itself into the water.

At night, he carefully crawls out of the old shell. At night, they can climb rocks, to a height of 3-5 m. They cannot burrow into the sand, but they are perfectly camouflaged among algae and mussels. If a crab loses a leg or a claw, then the lost organ is restored after 2-3 molts. The lifespan of a spider crab is 3 years.

Reproduction of marble crabs

The breeding season for sea spiders takes place in July-August at a water temperature of about 17 degrees.

One female lays up to 87 thousand eggs. Incubation lasts 25 days. Crab larvae eat plankton. Metamorphosis takes place in 4 stages. Puberty in females occurs at 2 years.

Population of marble crabs

Like other Black Sea crabs, sea spiders are used to make souvenirs, but they are not a commercial species.

Spider crabs are included in the Red Book of Ukraine, as their number has sharply decreased recently. These crabs are protected in the natural reserves of Karadagsky and Cape Martyan.

The closest relatives of spider crabs

There are more than 10 thousand species of decapod crabs with five pairs of legs and bulging stalked eyes. For example:
Stone crabs are the largest crabs in the Black Sea. The width of the shell of a stone crab is about 10 centimeters. They prefer to live deeper, but can be found close to the shore;
The hairy crab looks like a stone crab, but has a more modest size, and its shell is covered with numerous yellowish bristles-hairs. They live closer to the shore, under rocks;
Mediterranean or grass crabs have a green shell, which is why they are called "grass". Grass crabs are shallow water dwellers;
Aquatic crab or lilac crab. It is slower and prefers to live exclusively in shallow water;

The swimming crab is a lover of digging into the ground. Its small hind legs look like shoulder blades; with their help, the crab throws sand on itself. The crab also uses these legs for swimming, the swimming crab is the only one among the Black Sea crabs that can swim;
Blue crab came to the Black Sea from the Mediterranean in the 60s. He arrived in our latitudes with the ballast water of ships. But the water of the Black Sea is too cold for young blue crabs, so they are extremely rare;
The invisible crab got its name because it is almost impossible to notice it in algae. These long-legged, lean sea creatures are excellent at camouflage;
Pea crab usually lives among mussels, and sometimes can even climb inside the shell. It is extremely difficult to see this crab, since an adult has a size of no more than a ten-kopeck coin;
Freshwater crab is an unusual Crimean crab. It differs not in size, but in origin and way of life. From the name it is clear that it lives in fresh water: in mountain rivers and ponds.

Freshwater crabs cannot be dispersed by the current, so they have to travel over land at night. In this pedestrian way, they once crossed the entire mainland, it is believed that they originated in Southeast Asia.

Keeping marble crabs in an aquarium

Sea spiders do not dig holes, they prefer to hide under stones, so the bottom of the terrarium is covered with pebbles or sand, while at the bottom there should be a variety of shelters, for example, snags, stones, ceramics. To make the aquaterrarium look more beautiful, it can be revived with the help of plants.

The systematic and evolutionary position of which has not yet been fully determined. Despite the name, sea spiders (Pycnogonida) have nothing to do with real spiders, although they are considered as an early isolated group of the chelicerate subtype, which includes arachnids and merostomes, that is, horseshoe crabs and crustaceans.

Sea spiders are a relatively small group, numbering about 1300 species today. The earliest finding of a sea spider in the form of a larva dates back to the Cambrian period, there are also descriptions of finds from the Silurian and Devonian deposits.

These are very strange, morphologically unlike animals, consisting almost entirely of legs alone. Their body is so tiny that it does not even fit half of the internal organs that normal animals should have there. Therefore, for example, the reproductive and digestive systems of sea spiders are located entirely in the legs. And their legs, although luxurious, are rather frail due to weak muscles, so sea spiders are very unhurried creatures and can spend 40 minutes without any movement at all. Because of this, bryozoans and all sorts of polyps grow on them, and amphipods and sea goats are happy to use these stilts as a substrate. Particularly leisurely individuals even manage to fall into a trap - they do not move for so long that a sponge has time to grow around their legs. But long legs allow you to move on any, even the softest substrate, and sea spiders can be found almost everywhere, from the tidal zone to deep-sea habitats.

The life of a sea spider is the life of a leisurely benthic vagrant. Any mobile prey is faster than this predator, and therefore it mainly feeds on attached soft organisms like hydroid polyps. At the front end of the spider's body there is a tiny head with a rigid trunk and heliphors armed with claws. The spider uses a trunk to suck out polyps, and with claws it tears off soft pieces from the victim, which are then digested in the processes of the midgut located in the legs (!). I must say that real spiders also have intestines with lateral processes, but they are much shorter and do not go into the limbs. By the way, it is interesting that sea spiders do not have any gas exchange organs - it is believed that with such a leisurely lifestyle, the tiny amount of oxygen that is absorbed through the surface of the body is enough.

On the tiny head of a sea spider is a small eye tubercle with two pairs of eyes that distinguish between light and shadow and, possibly, the contours of objects. With the help of these eyes, the male spider finds the female, whose slender legs are filled with maturing eggs, sits on top of her and rides on her, waiting for the eggs to mature. Most sea spiders have separate sexes, but one hermaphroditic species is also known - Ascorhynchus corderoi.

Unlike other arthropods, sea spiders have several pairs of genital openings, and they are located on walking legs. After the eggs have matured, the female lays them, and the male immediately fertilizes the clutch. Then the male collects eggs in cocoons, fastening them with a gelatinous substance, which is secreted by cement glands, also located on his legs, and puts them on special egg-bearing legs. Mating of sea spiders lasts from half an hour to several hours, and in some species it can last for weeks. After the end of this unhurried process, the care of the offspring falls entirely on the shoulders of the male, and in the literal sense: he wears cocoons on himself until the very late stages of embryonic maturation. Moreover, during the season, the male can mate with several females, and then there will be several cocoons from different mothers on his egg-bearing legs.

See also:
Sea spiders, "Nature", No. 8, 2006.

Veronika Samotskaya

(the average: 4,62 out of 5)

Yesterday, September 26, was World Maritime Day. In this regard, we bring to your attention a selection of the most unusual sea creatures.

World Maritime Day has been celebrated since 1978 on one of the days of the last week of September. This international holiday was created in order to draw public attention to the problems of pollution of the seas and the disappearance of animal species living in them. Indeed, over the past 100 years, according to the UN, some species of fish, including cod and tuna, have been caught by 90%, and every year about 21 million barrels of oil enter the seas and oceans.

All this causes irreparable damage to the seas and oceans and can lead to the death of their inhabitants. These include those that we will discuss in our selection.

This animal got its name due to the ear-like formations protruding from the top of its head, which resemble the ears of the Disney elephant Dumbo. However, the scientific name of this animal is Grimpoteuthis. These cute creatures live at depths of 3,000 to 4,000 meters and are among the rarest octopuses.

The largest individuals of this genus were 1.8 meters long and weighed about 6 kg. Most of the time, these octopuses swim above the seabed in search of food - polychaete worms and various crustaceans. By the way, unlike other octopuses, these swallow their prey whole.

This fish attracts attention, first of all, with its unusual appearance, namely, bright red lips on the front of the body. As previously thought, they are necessary to attract marine life, which feeds on the bat. However, it was soon found out that this function is performed by a small formation on the head of the fish, called an eska. It emits a specific smell that attracts worms, crustaceans and small fish.

The unusual "image" of the bat complements the no less amazing way of its movement in the water. Being a poor swimmer, he walks along the bottom on his pectoral fins.

The short-nosed bat is a deep-sea fish, and lives in waters near.

These deep sea animals have many branched rays. Moreover, each of the rays can be 4-5 times larger than the body of these brittle stars. With the help of them, the animal catches zooplankton and other food. Like other echinoderms, branched brittle stars have no blood, and gas exchange is carried out using a special water-vascular system.

Usually branched brittle stars weigh about 5 kg, their rays can reach 70 cm in length (in branched brittle stars Gorgonocephalus stimpsoni), and the body is 14 cm in diameter.

This is one of the least studied species that can, if necessary, merge with the bottom or imitate a twig of algae.

It is near the thickets of the underwater forest at a depth of 2 to 12 meters that these creatures try to stay so that in a dangerous situation they can acquire the color of the ground or the nearest plant. In the “calm” time for harlequins, they slowly swim upside down in search of food.

Looking at a photo of the harlequin pipe-nosed, it is easy to guess that they are related to seahorses and needles. However, they differ markedly in appearance: for example, the harlequin has longer fins. By the way, this form of fins helps the ghost fish to bear offspring. With the help of elongated pelvic fins, covered on the inside with filamentous outgrowths, the female harlequin forms a special bag in which she bears eggs.

In 2005, an expedition exploring the Pacific Ocean discovered extremely unusual crabs that were covered with "fur" at a depth of 2,400 meters. Because of this feature (as well as coloration), they were called "yeti crabs" (Kiwa hirsuta).

However, it was not fur in the truest sense of the word, but long feathery bristles covering the chest and limbs of crustaceans. According to scientists, many filamentous bacteria live in the bristles. These bacteria purify water from toxic substances emitted by hydrothermal springs, next to which "yeti crabs" live. And there is also an assumption that these same bacteria serve as food for crabs.

Found in the coastal waters of the Australian states of Queensland, New South Wales and Western Australia, this fish is found on reefs and in bays. Due to its small fins and hard scales, it swims extremely slowly.

Being a nocturnal species, the Australian pine cone spends the day in caves and under rock ledges. So, in one marine reserve in New South Wales, a small group of cones was registered, which hid under the same ledge for at least 7 years. At night, this species leaves its shelter and goes hunting on sandbars, illuminating its path with the help of luminous organs, photophores. This light is produced by a colony of symbiotic Vibrio fischeri bacteria that have settled in photophores. Bacteria can leave the photophores and simply live in seawater. However, their luminescence dims a few hours after they leave the photophores.

Interestingly, the light emitted by the luminous organs is also used by fish to communicate with relatives.

The scientific name of this animal is Chondrocladia lyra. It is a species of carnivorous deep-sea sponge, and was first discovered off the California coast at a depth of 3300-3500 meters in 2012.

The sponge lyre gets its name from its harp or lyre-like appearance. So, this animal is kept on the seabed with the help of rhizoids, root-like formations. From their upper part stretches from 1 to 6 horizontal stolons, and on them vertical "branches" with spatulate structures at the end are located at an equal distance from each other.

Since the lyre sponge is carnivorous, it captures prey, such as crustaceans, with these “branches”. And as soon as she manages to do this, she will begin to secrete a digestive membrane that will envelop her prey. Only after that, the lyre sponge will be able to suck in the split prey through the pores.

The largest recorded sponge-lyre reaches almost 60 centimeters in length.

Living in almost all tropical and subtropical seas and oceans, clownfish are one of the fastest predators on the planet. After all, they are able to catch prey in less than a second!

So, having seen a potential victim, the "clown" will track it down, remaining motionless. Of course, the prey will not notice it, because the fish of this family usually resemble a plant or a harmless animal with their appearance. In some cases, when the prey comes closer, the predator will begin to move the esca, an outgrowth of the anterior dorsal fin that resembles a "fishing pole", which causes the prey to get even closer. And once a fish or other marine animal gets close enough to the clown, it will suddenly open its mouth and swallow the prey in just 6 milliseconds! Such an attack is so lightning fast that it cannot be seen without slow motion. By the way, the volume of the oral cavity of the fish while catching the victim often increases 12 times.

In addition to the speed of clownfish, an equally important role in their hunting is played by the unusual shape, color and texture of their cover, allowing these fish to mimic. Some clownfish resemble rocks or coral, while others resemble sponges or sea squirts. And in 2005, the Sargassum sea clown was discovered, which imitates algae. The "camouflage" of clown fish can be so good that sea slugs often crawl on these fish, mistaking them for corals. However, they need "camouflage" not only for hunting, but also for protection.

Interestingly, during the hunt, the "clown" sometimes sneaks up on prey. He literally approaches her using his pectoral and ventral fins. These fish can walk in two ways. They can alternately move their pectoral fins without using the pelvic fins, or they can transfer body weight from the pectoral fins to the pelvic fins. Gait in the latter way can be called a slow gallop.

The small-mouthed macropinna living in the depths of the northern part of the Pacific Ocean has a very unusual appearance. She has a transparent forehead, through which she can look out for prey with her tubular eyes.

A unique fish was discovered in 1939. However, at that time it was not possible to study it well enough, in particular the structure of the cylindrical eyes of fish, which can move from a vertical position to a horizontal one and vice versa. This was only done in 2009.

Then it became clear that the bright green eyes of this small fish (it does not exceed 15 cm in length) are in the head chamber filled with a transparent liquid. This chamber is covered by a dense, but at the same time elastic transparent shell, which is attached to the scales on the body of the small-mouth macropinna. The bright green color of the fish's eyes is due to the presence of a specific yellow pigment in them.

Since the small-mouthed macropinna is characterized by a special structure of the eye muscles, its cylindrical eyes can be both in a vertical position and in a horizontal position, when the fish can look straight through its transparent head. Thus, the macropinna can notice the prey, both when it is in front of it, and when it swims above it. And as soon as the prey - usually zooplankton - is at the level of the fish's mouth, it quickly grabs it.

These arthropods, which are not actually spiders or even arachnids, are common in the Mediterranean and Caribbean Seas, as well as in the Arctic and Southern Oceans. Today, more than 1300 species of this class are known, some of which reach 90 cm in length. However, most sea spiders are still small in size.

These animals have long legs, of which there are usually about eight. Also, sea spiders have a special appendage (proboscis) that they use to suck food into the intestines. Most of these animals are carnivorous and feed on cnidarians, sponges, polychaete worms and bryozoans. So, for example, sea spiders often feed on sea anemones: they insert their proboscis into the body of an anemone and begin to suck in its contents. And since sea anemones are usually larger than sea spiders, they almost always survive such “torture”.

Sea spiders live in different parts of the world: in the waters of Australia, New Zealand, off the US Pacific coast, in the Mediterranean and Caribbean seas, as well as in the Arctic and Southern oceans. Moreover, they are most common in shallow water, but can be found at a depth of up to 7000 meters. Often they hide under rocks or camouflage themselves among algae.

The color of the shell of this orange-yellow snail seems very bright. However, only the soft tissues of a live mollusk have this color, and not the shell. Usually Cyphoma gibbosum snails reach 25-35 mm in length, and their shell is 44 mm.

These animals live in the warm waters of the western Atlantic Ocean, including the Caribbean Sea, the Gulf of Mexico and the waters of the Lesser Antilles at a depth of up to 29 meters.

Living at shallow depths in tropical and subtropical seas, mantis shrimp have the most complex eyes in the world. If a person can distinguish 3 primary colors, then the mantis shrimp - 12. Also, these animals perceive ultraviolet and infrared light and see different types of light polarization.

Many animals are able to see linear polarization. For example, fish and crustaceans use it to navigate and locate prey. However, only mantis shrimp are able to see both linear polarization and the rarer, circular polarization.

Such eyes enable mantis shrimp to recognize different types of corals, their prey and predators. In addition, during the hunt, it is important for cancer to deliver accurate blows with its pointed grasping legs, which is also assisted by its eyes.

Sea spiders are often referred to as multi-legged animals. They belong to the class Cheliceraceae, the type of these creatures is Arthropods. Also acceptable is the classification by which the term "Chelicerate" is defined as the subtype from which sea spiders are separated into a class of their own. There are several more variants of scientific names for this class - Pantopods, Pycnogonids and others.

Some general information

The concept of "sea spider" includes more than 1300 different species from a dozen families. They live in the seas all over the world. You can meet marine arthropods at different depths. Some species prefer the lower littoral (tidal section of the coast), others descend to the abyssal (deep zone). In saline and weakly saline waters, multi-elbows are much more common than in desalinated inland seas. In coastal areas, spiders settle in thickets of algae and on the ground.

Deep-sea and littoral spider species have differences in both body structure and size. In deeper layers of water, the sea spider will be larger, it will have significantly longer and thinner legs, which may have long hairs. These devices allow you to reduce the rate of immersion. The spider does not just swim, but seems to soar in the water. To sink to the bottom, it is enough for him to compactly fold his long limbs under the body.

Coastal forms are more compact. Their legs are thicker and shorter, but they have developed tubercles and spikes necessary for hunting and protection.

Structural features

Any sea spider, both deep-sea and coastal species, has a typical structure. The body is divided into two tagmas (sections). Their names are segmented prosoma and non-segmented opisoma. The prosoma is cylindrical or disc-shaped.

The torso of sea spiders is smaller than the limbs and is covered with a chitinous cuticle. There is a division into the cephalothorax and abdomen (it is rudimentary). There are from 7 to 9 segments in the cephalothorax, 4 of them are fused together. The fused part of the cephalothorax is called the head segment. The remaining segments can be either fused or dissected. In front of the head segment is a cylindrical or ovoid trunk. On the lateral parts of the trunk, 2 pairs of limbs are fixed: heliphores and palps. The third pair of limbs (ten-segmented egg-bearing legs) is fixed on the ventral side of the head section. One of the structural features of sea spiders is that 3 front pairs of legs do not reach the ground and do not participate in walking.

The walking legs of the sea spider are attached to the lateral processes of the head segment of the body. Most often there are 4 pairs, but some representatives have 5-6 pairs.

Digestive system

The sea spider has a digestive system in the form of a poorly differentiated through tube with diverticula. The diverticulum in this case is a process of the intestine that goes into each leg. The digestion of these arthropods is combined. Both cavity and intracellular form are used in common.

diet

It is not difficult to guess what sea spiders eat. Most of them are predators. Their diet consists of sessile and inactive invertebrates. These can be polychaetes, bryozoans, ciliates, anemones, intestinal and cephalobranch mollusks, small echinoderm starfish. Prey is held by claws on heliphors. They also break off pieces of food and go into the mouth.

gigantomania

Not so long ago, a giant sea spider was found in the waters of Antarctica. Studying an individual, scientists drew attention to a mysterious phenomenon, which they called polar gigantism. For some as yet unknown reason, Antarctica's icy waters are transforming common sea spider species into giants. Perhaps the increased growth is due to the amount of oxygen, which is more in cold water than in warm water.

It has been established that not only spiders, but also some mollusks, crustaceans and echinoderms suffer from gigantomania in Arctic waters. Research is ongoing.

"Starfish and Spider"

Do you think we will continue to discuss the structure and life of marine animals? But you are wrong! In this section, we will talk about a fascinating book that explains the principle of success for various companies and organizations. Some of them are traditional, like spiders: they have legs growing from the body, they have a head and eyes. They may function with part of a leg or an eye missing, but without a head they will die.

Another thing is the starfish, although its body parts look ordinary, they have completely different functions: the animal has no head and brain at all, and the main organs are repeated in each limb. Moreover, if you cut off a limb of a star, it will be restored. Even if you cut the sea beauty into several parts, it will not die, and after a while the halves will become independent animals. In fact, using this unique animal as an example, we can consider companies that function like decentralized networks.

The book "The Starfish and the Spider" is a vivid example of the fact that everything in nature is reasonable, and it is useful to apply many laws of development in other areas of human activity.

Sea spiders breathe through their legs, or rather through their tips. In the course of evolution, their limbs began to function as gills.

Sea spiders or pantopods are a class of marine arthropods. More than 1300 species have been described. Such spiders live in all seas and at different depths. Pantopods are especially widespread in the oceans. In seas with fresh water, they are almost never found. Sea spiders do not spin webs.

Deep-sea spider species are larger than coastal ones. The body length of sea spiders can reach from 1 mm to 90 cm. Coastal species have a compact body, short legs and developed tubercles and spines. Deep-sea species have longer and thinner limbs, a smooth body and correspondingly poorly developed spines and tubercles. Pantopods are capable of swimming or hovering in the water column. With sharp movements of the legs, they push off the ground and hang in the water, where they can soar almost without movement. They sink to the bottom, raising their legs up and folding them under the body.

Sea spiders are predators. Pantopods feed on sea anemones and sponges. Their mouth is located at the end of the proboscis and works like a pump, drawing in soft food. In the back half of the pharynx is a kind of filter, which serves to crush and strain food. The sense organs of sea spiders are poorly developed. For touch, they use sensitive hairs and bristles located throughout the body. The organs of vision in spiders are 2 pairs of eyes located on the dorsal side of the head. Deep-sea forms may lack eyes. With the help of the eyes, animals distinguish the direction of light and some movement.

Sea spiders are strange, unlike animals, consisting almost entirely of legs alone. The limbs are rather weak due to poorly developed muscles. Creatures lead a leisurely lifestyle and can spend 40 minutes without any movement at all. Their body is so tiny that some of the internal organs are located just in the legs. For example, these are the organs of the reproductive and digestive systems. Sea spiders are dioecious creatures. The reproductive system is represented by several pairs of genital openings located along the entire length of the walking legs.

The intestines of pantopods are distributed evenly throughout the body, going into each leg until its very end. In addition to digestion, it performs a kind of function of the circulatory system. With its help, hemolymph flows through the body - an analogue of blood in mammals. The movement of the hemolymph is created by contraction of the intestine. But that is not all. Sea spiders also breathe through their legs, or rather through their tips. In the course of evolution, their limbs began to function as gills. Based on this feature, sea spiders do not have the usual gas exchange organs. A leisurely lifestyle does not require a large amount of oxygen.