Sea spiders. Sea spider - a mysterious inhabitant of the depths

The systematic and evolutionary position of which has not yet been fully determined. Despite the name, sea spiders (Pycnogonida) have no relation to real spiders, although they are considered an early separated group of the chelicerate subtype, which includes arachnids and merostomids, that is, horseshoe crabs and crustaceans.

Sea spiders are a relatively small group, currently numbering about 1,300 species. The earliest record of a sea spider as a larva dates back to the Cambrian period, and there are also descriptions of finds from Silurian and Devonian deposits.

These are very strange animals, morphologically unlike anything else, consisting almost entirely of only legs. Their body is so tiny that even half of the internal organs that normal animals should have can fit in it. 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 leisurely creatures and can spend 40 minutes without moving at all. Because of this, bryozoans and all sorts of polyps grow on them, and amphipods and sea goats gladly 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 manages to grow around their legs. But their long legs allow them to move on any, even the softest, substrate, and sea spiders can be found almost everywhere, from the intertidal zone to deep-sea habitats.

The life of a sea spider is that of a leisurely bottom wanderer. Any mobile prey is faster than this predator, and therefore its food is mainly 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 heliphores armed with claws. The spider uses its trunk to suck out polyps, and with its claws it tears off soft pieces from the victim, which are then digested in the processes of the midgut located in the legs (!). It must be said that real spiders also have intestines with lateral processes, but they are much shorter and do not extend 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 volume of oxygen that is absorbed through the surface of the body is sufficient.

On the sea spider's tiny head is a small eye tubercle with two pairs of eyes that detect light and shadow and possibly the outlines of objects. Using these eyes, the male spider finds a female whose slender legs are filled with ripening eggs, sits on top of her and rides on her, waiting for the eggs to mature. Most sea spiders are dioecious, but one hermaphroditic species is also known - Ascorhynchus borderoi.

Unlike other arthropods, sea spiders have several pairs of genital openings, and they are located on walking legs. After the eggs mature, the female lays them, and the male immediately fertilizes the clutch. Then the male collects the eggs into 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 this slow process is over, caring for the offspring falls entirely on the shoulders of the male, and in the literal sense: he carries the cocoons on himself until the late stages embryonic maturation. Moreover, during a season, a male can mate with several females, and then on his egg-bearing legs there will be several cocoons from different mothers.

See also:
Sea spiders, “Nature”, No. 8, 2006.

Veronica Samotskaya

Sea spiders, also known as spider crabs, also known as marble crabs, live in the Mediterranean, Black Sea and Atlantic Ocean, near the coasts of Morocco and France. They are found on the Crimean peninsula and the Caucasus coast, 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 received the name “marble” due to the characteristic pattern on the shell.

Description of the sea spider

The spider crab is small and agile, its body length reaches only 38 millimeters and its width is 43 millimeters. The carapace is square and flat. The anterior edge, located between the eyes, is especially wide and straight, with 3 sharp teeth on each side. The upper part of the shell can become overgrown with small crustaceans called balanuses, as well as algae.

The skeleton is external, respiration is carried out using gills. The left claw has small teeth that tightly close together. The right claw is larger than the left, the teeth are curved, and there is a gap between them. Externally, the right claw resembles forceps. The marble crab is a decapod crustacean, has 10 long, strong legs, covered with hairs. The color of the shell ranges from brownish-greenish to brownish-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 depths of up to 10 meters.

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

Sea spiders feed on the remains of plants and animals, plankton, mollusks and polychaetes. They climb onto rocks 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 rushes into the water.

At night, he carefully crawls out of his old shell. At night they can climb onto 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 claw, 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 occurs 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.

Marble crab population

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 numbers have recently decreased sharply. These crabs are protected in nature reserves Karadag and Cape Martyan.

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 most large crabs at the Black Sea. The width of the stone crab's shell 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 is smaller in size, and its carapace is covered with numerous yellowish hairy bristles. They live closer to the shore, under the rocks;
Mediterranean or grass crabs have a green shell, which is why they are called “grass crabs.” Grass crabs are shallow water dwellers;
Water crab or lilac crab. It is slower and prefers to live exclusively in shallow water;

The swimming crab loves to burrow into the ground. Its small hind legs look like 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 waters of ships. But the Black Sea water 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 and thin sea creatures are excellent at camouflage;
The Pea Crab typically lives among the mussels and can sometimes even crawl inside the shell. It is extremely difficult to see this crab, since an adult is no larger than a ten-kopeck coin;
Freshwater crab is an unusual Crimean crab. It differs not in size, but in origin and lifestyle. From the name it is clear that it lives in fresh water: in mountain rivers and ponds.

Freshwater crabs cannot be spread by currents, so they must travel on land at night. They once crossed the entire continent on foot in this manner and are believed to have 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, and there should be a variety of shelters at the bottom, for example, driftwood, stones, and ceramics. To make the aquaterrarium look more beautiful, it can be enlivened with the help of plants.

Sea spiders breathe through their legs, or rather through their tips. During evolution, their limbs began to serve as gills.

Sea spiders or pantopods are a class of marine arthropods. More than 1,300 of its species have been described. Such spiders live in all seas and at different depths. Pantopods are especially widespread in the oceans. In the seas with fresh water they almost never occur. Sea spiders do not weave webs.

Deep-sea species of spiders 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, accordingly, poorly developed spines and tubercles. Pantopods are capable of swimming or soaring in the water column. With sudden movements With their feet they push off from the ground and hang in the water, where they can float almost motionless. They sink to the bottom, lifting their legs up and folding them under their 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 there is a kind of strainer that serves to grind 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 have no eyes. With the help of their eyes, animals distinguish the direction of light and some movement.

Sea spiders are strange, unlikeable animals, consisting almost entirely of legs alone. The limbs are rather weak due to poorly developed muscles. The creatures lead a leisurely lifestyle and can spend 40 minutes without moving at all. Their bodies are so tiny that some internal organs are located just in the legs. For example, these are the reproductive organs 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, extending into each leg to its very end. In addition to digestion, it performs a kind of function circulatory system. With its help, hemolymph flows through the body - an analogue of blood in mammals. The movement of hemolymph is created by intestinal contractions. But that is not all. Sea spiders also breathe through their legs, or rather through their tips. During evolution, their limbs began to serve as gills. Based on this feature, sea spiders lack the gas exchange organs familiar to us. A leisurely lifestyle does not require large amounts of oxygen.

(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 last week September. This international holiday was created in order to attract public attention to the problems of sea pollution and the extinction of animal species living in them. Indeed, over the past 100 years, according to the UN, some types 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 talk about in our selection.

This animal received its name due to the ear-like structures protruding from the top of its head, which resemble the ears of Disney's baby 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 one of the rarest octopuses.

The largest individuals of this genus were 1.8 meters in length 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 with bright red lips on the front of the body. As previously thought, they are necessary to attract marine life, which the pipistrelle bat feeds on. However, it was soon discovered that this function is performed by a small formation on the fish’s head, called the esca. It emits a specific odor that attracts worms, crustaceans and small fish.

The unusual “image” of the pipistrelle bat is complemented by an equally amazing way of moving in water. Being a poor swimmer, it walks along the bottom on its pectoral fins.

The short-snouted pipistrelle is a deep-sea fish and lives in the waters near.

These deep-sea marine animals have many branched arms. Moreover, each of the rays can be 4-5 times larger than the body of these brittle stars. With their help, the animal catches zooplankton and other food. Like other echinoderms, branched brittle stars lack blood, and gas exchange is carried out using a special water-vascular system.

Typically, branched brittle stars weigh about 5 kg, their rays can reach 70 cm in length (in the branched brittle stars Gorgonocephalus stimpsoni), and their 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 branch 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 soil or the nearest plant. During “quiet” times for harlequins, they slowly swim upside down in search of food.

Looking at a photograph of a harlequin tubesnout, it is easy to guess that they are related to seahorses and pipefish. However, they differ noticeably in appearance: for example, the harlequin has longer fins. By the way, this shape of fins helps the ghost fish bear offspring. With the help of elongated pelvic fins, covered on the inside with thread-like outgrowths, the female harlequin forms a special pouch in which she bears eggs.

In 2005, an expedition exploring the Pacific Ocean discovered extremely unusual crabs that were covered in “fur” at a depth of 2,400 meters. Because of this feature (as well as their coloring), they were called “Yeti crabs” (Kiwa hirsuta).

However, it was not fur in the literal 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 vents, near which “Yeti crabs” live. There is also an assumption that these same bacteria serve as food for crabs.

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

Being a nocturnal species, the Australian conefish spends the day in caves and under rocky outcroppings. Yes, in one marine reserve In New South Wales, a small group of coneworts has been recorded hiding under the same ledge for at least 7 years. At night, this species comes out of hiding and goes hunting on sandbanks, illuminating its path with the help of luminescent organs, photophores. This light is produced by a colony of symbiotic bacteria, Vibrio fischeri, which has taken up residence in the photophores. Bacteria can leave photophores and simply live in sea ​​water. However, their luminescence fades a few hours after they leave the photophores.

Interestingly, fish also use the light emitted by their luminescent organs to communicate with their relatives.

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

The lyre sponge gets its name from its appearance, which resembles a harp or lyre. So, this animal is held on seabed with the help of rhizoids, root-like formations. From 1 to 6 horizontal stolons extend from their upper part, and on them, at equal distances from each other, are vertical “branches” with spade-shaped structures at the end.

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

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

Living in almost all tropical and subtropical seas and oceans, fish from the clown family are among 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 fish of this family usually resemble a plant or a harmless animal in their appearance. In some cases, when the prey comes closer, the predator begins to move the tail, an extension of the front dorsal fin that resembles a “fishing rod,” which forces the prey even closer. And as soon as a fish or other sea animal is close enough to the “clown”, it will suddenly open its mouth and swallow its prey, spending only 6 milliseconds! This attack is so lightning fast that it cannot be seen without slow motion. By the way, the volume oral cavity When catching prey, the size of a fish 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, which allows these fish to mimic. Some clownfish resemble rocks or corals, while others resemble sponges or sea squirts. And in 2005, Sargassum clown sea, which imitates algae, was discovered. The “camouflage” of clownfish can be so good that sea slugs often crawl over these fish, mistaking them for coral. However, they need “camouflage” not only for hunting, but also for protection.

Interestingly, during a hunt, the “clown” sometimes sneaks up on its 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, and they can transfer their body weight from the pectoral fins to the pelvic fins. The latter method of gait can be called a slow gallop.

Living in the depths of the northern part Pacific Ocean smallmouth macropinna has a very unusual appearance. She has a transparent forehead through which she can look out for prey with her tubular eyes.

The 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 the fish, which can move from a vertical position to a horizontal one and vice versa. This was only possible in 2009.

Then it became clear that the bright green eyes of this small fish (it does not exceed 15 cm in length) are located in a 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 smallmouth macropinna. Bright green color The fish's eyes are explained by the presence of a specific yellow pigment in them.

Since the smallmouth macropinna is characterized by a special structure of the eye muscles, its cylindrical eyes can be in both a vertical position and in a horizontal position, when the fish can look directly through its transparent head. Thus, macropinna can notice 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 1,300 species of this class are known, some representatives 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. Sea spiders also have a special appendage (proboscis) that they use to absorb food into the intestines. Most of these animals are carnivorous and feed on cnidarians, sponges, polychaete worms and bryozoans. For example, sea spiders often feed on sea anemones: they insert their proboscis into the body of the sea anemone and begin to suck its contents into themselves. And since sea anemones are usually larger than sea spiders, they almost always survive such “torture.”

Sea spiders live in different parts world: in the waters of Australia, New Zealand, off the Pacific coast of the United States, 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 also be found at depths of up to 7000 meters. They often hide under rocks or camouflage themselves among algae.

The shell color of this orange-yellow snail seems very bright. However, only the soft tissues of a living mollusk have this color, and not the shell. Typically, 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, Gulf of Mexico and the waters of the Lesser Antilles at depths of up to 29 meters.

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

Many animals are able to see linear polarization. For example, fish and crustaceans use it to navigate and detect prey. However, only mantis crabs are able to see both linear polarization and a rarer, circular one.

Such eyes enable mantis crayfish to recognize Various types corals, their prey and predators. In addition, when hunting, it is important for the crayfish to deliver precise strikes with its pointed, grasping legs, in which its eyes also help.

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4. Giant sea spider (Pantopoda)

Giant sea Spiders are a relatively little studied group of organisms. And they are only indirectly related to spiders. Pantopods They are called sea spiders only for their external resemblance; in fact, they are not spiders.

Pantopods widespread in the world's oceans. They live in northern seas, and in the south. Some of their species can be found in the surface layer of water, and some sea spiders have been found even at a depth of 7300 meters.

The structural features of these animals include a big difference in the length of the torso and limbs. For example sea ​​spider with a body size of 15-18mm. has limb lengths up to 240mm. Cephalothorax pantopods consists of 7-9 segments, followed by a rudimentary abdomen.

Due to the disproportionately small body, some internal organs pantopod are on their limbs.

Sea spiders are predators. They eat soft tissues sea ​​anemones, sponges, hydroids.

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3. Vespa mandarinia (Asian giant hornet)

This Asian giant is one of the most dangerous animals on this list to humans. - the largest hornet in the world. The body length of the average male is 51mm, and the wingspan is 75mm. These giants live in Southeast Asia - in Primorye, Japan, China, Korea, Nepal, India and in the mountainous regions of Sri Lanka.

The sting of this hornet can be fatal to humans. has a sting about 6mm long, which stings with discharge large quantity poison. The venom of these hornets is very toxic. But hornets rarely use their sting. Hornets hunt with the help of powerful jaws, which tear apart their prey.

They feed in the same way as their smaller counterparts from the Vespa genus - their diet consists of various insects, fruits, and berries. Hornets do not disdain the meat of fish washed ashore.

Cause great harm to beekeepers. Just a few hornets can easily and quickly destroy an entire bee colony. Beekeepers quite often suffer from the invasion of giant hornets, suffering huge losses. Therefore, whenever possible, beekeepers try to destroy hornet nests. When destroying a nest, hornets fiercely defend themselves, biting and stinging people. It is among beekeepers that the mortality rate from giant hornet bites is very high - dozens of people die every year around the world.