Shchiten: why is it called a “living fossil”, and what else is it interesting about?

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Shrew (Triopsidae) is a genus of small crustaceans from the suborder Notostraca. Some species are considered living fossils, with origins dating back to the end of the Carboniferous period, namely 300 million years ago. Along with horseshoe crabs, shield crabs are the most ancient species. They have lived on Earth since the time of dinosaurs, and have not changed at all since those times, with the exception of decreasing in size. These are the most ancient animals existing today.

Origin of the species and description

Photo: Shchiten

The suborder Notostraca contains one family, Triopsidae, and only two genera, Triops and Lepidurus. By the 1950s, up to 70 species of shield bugs had been discovered. Many putative species are described based on morphological variation. There were two important revisions to the classification of the family - Linder in 1952 and Longhurst in 1955. These revised many of the taxa and defined only 11 species in two genera. This taxonomy was accepted for decades and was considered dogma.

Video: Shchiten

Interesting fact: More recent studies using molecular phylogenetics have demonstrated that the eleven currently recognized species harbor more reproductively isolated populations.

The shieldfish is sometimes called a “living fossil” because fossils belonging to the suborder were discovered in rocks of the Carboniferous period, some 300 million years ago. One extant species, the crustacean T. cancriformis, has remained virtually unchanged since the Jurassic period (about 180 million years ago).

There are many fossils of shieldfish found in a range of geological deposits. The absence of serious morphological changes that occurred in the family over the 250 million years of existence of these animals suggests that dinosaurs also saw shields in this form. Casachartra, an extinct group known only from Triassic and Jurassic fossils from western China and Kazakhstan, is closely related to shieldfishes and may belong to the order Notostraca.

Classification

The shield system is far from complete, since very few biologists are working on them. For 2008, 16 species have been preliminarily identified:

Genus Lepidurus (Leach, 1819)

• Spring shieldweed ( Lepidurus apus
  Linnaeus, 1758)
• Lepidurus arcticus (Pallas, 1776)
• Lepidurus batesoni (Lonhorst, 1955)
• Lepidurus bilobatus (Packard, 1883)
• Lepidurus couesii (Packard, 1875)
• Lepidurus cryptus (Rogers, 2001)
• Lepidurus lemmoni (Holmes, 1894)
• Lepidurus lynchi Linder, 1952
• Lepidurus mongolicus (Vekhoff, 1992)
• Lepidurus packardi Simon, 1886

Genus Triops (Schrank, 1803)

• Triops australiensis (Spencer & Hall, 1895)
• Summer or common or crustacean ( Triops cancriformis
  Bosc, 1801)
• Triops granarius (Lucas, 1864)
• Triops longicaudatus (LeConte, 1846)
• Triops numidicus (Grube, 1865)
• Triops newberryi (LeConte, 1846)

Appearance and features

Photo: What the shield looks like

Shields are 2–10 cm long, have a wide carapace in the front and a long thin abdomen. This creates an overall tadpole-like shape. The carapace is dorsoventrally flattened and smooth. The front portion includes the head, and two rocky eyes located together on the top of the head. Two pairs of antennas are significantly reduced, and the second pair is sometimes absent altogether. The oral cavities contain a pair of single-branched antennules and no jaws.

Ventral side of the scale, showing up to 70 pairs of legs. The torso contains a large number of "body rings", which look like body segments but do not always reflect the underlying segmentation. The first eleven body rings make up the thorax and bear one pair of legs, each of which also has a genital opening. In the female it is modified, forming a “brood pouch”. The first one or two pairs of legs are distinct from the rest and probably function as sensory organs.

The remaining segments form the abdominal cavity. The number of body rings varies both within and between species, and the number of pairs of legs per body ring can be up to six. The legs gradually become smaller along the abdomen, and in the last segments they are completely absent. The abdomen ends in a telson and a pair of long, thin, multi-jointed caudal branches. The shape of the telson varies between the two genera: in Lepidurus a rounded projection extends between the caudal rami, while in Triops there is no such projection.

Interesting fact: Some species have the ability to turn pink when there is a large amount of hemoglobin in their blood.

The color of shieldweed is often brown or grayish-yellow. On the proximal side of the abdomen, the animal has many small hair-like appendages (about 60) that move rhythmically and allow the individual to direct food towards the mouth. Males and females differ in both size and morphology. Males tend to have a slightly longer carapace length and possess larger secondary antennae that can be used as clamps during breeding. In addition, females have an egg sac.

Now you know what a shield looks like. Let's see where this crustacean lives.

Rare inhabitants

Among the inhabitants that are quite unusual for home aquariums is the following rare guest.
The octopus, a creature with numerous tentacles, can truly be considered the most outlandish inhabitant of the home aquarium. The unusual interest in this deep-sea creature can also be explained by the mysterious stories, legends and myths associated with it, which are countless in scientific and fiction literature, cinema and other sources. The only pity is that these magnificent representatives of marine cephalopods do not live long when kept at home - only 1 to 3 years at best.

Maintaining this deep-sea inhabitant is not cheap at all, because:

• the octopus itself costs a lot of money;
• he needs a huge aquarium with a volume of at least 0.3 cubic meters;
• For such an aquarium you need a powerful filter;
• eats only expensive live food: shrimp, shellfish, crabs and other seafood;
• he has an excellent appetite.

Most often purchased for home keeping are Californian two-spotted and Atlantic dwarf octopuses.

You can also make a small list of extraordinary inhabitants of aquariums, meeting whom among your acquaintances and friends can be considered a great success.

Rainbow crab. This seemingly most unusual animal among all arthropods is called differently everywhere: indigo, tricolor, patriot, land crab. It comes from the west coast of Africa, where it lives in burrows and among rocks. Its shell is painted blue, its legs are orange, and its belly is white with bluish streaks. In captivity, crabs live from 7 to 10 years, eat meat, various fruits and vegetables. To keep them, you need an aquarium of strict dimensions (60x45x45) and good water, which needs to be slightly salted.

Where does the shieldfish live?

Photo: Common shrew

Shrews can be found in Africa, Australia, Asia, South America, Europe (including the UK), and parts of North America where the climate is suitable. Some eggs remain unaffected from the previous group and hatch when rain soaks the area where they are located. This animal has calmly adapted to existence on all continents except Antarctica. It is found on most of the islands in the Pacific, Atlantic, and Indian oceans.

The habitat of the shieldweed is located in:

• Eurasia, 2 species live everywhere there: Lepidurus apus + Triops cancriformis (summer shieldweed);
• America, such species as Triops longicaudatus, Triops newberryi, etc. have been recorded;
• Australia, several subspecies live everywhere under the combined name Triops australiensis;
• Africa has become home to the species - Triops numidicus;
• the species Triops granarius has become a favorite in South Africa, Japan, China, Russia and Italy. Shield beetles are found throughout the world in freshwater, brackish or saline waters, as well as in shallow lakes, peat bogs and heathlands. In rice fields, Triops longicaudatus is considered a pest because it liquefies sediment, preventing light from reaching rice seedlings.

Mostly, scale insects are found at the bottom of warm (on average 15 - 31 ° C) reservoirs. They also prefer to live in highly alkaline waters and cannot tolerate a pH lower than 6. The water pools in which they live must retain water for a month and not experience significant temperature changes. During the day, shieldfish can be found in the soil of a reservoir or in its thickness, digging and collecting food. At night they tend to burrow into the mud.

Content

Micrantemum is a very practical and convenient plant. Even a novice amateur can cope with its cultivation and adaptation. In order for this flora to please with its appearance and grow well, it needs:

Aquarium. It can be of any volume. However, the optimal one is about 70 liters or more. This is due not so much to the whimsical nature of the plant, but to the ease of care. In small containers, if growth is not controlled, this flora can grow greatly and suppress other bushes;

Water parameters. The optimal temperature is 25-28 degrees, since in nature Micranthemum grows in the tropics and prefers warmth. It is advisable to maintain low hardness (about 6°) and medium acidity (6-7 pH);

Lighting. For good growth, diffused light, both artificial and natural, is desirable. Daylight hours are about 10-12 hours;

CO2 supply. Abundant addition of carbon dioxide will significantly accelerate plant growth, but not all species are dependent on this system;

Priming. A fine-fraction substrate is best, as it will allow the roots to spread unhindered;

Fertilizers. You can use liquid UDO, but clay balls placed under the rhizome will also help with growth.

What does the shield eagle eat?

Photo: Crustacean shield

Shields are omnivores, and they also dominate as predators in their niche, eating all animals that are smaller than them. Individuals tend to prefer animal detritus over plant detritus, but will eat both. Insect larvae, as well as various zooplankton, are also the subject of their dietary preferences. They prefer mosquito larvae over other insect larvae.

Fun Fact: When food is scarce, some species of shieldfish resort to cannibalism, eating juveniles or using their pectoral appendages to filter food into their mouths. The thrips longicaudatus species is particularly adept at chewing the roots and leaves of germinating plants such as rice.

Mostly shieldfish are at the bottom, rummaging in the ground in search of food. They are active around the clock, but they need lighting to spend their time productively. It happens that shieldfish are on the surface of the water with their belly upside down. It is not clear what influences this behavior. The original theory about a lack of oxygen was not confirmed. A similar behavior is observed in shieldfish in water saturated with oxygen. This is probably how the animal looks for food and bacteria that have accumulated near the surface.

Some parasitic bacteria of the genus Echinostoma use T. longicaudatus as a host organism. Additionally, more nutrients are provided by this crustacean's constant digging into the pond substrate and raising the sediment. Shitneys are known to significantly reduce the size of mosquito populations by consuming mosquito larvae.

How to properly care

Limnobium belongs to the category of the simplest and most unpretentious aquarium plants to care for, which even a beginner can cope with

However, for its full growth, development, and prevention of possible diseases, aquarists should pay attention to the following maintenance rules:

1. Limnobium requires fairly bright lighting. The optimal length of daylight is about 12 hours. Loves natural light and looks great in the sun. For additional illumination, especially in winter, it is recommended to use fluorescent and LED light bulbs, but it is better to refrain from incandescent lamps, as they can leave pronounced burn marks on the leaf plates. It should be noted that the plant can tolerate slight shading. But, in order for the limnobium to develop well and please the eye, it is better to provide it with a sufficient amount of light.
2. Water and soil quality. Limnobium is absolutely unpretentious to water quality. But experts recommend periodically changing and filtering it. In this case, you can refrain from using mineral fertilizers and other specialized fertilizers, since the plant receives all the necessary nutrients from water.
3. Temperature. The plant is quite resistant to temperature changes. At temperatures below 20°C, the processes of growth and development of limnobium slow down. Too high a temperature, on the contrary, can negatively affect the condition and external characteristics of the sheet plates.

For Limnobium, the acidity of water does not matter, but its hardness should be no more than 12°C.

Features of character and lifestyle

Photo: Summer Shield

Shields are relatively solitary species; their individuals are found separately in different areas of water bodies. This is due to the higher levels of predation that occur when they are in large groups. These small crustaceans use appendages called phyllopods to propel themselves forward in the water. They constantly move throughout the day and are found floating in the water column.

These crustaceans have exopods that allow them to dig through the mud in search of food. They are more active during the day. Research has shown that scale insects can reduce their metabolic rate during times when food becomes scarce or when other environmental conditions are unfavorable. They shed constantly, especially often shedding their tight shell early in their lives.

They most likely use their eyes to identify food items and potential mates (if reproduction occurs sexually). Behind the eyes is the dorsal, occipital organ, which is most likely used for chemoreception, that is, for the perception of chemical stimuli within the body or in the environment.

Shield bugs have a relatively short lifespan, both in the wild and in captivity. Their average lifespan in the wild is 40 to 90 days, unless the temporary pond dries out first. In captivity it can live on average from 70 to 90 days.

Moss as an element of aquadecor

When decorating an aquarium using a water moss gardener, you must consider the following:

• the simultaneous combination of several varieties looks beautiful, especially those that have different shades, for example, queen and singapore;
• if you don’t like the color of the moss, you can change it a little by choosing an unusual angle and lighting level;
• To prevent sphagnum moss from growing too much, it is recommended to cover the container with thin glass.

The culture can be placed either as a solid carpet along the bottom or as local inclusions. The first option is more suitable for a large, spacious aquarium, the second - for a small container. A group of different varieties arranged according to the principle of gradation of shades will look impressive - a gradual transition from the lightest shade to the darkest. If the fish are dark in color, it is better to plant light moss (in contrast), and vice versa, otherwise the inhabitants of the aquarium will be lost against the background of the green space, and it will be quite difficult to observe them.

Social structure and reproduction

Photo: A pair of shields

Within the suborder Notostraca, and even within species, there are significant differences in the mode of reproduction. Some populations reproduce sexually, others exhibit self-fertilization of females, and still others are hermaphrodites combining both sexes. Therefore, the frequency of males in populations varies greatly.

In the sexual population, sperm leaves the male body through simple pores and there is no penis. The cysts are released by the female and are then retained in a cup-shaped brood pouch. The cysts are retained by the female only for a short time before being laid, and the larvae develop directly without going through metamorphosis.

The female keeps the eggs in an egg sac for several hours after fertilization. If conditions are favorable, the female lays white eggs/cysts on various substrates present in the pond. If conditions are not favorable, the female will modify the eggs so that they go into a dormant state and will not hatch until conditions improve. In either case, the first larval stage after deposition is the metanauplius (the larval stage of crustaceans).

At this early stage they are orange in color and have three pairs of limbs and one eye. A few hours later, they lose their exoskeleton and the telson begins to form into plankton. After another 15 hours, the larva again loses its exoskeleton and begins to resemble a miniature adult scale insect.

The juveniles continue to molt and become adults over the next few days. After seven days, the crustacean has the color and shape of an adult and can lay its eggs because it has reached full sexual maturity.

Ecology

Shields live in small temporary (ephemeral) fresh water bodies, where they have no natural enemies (that is, they are at the top of the pyramid). They prefer standing waters.

The reservoirs in which shieldfish live are ephemeral, drying up at certain times of the year; puddles, ditches, ravines. After the lowland is filled with water, within 1-3 days the larvae (nauplii) of shield bugs, about 0.5 mm in size, hatch from the cysts in the ground. They develop very quickly, going through several stages, after about 2 weeks they become fully mature adults and lay cysts of the next generation in the ground. (The cysts through which scale insects reproduce are usually mistakenly called eggs. However, they are already developed embryos, covered with a membrane.)

Shields are omnivorous, in addition, they are the main predators in their ecological niche, eating everything that is smaller than them. In most species, cannibalism is widespread, but it usually occurs when there is a shortage of other food. In some regions, certain varieties of Triops are considered pests because they damage young rice shoots.

The lifespan of shieldfish in the laboratory coincides with field observations: Triops longicaudatus

lives approximately 50-60 days,
Triops cancriformis
- about 90 days.

Natural enemies of shieldfish

Photo: What the shield looks like

These small crustaceans are the main source of food for waterfowl. Many bird species prey on cysts and adults. In addition, wood frogs and other frog species often prey on shield frogs. In times when food is scarce, these crustaceans may resort to cannibalism.

To reduce intraspecific predation, shieldbills tend to be solitary, becoming a smaller target and less visible than a larger group. Their brown coloration also acts as camouflage, blending in with the sediment at the bottom of their pond.

The main predators that hunt shieldfish include:

• birds;
• frogs;
• fish.

Shield bugs are considered human allies against West Nile virus because individuals consume culex mosquito larvae. They are also used as biological weapons in Japan by eating weeds in rice fields. T. cancriformis is used most often for this purpose. In Wyoming, the presence of T. longicaudatus usually indicates a good chance of frogs hatching.

Purchased scalefish are often kept in aquariums and feed on a diet consisting primarily of carrots, shrimp pellets and dried shrimp. Sometimes they are fed live shrimp or daphnia. Since they can eat almost anything, they are also fed regular lunches, crackers, potatoes, etc.

Tips for choosing

The problem of choosing exotic, rare and unusual inhabitants of aquariums for the home arises due to the fact that there is no one to consult with - you can count the number of professionals in this matter on one hand. You can only rely on the sellers - perhaps there will be an intelligent consultant among them. On the other hand, who would describe their product in a bad way? The most realistic option may be to obtain information on the Internet on forums on the topic of aquariums and keeping unusual animals in them.

For our part, we can recommend the following:

• Before choosing, first think about your idea from all sides: who do you decide to get as an unusual pet, what kind of equipment does it need for a comfortable existence, do you have the opportunity to create living conditions, proper feeding and reproduction of such an individual;
• find information about the basic rules for caring for and maintaining a pet, and think about whether you can adhere to them;
• ask the seller or external sources about the pitfalls of keeping and diseases of your future pet;
• Observe the animal in the store for a while to see how it behaves around other aquarium inhabitants or alone.

See below for possible inhabitants of the aquarium.

Javanese

This moss, the photo of which can be seen below, is especially popular among both experienced aquarists and beginners. When looking at it, the first thing that catches your eye is the chaotic interweaving of thin and branching stems, which are covered with a thick layer of leaves with a dark green color. But this impression is deceptive. So, if you detach a small piece from it and move it to another place, leaving it there for several months, you can see a fairly structured picture.

The first step is the growth of stems, which stretch both down and to the sides, completely enveloping the substrate, thereby creating a fairly stable connection with its surface. After this has happened, the moss produces a large number of different shoots, which are directed both horizontally and vertically. Under their influence, the entire mass of moss takes shape with a huge number of layers, arranged in an arched manner with each other. And the last to begin to grow are the stems, which are directed strictly vertically.

As for maintenance, these mosses are one of the most unpretentious representatives of plants in the aquarium. For them, temperature or hardness does not matter at all. They also feel great both in illuminated artificial reservoirs and in its dark areas. But it is worth noting that when placing this moss, it is best to use it on pebbles or driftwood.