The shield (Triopsidae) is a genus of small crustaceans from the suborder Notostraca. Some species are considered living fossils, the origin of which begins at the end of the Carboniferous period, namely 300 million years ago. Along with horseshoe crabs, shields are the most ancient species. They have lived on Earth since the time of the dinosaurs, and have not changed at all since then, with the exception of a decrease in size. These are the most ancient animals that exist today.
Origin of the species and description
The suborder Notostraca includes one family, Triopsidae, and only two genera, Triops and Lepidurus. By the 1950s, up to 70 species of shields had been discovered. Many putative species have been described based on morphological variability. There have been two important revisions to the classification of the — Linder in 1952 and Longhurst in 1955. They — revised many taxa and identified only 11 species in two genera. This taxonomy has been accepted for decades and considered dogma.
Interesting fact: More recent studies using molecular phylogenetics have shown that the eleven currently recognized species harbor more reproductively isolated populations.
The shield is sometimes referred to as a “living fossil” because fossils belonging to the suborder were found in the rocks of the Carboniferous period, somewhere, 300 million years ago. One species that has come down to us, the crustacean shield (T. cancriformis), has not changed much since the Jurassic period (about 180 million years ago).
There are many shield fossils in the range of geological deposits. The absence of serious morphological changes that have occurred in the family over the 250 million years of the existence of these animals suggests that dinosaurs were also seen in this type of shields. The Casachartra, an extinct group known only from Triassic and Jurassic fossils from western China and Kazakhstan, is closely related to shields and may belong to the order Notostraca.
Appearance and features
The shields are 2–10 cm long, have a wide shell in the anterior part, and a long, thin belly. This creates an overall tadpole-like shape. Carapace dorso-ventrally flattened, smooth. The front part includes the head, and two rock eyes placed together on the top of the head. Two pairs of antennas are significantly reduced, and the second pair is sometimes missing altogether. In the oral cavities they contain a pair of single-branched antennules and without jaws.
Ventral side of shield showing up to 70 pairs of legs. The trunk contains a large number of “body rings” that look like body segments but do not always reflect the underlying segmentation. The first eleven rings of the body make up the thorax and carry one pair of legs, each of which also has a genital opening. In the female, it is modified, forming a “brood sac”. The first one or two pairs of legs are different from the rest and probably function as sensory organs.
The remaining segments form the abdominal cavity. The number of body rings varies both within species and between different species, and the number of pairs of legs per body ring can be as high as six. The legs become gradually smaller along the abdomen, and on the last segments they are completely absent. The abdomen terminates in a telson and a pair of long, thin, multi-articular caudal branches. The shape of the telson varies between the two genera: Lepidurus has a rounded projection extending between the caudal branches, while Triops does not.
Fun fact: Some species have the ability to turn pink when in their blood contains a large amount of hemoglobin.
The color of the shield is often brown or grayish-yellow. On the proximal side of the abdomen, the animal has many small hair-like appendages (about 60), which move rhythmically and allow the individual to direct food to the mouth. Males and females differ in both size and morphology. Males tend to have slightly longer carapace lengths and possess larger secondary antennae that can be used as clamps during breeding. In addition, the females have an egg sac.
Now you know what a shield looks like. Let's take a look at where this crustacean lives.
Where does the shield-bill live?
The shield can be found in Africa, Australia, Asia, South America, Europe (including the UK), and parts of North America where the climate is right. Some eggs remain unaffected from the previous group and hatch when rain soaks the area. This animal has calmly adapted to existence on all continents except Antarctica. It is found on most of the islands in the Pacific, Atlantic, Indian Oceans.
The area of the shield is located in:
- Eurasia, 2 species live there everywhere: Lepidurus apus + Triops cancriformis (summer shield);
- America, such species as Triops longicaudatus, Triops newberryi and others were recorded;
- Australia , several subspecies live everywhere, under the combined name Triops australiensis;
- Africa, has become home to the species – Triops numidicus;
- species Triops granarius has chosen South Africa, Japan, China, Russia and Italy. Shields are found throughout the world in freshwater, brackish or salt water, as well as in shallow lakes, peat bogs and moorlands. In paddy fields, Triops longicaudatus is considered a pest because it thins the sediment, preventing light from reaching the rice seedlings.
Basically, shields are found at the bottom of warm (on average from 15 & # 8212; 31 ° C) reservoirs. They also prefer to live in highly alkaline waters and cannot tolerate a pH below 6. The water pools they inhabit must retain water for up to a month and not experience significant temperature changes. During the day, the shields can be found in the soil of the reservoir or in its thickness, swarming and collecting food. At night, they tend to burrow in mud.
What does a shield eat?
Shields are omnivorous, they also dominate as predators in their niche, eating all the animals that feed on them less. Individuals tend to prefer animal detritus over vegetable 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.
Interesting fact: During times of food shortage, some species of shield bugs resort to cannibalism, eating the young or using their pectoral appendages to filter food to their mouths. The thrips species longicaudatus is especially adept at chewing the roots and leaves of germinating plants such as rice.
Basically, the shields are at the bottom, rummaging in the ground in search of food. They are active 24/7, but they need light to thrive. It happens that shields are on the surface of the water turned upside down. It is not clear what influences this behavior. The initial theory about the lack of oxygen was not confirmed. A similar behavior is also observed in water saturated with oxygen. Probably, in this way the animal is looking for food, bacteria that have accumulated near the surface.
Some parasitic bacteria of the genus Echinostoma use T. longicaudatus as an organism — owner. In addition, more nutrients are provided as a result of this crustacean's constant digging into the pond substrate and uplifting the sediment. Shitneys are known to significantly reduce the size of mosquito populations by consuming mosquito larvae.
Personalities and lifestyle features
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 occurs 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 possess exopods that allow them to dig through mud in search of food. They are more active during the day. Research has shown that scutes can lower metabolism at times when food becomes scarce or when other environmental conditions are unfavorable. They constantly molt, especially often shedding their tight shell at the beginning of their lives.
They most likely use their eyes to identify food and potential partners (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 inside the body or in the environment.
Shields 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 reservoir dries up sooner. In captivity, it can live an average of 70 to 90 days.
Social Structure and Reproduction
Within the Notostraca suborder, and even within varieties, there are significant differences in the mode of reproduction. Some populations reproduce sexually, others show self-fertilization of females, and still others are hermaphrodites connecting both sexes. Therefore, the frequency of males in populations varies greatly.
In the sexual population, sperm leaves the male body through simple pores, and the penis is absent. The cysts are released by the female and then held in a cup-shaped brood pouch. The cysts are only retained by the female for a short time before laying, and the larvae develop directly without going through metamorphosis.
The female keeps the eggs in the egg pouch 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 dormant and will not hatch until conditions improve. In any case, the first larval stage after deposition is the metanauplius (crustacean larval stage).
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 shield bug.
Juvenile offspring continue to molt and become adults over the next few days. After seven days, the crustacean takes on the color and shape of an adult and can lay its eggs because it has reached full sexual maturity.
Natural enemies of shield bugs
These small crustaceans are the main food source for waterfowl. Many species of birds prey on cysts and adults. In addition, wood frogs, and other types of frogs, often prey on shield bugs. During times when food is scarce, these crustaceans may resort to cannibalism.
To reduce intraspecific predation, shield bugs tend to be solitary, becoming less of a target and less visible than a large group. Their brown coloration also acts as camouflage, blending into the sediment at the bottom of their pond.
Main predators of the shield hornet include:
Shield insects are considered human allies against West Nile virus, as individuals consume the larvae of Culex mosquitoes. They are also used as bioweapons in Japan by eating weeds in rice fields. T. cancriformis is the most commonly used for this purpose. In Wyoming, the presence of T. longicaudatus usually indicates a good chance of hatching frogs.
Purchased shield bugs are often kept in aquariums and feed on a diet consisting mainly 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 the usual lunch, crackers, potatoes, etc.
Population and species status
There is no threat to the shield populations. They are the ancient inhabitants of the planet Earth and over the years have adapted to survive in the most unfavorable conditions. Shield cysts are moved over long distances by animals or wind, thus expanding their range and preventing the appearance of isolated populations.
With the onset of favorable conditions, only a part of the cyst population begins to develop, which increases their chance of survival. If the developed adults die without leaving offspring, then the remaining cysts can try to start all over again. Dried cysts of some species of shield bugs are sold in aquarium pet kits.
Among cyst enthusiasts, the most popular are:
- American species – T. longicaudatus;
- European – T. cancriformis
- Australian – T. australiensis.
Other species also found in captivity include T. newberryi and T. granarius . Red (albino) forms are quite common among enthusiasts and have been the subject of numerous YouTube videos. Shields are unpretentious in content. The main thing to keep in mind is that they need fine sand as a substrate, and it is unnecessary to place them with fish, because they can eat small fish, and large ones will eat them.
The shield is the oldest animals that are in the Triassic period reached a length of two meters. In large bodies of water, they have become an important part of the food chain. It should be borne in mind that they can harm fry and small fish, as well as other crustaceans.