Notostraca

These tiny bugs are called tadpole shrimp.

They have a hard shell on their front. This shell covers their head. They have a long body with many legs.

These shrimp live in shallow pools of water. They eat small things on the bottom. They have been on Earth for a very long time. They look much like their old ancestors. It is fun to look for them in a pond!

Tadpole shrimp are small animals that live in water. They belong to a group called Notostraca. These shrimp have a flat shell called a carapace. This shell covers their head. They also have a long body. This shape looks like a tadpole.

They live on the bottom of shallow lakes or pools. They are omnivores. This means they eat many things, like small animals. They eat tiny fish and fairy shrimp.

These shrimp are very old. Some look like fossils. Scientists call them living fossils. This is because they look like ancestors from long ago. One kind lived 365 million years ago! They have stayed much the same for a very long time.

Female shrimp have a special part. It is a brood pouch. They use it to hold their eggs. The eggs are often pink.

In some places, they can be a pest. In California, they live in rice fields. They stir up mud from the bottom. This mud can block light from the rice plants.

Tadpole shrimp are small, swimming animals known as Notostraca. They belong to a group of crustaceans. You might also hear them called shield shrimp. These creatures are important because they have stayed nearly the same for millions of years. Scientists call them living fossils. They live in many types of water. This includes fresh water, salt water, or even slightly salty water. You can find them in shallow lakes, peat bogs, or moorland pools.

These shrimp have a very distinct shape. They have a wide, flat shell called a carapace. This shell covers their head and eyes. They have two eyes that sit together on top of their heads. Their body is long and slender like a tadpole. The body has many pairs of flat legs. These legs help them move along the bottom. The body ends with a tail called a telson. This tail has two long, thin parts called caudal rami.

Notostracans are omnivores, which means they eat many different things. They live on the bottom of pools and eat small animals. They often eat tiny fish or fairy shrimp. They also eat particles found in the mud. Some of these shrimp can even be a pest. In California rice paddies, the species Triops longicaudatus can cause trouble. They stir up sediment from the bottom of the water. This mud can block light from reaching young rice seedlings.

The history of these animals is truly amazing. The oldest known kind is called Strudops goldenbergi. Scientists found fossils of this species in Belgium. These fossils are from the Late Devonian period. That was about 365 million years ago! Because they have not changed much since then, they are living fossils. Other related fossils have been found in Kazakhstan and China. These fossils come from the Triassic and Jurassic periods.

Reproducing is a very interesting part of their life. There is a lot of variety in how they make new shrimp. Some groups reproduce sexually. This means they use both males and females. In these groups, sperm leave the male through small pores. Some females can even use self-fertilization. This means they can make eggs without a male. Females have a special part called a brood pouch. They use this cup-like pouch to hold their eggs.

Notostraca is an order of crustaceans commonly known as tadpole shrimp or shield shrimp. This group belongs to a single family called Triopsidae. They are famous among scientists for being "living fossils." This means their physical forms have remained very similar for hundreds of millions of years. They are primarily benthic organisms, which means they live on the bottom of water bodies. They inhabit a wide variety of environments, including freshwater, brackish water, and saline pools. You can find them in shallow lakes, peat bogs, and moorlands across the globe.

The anatomy of a notostracan is highly specialized for life on the sediment floor. They possess a large, flat, and smooth carapace that covers the head. This carapace is dorso-ventrally flattened, meaning it is wide and thin from top to bottom. On top of the head, they have two sessile compound eyes. These eyes sit close together but remain two separate structures. Their antennae are greatly reduced, and the second pair is sometimes missing entirely. The body is divided into three distinct regions: thorax I, thorax II, and the abdomen.

Detailed examination of their body segments reveals a complex structure. Thorax I consists of 11 segments, each with a pair of well-developed limbs. In females, the eleventh segment is modified into a brood pouch to hold eggs. The first one or two pairs of legs likely serve as sensory organs. Thorax II is composed of rings rather than individual segments. These rings are formed by the fusion of two to six segments. The number of legs on each ring matches the number of segments within it. The abdomen is long and slender, ending in a telson and two thin caudal rami.

Notostracans exhibit significant variation in how they reproduce. Some populations reproduce sexually, requiring both males and females. In these cases, males release sperm through simple pores rather than a penis. Other populations utilize self-fertilization, where females can produce offspring without a male. Some groups use a mixture of both methods. Females use a cup-like brood pouch to protect their eggs for a short time. Unlike many other crustaceans, their larvae develop directly. This means they do not undergo a complex metamorphosis to reach adulthood.

The evolutionary history of this order is recorded extensively in the fossil record. The oldest known species is Strudops goldenbergi, found in Belgium. This species dates back to the Late Devonian period, approximately 365 million years ago. This extreme longevity in form is a key reason they are called living fossils. Related groups, such as Kazacharthra, are known from Triassic and Jurassic fossils in Kazakhstan and China. A major evolutionary change for Notostraca was the shift to a benthic lifestyle. They abandoned filter feeding in open water to prey on small animals and sediment particles.

Taxonomy, or the naming of these species, has been historically difficult. This difficulty is caused by phenotypic plasticity, which is when an organism's appearance changes based on its environment. In the 1950s, scientists recognized as many as 70 different species. However, major revisions by researchers like Linder and Longhurst reduced this number to only 11 species. These 11 species belong to two main genera: Triops and Lepidurus. While Triops is found worldwide except in Antarctica, Lepidurus is also found everywhere except Antarctica. Recent molecular studies suggest there may actually be more distinct populations than previously thought.

These creatures can have a significant impact on their ecosystems and human activities. As omnivores, they eat small animals like fishes and fairy shrimp. In certain areas, they are viewed as agricultural pests. For example, the species Triops longicaudatus is a pest in California rice paddies. These shrimp stir up the sediment from the bottom of the water. This action makes the water cloudy and prevents light from reaching rice seedlings. This shows how a small crustacean can influence entire agricultural systems.