Caridea

The Caridea are a specific group of animals known as true shrimp. This group is an infraorder within the larger order Decapoda. While many animals are called shrimp, only those in Caridea are "true" shrimp. They are found in almost every aquatic habitat on Earth. You can find them in both salt water and fresh water. They live on every continent except for Antarctica.

Carideans have very different body shapes and sizes. Some species are only a few millimeters long when they grow up. Other species can grow to be over 30 centimeters long. Most of these animals live on the bottom of the water, which is called a benthic habitat. They have a hard shell called a carapace. This shell covers the cephalothorax, which is the head and chest area. The carapace also protects the gills. The shrimp use their mouthparts to pump water through these gills to breathe.

These animals use many different methods to find food. Most carideans are omnivorous, meaning they eat many types of things. Some species are filter feeders. They use their setose legs, which are bristly, to act like a sieve. These legs catch tiny food particles from the water. Other shrimp scrape algae off of rocks. The snapping shrimp, from the genus Alpheus, have a very special way to hunt. They snap their claws to create a shock wave. This shock wave stuns their prey so they can eat it.

The life cycle of a true shrimp is quite complex. Unlike prawns, which are in the sub-order Dendrobranchiata, carideans brood their eggs. This means the mother carries the eggs rather than releasing them into the open water. The larvae undergo all their naupliar development while still inside the egg. When they hatch, they emerge as a stage called a zoea. The zoea stage eats phytoplankton to grow. Depending on the species, they may have as few as two zoea stages or as many as 13. After this, they become a decapodid, which looks like a tiny adult. Finally, they metamorphose into a post-larval juvenile.

Scientists can tell true shrimp apart from prawns by looking at specific body parts. One way is to check the gill structure. Carideans have lamellar gills, which look like flat plates. Prawns have branching gills instead. You can also look at the second abdominal segment of the body. In a true shrimp, this segment overlaps both the first and the third segments. In a prawn, it only overlaps the third segment. Most carideans also have two pairs of chelae, or claws, while prawns have three.

True shrimp are very important to the global food industry. The species Pandalus borealis, known as the pink shrimp, is a major commercial species. It is followed in importance by Crangon crangon, the brown shrimp. In 1950, people caught much more brown shrimp than pink shrimp. However, by 2010, the production of pink shrimp was about ten times higher than brown shrimp. In 2010, global aquaculture produced 3.5 million tonnes of shrimp and prawns. Wild capture production was about 3.2 million tonnes. Carideans made up about 430,000 tonnes of that wild catch. This represents about 13% of the total wild capture.

The history of these animals is visible in the fossil record. The record for Carideans is considered sparse. Scientists have identified 57 species that are known only from fossils. These fossils date back to the Lower Jurassic and Cretaceous periods. This shows that true shrimp have existed for a very long time. Within the Caridea, there are 15 different superfamilies. These include groups like Alpheoidea, which contains the snapping shrimp, and Atyoidea, which contains many freshwater species.