Dendrobranchiata

Dendrobranchiata is a group of animals called prawns, which belong to a larger family known as decapods. There are about 540 different kinds of these prawns, found in seven families, and scientists have discovered fossils that show they have been around since a very old time called the Devonian period.

What makes prawns different from other similar animals, like certain shrimp and other small sea creatures, is the special branching shape of their gills. This shape gives them their scientific name, Dendrobranchiata. Unlike some other sea animals, prawns do not keep their eggs safe close to their bodies. Instead, they release the eggs directly into the water.

Prawns can grow quite large, reaching lengths of more than 330 millimetres (about 13 inches) and weighing as much as 450 grams (a little more than one pound). Because they are tasty and nutritious, many people around the world catch prawns from the wild and also grow them on farms to eat.

Nomenclature

See also: Common name

Dendrobranchiata and Caridea look very similar, so in places like farming and fisheries, people often call both of them "shrimp" or "prawn". In the United Kingdom, Australia, and some other countries, "prawn" is the word most used. But in North America, it's usually "shrimp". Sometimes, the word "prawn" is used for bigger shrimp, like "king prawns".

Even though they look alike, scientists now know that Dendrobranchiata and Caridea are not closely related. You can read more about how they are classified explained below.

Description

Dendrobranchiata, together with other swimming Decapoda, have a shrimp-like shape. Their bodies are usually strong and can be split into a cephalothorax (a mix of the head and thorax) and a pleon (abdomen). The body is often slightly flattened from side to side. The largest species, Penaeus monodon, can grow to about 450 grams and 336 millimetres long.

The head has two sets of antennae, with the second set often being much longer than the body. The mouth has parts like mandibles and maxillipeds for eating, and there are eyes on stalks looking forward. The thorax is covered by a shell called a carapace, which extends forward between the eyes into a rostrum. The thorax also has walking legs, with the first three ending in small pincers. Gills, which look like trees, are located here and are protected under the carapace. This tree-like structure of the gills gives the group its scientific name, Dendrobranchiata. The pleon, or abdomen, is about the same length as the cephalothorax and has six segments. It has special appendages called pleopods and uropods that help with movement. Inside, prawns have muscles for moving, a nervous system for sensing their environment, and a digestive system for processing food. Their circulatory system has a heart that pumps blood, and they remove waste mostly through their gills.

Life cycle

Main article: Biological life cycle

Prawns can be split into two groups based on the structure of the female part, called the thelycum. In one group, mating happens at the end of the moulting cycle, usually at sunset. In the other group, mating happens right after moulting when the outer shell is still soft, usually at night. Mating can take up to 3 hours in some prawns, while in others it lasts only 4–5 seconds. Spawning, or laying eggs, can happen several times during the moulting cycle and usually occurs at night.

Except for one family, prawns release their eggs directly into the water instead of keeping them close. The eggs hatch into tiny nauplius larvae, followed by zoea larvae and then a postlarva, before becoming adults. The changes between moults happen slowly, so the development is gradual rather than sudden.

Systematics

Dendrobranchiata were once grouped with other swimming shrimp as "Natantia", different from walking decapods called Reptantia. In 1888, a scientist named Charles Spence Bate noticed differences in their gills and separated them into groups, including Dendrobranchiata. Modern science shows Dendrobranchiata is closely related to all other decapods, called Pleocyemata.

Fossils of these prawns were first found in rocks from Madagascar that are about 250 million years old. But in 2010, an even older fossil was discovered in Oklahoma, dating back to 360 million years ago. Well-known fossils come from Germany.

Today, there are seven families of these prawns, with 540 living species and nearly 100 that only exist as fossils.

Diversity

Dendrobranchiata includes these superfamilies and families:

Superfamily Penaeoidea Rafinesque-Schmaltz, 1815

† Aciculopodidae Feldmann & Schweitzer, 2010 – one species from Famennian times

† Aegeridae Burkenroad, 1963 – two Mesozoic genera: Aeger and Acanthochirana

Aristeidae Wood-Mason, 1891 – 26 living species in 9 genera, and one fossil genus

Benthesicymidae Wood-Mason, 1891 – 41 species in 4 genera

† Carpopenaeidae Garassino, 1994 – two Cretaceous species of Carpopenaeus

Penaeidae Rafinesque-Schmaltz, 1815 – 216 living species in 26 genera, and several extinct genera, mostly from Mesozoic times

Sicyoniidae Ortmann, 1898 – 43 species of Sicyonia

Solenoceridae Wood-Mason, 1891 – 81 species in 9 genera

Superfamily Sergestoidea Dana, 1852

Luciferidae De Haan, 1849 – 7 species in 2 genera

Sergestidae Dana, 1852 – 90 living species in six genera, and two extinct genera

Distribution

The variety of prawns gets smaller as you move farther from the equator. Most prawn species live between 40° north and 40° south of the equator. However, some prawns can be found even farther away. For example, Bentheogennema borealis is common at 57° north in the Pacific Ocean, and Gennadas kempi has been found as far south as 61° south in the Antarctic Ocean.

Ecology and behaviour

Prawns live in many different places. Some live in fresh water, but most live in the sea. Some prawns live deep underwater, while others stay near the shore. One type, called Lucifer, floats in the open water. Some prawns hide in mud during the day and come out at night to find food.

Prawns eat many things, such as tiny plants, small animals, and even bits of dead material. They eat less when they are molting their shells and need to eat more afterward to make up for it.

Many animals like to eat prawns. Small prawns are eaten by jellyfish, fish, and other sea creatures. As prawns grow bigger, they are safer but can still be eaten by some fish.

Economic importance

Prawns are very important for the economy. In some countries, like the United States, people mainly catch them from the wild. Other countries, such as Ecuador, focus on farming them in special places called shrimp farms. Some countries get prawns from both wild catches and farms, like Mexico, China, India, and Indonesia.

Certain types of prawns are important for deep-water fishing, especially in the Mediterranean Sea. In Brazil, some specific prawns are also valuable. But the most common prawns come from shallow waters, and one of the most caught is Fenneropenaeus chinensis, with over 100,000 tons caught in 2005.

For farming, the most important prawns are Marsupenaeus japonicus (Kuruma prawn), Fenneropenaeus chinensis (Chinese prawn), Penaeus monodon (giant tiger prawn), and Litopenaeus vannamei (whiteleg prawn).