shrimp Shrimp are small crustaceans. They have long feelers, a double fishlike tail, and ten paddle-likelegs for walking on the bottom. Its other appendages are used for swimming. Shrimp have elongated bodies. Swimming is their primarily mode of locomotion. They belong to the Caridea and Dendrobranchiata decapod order, although some crustaceans outside of this order are referred to as "shrimp".
In many cases, any small crustacean that resembles a shrimp is called one. Under some broad definition, shrimps and prawns are lumped together. They both have shell coverings, stalk-eye long, narrow muscular tails (abdomens), long whiskers (antennae), and slender legs. A true shrimp has two appendages on the side of its head. The prawn has a single sharp beak. Prawns are usually larger than shrimp.
Shrimp are widespread and abundant. There are thousands of species. They are found in a variety of habitats: reefs, mangroves, coastal areas. Those served at restaurants usually live on the ocean floor and are caught in coastal areas with dredging nets or raised in shrimp farms.
Shrimp are caught in sandy and slightly muddy water where the salinity favors the growth of plankton. Shrimp fishing stops when shrimps lay their eggs and the larvae hatch. The larvae migrate to an area in the sea where the salinity is low. The main shrimp season begins when the shrimp swim quickly from low to high saline water.
Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems
Unlike crabs and lobsters, shrimp have well developed pleopods (swimmerets) and slender walking legs. They are more adapted for swimming than walking. Shrimp swim forward by paddling with swimmerets on the underside of their abdomens. Their escape response is typically repeated flicks with the tail driving them backwards very quickly. Crabs and lobsters have strong walking legs, whereas shrimp have thin, fragile legs which they use primarily for perching. [Source: Wikipedia]
The body of the shrimp is divided into two main parts: 1) the head and thorax which are fused together to form the cephalothorax; and 2) a long narrow abdomen. The shell which protects the head and thorax — the carapace — is harder and thicker than the shells found on other parts of the shrimp. The carapace typically surrounds the gills, through which water is pumped by the action of the mouthparts. The rostrum, eyes, whiskers and legs also emerge from the carapace. sThe rostrum, from the Latin rōstrum meaning beak, looks like a beak. Located at the front of the shrimp's head, it is a rigid forward extension of the carapace and can be used for attack or defense. It may also stabilize the shrimp when it swims backward — serving as kind of a backward tail. Two bulbous eyes on stalks are situated on either side of the rostrum. These are compound eyes which offer the shrimp a panoramic view and are very good at detecting movement. The two pairs of whiskers (antennae) that issue from the head serve as sense organs. One of the pairs is very long and can be twice the length of the shrimp, while the other pair is quite short. Sensors on the antennae feel as well as "smell" and "taste" things by sampling the chemicals in the water. The long antennae help the shrimp orient itself with regard to its immediate surroundings, while the short antennae help assess the suitability of prey.
Eight pairs of appendages issue from the head and thorax of the shrimp. The first three pairs, the maxillipeds (Latin for "jaw feet") are used as mouthparts. In many species the first pair, the maxillula, pumps water into the gill cavity. After the maxilliped come five more pairs of appendages, the pereiopods. These form the ten decapod legs. Again in many species the first two pairs of pereiopods have claws or chela. They can can grasp food items and bring them to the mouth. They can also be used for fighting and grooming. The remaining four legs are long and slender, and are used for walking or perching.
The shrimp’s muscular abdomen has six segments and has a thinner shell than the carapace. Each segment has a separate overlapping shell, which can be transparent. The first five segments each have a pair of paddle-shaped appendages — called pleopods or swimmerets — on their underside. They are used for swimming forward and can also be used for things like brooding eggs. Some species have gills on them for breathing. The males of other species use the first pair or two for insemination. The sixth segment terminates in the tail-like telson, which is flanked by two pairs of appendages called the uropods. The uropods propel the shrimp when it swims backward, and serves like rudder, steering the shrimp when it swims forward. Together, the telson and uropods form the shrimps’s splayed tail fan. When alarmed, a shrimp it can quickly flex its tail, propelling it backwards in what is called the caridoid escape reaction (lobstering).
Five-Eyed, 520-Million-Year-Old 'Missing Link' Shrimp
Only 57 exclusively fossil species are known in the shrimp fossil record. The earliest dates from the Lower Jurassic (201 to 174 million years ago), followed by specimens from the Cretaceous (145 to 66 million years ago)
In 2020, scientists announced the discovery of a five-eyed shrimp-like creature that lived about 520 million years ago that may lay to rest a long-running debate about the evolution of Earth's most common animals. AFP reported: “Arthropods, ranging from lobsters and crabs to spiders and millipedes, make up around 80 percent of all animal species alive today and are characterised by their hard exoskeleton. “But their evolution has long remained something of a mystery, because their ancient ancestors carry a variety of features that their modern counterparts do not. [Source: Sara Hussein, AFP, November 5, 2020]
“Enter Kylinxia zhangi, a shrimp-like creature preserved in fossils found in China's Yunnan province — a discovery that researchers now say could be a key "missing link" in arthropod evolution. Like today's arthropods, Kylinxia had a hard shell, a segmented body and legs with joints. But the ancient creature also had characteristics in common with even older animals, leading researchers to name it after the "Kylin", a creature in traditional Chinese mythology with attributes from a variety of animals.
“First there are those eyes — three smaller ones in a row on its head, with two larger ones directly behind. It might sound bizarre, but it's a feature scientists have seen before, in an ancient creature called Opabinia, known informally as a "weird wonder". And the Kylinxia's two spiky front appendages, researchers say, are reminiscent of another creature thought to be an arthropod ancestor: the Anomalocaris.
“While both have been theorised as precursors to modern arthropods, an evolutionary gap in the fossil record made that difficult to prove — until this week. “Kylinxia represents a crucial transitional fossil predicted by Darwin's evolutionary theory," said Han Zeng, first author of a study published in the journal Nature. “It bridges the evolutionary gap from Anomalocaris to true arthropods and forms a key 'missing link' in the origin of arthropods," added Zeng, a researcher at the Nanjing Institute of Geology and Paleontology (NIGPAS), in a press release.
“In fact, when the first of the fossils was revealed, only its front legs were visible, and researchers assumed it was another specimen of Anomalocaris, said Diying Huang, a professor at NIGPAS. “It looked strange, like a frontal appendage of Anomalocaris attached to the body of a common arthropod," Huang, the study's corresponding author, told AFP. “After careful preparation... I knew it was a new and very important arthropod." Part of the value of Kylinxia lies in the unusual detail preserved in the fossils. “The Kylinxia fossils exhibit exquisite anatomical structures," said Fangchen Zhao, co-author of the study. “For example, nervous tissue, eyes, and digestive system — these are soft body parts we usually cannot see in conventional fossils."
Defining Shrimp, Decapods, Crabs and Lobsters
There is a lot of debate among taxonomists on the phylogeny of crustaceans, with disagreement more the norm than agreement. Most are decapods (literally "ten-footed"), an order of crustaceans within the class Malacostraca, including many crabs, lobsters, crayfish, shrimp, and prawns. But within the decapods "every study gives totally different results. Nor do even one of these studies match any of the rival morphology studies". Some taxonomists identify shrimp with the infraorder Caridea and prawns with the suborder Dendrobranchiata. While different experts give different reasons, one thing that everyone agrees on is that the caridean species are shrimp. There are over 3000 caridean species. They are sometimes referred to as "true shrimp".
Caridea shrimp are more closely related to lobsters and crabs than they are to prawns (members of the sub-order Dendrobranchiata). Biologists distinguish between Caridea shrimp and prawns based on differences in their gill structures. The gill structure is lamellar in carideans but branching in dendrobranchiates. The easiest way to determine this is to examine the second abdominal segment. The second segment of a carideans overlaps both the first and the third segment, while the second segment of a dendrobranchiate overlaps only the third segment.
A wide variety of non-decapod crustaceans are also commonly referred to as shrimp. These include: 1) brine shrimp, clam shrimp, fairy shrimp and tadpole shrimp belonging to the branchiopods; 2) lophogastridan shrimp, opossum shrimp and skeleton shrimp belonging the Malacostraca; and 3) seed shrimp which are ostracods. Many of these species look quite different from commercial decapod shrimp that are eaten as seafood. Skeleton shrimp, for example, have short legs and a slender tail like a scorpion tail, Fairy shrimp swim upside down with swimming appendages that look like leaves. Krill resemble shrimp but are caridea.
On the differences between shrimp, lobster and crabs, shrimp look somewhat like small lobsters, but not like crabs. Lobsters are viewed a an intermediate evolutionary development between shrimp and crabs. Crabs evolved from early shrimp but unlike shrimp, their abdomens are small, and they have short antennae and short carapaces that are wide and flat. They have prominent grasping claws as their front pair of limbs. The abdomens of lobsters and shrimp are large and long. The lower abdomens of shrimp support pleopods which are well-adapted for swimming. The carapaces of lobsters and shrimp are cylindrical. The antennae of lobsters and shrimp are usually long, reaching more than twice the body length in some shrimp species.
Shrimp Behavior Feeding and Mating
Shrimp are generally cold blooded (ectothermic, use heat from the environment and adapt their behavior to regulate body temperature) and heterothermic (have a body temperature that fluctuates with the surrounding environment). Some shrimp are very territorial and will fight off any intruders. Crustaceans have setae and sensilla found all over their body. Sensilla are mechanoreceptors or chemoreceptors. Special chemoreceptors are on the antennae. Well developed receptors provide information about appendage position and movement.
Most shrimp are omnivorous (feeds on a variety of both plant and animal food). Some are specialized for particular modes of feeding or particularly foods.. Cleaner shrimp feed on the parasites and necrotic tissue of the reef fish they groom. Filter feeders use their setose (bristly) legs as a sieve. Some scrape algae from rocks. Others known to cannibalize their own kind if other food sources are not readily available. In turn, shrimp are eaten by a lot of animals, both on land and in the sea, particularly fish and seabirds.
In regards to mating, the females of some freshwater shrimp can store sperm from multiple partners, and thus can produce offspring progeny from different fathers. Reproductive success of males was found to correlate inversely with their genetic relatedness to the mother. This suggests that sperm competition and/or pre- and post-copulatory female choice occurs and may increase the fitness of offspring by reducing inbreeding.
Super Materials Made from Shrimp Shells and Silk
Scientists have combine shrimp shells and silk proteins to create a super strong and flexible material. National Geographic reported: “Shrilk” was invented by researchers at the Wyss Institute at Harvard, who layered the two components in a way that mimicked structures found in shells and insect cuticles. Shrilk is inexpensive to manufacture but has invaluable virtues: It’s tough, flexible, and biodegradable. In the future it may be used to make everything from wound dressings to trash bags to disposable diapers. And it might make many landfill-choking plastics obsolete. [Source: A. R. Williams, National Geographic, May 2013]
According to the Wyss Institute: Shrilk is a fully degradable bioplastic made using a material called chitosan (found in shrimp shells) and a protein from silk called fibroin that mimics the microarchitecture of insects’ exoskeletons. Shrilk can be used to manufacture objects without the environmental damage caused by conventional synthetic plastics, and it rapidly biodegrades when placed in compost, releasing nitrogen-rich nutrient fertilizer. Because chitosan and fibroin are both used in FDA-approved devices, Shrilk also may be useful for creating implantable foams, films, and scaffolds for surgical closures, wound healing, tissue engineering, and regenerative medicine applications.
Many of biodegradable materials available today are based on cellulose, a polysaccharide material derived from plants. These materials are widely used in packaging, as containers for food, drinks and other things. However, the main drawback of these materials is their lack hardness, which is not as high as in conventional plastics. One aim of the Wyss Institute was to develop a new material that can serve as a ‘hard’ biodegradable alternative to plastic. [Source: Prescouter]
Types of Shrimp
Many of the shrimp consumed by humans and fish are opossum shrimp. Found mostly in esturine or marine waters, they are free swimmers with long, soft elongated bodies and distinctive movement sensors at the base of an inner pair of flaplike appendages on either side of their tail fan. Many are pale or translucent. Some are red.
Cleaner shrimp pick off parasites, fungus and pests from fish. Some fish pull up to sections of reef inhabited with cleaner shrimp like cars pulling up to a car wash and wait on line for their turn to be cleaned. The shrimp even climb into the mouth's of moral eels to clean their teeth. They also provide free medical service by cleaning parasites which congregate around the fish's open wounds and drive away small predators that feed on the fishes eggs.
There are all kinds of shrimp out there. Pistol shrimp produce a loud cracking noise by dislocating their claws. King shrimp are often found in places where dead sea plants, mud and fine sand accumulate. Caribbean peppermint shrimp are born male and become female as they mature. "Females" with sperm-producing organs and ducts that can be used to fertilize other "females." Spot prawns have a similar life cycle. The larger the prawn the more eggs she can carry.
A number of shrimp have symbiotic relations with other marine life. Commensal shrimps live among the tube-feet on starfish's arm, grazing on dead skin cells, mucus and other detritus. Sea urchins that look like they trapped inside a small localized blizzard are in fact surrounded by hundreds of tiny shrimp in the process of laying their eggs. Some of these shrimp have kangaroo-like pouches. Shrimpfish are small fish that search for minuscule shrimp and inhale them in their tubelike mouths.
Snapping shrimp produce a noise that is so loud that submarines use the noise to hide from sonar. The shrimp make the noise through "cativation," which is normally produced by the turbulence caused by objects moving extremely quickly through water like the propellor of a submarine. Snapping shrimp have a relatively giant claw that snaps, producing a stream of water that moves at 70 metersph. The pressure of the water causes tiny bubbles to expand. Within a microsecond the pressure is equalized and the bubbles compress, producing a loud sound and a shock wave, powerful enough to stun prey. Snapping shrimp are heard much than they are observed. They often live inside sponges and are the only known marine species that live in colonies that resemble the colonies of bees and wasps. The colony often consists of a two parents and a whole bunch of grown male children.
Asian Tiger Prawns: the World’s Largest Shrimp
Asian tiger shrimp (Scientific name: Penaeus monodo) are one of the largest of all shrimp. Also known as giant tiger prawns, black tiger shrimp, Asian prawn shrimp, ghost prawns, grass shrimp and and other names, they range in weight from 100 to 320 grams (3.52 to 11.28 ounces) and range in length from 3.7 to 17.4 centimeters (1.46 to 6.85 inches). The lifespan in the wild and captivity is about two years, though individuals introduced into the Gulf of Mexico may have a lifespan closer to three years.[Source: Jennifer Kiel, Animal Diversity Web (ADW) /=]
Asian tiger shrimp are native to the coasts of the Arabian peninsula and the Pacific and Indian Ocean coasts of Australia, Indonesia, south and southeast Asia, and South Africa. They were accidentally introduced to the United States off the coast of South Carolina in 1988, by an unexpected release from an aquaculture center. They had spread as far south as Florida's coastline by 1990 and, since 2006, have been found in the Gulf of Mexico; they are found along the coastlines of Alabama, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina and Texas.
Farmed Asian tiger shrimp constitutes about 20 percent of total world shrimp production. In the wild, they are nocturnal (active at night), often feeding at night and burrowing into the sea floor during the day. They move about the ocean floor searching for food, which is picked up and manipulated by their pereopods and mouthparts.
Asian Tiger Shrimp Characteristics
According to Animal Diversity Web: Asian tiger shrimp have a typical prawn body plan including a head, tail, five pairs of swimming legs (pleopods) and five pairs of walking legs (pereopods), as well as numerous head appendages. A carapace (hard exoskeleton) encloses the cephalothorax (head and thorax). Their heads have a rostrum (an extension of the carapace in front of the eyes) and six to eight dorsal teeth, as well as two to four sigmoidally-shaped ventral teeth. A posterior ridge called the adrostral carina extends from the rostrum to the edge of the epigastric spine, which reaches to the posterior end of the carapace. Their first three pairs of pereopods have claws and they are distinguished from other shrimp species by the lack of an exopod (an external branch) on their fifth pleopodia. The telson at the posterior end of the prawn is unarmed, with no spines. [Source: Jennifer Kiel, Animal Diversity Web (ADW) /=]
Asian tiger shrimp are identified by distinct black and white stripes on their backs and tails; on their abdomens, these stripes alternate black/yellow or blue/yellow. Base body color varies from green, brown, red, grey, or blue. These prawns are very large, reaching 330 millimeters or greater in length (largest individual found at 336 millimeters total length) and are sexually dimorphic, with females are larger than males. At sexual maturity, female carapace lengths range from 47-164 millimeters and their total lengths from 164-190 millimeters, while male carapace lengths fall between 37 and 71 millimeters, with total lengths of up to 134 millimeters. On average, females weigh 200-320 grams and males weigh 100-170 grams.
Females have a sperm receptacle (thyelycum) located ventrally on the last thoracic segment. After mating, sperm remain in this receptacle until eggs are released. Females have a pair of internal fused ovaries that extend almost the entire length of their bodies, from the cardiac region of the stomach to the anterior portion of the telson. Males have a copulatory organ (petasma, formed by the longitudinally folded endopods of the first pair of pleopods. The presence of an appendix masculina (an oval flap on the second pleopod) can distinguish males from females. Testes are unpigmented/translucent and are found dorsal to the hepatopancreas under the carapace. The vas deferens is also internal, and arises from the posterior margins of the main axis of the testes. Sperm are released through genital pores on the fifth pereopod. /=\
Asian tiger shrimp communicate with vision, vibrations, touch and chemicals usually detected by smelling, and sense using vision, touch, vibrations and chemicals usually detected with smell. Asian tiger shrimp have eyestalks on their heads which enable them to detect predators and search out prey. The eyes are called ommatidia, and are composed of clusters of photoreceptors. Since Asian tiger shrimp are nocturnal (active at night),, they must have very good vision at night to detect predators and prey, but can also see well in daylight. Eyestalks have the ability to change their optical properties based on light-dark adaptations. In dark light, eyestalks receive light from a wide angle and create a superposition image, formed by mirrors in the sides of the cornea instead of by lenses. This superposition image is very effective at detecting movement. In bright light, eyestalks have the ability to see almost 360 degrees and form apposition images, a more efficient detector of light than superposition images. Molting Inhibition Hormone (MIH), which controls the molting cycle, is produced in the eyestalks; a recent study showed that when eyestalks are ablated, molting is accelerated. It is also known that ablating eyestalks in this species induces ovulation and jeopardizes growth. Asian tiger shrimp also have flagellae on their antennae, which detect predators and prey through vibrations. These flagellae also have chemosensors, which detect amino acids and differences in pH, salinity and food stimulants.
Asian Tiger Shrimp Eating Behavior and Predators
In the wild, adult Asian tiger shrimp feed on mollusks, squid, blood clams, oysters, small crustaceans including isopods, crabs and their eggs, and young penaeid prawns, including their own species. In aquaculture, these prawns feed on artificial diets consisting mainly of fishmeal; it has been noted that individuals grow more quickly when fed this diet. In their first larval stage, they feed on their yolk reserves. Later larval stages filter feed on plankton, diatoms, and other small organisms in the water column before becoming benthic (living on or near the bottom of the sea) feeders with a diet composed of organisms such as polycheate worms. [Source: Jennifer Kiel, Animal Diversity Web (ADW) /=]
Asian tiger shrimp face a variety of predators, including birds, comb jellies, crustaceans, and fishes. Their main known predators are black cormorants, green herons, grey herons, purple herons, cuttlefish, squid, barramundi, red snapper, sea basses, sharks, rays, skates, mantis shrimp blue swimmer crabs and mud crabs. When adult prawns move from shallow inshore areas to deeper water, their mortality rates decline. /=\
According to Animal Diversity Web: Asian tiger shrimp have developed a variety of defenses to protect themselves from predation. Prawns have spines on either end of their body (a rostrum above the mouth, and a telson located at the dorsal end of the body). Their distinctive stripes and body color, which is similar to their muddy environment, help to camouflage them from predators. These prawns also bury themselves in substrate, not only hiding their bodies but also masking their waste, which would otherwise likely be detected by potential fish predators' chemosensory systems.
Asian Tiger Shrimp Mating, Reproduction and Offspring
Asian tiger shrimp are oviparous (young are hatched from eggs) and iteroparous (offspring are produced in groups). Reproduction is external, meaning the male’s sperm fertilizes the female’s egg outside her body. These shrimp employ broadcast (group) spawning, the main mode of reproduction in the sea. It involves the release of both eggs and sperm into the water and contact between sperm and egg and fertilization occur externally. They use delayed fertilization in which there is a period of time between copulation and actual use of sperm to fertilize eggs; due to sperm storage and/or delayed ovulation. They also employ sperm-storing (producing young from sperm that has been stored, allowing it be used for fertilization at some time after mating). [Source: Jennifer Kiel, Animal Diversity Web (ADW) /=]
Asian tiger shrimp engage in year-round breeding. Females spawn four times during their lifespan at carapace lengths of five 6.2, 6.6, and 7.2 centimeters. It is unknown how many times males mate. The breeding season is year round. The number of offspring ranges from 248,000 to 810,000. The gestation period ranges from 12 to 15 hours. Parental care and pre-fertilization provisioning and protecting is provided by females. Males are not engaged in parenting in any way after mating. Females provide food (yolk) and egg protection while the eggs are still in their bodies. They are not engaged in parenting after eggs are released.
Asian tiger shrimp are polygynandrous (promiscuous), with both males and females having multiple partners. According to Animal Diversity Web: They are known to mate prior to ovarian maturation; females store sperm in sacs within their closed thelycum until eggs are fully mature. Although little is known regarding specific mating behaviors, it has been noted that this species mates nocturnally, in off-shore waters, shortly after females have molted and their carapaces are still soft (males typically still have hard carapaces during breeding).
Copulation begins with a male swimming parallel to a female. The male bends his body and first pair of pleopods with the petasma (caught by the appendix masculina) stretched vertically down, in order to facilitate the forward swinging of the second pair of pleopods. The first pair of pleopods pulls apart the petasmal halves, preventing the loss of sperm during copulation. The pair then takes an abdomen-to-abdomen position. The female exerts pressure on the male's petasma using her 4th pair of pereiopods and a spermatophore (sac of sperm) is thrust into her thyelycum, after which the pair separate. /=\
Asian Tiger Shrimp Development
According to Animal Diversity Web: Once eggs are mature, they are expelled in a greenish-white cloud, along with stored spermatophores, into the ocean where external fertilization occurs. Eggs range in size from 0.27-0.31 millimeters. Eggs begin development by slowly sinking to the bottom of outer littoral areas. Asian tiger shrimp develop through a complex life cycle beginning with three larval stages. [Source: Jennifer Kiel, Animal Diversity Web (ADW) /=]
Naupilii hatch twelve to fifteen hours after spawning is completed and look like tiny spiders. Larvae at this stage do not feed, instead surviving on their yolks as they are carried by tidal currents from open ocean towards shore. Naupilii larvae pass through six quick molts, increasing their body size. Individuals in the next larval stage, called protozoea, are identified by increased body size and length, the appearance of feathery appendages and, though still planktonic, beginning to feed.
After molting three more times, protozoea proceed into the mysis larval stage. At this stage, they begin to have characteristics of adult prawns including segmented bodies, eye stalks, and tails. Mysis larvae molt three more times, becoming postlarvae. At this point in the life cycle, they change from planktonic to benthic (living on or near the bottom of the sea) feeding. This entire process takes two to three weeks. Prawns continue to molt through a juvenile phase, lasting 1-6 months. Juveniles and adults are distinguished mainly by location and carapace length. Carapace lengths of juveniles range from 2.2-11 millimeters and they are found mainly in estuarine areas located at the mouth or middle of bays and mangroves while adults are found in outer littoral areas of full salinity, and have carapace lengths ranging from 37-81 millimeters. It is difficult to estimate age at sexual maturity, but males become mature upon reaching an average carapace size of 37 millimeters, females at 47 millimeters.
Image Sources: Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated April 2023