Thor amboinensissquat anemone shrimp

Geographic Range

Sexy shrimp are most commonly found in areas of the Atlantic and Indo-Pacific Oceans. Specific localities include the Atlantic coast of Florida and Gulf of Mexico, Caribbean Sea, and areas around Hawaii, the western coast of Africa, French Polynesia, Mozambique, Taiwan, China, the Canary Islands, New Caledonia, and within the Red Sea. ("Common and Scientific Names of Aquatic Invertebrates from the United States and Canada: Decapod Crustaceans", 2005; "The official site for Thor ambionesis", 2010; "Thor amboinensis", 2009; DeGrave, et al., 2013)


Sexy shrimp require water temperatures of 22-27°C . These shrimp form symbiotic relationships with anemones such as Entacmaea quadricolor, Macrodactyla doreensis, Stichodactyla tapetum, and Zoanthus sp., living on and around their oral discs, tentacles, or substrate very near to anemone bases. Although some populations seem to exhibit a slight preference for certain anemone species, on the whole they are considered generalists as far as which species they develop relationships with. Most often, only one or two shrimp live on and in a host, but in some populations as many as 11-18 individuals have been observed inhabiting one anemone. These shrimp typically live where there is gentle to moderate water movement, although they are capable of withstanding strong currents as well. Sexy shrimp can be found in depths ranging from 0.5-2.8 m. ("The official site for Thor ambionesis", 2010; "Thor amboinensis", 2009; Baeza and Piantoni, 2010; DeGrave, et al., 2013; Guo, et al., 1996)

  • Range depth
    0.5 to 2.8 m
    1.64 to 9.19 ft

Physical Description

Sexy shrimp are very small, ranging in length from 1.5-13 mm. Base body color is drab (olive or brown), with iridescent yellow-white spots bordered by thin white and blue bands, symmetrically arranged over their bodies. They have five pairs of pereopods (thoracic appendages) and five pairs of pleopods (swimming legs). Their first pair of pleopods are enlarged into chelae, used for both intra- and interspecific interaction. Their second abdominal segment is greatly enlarged; females carry developing eggs under this segment. Sexy shrimp have a telson and uropods, which form a fanlike tail, which is glossy and light brown in color, and is used for steering while swimming. They have white eyes, located at the ends of short stalks. This species differs from others in that, when at rest, their abdomens and tails arch upward towards the head. ("The official site for Thor ambionesis", 2010; "Thor amboinensis", 2009; Baeza and Piantoni, 2010)

Sexy shrimp display sexual dimorphism in a number of ways. Males are typically smaller than females and have gonopores located on their fifth pereopods, with paired testes and lateral sperm ducts. Males have appendices masculinae, which are male organs used in copulation or spermatophore transfer, located on their second pleopods. Females have gonopores on their third pereopods and paired ovaries located above their hepatopancreas. They also have white spots on their pleopods. (Baeza and Piantoni, 2010)

  • Sexual Dimorphism
  • female larger
  • sexes colored or patterned differently
  • sexes shaped differently
  • Range length
    1.5 to 13 mm
    0.06 to 0.51 in


Most information regarding mating and development of this species comes from observations by aquarium enthusiasts. Eggs are light brown in color and are cared for as they develop by the female, who carries them on her pleopods and continually cleans and aerates them. Within 2-3.5 weeks after fertilization, eggs hatch, usually at night. Larvae are tiny and slender, averaging about 2 mm in length, and are phototaxic upon hatching. They drift in ocean currents for 20-30 days as they develop, undergoing 10-12 different larval stages, with physical changes occurring in each stage. Larve molt every 2 to 3 days, most often at night. Although larvae eventually settle on a host anemone, they do not require a chemical cue from a certain host to do so; it has been hypothesized that individuals settle first and seek out an appropriate host second. In captivity, metamorphosis and settling have been observed to occur within 26 days of hatching. ("Breeding Journal: Species Thor amboinensis", 2011; "The official site for Thor ambionesis", 2010; Sarver, 1979)

Sexy shrimp are protandric hermaphrodites; researchers suspect that there are no primary females but that all individuals are born male and transition into females later in life. (Baeza and Piantoni, 2010)


Sexy shrimp appear to exhibit a "pure-search" strategy for mating, in which males search continuously for females and then, with no courtship, the pair rapidly copulate. It is assumed that at this point the pair separate quickly, although reports from captive breeders indicate that males may guard females once they release eggs. It is unknown if females are passive or active regarding mate choice. During copulation, a male transfers sperm cells from his gonopores (located on his fifth pereopods) to a female's gonopores (on her third pereopods). The appendices masculinae may aid in this transfer. ("Breeding Journal: Species Thor amboinensis", 2011; "The official site for Thor ambionesis", 2010; Baeza and Piantoni, 2010)

Little is known about the reproductive cycle of this species in the wild. Sexy shrimp are capable of breeding year-round in captivity, assuming that environmental conditions are kept at consistently optimal levels. These shrimp are protandric hermaprhodites; they are born male and may change into females later in life. Transitional individuals, exhibiting characteristics of both sexes, have been found in the wild (transitional individuals most closely resemble females physically). Males can change into females in relatively short periods of time (less than 23 days); typically, larger males are the ones who undergo sex change. ("The official site for Thor ambionesis", 2010; Baeza and Piantoni, 2010)

  • Breeding interval
    Sexy shrimp may breed multiple times throughout the year.
  • Breeding season
    Breeding season may be year round, under optimal environmental conditions, as well as in captivity.
  • Range number of offspring
    200 to 500
  • Range gestation period
    2 to 3.5 weeks

Females carry, clean, and oxygenate eggs under their forward tail section, on the pleopods. While bearing eggs, they hold their legs under the tail to protect them. There is no known parental investment by males. ("The official site for Thor ambionesis", 2010; Baeza and Piantoni, 2010)


The average lifespan of sexy shrimp is thought to be about 3.5 years in the wild, but they are known to live up to 5 years. Little is definitively known of their expected lifespan in captivity due to limiting factors, such as tank environment. ("The official site for Thor ambionesis", 2010)

  • Typical lifespan
    Status: wild
    5 (high) years
  • Average lifespan
    Status: wild
    3.5 years


Sexy shrimp are known to vibrate their abdomen to signal or warn others. They are capable of moving very quickly, at rates of 10-15 cm/s, to escape perceived threats. ("The official site for Thor ambionesis", 2010; "Thor amboinensis", 2009)

Sexy shrimp are usually found in pairs or in small groups on a single anemone host. There do not appear to be any complex social hierarchies at play within groups. When an unacclimated shrimp is introduced to an anemone, it will endure the attacks from the anemones' nematocysts. Some studies state that a shrimp acclimates to an anemone by collecting its mucus, which camouflages it from the anemone. Other studies say that a shrimp acclimates by building up chemicals that inhibit the excretions of nematocysts from anemones. It is uncertain how long it takes for a shrimp to become acclimated to a host anemone, but it is known that these shrimp are generalists, not requiring particular species of anemones as hosts. The spatial and temporal distribution of shrimp depends upon their feeding activities and the degree of anemone expansion. (Baeza and Piantoni, 2010; Guo, et al., 1996; Khan, et al., 2004; Michael, 2012; Wirtz, 1997)

Home Range

Although specific home ranges have not been identified for these shrimp, individuals tend to stay within a few centimeters of their anenome host. They do not appear to defend territories. (Baeza and Piantoni, 2010)

Communication and Perception

Sexy shrimp select a host anemone by using visual and chemical cues. They use their first pair of chelae for intersexual communication and may make a sound to signal others or to grab a female. Little else is known about how sexy shrimp communicate with each other but other shrimp species are known to emit sex pheromones, which can be perceived by both sexes. They have antennular flagella, the function of which is not fully known, but which are suspected to play a role as chemoreceptors. Sexy shrimp also sense their environments through tactile means, using their antennae. ("The official site for Thor ambionesis", 2010; Baeza and Piantoni, 2010; Bauer, 2001; Guo, et al., 1996)

Food Habits

Sexy shrimp are carnivorous. These shrimp feed on matter trapped in a host anemone's mucus, including plankton. Their diet may also include other small crustaceans, such as brine shrimp (Artemia sp.), Mysida sp., and krill (Euphausiacea sp.). When resources are scarce, shrimp may resort to feeding on the tentacles of their hosts. ("Thor amboinensis", 2009; Baeza and Piantoni, 2010)

  • Animal Foods
  • aquatic crustaceans
  • other marine invertebrates
  • zooplankton


Various fishes are predators of sexy shrimp. They avoid predation by relying on their hosts, who are capable of stinging and sometimes consuming potential predators. Also, their vibrant colors allow them to blend in with their environments. If threatened outside of their anemone host, these shrimp have been observed to flip their tails backwards, propelling them back into the safety of its tentacles. ("The official site for Thor ambionesis", 2010; "Thor amboinensis", 2009; Baeza and Piantoni, 2010)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Sexy shrimp have a commensal relationships with a large variety of anemones (as these shrimp are generalists, the list below is by no means a complete representation of their hosts); they keep the anemones clean from mucus while the anemones provide protection to the shrimp. Sexy shrimp may also found on rocks and corals, as well as other animals (including Ricordea and Crinoidea sp.). Sexy shrimp have been observed cleaning mantis shrimp (Lysiosquillina lisa), picking parasites off of their carapaces, although this activity is not considered a primary mode of feeding or behavior for this species. These shrimp may be infected with isopod parasites. ("The official site for Thor ambionesis", 2010; "Thor amboinensis", 2009; Baeza and Piantoni, 2010; Criales, 1984; Guo, et al., 1996; Khan, et al., 2004; Wirtz, 1997)

Mutualist Species
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Sexy shrimp are popular in home aquaria due to their appearance and relatively easy maintenance. Also, they are useful to researchers in studying their natural history and sexual systems, as well as the importance of environmental conditions in explaining the evolution of sex determination in crustaceans. ("The official site for Thor ambionesis", 2010; "Thor amboinensis", 2009; Baeza and Piantoni, 2010)

  • Positive Impacts
  • pet trade
  • research and education

Economic Importance for Humans: Negative

There are no known adverse affects of this species on humans.

Conservation Status

This species has not been evaluated by the IUCN, nor is it currently considered threatened or endangered by any agency. ("International Union for the Conservation of Nature and Natural Resources", 2013)


Seona Choi (author), University of Michigan-Ann Arbor, Renee Mulcrone (editor), Special Projects, Jeremy Wright (editor), University of Michigan-Ann Arbor.


Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

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Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

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living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat


uses smells or other chemicals to communicate


the nearshore aquatic habitats near a coast, or shoreline.


having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

  1. active during the day, 2. lasting for one day.

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females


union of egg and spermatozoan


a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

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Found in northern North America and northern Europe or Asia.

internal fertilization

fertilization takes place within the female's body


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


seaweed. Algae that are large and photosynthetic.


A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.


having the capacity to move from one place to another.


specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.


active during the night


found in the oriental region of the world. In other words, India and southeast Asia.

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reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.


chemicals released into air or water that are detected by and responded to by other animals of the same species


an animal that mainly eats plankton


the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.


condition of hermaphroditic animals (and plants) in which the male organs and their products appear before the female organs and their products


structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


uses sight to communicate

year-round breeding

breeding takes place throughout the year

young precocial

young are relatively well-developed when born


animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)


2011. "Breeding Journal: Species Thor amboinensis" (On-line). Marine Breeding Initiative. Accessed February 02, 2012 at

ITIS. Common and Scientific Names of Aquatic Invertebrates from the United States and Canada: Decapod Crustaceans. TSN 96920. Bethesda, Maryland, USA: American Fisheries Society. 2005. Accessed February 02, 2012 at

2013. "International Union for the Conservation of Nature and Natural Resources" (On-line). Accessed August 09, 2013 at

2010. "The official site for Thor ambionesis" (On-line). Accessed February 02, 2012 at

2009. "Thor amboinensis" (On-line). Tropical Fish Hobbyist Magazine. Accessed February 02, 2012 at

Baeza, J., C. Piantoni. 2010. Sexual system, sex ratio, and group living in the shrimp Thor amboinensis (De Man): Relevance to resource-monopolization and sex-allocation theories. Biological Bulletin, 219/2: 151-65. Accessed February 02, 2012 at

Bauer, R. 2001. Chemical communication in decapod shrimps: The influence of mating and social systems on the relative importance of olfactory and contact pheromones. Pp. 277-296 in T Breithaupt, M Thiel, eds. Chemical Communication in Crustaceans. New York, New York: Springer Science + Business Media. Accessed August 05, 2013 at

Calado, R., L. Narciso, R. Araújo, J. Lin. 2003. Overview of marine ornamental shrimp aquaculture. Pp. 221-232 in J Cato, C Brown, eds. Marine Ornamental Species: Collection, Culture & Conservation. Iowa City, Iowa: Iowa State Press. Accessed February 02, 2012 at

Criales, M. 1984. Shrimps associated with coelenterates, echinoderms, and molluscs in the Santa Marta Region, Colombia. Journal of Crustacean Biology, 4/2: 307-317. Accessed February 02, 2012 at

De Grave, S. 2007. Notes on some shrimp species (Decapoda : Caridea) from the Persian Gulf. Annalen des Naturhistorischen Museums in Wien. Serie B für Botanik und Zoologie, 108: 145-152. Accessed February 23, 2012 at

DeGrave, S., C. Fransen, M. Türkay. 2013. "Thor amboinensis" (On-line). World Register of Marine Species. Accessed August 07, 2013 at

Guo, C., J. Hwang, D. Fautin. 1996. Host selection by shrimps symbiotic with sea anenomes: a field survey and experimental laboratory analysis. Journal of Experimental Marine Biology and Ecology, 202: 165-176. Accessed August 07, 2013 at

Khan, R., J. Becker, A. Crowther, I. Lawn. 2004. Spatial distribution of symbiotic shrimps (Periclimenes holthuisi, P. brevicarpalis, Thor amboinensis) on the sea anemone Stichodactyla haddoni. Journal of the Marine Biological Association of the UK, 84/1: 201-203. Accessed February 02, 2012 at

Michael, S. 2012. "Anemone Shrimp" (On-line). Fishchannel. Accessed April 06, 2012 at

Sarver, D. 1979. Larval culture of the shrimp Thor amboinensis (De Man, 1888) with reference to its symbiosis with the anemone Antheopsis papillosa (Kwietniewski, 1898). Crustaceana Supplement, 5: 176-178. Accessed February 02, 2012 at

Wirtz, P. 1997. Crustacean symbionts of the sea anemone Telmatactis cricoides at Madeira and the Canary Islands. Journal of Zoology, 242/4: 799-811. Accessed February 24, 2012 at