Linuche unguiculataThimble jellyfish

Geographic Range

Linuche unguiculata medusae are prevalent in the western, tropical Atlantic Ocean. In the neotropical region, it is found in the West Indian and Bahama regions. (Calder, 2009; Fautin, 2004; Mayer, 1910)

Linuche aquila, a sister species to L. unguiculata, has also been found near the Julian Reef of Palau, Papua New Guinea, in the Pacific and Indian Ocean region. (Mayer, 1910)


Linuche unguiculata occupies the shallow, warm, marine waters of the subtropics and tropics. While it prefers shallow water, it can occupy the epipelagic (surface to 200 m), mesopelagic (200 to 1000 m), bathypelagic (1000 to 4000 m), or abyssopelagic (4000 to 6000 m) regions. Buoyancy, light, pressure, presence of prey, temperature, salinity, and oxygen gradients affect the depth ranges occupied by L. unguiculata. (Arai, 1997; Calder, 2009)

  • Range depth
    0 to 5000 m
    0.00 to 16404.20 ft
  • Average depth
    200-4000 m

Physical Description

Linuche unguiculata is commonly called the "Sea thimble," "Thimble jellyfish," and "Button jellyfish," which describe the radially symmetric body shape of its umbrella medusa. Eight gonads (arranged in pairs) in four gastric pouches connect to 16 peripheral stomach pouches, which extend into 16 blunt, oval, marginal lappets. Between the folds of the lappets are an alternating eight tentacles and eight rhopaliums (sense organs). The tentacles are quite short and not easily noticeable. No marginal ring canal exists. There is one mouth in the center on the underside of the medusa umbrella. Linuche unguiculata is dioecious, but not sexually dimorphic. (Calder, 2009; Hickman, et al., 2009; Mayer, 1910)

The thimble-shaped umbrella has a width of 16 mm and a height ranging from 13 to 20 mm.

The polyp form of L. unguiculata can be colonial or solitary. The polyp is composed of hard, thin tubes of chitin, taking on a hydra-like stalk form. The branched polyp can grow to a height of 150 mm. (Arai, 1997; Calder, 2009; Jamison, 2007)

Symbiotic zooxanthellae attach to the surface of L. unguiculata, giving it an overall brownish color. Underneath the zooxanthellae, the umbrella has a transparent outer coating. The umbrella's inside surface is white with spots of green and brown. (Calder, 2009; Mayer, 1910)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    13 to 20 mm
    0.51 to 0.79 in


Linuche unguiculata follows the typical life cycle of all scyphozoans. This undergoes metamorphosis, with two body forms: an adult, dominant medusa form and a larval, flower-like polyp form. After the eggs are fertilized, early embryonic development of zygotes begins inside the female. Small, ciliated planula larvae form and swim from the female back into the water. After several days the larvae settle and attach themselves to a hard, sedentary structure on the sea floor and undergo scyphistoma. During scyphistoma, the planula larvae gradually transform into polyps. Eventually, the fully developed polyps undergo strobilation, developing a stack of saucerlike buds (a larval stage). Each saucerlike bud develops into a tiny jellyfish, breaks off from the stack, and becomes free swimming young ephyra jellyfish. After a few weeks, the young ephyrae will grow into adult medusae jellyfish, completing the life cycle. (Hickman, et al., 2009; Whitaker, et al., 2006)

The polyp form of L. unguiculata has dormant stages. Also, polyps can reproduce asexually to form polyp colonies, rather than complete growth to the adult medusa form. These unique life cycle characteristics of the polyp form make it difficult to determine the exact growth and life cycle of an individual planula larva. (Calder, 2009)

Whether the sex of L. unguiculata is determined genetically or developmentally is still being studied. Cnidarians are not known to have sex chromosomes, suggesting that genes of several other chromosomes define the sex of an individual jellyfish. (Fautin, 1992)


Linuche unguiculata seasonally forms aggregations, which assists in finding mates. Aggregation formation increases sperm concentration and improves reproductive success. In March and April, large aggregations, 500 to 1000000 square meters, have been recorded in the Atlantic Ocean and Carribean Sea.

Linuche unguiculata is polygynandrous, where males and females have multiple mates. There is no known information on how mating behaviors affect the social structure of L. unguiculata. (Hickman, et al., 2009; Jamison, 2007; Larson, 1992)

Linuche unguiculata is dioecious (individuals are either male or female). This species generally reproduces sexually, by strobilation. However, the polyp form of L. unguiculata can reproduce asexually to form colonial polyps. (Hickman, et al., 2009)

Four gastric pouches, containing the gonad reproductive organs, connect with the stomach lining of mature L. unguiculata. During reproduction, the male releases sperm out of its mouth into the open seawater. By way of cilia currents, some of the swimming sperm are swept into the female's mouth and then into the female's gatric pouch. Fertilization is internal. Early embryonic development of the zygote begins in the open seawater or in brood pouches along the oral arms of the female parent medusa. Eventually, a ciliated planula larva develops, settles, and forms a hydra-like scyphistoma. The scyphistoma may reproduce asexually to form a colonial polyp or it may form a strobila stack of ephyrae buds. Ephyrae break from the strobila to form mature medusa jellyfish. (Hickman, et al., 2009; Whitaker, et al., 2006)

Seasonal breeding begins in the spring and early summer months, when mature L. unguiculata form aggregations in the northern Atlantic Ocean. The sexually reproductive jellyfish accumulate on hard surfaces, floats, and pilings, zygotes form, and planula larvae form, settle, and undergo scyphistoma. By late summer, the polyps grow and undergo strobilation, then ephyrae buds break off to become free-swimming young jellyfish. (Jamison, 2007)

  • Breeding interval
    Linuche unguiculata breed seasonally in large swarms.
  • Breeding season
    Medusae form patches in spring and early summer, and become young ephyra buds by late summer.

Linuche unguiculata does not exhibit parental investment. Linuche unguiculata can initially gain symbiotic zooxanthellae from its mother's supply, even though the mother is not intentionally involved in supplying this algae. (Fautin, 2004)

  • Parental Investment
  • no parental involvement


The lifespan of a typical jellyfish is a few months; however, specific information on the longevity of L. unguiculata is not known. (Whitaker, et al., 2006)

  • Typical lifespan
    Status: wild
    0 to 6 months


Linuche unguiculata can form sessile, asexual, colonial polyps or motile, sexual, solitary medusae. The mature medusa form of L. unguiculata moves by way of typical jellyfish bell pulsation.

Generally, L. unguiculata does not exhibit social behavior with other individuals of its species nor does it exhibit hierarchy in a social system. (Arai, 1997; Hickman, et al., 2009)

Home Range

Linuche unguiculata medusae do not have a home range, instead drifting over large areas of ocean, but the polyps are sessile. Medusae form aggregations that can cover 500 to 1000000 square meters. (Calder, 2009; Fautin, 2004; Jamison, 2007; Larson, 1992)

Communication and Perception

Linuche unguiculata medusa possesses eight rhopalium (marginal, club-shaped structures) sense organs. A rhopalium includes statocysts (sense organs for equilibrium and balance), two sensory pits (concentrated areas of sensory cells), and occasionally an ocellus (simple, photoreceptive eye). Linuche unguiculata responds to gravity, light, touch, various chemicals, pressure, and temperature, although it does not possess specific receptors for each of these stimuli. (Arai, 1997; Calder, 2009; Hickman, et al., 2009)

No form of communication among L. unguiculata has been reported.

Food Habits

The primary prey of L. unguiculata consists of crustacean plankton, including copepods and barnacle larvae. (Jamison, 2007)

Linuche unguiculata also relies on zooxanthellae in feeding, as these endosymbiotic algae can produce organic food from carbon dioxide in photosynthesis.

Linuche unguiculata also absorbs phosphate, ammonium, nitrate, and amino acids from the marine saltwater. (Arai, 1997)

Linuche unguiculata begins feeding by with swimming with bell pulsation to create a flow that draws in prey. Then the jellyfish extends four fishing tentacles, remain in a still position, and waits for prey to pass by. If a prey contacts one of the four outstretched fishing tentacles, then nematocyts, which cover the tentacles, discharge and attach to the prey's exoskeleton. The tentacles complete feeding by bringing the captured prey into the mouth of the jellyfish to be digested. (Costello and Colin, 1995; Jamison, 2007)

Linuche unguiculata uses chemical stimuli as one means of locating prey and controlling its feeding behavior. (Arai, 1997)

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


Spadefish, sunfish, sea turtles and other marine organisms prey on L. unguiculata medusa.

Nudibranch sea slugs consume the hydroid form of L. unguiculata. (Jamison, 2007; Whitaker, et al., 2006)

Linuche unguiculata medusa uses nematocysts (organelles that uncoil and sting upon internal pressure stimulation) as a defense mechanism against predators. Nematocyts contain a venom that defends the jellyfish against predation by paralyzing, or even killing, stung predators. (Calder, 1974; Hickman, et al., 2009; Whitaker, et al., 2006)

The medusa and polyp of L. unguiculata also use chemical stimuli to sense behaviors of their predators. (Arai, 1997)

Ecosystem Roles

Aggregations of symbiotic zooxanthellae algae cover the subumbrella of L. unguiculata. They expand over the subumbrella's surface during the day, producing organic food from carbon dioxide in photosynthesis and conducting nitrogen assimilation, then contract in the evening.

The ratio of oxygen production (P) by zooxanthellae to oxygen consumption (C) by the medusa is 1.5 to 1.8. This means that the symbiotic photosynthesis not only meets the respiration needs of the zooxanthellae and the jellyfish, but also provides extra energy that can be used towards growth and reproduction of the L. unguiculata medusa. This symbiotic relationship is necessary for these jellyfish to thrive. (Arai, 1997; Fautin, 2004)

Linuche unguiculata initially acquires zooxanthellae from its mother's supply of symbiotic algae. Eventually, it gains zooxanthellae entirely from the environment. (Fautin, 2004)

Mutualist Species
  • zooxanthellae

Economic Importance for Humans: Positive

There are no known positive effects of L. unguiculata on humans.

Economic Importance for Humans: Negative

Seabather's Eruption (SBE) is an adverse effect of L. unguiculata planula larva, ephyra, or medusa on humans. Linuche unguiculata becomes trapped underneath the swimsuits of Atlantic Ocean swimmers and discharges venom. This discharge causes a hypersensitive, itchy, bumpy rash on the skin of the swimmer, underneath the swimsuit. This irritation caused by L. unguiculata occurs independent of age, sex, and race, although symptoms tend to be more severe in children than adults. SBE has never been reported to have caused death.

SBE is seasonal, peaking between May and August, when L. unguiculata larvae are prevalent. In 1997, 16% of Palm Beach swimmers were recorded with SBE. (Brown, 2008; Calder, 2009)

  • Negative Impacts
  • injures humans
    • bites or stings

Conservation Status

The conservation status of species L. unguiculata, Family Linuchidae, Order Coronatae, or Class Scyphozoa is not listed on the IUCN Red List, CITES appendices, or the United States Endangered Species Act list.

Ocean pollution can affect the populations of L. unguiculata. Eutrophication may be caused by nutrients from agricultural lands and domestic sewage. Mortality may be caused by hydrocarbons and heavy metals. (Arai, 1997)

Other Comments

Occasionally, it is questioned if L. unguiculata belongs to the Order Beroida, Phylum Ctenophora because its "Sea thimble" body structure resembles that of comb jellies. Proper classification of L. unguiculata is Family Linuchidae, Order Coronatae, or Class Scyphozoa, Phylum Cnidaria, Kingdom Animalia. (Arai, 1997)

Current studies show scyphozoans are one of the first metazoans to develop ovarian accessory cells during their reproductive evolution. This scyphozoan ovarian morphology phylogenetically links Scyphozoa closer to Anthozoa than to Hydrozoa. (Eckelbarger and Larson, 1992)


Mary Kay DuBay (author), University of Michigan-Ann Arbor, Phil Myers (editor), University of Michigan-Ann Arbor, Renee Mulcrone (editor), Special Projects.


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.

World Map


living in the southern part of the New World. In other words, Central and South America.

World Map


reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents


uses smells or other chemicals to communicate


used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

colonial growth

animals that grow in groups of the same species, often refers to animals which are not mobile, such as corals.


a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.


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


union of egg and spermatozoan


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body


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.


generally wanders from place to place, usually within a well-defined range.


An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).


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.

radial symmetry

a form of body symmetry in which the parts of an animal are arranged concentrically around a central oral/aboral axis and more than one imaginary plane through this axis results in halves that are mirror-images of each other. Examples are cnidarians (Phylum Cnidaria, jellyfish, anemones, and corals).

saltwater or marine

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

seasonal breeding

breeding is confined to a particular season


remains in the same area


non-motile; permanently attached at the base.

Attached to substratum and moving little or not at all. Synapomorphy of the Anthozoa


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


lives alone


uses touch to communicate


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


an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).


uses sight to communicate


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


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