The thimble jellyfish (''Linuche unguiculata'') is a species of

cnidarian Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that th ...

found in the warm West

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

, including the

Caribbean The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean Se ...

. It is a tiny

jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella- ...

with a straight-sided, flat-topped bell. This jellyfish is the most common cause of seabather's eruption, a reaction caused by the injection of juvenile jellyfish

nematocyst A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida () or nematocyst) that can deliver a sting to other organisms. The presence of this ce ...

s into human skin.

Description

The medusa of the thimble jellyfish has straight sides with sixteen grooves, and a flat top. The coronal groove between the top and sides provides flexibility. The margin of the bell has sixteen lappets (folds), the niches between these bearing alternately rhopalia (sense organs) and short

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

s (eight of each). There is no marginal ring canal. Symbiotic zooxanthellae give the bell an overall orangish-brown colour and the translucent mesoglea has dark flecks. This jellyfish can reach a diameter of and a height of .

Distribution and habitat

The thimble jellyfish is found in the

tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

and

subtropical The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Geographical z ...

western Atlantic Ocean, particularly around the

West Indies The West Indies is a subregion of North America, surrounded by the North Atlantic Ocean and the Caribbean Sea that includes 13 independent island countries and 18 dependencies and other territories in three major archipelagos: the Greater A ...

and the

Bahamas The Bahamas (), officially the Commonwealth of The Bahamas, is an island country within the Lucayan Archipelago of the West Indies in the Atlantic Ocean, North Atlantic. It takes up 97% of the Lucayan Archipelago's land area and is home to ...

. Although it can occur in warm surface waters, it has been found at depths down to about . Its presence in any particular location is related to such factors as the presence of prey, temperature, salinity and oxygen saturation of the water.

Ecology

The thimble jellyfish swims constantly by pulsating its bell, rotating as it moves. It forms swarms in warm seas near the surface of the water. Aggregations have been reported covering a million square metres . The jellyfish feeds on

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

, drawing a water current past its outstretched tentacles by pulsating the bell. When edible

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

are encountered, they are immobilised by the cnidocytes (stinging cells) and passed by the tentacles to the mouth on the underside of the bell. Thimble jellyfish are consumed by fish, sea turtles and other predators.

Seabather's eruption

Larvae of the thimble jellyfish are the most common cause of seabather's eruption in the

and the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...

. The condition occurs when a swimmer comes in contact with a cloud of larvae, which stick to the swimmer's clothing and hair. When the swimmer exits the water and either bathes or drys out, the larvae are killed and in the process discharge their under-developed stinging cells. The stings are not painful, but can cause an itchy rash to form. In Florida, most cases occur between March and August. A similar condition occurs on the east coast of North America after exposure to the larvae of the sea anemone '' Edwardsiella lineata''.

References

{{Taxonbar, from=Q2193910 Linuchidae Animals described in 1788