Marine Invertebrates of Bermuda

Upside-down Jellyfish
Cassiopea xamachana

By Matt Berryman
Dr. James B. Wood and Kim Zeeh - Editors

Abstract  Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links 

Upside-down Jellyfish (Cassiopea xamachana)


Cassiopea xamachana is a jellyfish that is found in Bermuda, throughout the Caribbean Sea, and some areas of the warm western Atlantic Ocean (Sterrer, 1992; Fitt & Costley, 1998; Fleck & Fitt, 1999). The common name of this species is the upside-down jellyfish. Given its life style, it does not look like the typical jellyfish, appearing as a greenish gray-blue flower on the seafloor. It is found on the muddy bottoms of inshore bays and ponds (Sterrer, 1986) and is most commonly seen on Bermuda in Walsingham Pond and Harrington Sound (Sterrer, 1992). Because they live their lives on the bottom with large portions of their carbon and nutrition coming from their symbiotic zooxanthellae, they tend to be in shallow areas saturated with sunlight. This species reproduces through strobilation, similar to most other jellies, but with varying seasonality (Fitt & Costley, 1998). As with other cnidarians, C. xamachana has nematocysts covering its tentacles and digestive tract. It uses these stinging cells for both feeding and defense (Fitt & Costley, 1998). It is fairly common on the island and there are no specific Bermudian laws that protect C. xamachana. But it does make its home in several protected areas, leading to indirect protection of the species (Sterrer, 1992; Wood & Jackson, 2005).


Phylum: Cnidaria
  Class: Scyphozoa
    Order: Rhizostomae
      Family: Cassiopeidae


Cassiopea xamachana has a fairly wide distribution. Although xamachana means Jamaican, these jellies are found through out the Caribbean Sea and warm western Atlantic Ocean (Sterrer, 1992) and are very common in Bermuda. Within the Bermuda platform, C. xamachana is most commonly seen in Walsingham Pond, where they thrive in this nutrient rich anchialine pond, and Harrington Sound (Sterrer, 1992); but they have been seen throughout many inshore locations on the platform.

C. xamachana spends its life quite differently from that of other jellyfish. Instead of “swimming” about in the open ocean, it spends its life sitting on the muddy bottoms of inshore bays and ponds. It is commonly known as the upside-down jellyfish because it found laying on the substrate with its bell down and tentacles raised up in the water column. It is also referred to as the mangrove jellyfish (Fitt & Costley, 1998) or the cabbage-head jellyfish (Sterrer, 1986) although this name is also given to Stomolophus meleagris (Ruppert et al., 2004), a close relative to C. xamachana. C. xamachana are most often found in large aggregations (Sterrer, 1986); only occasionally being observed alone. This species is a benthic organism, rising into the water column rarely, usually when significantly disturbed. In these instances they launch upward in large groups, flopping about in a pulsing motion for a few moments before settling back into the mud (Sterrer, 1992).

Another unique trait about C. xamachana is their temperature tolerance. They strobilate during the summer and early fall with medusae found year round, while other temperate-zone scyphozoans usually strobilate over winter when their medusae form all but disappears (Fitt & Costley, 1998); more on this to follow. This species is entirely marine, none have been observed in fresh or brackish water.



In Cassiopea xamachana the medusae are dioecious. It is assumed that the eggs in the female are fertilized by sperm released from nearby males (Fitt & Costley, 1998; Müller & Leitz, 2002). The fertilized eggs are moved to knob-shaped tentacles near the center of the female where they develop into larvae. Once able to undergo metamorphosis, the larvae hatch as planulae which permanently attach to surrounding substrate with a microbial film (Hoffman et al., 1996) and metamorphose into a polyp with tentacles (scyphistoma). These scyphistomae can undergo asexual reproduction via budding when food is plentiful. Each new bud will settle and form a new scyphistoma (Fitt & Costley, 1998). Once the scyphistomae acquire a certain species of Symbiodinium and when temperatures reach or exceed 20ºC they will begin to strobilate (Hofmann et al., 1978; Rahat & Adar, 1980). C. xamachana undergo monodisc type strobilation (Sterrer, 1986; Ruppert et al., 2004). Although medusae are always found containing zooxanthellae, they do not pass this onto their larvae. Each scyphistoma must acquire its own zooxanthellae from the surrounding seawater through absorption or in conjunction with feeding, to complete its life cycle (Fitt, 1984).

As noted above, C. xamachana undergo strobilation during the summer and early fall, and that their medusae are seen all year round. This is a unique trait for this species as other temperate-zone species of scyphozoans undergo strobilation during the winter and their medusae disappear during this time. It appears that the tropical C. xamachana has “cold-sensitive scyphistomae and more temperature-tolerant medusae” (Fitt & Costley, 1998).

It has also been observed that the plaulae of C. xamachana are rather selective about where they settle. If present, the planulae will settle on submerged, degrading leaves of the Red Mangrove Rhizophora mangle. This is often the case when the C. xamachana are living in ponds surrounded by mangroves or mangrove swamps. They are even as selective as to prefer the shady side of the leaves. But most interesting is perhaps the natural, chemical cues received by the larvae to both settle and metamorphose on the leaves (Fleck & Fitt, 1999).


The most commonly seen stage in the life cycle, the medusa, is the adult phase of the life cycle. They have 4 pairs of elaborately branched but unfused oral arms. Embedded in the mesoglea of the arms and rest of the body are thousands of zooxanthellae, giving Cassiopea xamachana its greenish color. Exact coloration within the species is variable, the most common is greenish gray-blue. The umbrella, or bell, is flat, saucer shaped and has a well-defined central depression on the exumbrella. This acts as a sucker, helping to keep the jellyfish on the bottom as it gently pulsates. As for the more conspicuous stage, the polyps are of slender design (Sterrer, 1986).


Cassiopea xamachana contain thousands of tiny zooxanthellae within their mesoglea. This symbiotic relationship accounts for how the upside-down jellyfish obtains most of its carbon. It has been observed, however, that in most medusae of C. xamachana the carbon from the zooxanthellae does not “provide all of the energy necessary for basic respiratory metabolic needs” (Vodenichar, 1995). As a result of this the jellies must also feed themselves to some extent. This species either filter feed, absorbing dissolved nutrients from the water, or can capture prey through the use of nematocysts contained within their tentacles (Fitt & Costley, 1998). Nematocysts, a defining characteristic of cnidarians, are small stinging cells that are controlled by the cnidocil, a mechanical and chemical trigger. When the cnidocil is triggered, the nematocysts are fired from its cell, cnidoblast, stunning or paralyzing the unfortunate prey. The jelly then begin “digesting” the prey on its manubrial/oral surface reducing them to fragments that can be ingested through the secondary mouths (Ruppert et al., 2004). You heard right, secondary mouths. Instead of having one mouth at the center of the oral surface like most other jellies, C. xamachana has mutated in the form that this central mouth has closed and many secondary mouths have formed at the ends of the manubrial branches (Sterrer, 1992; Ruppert et al., 2004). Fitt & Costley discovered that feeding within scyphistomae is disrupted in low temperatures (1998). At temperatures <18ºC the scyphistomae were able to capture their prey but not transport it to the mouth for ingestion (Fitt & Costley, 1998).


The nematocysts not only function for prey capture, but also serve in the defense of the jelly. When an unlucky predator comes too close to Cassiopea xamachana it sets off the cnidocil and nematocysts are released into the surrounding water. The resulting sting is often enough of a deterrent for most predators, unless they have developed counter-defenses. As far as humans are concerned, C. xamachana often release their “grenades” into the surrounding waters when disturbed, which can cause an itching sensation on the skin (Sterrer, 1992). If significantly disturbed, there is a possibility of a large group of the jellies suddenly launching upward.


The zooxanthellae contained within the mesoglea of Cassiopea xamachana are part of the same symbiotic relationship seen within corals and other jellyfish. However, in corals the zooxanthellae provide a greater amount of the carbon necessary for respiratory metabolic needs than those within C. xamachana (Vodenichar, 1995). In jellies the zooxanthellae act as a supplement to regular food gathering. This is especially helpful in C. xamachana as its primarily sessile life style is not the best for obtaining large amounts of food except perhaps through absorption, which may be why the species is found so often in high nutrient areas such as Walsingham Pond, Bermuda and canals and near-shore areas in the Florida Keys.

Recent Research

A very recent study was conducted on Cassiopea xamachana on the toxicity and binding activity of acetylcholine muscarinic receptors of their venom. The crude venom was fractionated by gel filtration chromatography. Upon analyzing the six fractions, it was discovered that fraction VI contained “proteinaceous components contributing to most of cytolysis as well as membrane binding events”; while fraction IV most likely contributed to venom lethality and paralytic effects (Radwan et al., 2005). If these properties are further analyzed and the exact fraction/substance for causing them can be isolated, then perhaps C. xamachana venom can be of some use in the future.

Another study done on the upside-down jellyfish examined its spasm, strong patterned contractions, behavior and diffuse nerve-net (DNN). A quick sequence of DNN impulses is required to initiate “a patterned flurry of strong contractions” within the striated muscles of C. xamachana. It is suggested that these contractions, the ‘spasm’, are an integral and essential component in the behavior of C. xamachana and that the control through the use of the DNN demonstrates how complex behavior is generated (Passano, 2004). Understanding of this could aid and the understanding of complex behaviors in other organisms as well.

Commercial Importance

At the current date there appears to be no commercial importance for Cassiopea xamachana.

Bermuda Laws

This species itself does not receive specific attention from Bermudian laws. However, the two places they are most commonly seen in (Walsingham Pond and Harrington Sound) are both protected areas. “Walsingham Marine Reserve is Bermuda’s only Marine Park in which mooring, anchoring, and fishing are prohibited” (Wood & Jackson, 2005). There is no collection allowed from the Pond itself. This all exists under the Bermuda National Parks Act, 1985 (Wood & Jackson, 2005). Harrington Sound receives limited protection through the Fisheries Act, 1972, allowing only cast and bait net fishing (Wood & Jackson, 2005).

Personal Interest

I have visited the island of Bermuda for study and research several times now. In preparation for my first visit I was assigned a research project on jellyfish. This was a general assignment looking at all representatives of the class Scyphozoa and the basic characteristics shared by all of them. However, among all the various species, I found the upside-down jellyfish the most fascinating; most likely because it is so unique from other jellies. Cassiopea xamachana spends nearly its whole life upside-down and sitting on the sandy or mud substrate. In this position, the jellies look more like sea flowers than jellyfish; this is a unique form of disguise utilized by this species of jellyfish.


Fitt, W.K., 1984. The role of chemosensory behavior of Symbiodinium microadriaticum, intermediate hosts, and host behavior in the infection of coelenterates and mollusks with zooxanthellae. Mar. Biol. 81: 9-17.

Fitt, W.K., Costley, K., 1998. The role of temperature in survival of the polyp stage of the tropical rhizostome jellyfish Cassiopea xamachana. J. Exp. Mar. Biol. Ecol. 222: 79-91.

Fleck, J., Fitt, W.K., 1999. Degrading mangrove leaves of Rhizophora mangle Linne provide a natural cue for settlement and metamorphosis of the upside down jellyfish Cassiopea xamachana Bigelow. J. Exp. Mar. Biol. Ecol. 234: 83-94.

Hoffman, D.K., Neumann, R., Henne, K., 1978. Strobilation, budding and initiation of scyphistoma morphogenesis in the rhizostome Cassiopea andromeda. Mar. Biol. 47: 161-176.

Hoffman, D.K., Fitt, W.K., Fleck, J., 1996. Checkpoints in the life-cycle of Cassiopea spp.: control of metagenesis and metamorphosis in a tropical jellyfish. Int. J. Dev. Biol. 40: 331-338.

Müller, W.A., Leitz, T., 2002. Metamorphosis in the Cnidaria. Can. J. Zool. 80: 1755-1771.

Passano, L.M., 2004. Spasm behavior and the diffuse nerve-net in Cassiopea xamachana (Scyphozoa: Coelenterata). Hydrobiologia 530-531(1): 91-96.

Radwan, F.F.Y., Roman, L.G., Baksi, K., Burnett, J.W., 2005. Toxicity and mAChRs binding activity of Cassiopea xamachana venom from Puerto Rican coasts. Toxicon 45(1): 107-112.

Rahat, M., Adar, O., 1980. Effect of symbiotic zooxanthellae and temperature on budding and strobilation in Cassiopea andromeda. Biol. Bull. 159: 394-401.

Ruppert, E.E., Fox, R.S., Barnes, R.D., 2004. Invertebrate zoology. A functional evolutionary approach. Thomson, Brooks/Cole, USA. pp. 148-153.

Sterrer, W., 1986. Marine fauna and flora of Bermuda. A systematic guide to the identification of marine organisms. John Wiley & Sons, Inc. pp. 158-159.

Sterrer, W., 1992. Bermuda’s marine life. Bda. Zool. Soc., Island Press, Bda. pp. 43-44.

Vodenichar, J.S., 1995. Ecological physiology of the scyphozoan Cassiopea xamachana. M.S. Thesis, University of Georgia, Athens, USA.

Wood, J.B., Jackson, K.J., 2005. Bermuda. In: Caribbean marine biodiversity: the known and the unknown. Miloslavich, P. & Klein, E., Eds. DEStech Publications, Inc., Lancaster, PA. pp. 19-35.


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