Cubozoa

(Box jellies)

Phylum Cnidaria

Class Cubozoa

Number of families 2

Thumbnail description
Gelatinous animals that possess image-forming eyes and complex behavior, including internal fertilization in at least one species; often known as "killer box jellies," although only one of the seven genera (Chironex, in the family Chirodropidae) is potentially lethal to humans

Evolution and systematics

At one time cubozoans were placed within the class Scyphozoa (true jellyfishes), but recent research supports the Cubozoa at the class level. There is one order, Cubomedusae, with two families, Chirodropidae and Carybdeidae, and 19 described species. There is only one recognized fossil species, Anthracomedusa turnbulli, which was found near Chicago, Illinois, United States. This fossil dates from the Pennsylvanian age (323–290 million years ago), and with its square shape and clusters of tentacles, was likely within the family Chirodropidae.

Physical characteristics

The most obvious characteristic of cubozoans is the box-like shape of their bell. The manubrium and mouth are located inside the bell, and the velarium is along the edge of the bell. Pedalia are muscular extensions of the bell and the tentacles are attached to the pedalium. Chirodropids have multiple tentacles attached to each pedalium; carybdeids have only have one tentacle per pedalium. Between the pedalia are the unique sensory structures known as rhopalia. Each rhopalia has a statocyst and six eyes, four simple eyes, and two relatively complex eyes composed of an epidermal cornea, spheroidal cellular lens, and an upright retina. Antisera testing has revealed that cubozoans possess blue-, green-, and ultraviolet-sensing opsins in the both the small and large complex eyes. The cubomedusan nervous system is complex compared to that of other cnidarians. A diffuse synaptic nerve net throughout the bell region is connected to a subumbrellar nerve ring, and nerve processes extend from this ring into the rhopaliar stalks. The processing of visual images probably occurs on this nerve ring.

Distribution

Cubozoans can be found in most tropical and subtropical waters Carybdea marsupialis and Carybdea rastoni have been found in temperate waters as well. It is likely that the distribution records are incomplete as the transparent nature of these medusae make them very difficult to locate despite their shallow and coastal distribution.

Habitat

The preferred habitat of cubozoans appears to be over sandy substrate, with box jellies located just above the bottom during the day and moving up toward the surface at night. Field observation is extremely difficult, as the jellies react to the presence of divers by rapidly moving away. Carybdea

sivickisi possesses adhesive pads on the exumbrellar surface which enables it to attach to various substrates in the field.

Behavior

Cubozoans have the most complex behavior of any cnidarian. They are active swimmers capable of moving 9.8–19.7 ft (3–6 m) per minute. They are positively phototactic (move toward light) and are active during the day and night, although they may feed only during the night or predawn hours. Vision clearly plays a role in both feeding and reproduction. One characteristic that makes them interesting, their image forming eyes, also makes them difficult to study in the field or the laboratory because they react to the presence of their human observers by swimming away.

Feeding ecology and diet

Cubozoans are important predators in the nearshore ecosystem, feeding mainly on fishes and crustaceans. Additional prey items include polychaetes, crab megalopae (post-larvae), isopods, amphipods, stomatopod ("mantis shrimps") larvae, and chaetognaths (arrow worms). As active predators, cubozoans chase, catch, and eat fishes and other organisms. Feeding behavior varies slightly between species. The prey are caught on the tentacles and brought up towards the pedalia by the tentacle contracting. The medusa then either remains upright in the water or turns upside down. The pedalium with the prey item than bends inward toward the manubrium, and the prey are then engulfed.

Reproductive biology

Little is known about the reproductive biology of cubozoans. The life history includes a benthic stage, the polyp, which can reproduce asexually by budding, and a pelagic stage, the medusa. Eggs and sperm combine to form a ciliated larva (planula), which settles on the bottom and becomes a polyp. Unlike scyphozoans, cubozoan polyps do not undergo strobilation (asexual reproduction by division into body segments); rather, the entire polyp becomes the juvenile medusa. C. sivickisi uses spermatophores that can be stored by the female, and it has been hypothesized that female C. rastoni may collect sperm strands produced by the males. Other cubozoans may have internal fertilization as well, but most broadcast their gametes.

Conservation status

No species of cubozoans is listed by the IUCN.

Significance to humans

The presence of "stinger-resistant enclosures" on beaches in northern Queensland, Australia, is indicative of the impact that cubozoans can have on humans. Although deaths are reported almost every year from encounters with C. fleckeri, the overall impact of cubozoans is much greater as stings are not always reported. Carukia barnesi is now recognized as the cause of "Irukandji syndrome," which results in severe backache, muscle pains, chest and abdominal pains, headache, localized sweating, and piloerection, as well as nausea and reduced urine output. There is a box jelly antivenom that binds to both C. fleckeri and C. barnesi, and vinegar can inhibit unfired nematocysts from firing (although it stimulates nematocyst firing with other cnidarians).

Species accounts

List of Species

Irukandji

Carukia barnesi

family

Carybdeidae

taxonomy

Carukia barnesi Southcutt, 1967, Cairns, Australia.

other common names

English: Box jelly.

physical characteristics

The bell is transparent, reaching to 0.8 in (20 mm) in diameter and 1 in (25 mm) in depth; each of the four tentacles may extend to 25.6 in (650 mm).

distribution

Tropical Australian waters from central Queensland (Agnes Water) to Broome, Western Australia.

habitat

Occurs in deeper waters of the reef, although often swept inshore by currents.

behavior

Nothing is known.

feeding ecology and diet

Nothing is known.

reproductive biology

Nothing is known about the life cycle. The only time juveniles were collected was in 1997, when four small jellies were collected 3.1 mi (5 km) north of Mackay Harbor in Queensland. This led researchers to postulate that the early part of the life cycle may be in creeks or rivers as in C. fleckeri.

conservation status

Not listed by the IUCN.

significance to humans

Stingings were named the Irukandji syndrome (after a local aboriginal tribe) as early as 1943, but the species was not collected and identified until 1964 to 1966. The venom is extremely potent, and may be responsible for some fatalities. Research in 2002 focused on the use of magnesium infusions to counter the toxic sting.

Sea wasp

Chironex fleckeri

family

Chirodropidae

taxonomy

Chironex fleckeri Southcutt, 1956, Australia.

other common names

English: Box jelly.

physical characteristics

Reaches up to 11.8 in (30 cm) in diameter, but is difficult to see despite its large size. The as many as 15 tentacles in each corner can reach up to 98.4 ft (30 m) distance from the bell.

distribution

Tropical waters around Australia, from Exmouth, Western Australia, to Bustard Heads, Queensland, as well as around the Indo-west Pacific Ocean near Papua New Guinea, the Philippines, and Vietnam. Full extent of the distribution has not yet been determined.

habitat

Usually shallow waters around creek or mangrove outlets; often reported swimming around pier pilings in search of food.

behavior

Swims around pier pilings.

feeding ecology and diet

Primary diet items are fishes and prawns.

reproductive biology

The search for the polyp of Chironex fleckeri took years before polyps were found attached under some rocks in a northern Australian estuary. Polyps have been found in mangrove swamps and river outlets, but not much is known about how the planulae find their way to these locations. Polyps start to metamorphose into medusae in the Australian spring (September) and continue until the first large summer rains (January), when they are flushed out into the ocean.

conservation status

Not listed by the IUCN.

significance to humans

The venom is neurotoxic, cardiotoxic, and dermonecrotic (causes skin tissue to be damaged). Death can occur extremely rapidly while the victim is still in the water or on the beach. Antivenom is available but must be administered quickly. Vinegar can be used to remove undischarged nematocysts.

No common name

Tripedalia cystophora

family

Carybdeidae

taxonomy

Tripedalia cystophora Conant, 1898, Kingston Harbor, Puerto Rico.

other common names

None known.

physical characteristics

Small, mature jellies 0.02–0.4 in (0.5 mm–1.0 cm) in diameter. Bell slightly yellow brown, blends well with the mangrove habitat.

distribution

Puerto Rico and the Caribbean.

habitat

Shallow waters among mangrove roots.

behavior

As D. oculata aggregate in vertical lift shafts generated by the sun shining through the mangrove roots, T. cystophora change their swimming speed and turning rate in the light shafts, resulting

in the jellies spending more time in the light shafts where they can feed on the copepods.

feeding ecology and diet

Preys on dense swarms of the copepod Dioithona oculata in the mangrove prop-root habitat of Puerto Rico, where it has been intensely studied.

reproductive biology

Unique in cubozoans, broods fertilize eggs until they develop into planulae within gastral pockets. Planulae are released upon maturity. Show a preference for settling on substrates in the dark where they develop directly into a medusa.

conservation status

Not listed by the IUCN.

significance to humans

Not harmful to humans, but plays an important role in marine education as it is exhibited in many aquaria.

Resources

Periodicals

Collins, A. G. "Phylogeny of Medusozoa and the Evolution of Cnidarian Life Cycles." Journal of Evolutionary Biology 15, no. 3 (2002): 418–432.

Hartwick, R. F. "Distributional Ecology and Behaviour of the Early Life Stages of the Box-Jellyfish Chironex fleckeri." Hydrobiologia 216/217 (1991): 181–188.

Martin, V. J. "Photoreceptors of Cnidarians." Canadian Journal of Zoology. 80 (2002): 1703–1722.

Matsumoto, G. I. "Observations on the Anatomy and Behaviour of the Cubozoan Carybdea rastonii, Haacke." Marine and Freshwater Behaviour and Physiology 26 (1995): 139–148.

Wiltshire, C. J., S. K. Sutherland, K. D. Winkel, and P. J. Fenner. "Comparative Studies on Venom Extracts from Three Jellyfish: the Irukankji (Carukia barnesi), the Box Jellyfish (Chironex fleckeri, Southcott) and the Blubber (Catostylus mosaicus)." Toxicon 36 (1998): 1239.

George I. Matsumoto, PhD