Thursday, March 15, 2012

Jellyfish 30 Species

Jellyfish with box-shaped bodies or bells are called cubozoan jellyfish. They belong to the Phylum Cnidaria which also includes seaanemones, corals, true jellyfish and bluebottles. There are two main groups of cubozoan jellyfish chirodropids and carybdeids. Chirodropid jellyfish include the large box jellyfish Chironex fleckeri and species of Chiropsalmus. Carybdeids include the jimble Carybdea rastonii and Irukandji jellyfish such as Carukia barnesi.

Chirodropid jellyfish can be larger than carybdeid jellyfish. For example, Chironex fleckeri can grow 300-380mm across the bell and one species of Chiropsalmus can grow to 90mm across the bell. The carybdeid jellyfish Carukia barnesi usually only grows to about 10mm across the bell. Other carybdeids can grow to 80mm across the bell. Chirodropid jellyfish have multiple tentacles hanging from each of the four corners of their bells while carybdeids usually have a single tentacle hanging from each corner. For example, Chironex fleckeri can have up to 60 tentacles, 15 on each corner. Species of Chiropsalmus can have up to nine tentacles on each corner of the bell.

In contrast, the carybdeid jellyfish Carukia barnesi has a single retractile tentacle, up to 750mm long, hanging from each corner of its body. The jimble Carybdea rastonii also has a single tentacle from each corner of its bell which can be up to 300mm long. However, some species of carybdeids may have several tentacles from each corner. For example, Tripedalia binata has two tentacles from each corner of its bell. Chirodropid jellyfish usually only have stinging cells on their tentacles. Most carybdeid jellyfish such as Carukia barnesi have stinging cells on both the body and tentacles.

Box jellyfish can be found in most tropical seas around the world. In Australia, they are found in tropical waters predominantly in the wet season (November to May), but may be present throughout the year. Carukia barnesi, the first jellyfish shown to cause Irukandji syndrome, has been found from Port Douglas in north Queensland, to as far south as the Whitsundays. The  jellyfish are found offshore as well as along coastal beaches when northerly or north-easterly winds and currents are thought to carry them onshore. The number of jellyfish in inshore waters can vary between years, probably due to changing weather conditions. In 1999-2000, two scientists sampling north of Cairns every day for four months over summer caught 270 Carukia barnesi (most of them were caught in three days). The following year, only two jellyfish were caught in the same time.

There are almost 30 species of cubozoan or box jellyfish but the life cycles of only a few are known. The life cycle of the box jellyfish Chironex fleckeri was revealed in the early 1980s. Adult male and female jellyfish are thought to release sperm and eggs into the water. The fertilised eggs develop into ‘planula’ larvae which may swim for a few days before settling to the bottom of the creek. The planulae develop into polyps and crawl about for several days before attaching to rocks on the creek bed. The tiny polyps start feeding on plankton and then the polyps bud off extra polyps. Each polyp metamorphoses into a single miniature box jellyfish (called a medusa) about 1.5mm in size which grows and develops into larger jellyfish. These small jellyfish make their way to the creek mouth and along sandy beaches.

The life cycle of most carybdeid jellyfish including Carukia barnesi is unknown. The polyps of a carybdeid jellyfish from Puerto Rico have been found in creeks on dead bivalve shells.


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