Jellyfish and more – CREATURE OF THE MONTH; JANUARY 2019


January = Jellyfish.

shallow reef

Well technically Cnidarians which is inclusive of jellyfish, box jellies, corals, hydroids and anemones but everyone loves a bit of alliteration right… All species are aquatic and predominately marine.

Cnidarian is a strange word so let’s break that down to begin. The C is silent so you pronounce it like NI-DAR-RIANs coming from modern latin and greek meaning “nettle”. These organisms are definee by their stinging cells know as nematocysts.

All the groups have stingers but not all are strong enough to sting us (for instance most corals) Many species are colonial, able to asexually reproduce clones. organisms are either medusa-like (think jellyfish) or polyp-like(thing coral without skeleton), or both.


These mainly freeswimming organisms have umbrella shaped bells (tops) with long trailing tentacles. The tentacles are armed with stinging cells to capture prey and defend from predators. Although moost are free-swimming marine animals a few anchor themselves to the seabed using stalks. The bell can pulsate to provide propulsion for locomotion.

Extraordinarily, jellyfish range from about one millimeter in bell height and diameter, to nearly 2 metres (6.6 ft) in bell height and diameter; the tentacles and mouth parts usually extend way beyond this bell dimension. One of the biggest is the lion’s mane.

In Timor Leste we commonly see the upside down jelly but luckily it is not too common to come across other more harmful species.


Corals are tiny polyps but typically live in vast yet compact colonies of many identical individuals (clones).  Species include those that inhabit tropical oceans secreting calcium carbonate to form a hard skeleton thus crreating coral reef systems. Timor Leste and Atauro island are known for their healthy and extensive coral reef systems. Additionally, “soft corals” such as seasons, sea pens, whip corals are a common additional to reefs and muck dive sites.

Although some corals are able to catch small fish and plankton using their stinging cells,t corals obtain energy and nutrients from photosynthetic unicellular dinoflagellates known as zooxanthellae. These corals require lots sunlight and usually grow in clear, shallow water, typically at depths less than 60 metres (200 ft). Coral bleaching occurs when these algae leave the coral skeleton during stressful times such as high temperatures.


The majority of hydroids are colonial whereby the original polyp anchors to a solid substrate then it buds; each bud is attached to previous to form a stem. Many hydriods look like some sort of plant due to their “leaf like formation” however the arrangement of polyps and branching of the stem is actually characteristic of each species. The sting from one of this group can produce red welts and a burning sesnation which usually become iching but are commonly not dangerous.

One commonly misplaced hydroid is the portogese man o’war – in fact not a jellyfish as many people assume but a memeber of this group. unfortantely is tentacles deliver a painful sting, which is venomous can be deadly, in some cases to humans. Despite its appearance it is not actually a single multicellular organism but a colonial organism made up of specialized individual animals.


Funnily enough this group is named after a terrestrial flowering plant, because of the general colourful appearance. Sea anemones do not have a medusa  (free swimming) stage in their life cycle. Commonly, polps are attched to a hard surface or bury in the sand and rather that being colonial are singular. Found in both deep oceans and shallow coastal waters worldwide. With great diversity is in the tropics and many species adapted to relatively cold waters.

Similarly to corals, some additional nurishment can come from a symbiosis with zooxanthellae or with green algae, zoochlorellae. They are hunters too, catching prey in their tentacles which can retract inside the body cavity.

The sting from anemone usually radiates to a full burning sensation that can last a long while which eventually becomes iching. The skin will likely be red and inflamed.

How to deal with stings 

Divers should be aware of all the groups above, using good buoyancy techniques and awareness to aviod contact. If stings do happen the appropriate first aid for all is vinegar but do not ever rinse with fresh water. Remove any tentacles that may still be on the skin. Anti-inflamatories and anti itch cream can aid in treating the symptoms.


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