The colonial abilities of Hydrozoans (Siphonophorae)

(Post by Brennan Lindsay)

The Hydrozoans are the most diverse of the classes of phylum Cnidaria and are extremely variable in appearance, shape and size. Hydrozoans are small invertebrates that mostly like to inhabit salty marine environments. A common feature noted throughout class Hydrozoa is the long body stalk possessing a number of tentacles at one end of the body. Like many organisms in phylum Cnidaria, Hydrozoans can possess polyploid and medusoid cartier bracelet of anastasia steele fifty
stages in their life cycles, but most grow into one stage and stick to it throughout its existence. The most well-known organism of class Hydrozoa is the sessile Hydra, which completely lacks cartier love bracelet
the medusoid life stage mentioned above and instead prefers to attach fake cartier bracelet replica
to a substrate how much does a cartier bracelet cost
and stay there (Barnes 1982).

Two Hydra cartier bracelet
adhering to a surface, displaying their sessile polyp appearance. (Photo by Stephen Friedt)

Individuals in class Hydrozoa are dioecious and possess impressive colonial abilities. This is especially demonstrated in some organisms in the class, notably those in the order Siphonophorae. Physalia physalis, or more commonly known as the Portuguese Man O’ War, are colonial Hydrozoans from the order Siphonophorae. This organism may initially resemble a Scyphozoan Jellyfish, but after closer inspection, the intricacy and structural complexity of Physalia physalis is revealed. The Man o’ War is a floating hydrozoan colony, made up of four different kinds of polyp stage Hydrozoans; pneumatophores for floating on the ocean surface, dactylozooids for defense, gastrozooids for feeding, and gonozooids for reproduction. These zooids are so heavily specialized that if one were to be removed from the bulk colony it wouldn’t be able to survive on its own (Kurlansky 2004).

Since Physalia physalis lacks conventional muscles and eyes, it must use alternate strategies to achieve locomotion and to acquire nutrients. The organism spends all of its time drifting along the surface of the ocean, filling fake cartier bracelet its blue cartier bracelet bulbous pneumatophore with C02 and using it as a mast, capturing wind currents to sail around (Kirkpatrick and Pugh 1984). The pneumatophore develops lopsided to either the left or the right side, resulting in the organisms’ characteristic 45 degree surface float diagonal to the wind direction (Kurlansky 2004 and Kirkpatrick & Pugh 1984). This form of locomotion is extremely restrictive, making nutrient acquisition difficult. To counteract this, Physalia physalis stretch out up to 50 meters of nematocyst laden dactylozooids that act as a massive scale fishnet (Johnsen 2000), capturing any unsuspecting marine creatures below and paralyzing them. These nematocysts are variable in size, being either large or small on the organism (Kurlansky 2004).

Portugese Man o’ War (Physalia physalis). Photo by U.S. Department of Commerce, National Oceanic and Atmospheric Administration,


The long nematocyst laden tentacles used in the feeding of Physalia physalis poses cartier love necklace a particular problem to the tourism industry. These organisms aren’t endangered and can be found in abundance in certain oceanic areas. If people come into contact with the long tentacles of the Man o’ War they can be severely injured. Stings result in long red linear marks followed by intense rashes and pain. The pain can escalate and cause cardiac problems with anaphylactic shock in humans (Hoover 2015). Overall, Physalia physalis is a fascinating example of the Hydrozoans colonial abilities. The colonial zooids making up the organism all work together to form a motile, nutrient acquiring ecosystem floating on temperate ocean currents. The success of these organisms has allowed their lineage to continue cartier love bracelet replica until this day.


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  2. Johnsen, S. 2000. Transparent Animals. Scientific American. 282. (2).
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  4. Kurlansky, M. 2004. Physalia Physalis. Accessed Online. Animal Diversity Web.
  5. Lee, J. B. 2003. Portugese man of war. Accessed Online. Dangerous cartier love bracelet and venomous Hawaiian ocean organisms. Accessed 2/28/2016 at
  6. Sterrer, W. Bermuda’s Marine Life. Island Press. Bermuda, 1992.