Physalia
| Physalia | |
|---|---|
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| Physalia physalis | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Cnidaria |
| Class: | Hydrozoa |
| Order: | Siphonophorae |
| Suborder: | Cystonectae |
| Family: | Physaliidae Brandt, 1835 |
| Genus: | Physalia Lamarck, 1801 [1] |
| Species | |
Physalia is a genus of the order Siphonophorae, colonies of four specialized polyps and medusoids that drift on the surface of the Atlantic, Indian and Pacific oceans. Although these organisms look like a single multicellular organism, each specimen is actually a colony of minute organisms called zooids that have to work together for survival. A gas-filled bladder resembling a blue bottle provides buoyancy, and long tentacles of venomous cnidocytes provide a means of capturing prey. A sail on the float, which may be left or right-handed, propels Physalia about the sea, often in groups. These siphonophores sometimes become stranded on beaches, where their toxic nematocysts can remain potent for weeks or months in moist conditions. Both species of this siphonophore resemble a jellyfish in appearance, with their gas-filled float and cluster of polyps beneath, which can hang up to 30 or 165 ft (9 to 50 m) below the surface of the sea.
Because it frequently washes up on beaches on the coast of the Atlantic, Indian and Pacific Oceans and is seen in the open ocean, Physalia is the best-known genus of siphonophore, as nearly all siphonophores live in the cold, dark ocean depths where they can only be observed in their natural habitat by a submersible or ROV.
The genus was first described by Jean-Baptiste Lamarck in 1801.[1]
Diversity
[edit]The family Physaliidae is monotypic, consisting of only one genus, Physalia.[2] The genus is also monotypic, containing only P. physalis.[1][3] There is a long history of the genus being described with multiple species, such as the Pacific man o' war (P. utriculus), however most of these species are now considered synonyms for P. physalis.[4]
Drifting
[edit]Physalia drifting is mainly determined by wind, similar to drift migration seen in migrating birds. Which direction they drift from wind influence is determined by their dimorphism. Physalia have two forms of their enlarged pneumatophores that affect drift; left-handed, which shifts to the right of the downwind direction and right-handed, which moves to the left of the downwind.[5] In strong winds, Physalia drift with its float oriented in the same direction of the wind.[5]
It is thought that this drifting, controlled by the direct influence of wind drag, is what leads mass amounts of Physalia to wash up on beaches. Moderately strong winds, around 5 m/s, produce drifting velocities significantly higher than the typical speed of ocean currents. When Physalia get closer to the coast, they start to experience the influence of the slope-shelf currents, which are strong even in light winds.[6] Because of the Physalia's long tentacles, these currents can overtake the wind drift and wash them ashore.[6]
References
[edit]- ^ a b c "Physalia Lamarck, 1801". Integrated Taxonomic Information System.
- ^ "WoRMS - World Register of Marine Species - Physaliidae Brandt, 1835". www.marinespecies.org. Retrieved 2024-11-01.
- ^ "WoRMS - World Register of Marine Species - Physalia Lamarck, 1801". www.marinespecies.org. Retrieved 2024-11-01.
- ^ Bardi, Juliana; Marques, Antonio C (2007). "Taxonomic redescription of the Portuguese man-of-war, Physalia physalis (Cnidaria, Hydrozoa, Siphonophorae, Cystonectae) from Brazil". Iheringia. Série Zoologia. 97 (4): 425–433. doi:10.1590/S0073-47212007000400011.
- ^ a b Ferrer, Luis; González, Manuel (2021-01-01). "Relationship between dimorphism and drift in the Portuguese man-of-war". Continental Shelf Research. 212: 104269. Bibcode:2021CSR...21204269F. doi:10.1016/j.csr.2020.104269. ISSN 0278-4343.
- ^ a b Prieto, L.; MacÍas, D.; Peliz, A.; Ruiz, J. (2015). "Portuguese Man-of-War (Physalia physalis) in the Mediterranean: A permanent invasion or a casual appearance?". Scientific Reports. 5: 11545. Bibcode:2015NatSR...511545P. doi:10.1038/srep11545. PMC 4480229. PMID 26108978.