Siphonophore - WikiHQ

Siphonophores (from Ancient Greek σίφων (siphōn), meaning "tube" and -φόρος (-phóros), meaning "bearing") are cnidarian animals of the hydrozoan order Siphonophorae. According to the World Register of Marine Species, the order contains 194 species described thus far. Each specimen is composed of medusoid and polypoid zooids that are morphologically and functionally specialized.

Like other hydrozoans, some siphonophores emit light to attract and attack prey. While many sea animals produce blue and green bioluminescence, a siphonophore, Erenna sirena, was only the second life form found to produce a red light (the first being the scaleless dragonfish Chirostomias pliopterus).

Anatomy and morphology

Colony characteristics

Siphonophores are colonial hydrozoans that do not exhibit alternation of generations, but instead reproduce asexually through a budding process. Zooids are the multicellular units that build the colonies of a siphonophore. A single bud called the pro-bud initiates the growth of a colony by undergoing fission. Cystonects have a long stem with attached zooids.

Moreover, siphonophores possess multiple types of zooids. Scientists have determined two possible evolutionary hypotheses for this observation: 1. as time progresses, zooid types have increased; In general, siphonophore colonies have a modular body plan, with many different zooids making up the overall structure. These types can include feeding gastrozooids, movement zooids, and sensory zooids.

:Specifically, feeding zooids in siphonophores have undergone many unique adaptations to service the deep. Gastrozooids are uniquely specialized organisms that have feeding polyps (similar to a mouth) along with a long tentacle with side branches which is used to capture the prey. This adaptation is unique to zooids living in siphonophore colonies.

Nectophores

:Nectophores are medusae that assist in the propulsion and movement of some siphonophores in water. They are characteristic in physonectae and calycophores. The nectophores of these organisms are located in the nectosome where they can coordinate the swimming of colonies. They are gas-filled floats that are located at the anterior end of the colonies in these species.

Distribution and habitat

Currently, the World Register of Marine Species (WoRMS) identifies 175 species of siphonophores. Depending on where each individual nectophore is positioned within the siphonophore, their function differs. The velum becomes smaller and more circular during times of forward propulsion compared to a large velum that is seen during refill periods. Their diets consist of a variety of copepods, other small crustaceans, cnidarians, ctenophores, and small fish. Some siphonophores, such as Praya dubia, have been observed to feed on other species in the same order. Generally, the diets of strong swimming siphonophores consist of smaller prey, and the diets of weak swimming siphonophores consist of larger prey. Research has shown that specific diets vary even between different individuals of the same species depending on their particular environment. A majority of siphonophores have gastrozooids that have a characteristic tentacle attached to the base of the zooid. This structural feature functions in assisting the organisms in catching prey. The nematocysts then shoot millions The gelatinous body plan allows for flexibility when catching prey, but the gelatinous adaptations are based on habitat. They swim around waiting for their long tentacles to encounter prey. In addition, siphonophores in a group denoted Erenna have the ability to generate bioluminescence and red fluorescence while its tentilla twitches in a way to mimic motions of small crustaceans and copepods. These actions entice the prey to move closer to the siphonophore, allowing it to trap and digest it.

Predators of Siphonophores include narcomedusae, gastropods, other siphonophores, and large fish such as Mola mola. This species then proceeds to undergo "blanching," and emit a startlingly bright light. Nanomia, among other siphonophore species, can move both forward and backwards to escape a stimulus from the opposite side, using their nectophores for propulsion. While there are few observations of defensive behavior in situ, it is argued that these strategies help siphonophores evade predators. There is limited research on the mechanistic release of eudoxid fragments for reproduction, and studies are determining whether to consider them as clustered communities or individuals. Another notable recent discovery occurred in early 2025, when a team led by researchers at Yale University, the University of New South Wales, and Griffith University determined that the Portuguese man o'war is actually at least four distinct species. The discovery has implications for scientists' understanding of open-ocean biodiversity, and encourages further research into understanding what caused and maintained this genetic variation.

Modern taxonomy

Siphonophores are classified into the phylum Cnidaria and the class Hydrozoa. The phylogenetic relationships of siphonophores have been of great interest due to the high variability of the organization of their polyp colonies and medusae. and floats (pneumatophores).

Molecular phylogenetics has helped address some of the inequalities by using nuclear and mitochondrial gene sequences. Most of these scientific studies have provided more insight into the evolution of specialized zooids within colonies. Additionally, genomic analyses have used transcriptome datasets to improve phylogenetic resolution, allowing scientists and researchers to reconstruct patterns in evolutionary traits like the organization of colonies and the tentilla feeding structure. The manefish has been directly observed to associate with the Bathyphysa conifera, gaining shelter and access to food leftovers from the colony.

References

External links

<nowiki>Deep sea siphonophore</nowiki> (10 April 2017) YouTube. Imaged by the NOAA Okeanos Explorer on March 14, 2017, at 1,560 meters west of Winslow Reef complex. Retrieved 28 January 2018.