Physonectae

{{Short description|Suborder of siphonophores}} {{About|the taxon of marine animals||Hoei (disambiguation)}} {{Automatic taxobox | image = Physonect siphonophore Puerto Rico April 2015.png | image_alt = Physonect siphonophore Puerto Rico April 2015.png | image_caption = A physonect siphonophore near Puerto Rico | image2 = Haeckel Siphonophorae 37.jpg | image2_caption = Illustration of ''Physophora hydrostatica'' | taxon = Physonectae | authority = Haeckel, 1888<ref>Haeckel, E. (1888). System der Siphonophoren auf phylogenetischer Grundlage entworfen. Jenaische Zeitschrift für Naturwissenschaft. 22: 1-46., available online at http://www.biodiversitylibrary.org/item/43887#page/11/mode/1up page(s): 38</ref> | synonyms = | synonyms_ref = | subdivision_ranks = Families | subdivision_ref = <ref name=WoRMS>Schuchert, P. (2019). World Hydrozoa Database. Physonectae. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=135335 on 2019-03-11</ref> | subdivision = *Agalmatidae Brandt, 1834 *Apolemiidae Huxley, 1859 *Cordagalmatidae Pugh, 2016 *Erennidae Pugh, 2001 *Forskaliidae Haeckel, 1888 *Physophoridae Eschscholtz, 1829 *Pyrostephidae Moser, 1925 *Resomiidae Pugh, 2006 *Rhodaliidae Haeckel, 1888 *Stephanomiidae Huxley, 1859 }}

'''Physonectae''' is a suborder of siphonophores.<ref>Japan Agency for Marine-Earth Science and Technology. (2009 onwards). Biological Information System for Marine Life (BISMaL). Accessed on 2018-11-21. available online at http://www.godac.jamstec.go.jp/bismal</ref> Organisms in the suborder Physonectae follow the classic Siphonophore body plan. They are almost all pelagic, and are composed of a colony of specialized zooids that originate from the same fertilized egg.

== Distribution == The majority of physonect siphonophores are pelagic, with the exception of Rhodallidae, which are a family of benthic physonects first collected during the ''Challenger'' expedition and described by Ernst Haekel in his ''Challenger'' monograph.<ref name=":0">{{Cite journal |date=1983-06-14 |title=Benthic siphonophores: a review of the family Rhodaliidae (Siphonophora, Physonectae) |url=http://dx.doi.org/10.1098/rstb.1983.0025 |journal=Philosophical Transactions of the Royal Society of London. B, Biological Sciences |volume=301 |issue=1105 |pages=165–300 |doi=10.1098/rstb.1983.0025 |bibcode=1983RSPTB.301..165P |issn=0080-4622 |last1=Pugh |first1=P. R. |url-access=subscription }}</ref>

Physonects, and siphonophores in general, are known to be widely distributed globally, but are understudied. Few individuals have been collected and are often misidentified. As a result, their exact global distributions are unclear.<ref>{{Cite journal |last1=MAŃKO |first1=MACIEJ K. |last2=PUGH |first2=PHILIP R. |date=2018-06-27 |title=Agalma clausi (Bedot, 1888) (Siphonophora: Physonectae)—complementary description with notes on species distribution and ecology |url=http://dx.doi.org/10.11646/zootaxa.4441.2.7 |journal=Zootaxa |volume=4441 |issue=2 |pages=311–331 |doi=10.11646/zootaxa.4441.2.7 |pmid=30314012 |s2cid=52975339 |issn=1175-5334|url-access=subscription }}</ref>

== Morphology == All physonect siphonophores have an aboral, apical pneumatophore filled with gas, which is formed by invagination of the superficial cell layers of the apical side of the larva.<ref name=":0" /> In some species in the suborder Physonectae, the pneumatophore has a pore located either on the apical or basal pole of the organism and plays a role in controlling gas volume and pressure for buoyancy control.<ref name=":0" /> Gas in the pneumatophore is high in carbon monoxide and is secreted by the pneumadenia, or gas gland.<ref name=":0" />

Below the pneumatophore, an organism has a long stem with two distinct regions. The nectosome is more apical relative to the siphosome and is composed of asexual nectophores, or swimming bells.<ref name=":0" /> These swimming bells are the animal's zooids specialized for swimming. The siphophore includes the gastrozooids (feeding polyps) and sexual medusoids.<ref name=":0" />

== Reproduction == Each physonect colony is composed of individual organisms originating from the same fertilized egg, with specialized functions including locomotion, feeding, and reproduction.<ref>{{Cite journal |last1=Dunn |first1=Casey W. |last2=Pugh |first2=Philip R. |last3=Haddock |first3=Steven H. D. |date=2005-12-01 |title=Molecular Phylogenetics of the Siphonophora (Cnidaria), with Implications for the Evolution of Functional Specialization |url=http://dx.doi.org/10.1080/10635150500354837 |journal=Systematic Biology |volume=54 |issue=6 |pages=916–935 |doi=10.1080/10635150500354837 |pmid=16338764 |issn=1076-836X|url-access=subscription }}</ref> The ventral budding zone of the nectophores in the animal lies immediately below pneumatophore. As new buds are produced asexually, the swimming bells are displaced downwards.<ref name=":0" />

Sexual reproduction occurs to give rise to a new colony of zooids. The siphosome is made up of groups called cormidia, which consist of a gastrozooid with a tentacle, bracts and palpons, and the gonodentra.<ref name=":0" /> The gonodendra bears the gonophores, or sexual bodies. Among physonect Siphonophores, many are monoecious, some are protandrous, and few are dioecious. Eggs and sperm are deposited directly into the water and fertilization happens externally.<ref name=":1">{{Cite book |last=Mapstone |first=G. M. |title=Siphonophora (Cnidaria: Hydrozoa) of Canadian Pacific Waters |location=}}</ref>

== Life stages == While the life cycle of physonects has been studied in a limited number of species, in a typical physonect life cycle, external fertilization happens between eggs and sperm released by free-swimming eudoxids, which are released into the water from mature physonects.<ref name=":1" /> Like all siphonophores, physonect eggs are yolky, and act as the source of energy for their early development.<ref name=":1" /> The sperm are attracted to the egg by species-specific chemicals.<ref name=":1" /> A planula forms, which then develops into a bilaterally symmetric siphonula, then mature into a young colony, and eventually into a mature colony.<ref name=":1" /> Most physonectae are pelagic for their entire life cycles.

== Diet == Physonectae are carnivorous predators and vary in diet depending on the local availability of prey. In a study on the diets epipelagic siphonophores in the Gulf of California in the Sargasso Sea and in Friday Harbor, Washington, it was found that compared to other suborders of Siphonophores, species in the suborder Physonectae have fewer, large gastrozooids. They primarily consume large copepods, some smaller copepods, and a variety of other large, non-copepod prey.<ref name=":2">{{Cite journal |last=Purcell |first=J. E. |date=1981 |title=Dietary composition and diel feeding patterns of epipelagic siphonophores |url=http://link.springer.com/10.1007/BF00397071 |journal=Marine Biology |language=en |volume=65 |issue=1 |pages=83–90 |doi=10.1007/BF00397071 |s2cid=85011338 |issn=0025-3162|url-access=subscription }}</ref> Gastrozooid length appears to correlate to preferred and maximum size of prey.<ref name=":2" /> In Canadian Pacific waters, physonect diets similarly included larger copepods, but also larger arthropods, chaetognaths, and fish larvae.<ref name=":1" />

==References== {{Reflist|refs=Dunn, C. W., Pugh, P. R., & Haddock, S. H. D. (2005, December 1). Molecular phylogenetics of the Siphonophora (cnidaria), with implications for the evolution of functional specialization. OUP Academic. Retrieved April 25, 2022, from https://academic.oup.com/sysbio/article/54/6/916/1629643

Mapstone, G. M. (n.d.). Siphonophora (cnidaria:hydrozoa) of Canadian Pacific Waters. Google Books. Retrieved April 25, 2022, from https://books.google.com/books/about/Siphonophora_Cnidaria_Hydrozoa_of_Canadi.html?id=8epLkhYnBGYC

PMC, E. (n.d.). Agalma clausi (Bedot, 1888) (Siphonophora: Physonectae)-complementary description with notes on species distribution and ecology. Europe PMC. Retrieved April 25, 2022, from https://europepmc.org/article/med/30314012

Pugh, P. R. (1983). Benthic siphonophores: A review of the family Rhodaliidae (Siphonophora, physonectae). Royal Society.

Purcell, J. E. (n.d.). Dietary composition and diet feeding patterns of epipelagic siphonophores. SpringerLink. Retrieved April 25, 2022, from https://link.springer.com/article/10.1007/BF00397071}}

Category:Physonectae Category:Siphonophorae Category:Cnidaria suborders Category:Taxa named by Ernst Haeckel