Amphionides

{{Short description|Monotypic species of planktonic crustacean}} {{Speciesbox | image = Amphionides reynaudii 2.jpg | genus = Amphionides | parent_authority = Zimmer, 1904 | species = reynaudii | authority = (H. Milne-Edwards, 1833) | synonyms = * ''Amphion armata'' Koeppel, 1902 * ''Amphion provocatoris'' Bate, 1888 * ''Amphion reynaudii'' H. Milne-Edwards, 1833 * ''Amphionides valdiviae'' Zimmer, 1904 | synonyms_ref = <ref name="Williamson"/> }}

'''''Amphionides reynaudii''''' is a species of caridean shrimp, whose identity and position in the crustacean system remained enigmatic for a long time. It is a small (less than one inch long) planktonic crustacean found throughout the world's tropical oceans, which until 2015 was considered the sole representative of the order Amphionidacea, due to unusual morphological features. Molecular data however confirm it as a member of the caridean family Pandalidae, and the confusion of morphology is because only larval phases have so far been studied.<ref name=degrave/><ref name="Wang">{{cite journal |author=Yaqin Wang, Ka Yan Ma, Ling Ming Tsang, Kaori Wakabayashi, Tin-Yam Chan, Sammy De Grave, Ka Hou Chu |year=2021 |title=Confirming the systematic position of two enigmatic shrimps, ''Amphionides'' and Procarididae (Crustacea: Decapoda) |journal=Zoologica Scripta |volume=25 |issue=1 |pages= 812–823 |url=https://onlinelibrary.wiley.com/doi/10.1111/zsc.12509| doi=10.1111/zsc.12509 |s2cid= 238828671|url-access=subscription }}</ref>

==Description== ''Amphionides'' specimens observed have been up to {{convert|25|mm|1|abbr=on}} long. In view of adult shrimp morphology, ''Amphionides'' appears unusual, with many body parts being reduced or absent. For example, it has only one pair of mouthparts – the maxillae – the mandibles and maxillules being vestigial.<ref name="Williamson">{{cite journal |author=D. I. Williamson |author-link=Donald I. Williamson |year=1973 |title=''Amphionides reynaudii'' (H. Milne Edwards), representative of a proposed new order of Eucaridan Malacostraca |journal=Crustaceana |volume=25 |issue=1 |pages=35–50 |doi=10.1163/156854073X00470 |jstor=20102008}}</ref>

Males and females differ in the form of the antennae, and also by the presence in males of the eighth thoracic appendage, albeit in a reduced form. This is the site of the male gonopore (the female's gonopore is on the sixth thoracic appendage).<ref name="Williamson"/> The first pleopod of the female is greatly enlarged and almost encloses the enlarged carapace. This is assumed to be a chamber in which the eggs are fertilised and retained until hatching.<ref name="Williamson"/> The more streamlined carapace and pleopods of the male make it more hydrodynamic, so fewer males are caught than females.

==Distribution and ecology== ''A. reynaudii'' has a cosmopolitan distribution in the world's tropical oceans. It is planktonic, inhabiting waters less than {{convert|100|m|abbr=on}} deep as a larva.<ref name="Williamson"/>

==Classification== Originally described from earlier larval stages, ''Amphionides'' was actually first thought to be a shrimp. In 1969 it was connected to a supposed adult form described earlier by Carl Zimmer (1904), not recognisable as a caridean shrimp, and in 1973 was ''Amphionides'' placed in its own order Amphionidacea by Donald I. Williamson,<ref name="Williamson"/> i.e., at the same rank as the Decapoda and Euphausiacea. The specific epithet ''reynaudii'' was given by Henri Milne-Edwards in honour of a friend of his, possibly Count François Dominique Reynaud de Montlosier.<ref>{{cite web |url=http://www.tmbl.gu.se/libdb/taxon/personetymol/petymol.qr.html |title=Reynaud |work=Biographical Etymology of Marine Organism Names |author=Hans G. Hansson |publisher=Göteborgs Universitet |access-date=June 28, 2011| archive-url= https://web.archive.org/web/20110614003105/http://www.tmbl.gu.se/libdb/taxon/personetymol/petymol.qr.html| archive-date= 14 June 2011 | url-status= live}}</ref>

Based on molecular comparisons, the species was moved back to Decapoda and to the shrimp infraorder Caridea in 2015, while the adult stage still remains undiscovered.<ref name = degrave/> It was speculated that observations from different oceans represent larval stages of different shrimp species.<ref name = degrave>{{cite journal |author=De Grave, S., Chan, T. Y., Chu, K. H., Yang, C. H., & Landeira, J. M. |year=2015 |title=Phylogenetics reveals the crustacean order Amphionidacea to be larval shrimps (Decapoda: Caridea) |journal=Scientific Reports |volume=5 |article-number=17464 |doi= 10.1038/srep17464|pmid= 26642937|pmc= 4672333|bibcode= 2015NatSR...517464D}}</ref> Broader analyses confirmed that ''Amphionides'' belongs to the family Pandalidae, but it does not seem to be associated with any of the previously recognised pandalid genera, while it indeed has an inter-oceanic distribution.<ref name = Wang/>

==References== {{Reflist}}

==Further reading== * {{cite journal |author=Henri Milne-Edwards |author-link=Henri Milne-Edwards |year=1833 |title=Note sur un nouveau genre de Crustacés de l'ordre des Stomapodes |language=French |trans-title=Note on a new genus of crustaceans of the order Stomatopoda |journal=Annales de la Société Entomologique de France |volume=1 |pages=336–340 |url=https://www.biodiversitylibrary.org/page/14002205}} * {{cite journal |author=Poul Heegaard |year=1969 |title=Larvae of decapod crustacea. The Amphionidae |journal=Dana Report |volume=77 |pages=1–82 |url=http://decapoda.nhm.org/pdfs/11029/11029.pdf }}

==External links== {{Taxonbar|from1=Q11841068|from2=Q1139268}} {{Authority control}}

Category:Caridea Category:Monotypic decapod genera Category:Crustaceans of Brazil Category:Taxa named by Henri Milne-Edwards