# Hippocampini
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{{Short description|Subfamily of fishes}}
{{Use dmy dates|date=September 2025}}
{{Automatic taxobox
| fossil_range = {{fossil range|Middle Miocene|present}}
| image = Idiotropiscis australe.jpg
| image_upright = 1.15
| image_caption = ''[Idiotropiscis australe](/source/Southern_little_pipehorse)''
| taxon = Hippocampini
| authority = [Bonaparte](/source/Charles_Lucien_Bonaparte), 1835
| subdivision_ranks = Genera
| subdivision = Between 2 and 10 (see text)
}}
[[File:Kyonemichthys rumengani.jpg|right|253px|thumb|''[Kyonemichthys rumengani](/source/Kyonemichthys_rumengani)'', one of several small syngnathids discovered in the [West Pacific](/source/West_Pacific) in recent years]]
The '''Hippocampini''' are a [tribe](/source/Tribe_(biology))[{{Cite journal |last1=Stiller |first1=Josefin |last2=Short |first2=Graham |last3=Hamilton |first3=Healy |last4=Saarman |first4=Norah |last5=Longo |first5=Sarah |last6=Wainwright |first6=Peter |last7=Rouse |first7=Greg W. |last8=Simison |first8=W. Brian |date=2022-03-27 |title=Phylogenomic analysis of Syngnathidae reveals novel relationships, origins of endemic diversity and variable diversification rates |journal=BMC Biology |language=en |volume=20 |issue=1 |pages=75 |doi=10.1186/s12915-022-01271-w |issn=1741-7007 |pmc=8962102 |pmid=35346180 |doi-access=free}}][{{Cite journal |last=Brownstein |first=C D |date=2023 |title=Syngnathoid Evolutionary History and the Conundrum of Fossil Misplacement |url=https://academic.oup.com/iob/article/5/1/obad011/7152594 |journal=Integrative Organismal Biology |language=en |volume=5 |issue=1 |doi=10.1093/iob/obad011 |issn=2517-4843 |archive-url=https://web.archive.org/web/20240307223301/https://academic.oup.com/iob/article/5/1/obad011/7152594 |archive-date=7 March 2024 |pmc=10210065 |access-date=27 September 2025 |url-status=live }}] of small [marine](/source/Marine_(ocean)) [fish](/source/fish)es in the subfamily [Syngnathinae](/source/Syngnathinae) of the family [Syngnathidae](/source/Syngnathidae). Depending on the classification system used, it comprises either [seahorse](/source/seahorse)s and [pygmy pipehorses](/source/idiotropiscis),[Kuiter, R.H. (2000) "Seahorses, Pipefishes and their Relatives – A Comprehensive Guide to Syngnathiformes." TMC Publishing, Chorleywood, UK.] or only seahorses.[{{cite journal | author = Wilson N., Rouse G. | year = 2010 | title = Convergent camouflage and the non-monophyly of 'seadragons' (Syngnathidae: Teleostei): suggestions for a revised taxonomy of syngnathids. | journal = Zoologica Scripta | volume = 39| issue = 6 | pages = 551–558| doi = 10.1111/j.1463-6409.2010.00449.x | s2cid = 56351380 }}]
== Etymology ==
The subfamily Hippocampinae is named after the seahorse genus ''[Hippocampus](/source/Hippocampus_(fish))'', which is derived from the Ancient Greek ἱππόκαμπος (hippokampos), a [compound](/source/compound_(linguistics)) of ἵππος, "horse" and κάμπος, "sea monster". The morphologically intermediate nature of pygmy pipehorses is reflected in the name "pipehorse", a combination of the first syllable of "pipefish" and the second syllable of "seahorse". "Pygmy" is added to distinguish them from the larger pipehorses of the genus ''[Solegnathus](/source/Solegnathus)'', which are distant relatives of the pygmy pipehorses.[{{cite journal |author=Wilson, A.B., Ahnesjö, I., Vincent, A.C. and Meyer, A. |year=2003 |title=The dynamics of male brooding, mating patterns, and sex roles in pipefishes and seahorses (family Syngnathidae) |journal=[Evolution](/source/Evolution_(journal)) |volume=57 |issue=6 |pages=1374–1386 |doi=10.1111/j.0014-3820.2003.tb00345.x |pmid=12894945 |doi-access=free}}] Other common names that have been applied to pygmy pipehorses include "bastard seahorse", "little pipehorse" and "pygmy pipedragon".
==Taxonomy==
=== Genera ===
Based on Stiller ''et al'' (2022):[{{cite journal |journal = [Annales de Paléontologie](/source/Annales_de_Pal%C3%A9ontologie) |year=2012 |volume = 98 |pages=131–151 |title = The first known fossil record of pygmy pipehorses (Teleostei: Syngnathidae: Hippocampinae) from the Miocene Coprolitic Horizon, Tunjice Hills, Slovenia |author1=Žalohar, J. |author2=Hitij, B.|doi = 10.1016/j.annpal.2012.02.003 |issue = 2}}]
*''[Idiotropiscis](/source/Idiotropiscis)'' [Whitley](/source/Gilbert_Percy_Whitley), 1947
*''[Lissocampus](/source/Lissocampus)'' [Waite](/source/Edgar_Ravenswood_Waite) & [Hale](/source/Herbert_Mathew_Hale), 1921
*''[Trachyrhamphus](/source/Trachyrhamphus)'' [Kaup](/source/Johann_Jakob_Kaup), 1853
Other "pipehorses", such as ''[Amphelikturus](/source/Amphelikturus)'' are now placed in the tribe Syngnathini, having convergently evolved in the "pipehorse" morphology. The taxonomy of other pipehorses such as ''[Kyonemichthys](/source/Kyonemichthys_rumengani)'' remains uncertain.[{{cite journal |author1=Teske, P.R. |author2=Beheregaray, L.B. |year=2009 |title=Evolution of seahorses' upright posture was linked to Oligocene expansion of seagrass habitats |journal=[Biology Letters](/source/Biology_Letters) |volume=5 |issue=4 |pages=521–523 |doi=10.1098/rsbl.2009.0152 |pmc=2781918 |pmid=19451164}}] and hence share a common evolutionary origin. However, the same [phylogeny](/source/phylogeny) indicates that if the [subfamily](/source/subfamily) Hippocampinae is accepted as valid, then the [pipefish](/source/pipefish) [subfamily](/source/subfamily) [Syngnathinae](/source/Syngnathinae) is [paraphyletic](/source/paraphyletic), because the former is not a [sister group](/source/sister_group) of the latter, but is nested within it.[Healy Hamilton, Norah Saarman, Beth Moore, Graham Short, & W. Brian Simison: ''A Multigene Phylogeny of Syngnathid Fishes.'' [http://www.ipfc2009asfb.com/pdf/speaker_presentations/Hamiliton,%20Healy.pdf PDF] {{Webarchive|url=https://web.archive.org/web/20130421151552/http://www.ipfc2009asfb.com/pdf/speaker_presentations/Hamiliton,%20Healy.pdf|date=21 April 2013}}]
As the genus ''[Hippocampus](/source/Hippocampus_(fish))'' consists of two morphologically distinct forms, it has been suggested that it should be split into two distinct genera, ''[Hippocampus](/source/Hippocampus_(fish))'' and a new genus comprising the pygmy seahorses. Pygmy seahorses have a single gill opening on the back of the head (instead of two on the sides as in normal seahorses), and the males brood their young inside their trunk''',''' instead of in a pouch on the tail.[Smith, Richard E. [http://oceanrealmimages.com/blog/10/04/11/pygmy-seahorse-facts-images Pygmy seahorse research]] A molecular [phylogeny](/source/phylogeny) confirms that the pygmy seahorses are a [monophyletic](/source/monophyletic) sister [lineage](/source/lineage_(evolution)) of all other seahorses.[{{Cite web |last1=Fricke |first1=R. |last2=Eschmeyer |first2=W. N. |last3=Van der Laan |first3=R. |date=2025 |title=ESCHMEYER'S CATALOG OF FISHES: CLASSIFICATION |url=https://www.calacademy.org/eschmeyers-catalog-of-fishes-classification |access-date=2025-02-10 |website=California Academy of Sciences |language=en}}] In addition, the pipefish genus ''Halicampus'' was found to be the closest relative of ''Hippocampus''. These two genera were placed in the tribe '''Hippocampini''', [sister](/source/Sister_group) to the tribe Halliichthyini, containing the pygmy pipehorses. Brownstein ''et al'' (2023) found a similar taxonomy, but chose to retain the pygmy pipehorses within an expanded Hippocampini.[Wilson, M. E. J. & Rosen, B. R. 1998 Implications of paucity of corals in the Paleogene of SE Asia: plate tectonics or centre of origin? In Biogeography and geological evolution of SE Asia (eds R. Hall & J. D. Holloway), pp. 165–195. Leiden, The Netherlands: Backhuys Publishers.] Particularly important was the establishment of vast [seagrass meadow](/source/seagrass_meadow)s where there had previously been deeper water.[{{cite journal |author=Brasier, M.D. |year=1975 |title=An outline history of seagrass communities |journal=[Palaeontology](/source/Palaeontology_(journal)) |volume=18 |pages=681–702}}] This has led to speculation that the earliest seahorses managed to establish themselves as a new species because, unlike pygmy pipehorses, they were selectively favoured in such habitats. Not only can seahorses manoeuver exceptionally well in dense seagrass meadows,[{{cite journal |author1=Flynn, A. J. |author2=Ritz, D. A. |year=1999 |title=Effect of habitat complexity and predatory style on the capture success of fish feeding on aggregated prey. |journal=[Journal of the Marine Biological Association of the United Kingdom](/source/Journal_of_the_Marine_Biological_Association_of_the_United_Kingdom) |volume=79 |issue=3 |pages=487–494 |doi=10.1017/S0025315498000617 |s2cid=86160386}}] but the upright seagrass blades would have provided camouflage for their bodies and in that way improved their ability to ambush prey and avoid detection by predators.[{{cite journal |author=van Wassenbergh, S., Roos, G. and Ferry, L. |last2=Roos |last3=Ferry |year=2011 |title=An adaptive explanation for the horse-like shape of seahorses |journal=[Nature Communications](/source/Nature_Communications) |volume=2 |issue=1 |pages=164 |bibcode=2011NatCo...2E.164V |doi=10.1038/ncomms1168 |pmid=21266964 |doi-access=free}}] In that case, the evolution of an upright posture would merely be a means of maximising the angle between head and abdominal axis.
There is as yet no fossil evidence for the evolution of seahorses from a pygmy pipehorse ancestor, as the fossil record of both groups is very sparse. The only pygmy pipehorse species of which fossils have been found (''[Hippotropiscis](/source/Hippotropiscis) frenki'') lived in the Central [Paratethys Sea](/source/Paratethys) (the modern-day [Tunjice Hills](/source/Tunjice_Hills) of [Slovenia](/source/Slovenia), north of the [Mediterranean Sea](/source/Mediterranean_Sea)) during the [Middle Miocene](/source/Middle_Miocene),[{{cite journal |vauthors=Teske PR, Cherry MI, Matthee CA |year=2004 |title=The evolutionary history of seahorses (Syngnathidae: Hippocampus): molecular data suggest a West Pacific origin and two invasions of the Atlantic Ocean |journal=[Molecular Phylogenetics and Evolution](/source/Molecular_Phylogenetics_and_Evolution) |volume=30 |issue=2 |pages=273–86 |doi=10.1016/S1055-7903(03)00214-8 |pmid=14715220}}] these regions are the most likely candidates for such a site.
==Description==
All seahorse and pygmy pipehorse species have a [prehensile tail](/source/prehensile_tail) (a character shared with some other [syngnathids](/source/Syngnathidae)),[{{cite journal |journal = [Records of the Australian Museum](/source/Records_of_the_Australian_Museum) |year=1982 |volume = 34 |pages=575–605 |title = Review of the Indo-Pacific pipefish genus Stigmatopora (Syngnathidae) |issue = 13 |author= Dawson, C.E. |doi=10.3853/j.0067-1975.34.1982.243|doi-access= free }}] a fully enclosed [brood pouch](/source/Brood_pouch_(Syngnathidae)), a short head and snout angled ventrally from the abdominal axis, and no caudal fin.[{{cite journal |journal = [Aqua, International Journal of Ichthyology](/source/Aqua%2C_International_Journal_of_Ichthyology) |year=2007 |volume = 13 |title = A new genus and miniature species of pipehorse (Syngnathidae) from Indonesia |issue = 1 |author= Gomon, M.F.}}] The species in the genera ''Acentronura'', ''Amphelikturus'' and ''Kyonemichtys'' resemble pipefishes, which explains why pygmy pipehorses are sometimes grouped in the pipefish subfamily [Syngnathinae](/source/Syngnathinae).[{{FishBase| genus=Acentronura | species=tentaculata | year=2013 | month=May }}] The species of ''[Idiotropiscis](/source/Idiotropiscis)'' are more seahorse-like in appearance in having a deeper body and discontinuous superior trunk and tail ridges.[{{cite journal |journal=[Records of the Australian Museum](/source/Records_of_the_Australian_Museum) |year=2004 |volume=56 |issue=2 |pages=163–165 |title=A New Pygmy Pipehorse (Pisces: Syngnathidae: Idiotropiscis) from Eastern Australia |author=Kuiter, R.H. |url=http://australianmuseum.net.au/Uploads/Journals/17992/1420_complete.pdf |doi=10.3853/j.0067-1975.56.2004.1420 |access-date=9 May 2013 |archive-date=6 November 2013 |archive-url=https://web.archive.org/web/20131106081831/http://australianmuseum.net.au/Uploads/Journals/17992/1420_complete.pdf |url-status=dead }}] The main differences between this pygmy pipehorse genus and the seahorses is that the latter have an upright posture, and the angle of their head relative to the abdominal axis is greater.