Hippocampini

{{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'' | taxon = Hippocampini | authority = Bonaparte, 1835 | subdivision_ranks = Genera | subdivision = Between 2 and 10 (see text) }} [[File:Kyonemichthys rumengani.jpg|right|253px|thumb|''Kyonemichthys rumengani'', one of several small syngnathids discovered in the West Pacific in recent years]]

The '''Hippocampini''' are a tribe<ref name=":1">{{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}}</ref><ref name=":0">{{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 }}</ref> of small marine fishes in the subfamily Syngnathinae of the family Syngnathidae. Depending on the classification system used, it comprises either seahorses and pygmy pipehorses,<ref name="Kuiter2000">Kuiter, R.H. (2000) "Seahorses, Pipefishes and their Relatives – A Comprehensive Guide to Syngnathiformes." TMC Publishing, Chorleywood, UK.</ref> or only seahorses.<ref name="Wilson&Rouse2010">{{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 }}</ref>

== Etymology == The subfamily Hippocampinae is named after the seahorse genus ''Hippocampus'', which is derived from the Ancient Greek ἱππόκαμπος (hippokampos), a compound 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'', which are distant relatives of the pygmy pipehorses.<ref name="Wilson2003">{{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 |volume=57 |issue=6 |pages=1374–1386 |doi=10.1111/j.0014-3820.2003.tb00345.x |pmid=12894945 |doi-access=free}}</ref> 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):<ref name=":1" /> *''Hippocampus'' Rafinesque, 1810 *''Halicampus'' Kaup, 1856

==== Alternative taxonomy ==== Brownstein ''et al'' (2023) include the pygmy pipehorses within the tribe.<ref name=":0" /> Stiller ''et al'' instead treated these genera as a separate tribe sister to the Hippocampini, within the tribe Haliichthyini.<ref name=":1" /> *''Acentronura'' Kaup, 1853 * ''Cylix'' Short & Trnski, 2021 (Manaia pygmy pipehorse) * ''Filicampus'' Whitley, 1948 * ''Haliichthys'' Gray, 1859 *†''Hippotropiscis'' Žalohar & Hitij, 2012 (known only from Miocene fossils)<ref name="Zalohar&Hitij2012">{{cite journal |journal = Annales de Paléontologie |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}}</ref> *''Idiotropiscis'' Whitley, 1947 *''Lissocampus'' Waite & Hale, 1921 *''Trachyrhamphus'' Kaup, 1853 Other "pipehorses", such as ''Amphelikturus'' are now placed in the tribe Syngnathini, having convergently evolved in the "pipehorse" morphology. The taxonomy of other pipehorses such as ''Kyonemichthys'' remains uncertain.<ref name=":1" />

=== Systematics === In the past, due to the morphologically intermediate nature of the pygmy pipehorses between pipefishes and seahorses, the taxonomic placement of this group (then known as the subfamily Hippocampinae) was contentious, and three different classifications were proposed for it:

*''Hippocampinae comprises both seahorses and pygmy pipehorses''<ref name="Kuiter2000" />

:Phylogenetic analyses based on five nuclear genetic loci recovered the genera ''Hippocampus'' and ''Idiotropiscis'' as sister taxa, suggesting that seahorses and pygmy pipehorses are a monophyletic group<ref name="Teske&Beheregaray2009">{{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 |volume=5 |issue=4 |pages=521–523 |doi=10.1098/rsbl.2009.0152 |pmc=2781918 |pmid=19451164}}</ref> and hence share a common evolutionary origin. However, the same phylogeny indicates that if the subfamily Hippocampinae is accepted as valid, then the pipefish subfamily Syngnathinae is paraphyletic, because the former is not a sister group of the latter, but is nested within it.<ref name="Teske&Beheregaray2009" />

*''Hippocampinae includes only seahorses, pygmy pipehorses are placed into the pipefish subfamily Syngnathinae''<ref name="tentaculata" />

:This classification system disregards both genetic data and the morphological characters shared by seahorses and pygmy pipehorses. As seahorses have a sister taxon relationship with ''Idiotropiscis'', and other pygmy pipehorse genera are likely basal to this group (given their more pipefish-like appearance), this classification would also make the Syngnathinae paraphyletic.

*''Hippocampinae includes only seahorses, pygmy pipehorses are placed into own subfamily''<ref name="Wilson&Rouse2010" />

:This classification places all pygmy pipehorses into the subfamily Acentronurinae. Based on the nuclear DNA phylogeny, the exclusion of the seahorses from this group likely makes it paraphyletic. However, such a placement is partially supported by an alternative molecular phylogeny that is based on a combination of nuclear and mitochondrial markers and that recovered a group comprising pygmy pipehorses and several pipefishes as a sister lineage of ''Hippocampus''.<ref name="Hamilton">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}}</ref>

As the genus ''Hippocampus'' consists of two morphologically distinct forms, it has been suggested that it should be split into two distinct genera, ''Hippocampus'' 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.<ref name="smith1">Smith, Richard E. [http://oceanrealmimages.com/blog/10/04/11/pygmy-seahorse-facts-images Pygmy seahorse research]</ref> A molecular phylogeny confirms that the pygmy seahorses are a monophyletic sister lineage of all other seahorses.<ref name="Hamilton" />

A high-resolution 2022 study sampling across all syngnathids refuted the former taxonomic treatment of Hippocampinae as its own subfamily, instead finding it to be deeply nested within the subfamily Syngnathinae, the tail-brooding pipefishes. Due to this, Hippocampinae is no longer recognized as a distinct subfamily by ''Eschmeyer's Catalog of Fishes''.<ref name=":1" /><ref name=":13">{{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}}</ref> 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 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.<ref name=":0" />

=== Evolution and fossil record === right|450px|thumb|A simplified reconstruction of the evolution of seahorses from a pipefish-like ancestor based on a combination of genetic data, fossils and the body structure of living species. Although some species have become extinct, the major stages of evolution are still represented in living species. The timing of only two evolutionary events is known with some certainty: the evolution of the first pipefishes and the evolution of seahorses. The placement of the pipefish-like pygmy pipehorses has yet to be confirmed by genetic data.

The morphology of pygmy pipehorses suggests that they are an evolutionary link between pipefishes and seahorses, and that seahorses are upright-swimming pygmy pipehorses. Molecular dating indicates that ''Hippocampus'' and ''Idiotropiscis'' diverged from a common ancestor during the Late Oligocene.<ref name="Teske&Beheregaray2009" /> During this time, tectonic events in the Indo-West Pacific resulted in the formation of shallow-water areas, which considerably changed marine habitats in this region.<ref name="Wilson&Rosen1998">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.</ref> Particularly important was the establishment of vast seagrass meadows where there had previously been deeper water.<ref name="Brasier1975">{{cite journal |author=Brasier, M.D. |year=1975 |title=An outline history of seagrass communities |journal=Palaeontology |volume=18 |pages=681–702}}</ref> 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,<ref name="Flynn&Rits1999">{{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 |volume=79 |issue=3 |pages=487–494 |doi=10.1017/S0025315498000617 |s2cid=86160386}}</ref> 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.<ref name="Teske&Beheregaray2009" /> An alternative explanation for the evolution from pygmy pipehorse to seahorse is based on the finding that a vertically bent head is more efficient in capturing prey because it increases the animal's strike distance, which is considered particularly useful in tail-attached sit-and-wait predators.<ref name="vanWassenbergh2011">{{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 |volume=2 |issue=1 |pages=164 |bibcode=2011NatCo...2E.164V |doi=10.1038/ncomms1168 |pmid=21266964 |doi-access=free}}</ref> 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 frenki'') lived in the Central Paratethys Sea (the modern-day Tunjice Hills of Slovenia, north of the Mediterranean Sea) during the Middle Miocene,<ref name="Zalohar&Hitij2012" /> i.e. during a time when seahorses had already evolved.<ref name="Teske&Beheregaray2009" /> In fact, the oldest known seahorse species, ''Hippocampus sarmaticus'' and ''H. slovenicus'', were found at the same site.<ref name="Zalohar&Hitij2012" /> Independent geological confirmation of the genetic data would require finding a fossil site from the Oligocene in which seahorse-like pygmy pipehorses are present, but seahorses are not. Given the fact that ''Idiotropiscis'' is endemic to temperate Australia and the most basal seahorse lineages occur in Australia and the tropical West Pacific,<ref name="Teske2004">{{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 |volume=30 |issue=2 |pages=273–86 |doi=10.1016/S1055-7903(03)00214-8 |pmid=14715220}}</ref> these regions are the most likely candidates for such a site.

==Description== All seahorse and pygmy pipehorse species have a prehensile tail (a character shared with some other syngnathids),<ref name="Dawson1982">{{cite journal |journal = 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 }}</ref> a fully enclosed brood pouch, a short head and snout angled ventrally from the abdominal axis, and no caudal fin.<ref name="Gomon2007">{{cite journal |journal = Aqua, 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.}}</ref> The species in the genera ''Acentronura'', ''Amphelikturus'' and ''Kyonemichtys'' resemble pipefishes, which explains why pygmy pipehorses are sometimes grouped in the pipefish subfamily Syngnathinae.<ref name="tentaculata">{{FishBase| genus=Acentronura | species=tentaculata | year=2013 | month=May }}</ref> The species of ''Idiotropiscis'' are more seahorse-like in appearance in having a deeper body and discontinuous superior trunk and tail ridges.<ref name="Kuiter2004">{{cite journal |journal=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 }}</ref> 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.<ref name="Kuiter2004" />

<gallery class="center" widths="200"> File:Short-pouch pygmy pipehorse.jpg|''Acentronura breviperula'', a species of pygmy pipehorse that looks like a short pipefish File:Pygmy seahorse.jpg|The pygmy seahorse ''Hippocampus bargibanti'' File:PotbellySeahorse TNAquarium.jpg|The Australian potbelly seahorse, ''Hippocampus abdominalis'', the largest species in the subfamily Hippocampinae. </gallery>

==References== {{Reflist}}

==External links== * [https://web.archive.org/web/20120510091415/http://news.nationalgeographic.com/news/2012/05/pictures/120508-new-species-seahorses-pygmy-pipehorses-animals-science/#/seahorse-missing-link-found-fossil-specimen_52560_600x450.jpg Pictures: Ancient pygmy pipehorse species found] ''National Geographic'', 8 May 2012. * [https://web.archive.org/web/20110221070917/http://news.nationalgeographic.com.au/news/2009/05/090522-seahorses-stand-up.html How seahorses evolved to swim "standing up"] ''National Geographic News'', 22 May 2009 * [https://www.youtube.com/watch?v=yOt1BSy0KdY How the seahorse got its shape] ''Nature Video'', 21 January 2011 * [http://australianmuseum.net.au/Sydneys-Pygmy-Pipehorse-Idiotropiscis-lumnitzeri-Kuiter-2004/ Sydney's pygmy pipehorse] ''Australian Museum'' 14 September 2012 * [https://web.archive.org/web/20130402205003/http://www.wakatobi.com/fishID/articles/pygmypipehorse.html Wakatobi pygmy pipehorse] ''Wakatobi Dive Resort''

Category:Syngnathidae Category:Taxa named by Charles Lucien Bonaparte Category:Fish tribes