Syngnathidae

The Syngnathidae is a family of fish which includes seahorses, pipefishes, and seadragons (Phycodurus and Phyllopteryx). The family name comes from Ancient Greek σύν (sún), meaning "together", and γνάθος (gnáthos), meaning "jaw", referring to the fused jaw that the entire family have in common.

Description and biology

Syngnathids are found in temperate and tropical seas across the world. Most species inhabit shallow, coastal waters, but a few are known from the open ocean, especially in association with sargassum mats. They are characterised by their elongated snouts, fused jaws, the absence of pelvic fins, and by thick plates of bony armour covering their bodies. The armour gives them a rigid body, so they swim by rapidly fanning their fins. As a result, they are relatively slow compared with other fish but are able to control their movements with great precision, including hovering in place for extended periods.

Uniquely, after syngnathid females lay their eggs, the male then fertilizes and carries the eggs during incubation, using one of several methods. Male seahorses have a specialized ventral brood pouch to carry the embryos, male sea dragons attach the eggs to their tails, and male pipefish may do either, depending on their species. The most fundamental difference between the different lineages of the family Syngnathidae is the location of male brood pouch. The two locations are on the tail (Urophori) and on the abdomen (Gastrophori). There is also variation in Syngnathid pouch complexity with brood pouches ranging from simple ventral gluing areas to fully enclosed pouches. In species with more developed, enclosed pouches it has been demonstrated that males directly provide their brood with not only nutrients but also immunity to pathogens. Syngnathids with more developed brood pouches are also known to be able to partially or completely abort a brood from a female with low fitness.

A wide variety of mate choice and mating competition has been observed in Syngnathidae. For example, Hippocampus fuscus exhibits conventional sex roles of males competing for female access while Corythoichthys haematopterus is completely sex role reversed. Most conventional sex role syngnathids are monogamous whereas sex role reversed species mostly exhibit polygamous behavior.

Evolution

Phylogenetic analysis implies that the most recent common ancestor of all syngnathids was likely pouchless. The family Solenostomidae (ghost pipefish) is a family in the order Syngnathiformes. Female ghost pipefish incubate their developing embryos inside fused pelvic fins. Evolutionary transitions from female to male care are practically nonexistent in teleosts, so brood pouches were likely not ancestral. Genome sequencing supports this, revealing multiple different origins across and within different brood pouch types. Oviparity was the ancestral trait, and the evolution of viviparity must have relied on the evolution and integration of multiple complex traits such as morphology, physiology, and behavior.

Syngnathidae was historically divided into two major lineages based on brood pouch location: Neophinae (located on the trunk) and Syngnathinae (located on the tail). The advantage of a more controlled and protected embryonic development seemed to be enough to enact evolutionary development throughout Syngnathidae to varying degrees.

In species with the most complex brood pouch systems, many traits (behavioral, physiological, morphological, and immunological) must have co‑evolved to allow for male pregnancy, driven by the increase of the fitness of those individuals’ offspring. The evolution of these traits resulted in a sex-role reversal in which females may exhibit competitive behavior for a mate.

Recent research, especially whole-genome sequencing,

Classification

In the past, this family was divided into two subfamilies: the elongated Syngnathinae, containing pipefish & seadragons, and the coiled Hippocampinae, containing seahorses and their presumed relatives. However, more recent genetic studies have found these divisions to be paraphyletic, with the seahorses being deeply nested within the pipefish, and the major division within the family being tail-brooding vs. trunk-brooding species. Due to this, the family has been re-circumscribed with its two major subfamilies being Nerophinae (trunk-brooders) and Syngnathinae (tail-brooders, including seahorses and seadragons). The split between these two families is thought to have occurred during the Paleocene.

Taxonomy

The following classification is based on Eschmeyer's Catalog of Fishes, with tribal divisions based on Stiller et al (2022):

Genus Heraldia Paxton, 1975
Genus Maroubra Whitley, 1948
Tribe Nerophini
Genus Entelurus Duméril, 1870
Genus Nerophis Rafinesque, 1810
Genus Leptoichthys Kaup, 1853
Tribe Doryrhamphini
Genus Doryrhamphus Kaup, 1856
Genus Dunckerocampus Whitley, 1933
Tribe Microphini
Genus Belonichthys Peters, 1868
Genus Choeroichthys Kaup, 1856
Genus Coelonotus Peters, 1855
Genus Microphis Kaup, 1853 (=Doryichthys)
Subfamily Syngnathinae Bonaparte, 1831 (tail-brooding pipefishes)
Genus Bulbonaricus Herald, 1953
Genus Stipecampus Whitley, 1948
Genus Kimblaeus Dawson, 1980
Genus Kyonemichthys Gomon, 2007
Genus Notiocampus Dawson, 1979
Tribe Solegnathini (seadragons and allies)
Genus Phycodurus Gill, 1896
Genus Phyllopteryx Swainson, 1839
Genus Solegnathus Swainson, 1839
Genus Syngnathoides Bleeker, 1851
Tribe Stigmatoporini
Genus Corythoichthys Kaup, 1853
Genus Stigmatopora Kaup, 1853
Tribe Leptonotini
Genus Apterygocampus Weber, 1913
Genus Bhanotia Hora, 1926
Genus Campichthys Whitley, 1931
Genus Cosmocampus Dawson, 1979 (in part)
Genus Hippichthys Bleeker, 1849
Genus Histiogamphelus McCulloch, 1914
Genus Hypselognathus Whitley, 1948
Genus Festucalex Whitley, 1931
Genus Ichthyocampus Kaup, 1853
Genus Leptonotus Kaup, 1853
Genus Micrognathus Duncker, 1912
Genus Minyichthys Herald & J. E. Randall, 1972
Genus Mitotichthys Whitley, 1948
Genus Nannocampus Günther, 1870
Genus Phoxocampus Dawson, 1977
Genus Pugnaso Whitley, 1948
Genus Kaupus Whitley, 1951
Genus Siokunichthys Herald, 1953
Genus Vanacampus Whitley, 1951
Genus Urocampus Günther, 1870
Tribe Syngnathini
Genus Amphelikturus Parr, 1930
Genus Anarchopterus Hubbs, 1935
Genus Bryx Herald, 1940
Genus Cosmocampus Dawson, 1979 (in part)
Genus Enneacampus Dawson, 1981
Genus Halicampus Kaup, 1856
Genus Penetopteryx Lunel, 1881
Genus Pseudophallus Herald, 1940
Genus Syngnathus Linnaeus, 1758 (type genus)
Tribe Haliichthyini
Genus Acentronura Kaup, 1853
Genus Cylix Short & Trnski, 2021
Genus Filicampus Whitley, 1948
Genus Haliichthys Gray, 1859
Genus Idiotropiscis Whitley, 1947
Genus Lissocampus Waite & Hale, 1921
Genus Trachyrhamphus Kaup, 1853
Tribe Hippocampini
Genus Halicampus Kaup, 1856
Genus Hippocampus Rafinesque, 1810 (seahorses)

thumb|Fossil specimen of [[Hipposyngnathus]]

Fossil taxa

Species "Syngnathus" bolcensis de Zigno, 1887 (Early Eocene of Italy)
Species "Syngnathus" heckeli de Zigno, 1874 (Early Eocene of Italy)
Genus Nepigastrosyngnathus Pharisat, 1993 (Early Oligocene of France)
Genus Hippotropiscis Žalohar & Hitij, 2012 (Middle Miocene of Slovenia)

Images

File:Hippocampus.jpg|Seahorse

File:Leafydragon.jpg|Leafy seadragon

File:Phyllopteryx taeniolatus1.jpg|Weedy seadragon

File:Ruby seadragon.jpg|Ruby seadragon

File:Alligator Pipefish 2.jpg|Pipefish

File:Banded Pipefish skeleton.jpg|Skeleton of a banded pipefish (Dunckerocampus dactyliophorus) on display at the Museum of Osteology.

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