Gasterosteiformes

(vertebrate zoology) An order of actinopterygian fishes characterized by a ductless swim bladder, a pelvic fin that is abdominal to subthoracic in position, and an elongate snout.

(Sticklebacks, seahorses, and relatives)

Class: Actinopterygii

Order: Gasterosteiformes

Number of families: 11

Evolution and systematics

The evolutionary affinities and composition of the Gasterosteiformes have been the subject of much debate; presently they are considered to be closely related to the teleost fish orders Synbranchiformes (swamp eels), Elassomatiformes (pygmy sunfish, Elassoma), Mugiliformes (mullets), and the collective Atherinomorpha (silversides, needlefishes, killifishes, and allies) and are placed with them in the larger group Smegmamorpha. Smegmamorphs are characterized by a unique configuration of the first vertebra and its associated intermuscular bone. Within this group, gasterosteiforms may be more closely related to the Synbranchiformes, but relationships within smegmamorphs are still the subject of controversy. The smegmamorphs, in turn, are closely related to the largest of all teleost groups, the Percomorpha. This evolutionary arrangement is the most recent and best-supported hypothesis based on morphological evidence, but alternative schemes of relationship have been proposed (including molecular studies), and a true consensus has not yet emerged.

The Gasterosteiformes, as described in this chapter, comprises two suborders, the Gasterosteoidei and the Syngnathoidei. Other authors sometimes have recognized these as separate orders, but evidence exists that they are each other's closest relative and therefore warrant being classified together. Gasterosteiformes share various specializations, such as pelvic bones without anterior processes, absence of Baudelot's ligament (a stout ligament connecting the shoulder girdle to either the posterior cranial base or an anterior vertebra—also absent in synbranchiforms), certain features of their branchial and caudal skeletons, and a particular configuration of their scales, which are represented by enlarged scutes, or plates. (Scales are absent in Hypoptychus, Aulostomus has small ctenoid scales, and Fistularia has embedded spines).

The extent to which these features (and others) are truly indicative of a common ancestry for Gasterosteiformes is not completely understood.

The Gasterosteoidei includes the following families: Hypoptychidae (for the sand eel, Hypoptychus dybowskii), Aulorhynchidae (tubesnouts, two monotypic genera), Indostomidae (Indostomus, with three species), and Gasterosteidae (some five genera and, conservatively, seven spp.). The Syngnathoidei comprises the families Syngnathidae (seahorses and pipefishes, with about 52 genera and 220 spp.), Aulostomidae (trumpetfishes, Aulostomus, with some three spp.), Fistulariidae (cornetfishes, Fistularia, with four spp.), Macroramphosidae (snipefishes, three genera with 12 spp.), Centriscidae (shrimpfishes, two genera with four spp.), Solenostomidae (ghost pipefishes, Solenostomus, with some four spp.), and Pegasidae (seamoths, two genera with five spp.). Altogether, the order Gasterosteiformes is represented by 11 families, 70 genera, and at least 265 species, but undescribed species have been discovered (including some 20 species of pipefishes and seahorses), and numerous nominal species presently in synonymy, in fact, may be valid (such as for sticklebacks). Much work remains to be done concerning their taxonomy, and the phylogenetic position of Indostomus is still debated.

The fossil record of the Gasterosteiformes is extensive and dates back at least some 75 million years to the Calcare di Mellissano deposits near Nardò, in southeastern Italy (Apulia). This early fossil, Gasterorhamphosus zuppichinii, is known from skeletal remains and is similar to modern snipefishes. Additional gasterosteiform fossils, known from more or less complete skeletons, have been described from the extensive Monte Bolca beds of northeastern Italy (dating back some 52 million years). These include representatives of the Syngnathidae (at least five genera), Solenostomidae (some three genera), Centriscidae (three genera), Aulostomidae (four genera), and Fistulariidae (some three genera and four spp.). The actual number of species from Monte Bolca is difficult to estimate with precision, but this formation represents the greatest extinct diversity of the order. The gasterosteiform species present in both the Nardò and Monte Bolca deposits were inhabitants of the former Tethys Ocean, which separated the extinct continents Laurasia and Gondwana during much of the Cretaceous and Tertiary periods. Other fossils, mostly represented by fragmentary material and allied to the Aulostomidae and Fistulariidae, are known from Turkmenia, in deposits almost contemporaneous with Monte Bolca. Fossil sticklebacks have been found in the Tertiary of California (Monterey Formation) and Siberia. Tertiary pipefishes have been described from the Modelo and Puente Formations of southern California as well as from the Caucasus and Carpathian Mountains of eastern Europe.

Physical characteristics

The morphological characteristics of various gasterosteiform families are highly modified and specialized; some of the members of this order are among the most morphologically interesting of all fishes. Some forms are more pelagic and streamlined (e.g., aulorhynchids), whereas others are benthic and highly cryptic (e.g., pegasids). Many forms are elaborately camouflaged and blend in perfectly with their surroundings (some of the most notable examples are Syngnathus typhle, Solenostomus cyanopterus, and Histiogamphelus cristatus); some syngnathid species have been discovered only after their particular substrate was collected and examined. Additionally, some species carry algal growths and complex dermal projections that further aid in their concealment (the most striking example may be the leafy seadragon Phycodurus eques), and many species have the ability to change color at will (e.g., Aulostomus chinensis). Most species have the head and body on the same plane, as in "typical" fishes, but seahorses have the head at more or less a right angle to the body, a unique condition among fishes.

There is much morphological variation among the families and subfamilies, and many are recognized easily by their unique designs. Gasterosteids (sticklebacks) resemble more "typical fishes," with an unmodified head and clearly demarcated fins, but most gasterosteiforms have elongated snouts, with small upturned mouths, and may lack some fins or even all of them (Bulbonaricus). The snout may be absent (Bulbonaricus); truncated (Histiogamphelus); mildly elongated (Indostomus); or very long and tubular, reaching up to one-third of their total length (e.g., Aulostomus and Fistularia). The mouth usually is very small, located at the end of the snout (except in pegasids, where the mouth is underneath the snout), and most species lack teeth. The eyes typically are round and vary from large to small. Most species have very slender and elongated bodies, but gasterosteoids (except Indostomus) and some syngnathoids (e.g., Macroramphosidae, Centriscidae) are laterally compressed.

The fins typically are highly modified. They have either one or two dorsal fins; the single dorsal fin may be preceded by numerous spines (gasterosteoids, Aulostomus), but in some forms the spines represent the first dorsal fin (Solenostomus, centriscids, and macroramphosids). In most species, however, there is a single dorsal fin with soft rays only. Pelvic fins are absent in Hypoptychus and syngnathids, and the caudal fin is absent in most syngnathids. Many syngnathids have prehensile tails that enable them to cling to soft corals and algae. Most gasterosteiforms are covered in bony plates, scutes, or rings and have numerous elaborate dermal projections on the head, body, and tail. There is also great morphological variation internally (e.g., lack of true stomachs in seahorses and reduction of the number of cephalic bones in many species). Details of the morphological features of the different families are elaborated in the species accounts.

Gasterosteiforms are among the most colorful fishes, displaying a wide spectrum of colors and patterns. There is also much diversity in coloration within certain species, and some individuals may change color while breeding or to blend into different backgrounds. Every conceivable color pattern seems to be present within the order, as some species combine strong colors (e.g., red, orange, yellow, green, white, black, and blue) with spots, blotches, ocelli, mottlings, and stripes of various kinds. Gasterosteiformes also vary considerably in size, from some 0.8 in (2 cm) in length among pygmy seahorses to more than 4.9 ft (1.5 m) for cornetfishes (Fistularia).

Distribution

Worldwide in tropical and temperate marine waters as well as in temperate freshwaters of the Northern Hemisphere. Species are more abundant in the tropical Indo-West Pacific region, where several undescribed pipefish species are known. Some species are widespread (e.g., the red cornetfish, Fistularia petimba), whereas others are very restricted in distribution (e.g., Festucalex cinctus off central New South Wales and southern Queensland, Australia). A few species with wide distributions, such as Hippocampus erectus and Doryrhamphus dactyliophorus, may require subdivision.

Habitat

Most species are coastal residents, present in shallow continental shelf areas in a variety of habitats, such as coral reefs, atolls, offshore reefs, sea grass meadows, kelp forests, tide pools, estuaries, bays, and lagoons and over sandy or muddy bottoms. Many species live cryptically, hiding among rocks and crevices in reefs or blending in with gorgonian corals or sea grasses. Many species have pelagic young, which eventually settle closer to the bottom. Some 20 gasterosteiform species are freshwater (at least one stickleback is exclusively so, along with Indostomus and pipefishes of the genera Microphis, Hippichthys, and Dorichthys) and are present in a variety of habitats, including lakes, coastal rivers, creeks, marshes, and protected coastal inlets. Some 40 species are euryhaline, found in brackish environments. As far as is known, no species occurs in deep-water environments.

Behavior

Gasterosteiforms are diurnal as far as is known. Most species are solitary or live in pairs or small groups or sometimes in larger groups (e.g., aulorhynchids). Many species have pelagic young, but most adults are benthic. A few species, such as macroramphosids and aulorhynchids, form schools, sometimes containing thousands of individuals. Most species remain in association with soft corals, hard corals (Hippocampus barbouri), algae, sea grasses, or other substrates, where they are well camouflaged; in many cases they grasp the reef with their prehensile tails. Many species appear sluggish owing to their somewhat sedentary lifestyle and lack of ability to move very swiftly. Syngnathids swim by a combination of movements of their pectoral and dorsal fins, and some species swim by moving their tails from side to side. Many syngnathids appear to hover in one location, controlling their position by coordinated movements of their pectoral and dorsal fins. Some pipefishes (e.g., Heraldia) are able to swim in an upside-down position in caves and crevices. Centriscids remain in a vertical position, with their mouths directed toward the bottom, sometimes in association with urchins. Species of pipefishes, Solenostomus, Aulostomus, and macroramphosids also maintain a vertical position at times. Many species can change their coloration according to their background, using this ability to sneak up on prey or to hide from predators. Some species, especially pipefishes (e.g., Doryrhamphus spp.), have been documented to clean other fishes (e.g., moray eels and damselfishes), removing their parasites while in reefs.

Feeding ecology and diet

Most syngnathoids feed on a wide variety of small crustaceans (e.g., copepods and mysids), sometimes almost exclusively, as well as on other small invertebrates and the larvae of other fishes. The larger species, such as cornetfishes and trumpetfishes, also feed on larger fishes. Most gasterosteiform species ingest prey whole by quickly opening their mouths to produce a strong inward current, a suction mechanism called pipette feeding. In this manner, large prey items cannot be ingested, owing to the small terminal mouths, lack of teeth, and tubular snouts of many syngnathoid species. Most prey items are ingested from the substrate or when just hovering above it. Many gasterosteiforms rely on their highly developed camouflage to surprise prey items. This is the case in numerous species of pipefishes that slowly cruise over sandy bottoms with sea grasses, feeding on small crustaceans that fail to perceive them as a result of their cryptic appearance. Many species feed on small mysids and other crustaceans that are more free-swimming as well as fish larvae; they remain in strategic positions along the fringes of reefs, where they are exposed to currents that may contain these prey items. Some species, however, eat primarily in the water column (e.g., macroramphosids and aulorhynchids). Gasterosteiforms are preyed upon by larger carnivorous fishes, such as flatheads (Platycephalidae) and snappers (Lutjanidae). Because they move slowly, gasterosteiforms are ingested easily once they are discovered.

Reproductive biology

A great variety of reproductive strategies occur in this order, including some of the most elaborate known for any group of fishes. In a few families (Centriscidae, Macroramphosidae, Pegasidae, and perhaps Aulorhynchidae), the eggs and larvae are pelagic, and spawning probably is accomplished (at least in some of these families) in a style similar to broadcast spawning, in which eggs and sperm are released directly into the water column. In pegasids, spawning involves a courtship ritual whereby a female and a male swim vent to vent, releasing eggs and sperm simultaneously. In other families, reproduction is a far more complex process in which the male carries the eggs, sometimes in a special pouch, within which the eggs may be fertilized. In Solenostomus, the females carry the fertilized eggs in pouches made of their greatly extended pelvic fins, repeatedly opening and closing them to fan the eggs. As a preliminary behavior to spawning, many species employ complex courtship rituals, in which males compete for the female by dancing, inflating their pouches, or performing in some other way. A male stickleback lures the female into his nest and fertilizes the eggs there, sometimes attracting several females in succession. Some species are reproductively active throughout the year, whereas others are seasonal. Many species of syngnathids form monogamous pairs.

Reproduction has been studied in detail for many syngnathids. In seahorses, the females insert their eggs into the pouch of the males, using an abdominal projection known as the ovipositor (an everted egg duct); the eggs are fertilized by the sperm located in the pouches. During this process the male and female face each other. Inside the pouch the eggs are enveloped in tissue that supplies oxygen to the eggs (through diffusion from capillaries) as well as hormones by bathing the small portion of the egg that protrudes from the surrounding tissue. The pouch remains sealed. The male carries the eggs to term (incubation may last from 10 days to six weeks, depending on the species and surrounding temperature), during which time he appears very pregnant. The male actively expels the young (by forcefully moving back and forth) over a period of a few hours through an opening at the top of the pouch. Usually, about 100 young are born in this manner, but some species produce up to 400 young, whereas others produce between 10 and 50 (measuring close to 0.4 in, or 1 cm); pairs may have several broods in one year. The young do not receive any further parental care and are on their own immediately after birth. Young may congregate, and their sexes can be distinguished after a few months, when the pouches of the males become apparent (i.e., when they become sexually mature). Young resemble adults shortly after birth. As many as 1,000 young are produced per year by each couple in this manner, although the actual number varies between species, as reproduction may occur continuously.

Many pipefish males carry the eggs in the anterior tail region (just underneath the dorsal fin) without enclosing them in a pouch, fertilizing the eggs when they are deposited. The eggs are clearly visible in these cases. Courtship has been observed in detail in the species Corythoichthys isigakius from Japan. In this species, after a couple has consented to mate, the male and female repeatedly circle each other with their heads raised, exposing their undersides while remaining in an almost vertical position. When the male is ready to incubate the brood and the female is full of eggs, they practice egg transfer for several days until the process is actually enacted. The male's tail is flattened laterally as an indication that he is able to receive the eggs. The female places her small, greenish eggs on his tail, pushing them into place so that they remain attached. The eggs hatch after a few weeks. Hatching may be helped by the male, who shakes vigorously until all the eggs have separated. The young then are ready to begin their short pelagic life.

Conservation status

A relatively large number of gasterosteiform species are listed by the IUCN. Most of the threats that these species face are related to the pervasive seahorse trade, especially in southeastern and eastern Asia, and to widespread habitat degradation. Gasterosteiforms generally are not directly consumed in quantities that would otherwise place them in danger of overexploitation. Overexploitation of seahorses is a result of their use as ingredients for prepackaged medicines, where demand far exceeds supply, and for the curio and aquarium trade. Many species live in coastal or estuarine habitats, which typically are more affected by development and pollution. Furthermore, the vulnerability of seahorses is enhanced by their low fecundity, parental care, and complex social structures. The IUCN presently includes in their compilation of threatened taxa about 51 species of gasterosteiformes. The majority of species are listed either as Data Deficient or Vulnerable (all species of seahorses and many species of pipefishes). The Cape seahorse (Hippocampus capensis) is listed as Endangered (mostly due to commercial development of its restricted habitat), and the stickleback (Pungitius hellenicus) and the river pipefish (Syngnathus watermeyeri) are listed as Critically Endangered. Conservation efforts, mostly geared toward seahorses, are presently being undertaken by Project Seahorse, a praiseworthy initiative that aims to promote the sustainable exploitation of seahorses and their relatives.

Significance to humans

Numerous species of this order are popular fishes sought out by recreational divers. Many are important aquarium fishes and, fortunately, are now reared in captivity. Their popularity stems from their complex and highly modified morphological features and ornate coloration as well as the particular breeding habits of various species, in which there are elaborate courtship rituals and males fertilize the eggs and carry the young (in most species). Gasterosteiforms typically are not consumed as food fishes, but some syngnathids are commercialized heavily as curios. In particular, seahorses and seamoths are made into souvenirs (even as Christmas ornaments) and used as ingredients in traditional Chinese and related East Asian medicines. Some 47 countries worldwide participate in the seahorse market, and the total global consumption of seahorses in 1995 was at least 20 million specimens, roughly more than 62 tons (56 metric tonnes). The seahorse trade is not sustainable as it is currently implemented, leading to fears that many populations of seahorses have been exploited past the possibility of recovery.

Species accounts

Resources

Allen, G. R. Marine Fishes of Tropical Australia and South-east Asia. Perth: Western Australian Museum, 1997.

Berra, T. M. Freshwater Fish Distribution. San Diego: Academic Press, 2001.

Browne, P. S. "Systematics and Morphology of the Gasterosteiformes." In The Evolutionary Biology of the Threespine Stickleback, edited by Michael A. Bell and Susan A. Foster. New York: Oxford University Press, 1996.

Dawson, C. E. Indo-Pacific Pipefishes (Red Sea to the Americas). Ocean Springs, MS: Gulf Coast Research Laboratory, 1985.

Fritzsche, Ronald A. "Gasterosteiformes: Development and Relationships." In Ontogeny and Systematics of Fishes, edited by H. G. Moser, W. J. Richards, D. M. Cohen, M. P. Fahay, A. W. Kendall, Jr., and S. L. Richardson. Special Publication no. 1. Lawrence, KS: American Society of Ichthyologists and Herpetologists, 1984.

Gomon, M. F., J. C. M. Glover, and R. H. Kuiter, eds. The Fishes of Australia's South Coast. Adelaide: State Print, 1994.

Kuiter, Rudie H. Guide to Sea Fishes of Australia. London: New Holland, 1996. ——. Seahorses, Pipefishes and Their Relatives: A Comprehensive Guide to Syngnathiformes. Chorleywood, U.K.: TMC Publishing, 2000.

Leis, J. M., and D. S. Renis. "Centriscidae, Fistulariidae." In The Larvae of Indo-Pacific Coastal Fishes: An Identification Guide to Marine Fish Larvae, edited by Jeffrey M. Leis and Brooke M. Carson-Ewart. Leiden: Brill, 2000.

Lieske, Ewald, and Robert Myers. Coral Reef Fishes: Caribbean, Indian Ocean and Pacific Ocean: Including the Red Sea. Princeton, NJ: Princeton University Press, 1996.

Lourie, S. A., A. C. J. Vincent, and H. J. Hall. Seahorses: An Identification Guide to the World's Species and Their Conservation. London: Project Seahorse, 1999.

Masuda, H., K. Amaoka, C. Araga, T. Uyeno, and T. Yoshino. Nihon-san Gyorui Daizukan (The Fishes of the Japanese Archipelago). 2 vols. Tokyo: Tokai University Press, 1984.

Nelson, J. S. Fishes of the World. 3rd edition. New York: John Wiley and Sons, 1994.

Orr, J. W., and T. W. Pietsch. "Pipefishes and Their Allies." In Encyclopedia of Fishes, edited by John R. Paxton and William N. Eschmeyer. San Diego: Academic Press, 1994.

Patterson, C. "Osteichthyes: Teleostei." In The Fossil Record 2, edited by M. J. Benton. London: Chapman and Hall, 1993.

Randall, John E., Gerald R. Allen, and Roger C. Steene. Fishes of the Great Barrier Reef and Coral Sea. Honolulu: University of Hawaii Press, 1997.

Reader, S. E., J. M. Leis, and D. S. Rennis. "Pegasidae." In The Larvae of Indo-Pacific Coastal Fishes: An Identification Guide to Marine Fish Larvae, edited by Jeffrey M. Leis, and Brooke M. Carson-Ewart. Leiden: Brill, 2000.

Smith, C. Lavett. National Audubon Society Field Guide to Tropical Marine Fishes of the Caribbean, Gulf of Mexico, Florida, the Bahamas, and Bermuda. New York: Knopf, 1997.

Trnski, T., and J. M. Leis. "Solenostomidae." In The Larvae of Indo-Pacific Coastal Fishes: An Identification Guide to Marine Fish Larvae, edited by Jeffrey M. Leis, and Brooke M. Carson-Ewart. Leiden: Brill, 2000.

Walker, H. J. "Aulostomidae." In The Larvae of Indo-Pacific Coastal Fishes: An Identification Guide to Marine Fish Larvae, edited by Jeffrey M. Leis, and Brooke M. Carson-Ewart. Leiden: Brill, 2000.

Banister, K. E. "The Anatomy and Relationships of Indostomus paradoxus." Bulletin of the British Museum of Natural History 19 (1970): 179–209.

Britz, Ralf. "Aspects of the Reproduction and Development of Indostomus paradoxus (Teleostei: Indostomidae)." Ichthyological Exploration of Freshwaters 11, no. 1 (2000): 305–314.

Britz, Ralf, and G. David Johnson. "'Paradox Lost': Skeletal Ontogeny of Indostomus paradoxus and Its Significance for the Phylogenetic Relationships of Indostomidae (Teleostei, Gasterosteiformes)." American Museum Novitates 3383 (Dec. 2002): 43 pp.

Britz, Ralf, and Maurice Kottelat. "Two New Species of Gasterosteiform Fishes of the Genus Indostomus (Teleostei: Indostomidae)." Ichthyological Exploration of Freshwaters 10, no. 1 (1999): 327–336.

Dawson, C. E. "The Pipefishes (Subfamilies Doryrhamphinae and Syngnathinae)." Memoirs of the Sears Foundation for Marine Research 1, no. 8 (1982): 4–172.

Fritzsche, Ronald A. "A Review of the Cornetfishes, Genus Fistularia, (Fistulariidae), with a Discussion on Intrageneric Relationships and Zoogeography." Bulletin of Marine Science 26, no. 2 (1976): 196–204. ——. "A Revisionary Study of the Eastern Pacific Syngnathidae (Pisces: Syngnathiformes), Including Both Recent and Fossil Forms." Proceedings of the California Academy of Sciences 42, no. 6 (1980): 181–227.

Gosline, W. A. "Notes on the Osteology and Systematic Position of Hypoptychys dybowskii Steindachner and Other Elongate Perciform Fishes." Pacific Science 17 (1963): 90–101.

Herold, D., and E. Clark. "Monogamy, Spawning and Skin-Shedding of the Sea Moth, Eurypegasus draconis (Pisces: Pegasidae)." Environmental Biology of Fishes 37 (1993): 219–236.

Johnson, G. D., and C. Patterson. "Percomorph Phylogeny: A Survey of Acanthomorphs and a New Proposal." Bulletin of Marine Science 52, no. 1 (1993): 554–626.

Kuiter, Rudie. "The Remarkable Sea Moth." Scuba Diver 3 (1985): 16–18.

Lourie, S. A., J. C. Pritchard, S. P. Casey, S.-K. Truong, and A. C. J. Vincent. "The Taxonomy of Vietnam's Exploited Seahorses (Family Syngnathidae)." Biological Journal of the Linnean Society 66 (1999): 231–256.

Masonjones, H. D., and S. M. Lewis. "Courtship Behaviour in the Dwarf Seahorse, Hippocampus zosterae." Copeia 1996, no. 3 (1996): 634–640.

Orr, James W., and Ronald A. Fritzsche. "Revision of the Ghost Pipefishes, Family Solenostomidae (Teleostei: Syngnathoidei)." Copeia 1993, no. 1 (1993): 168–182.

Palsson, W. A., and T. W. Pietsch. "Revision of the Acanthopterygian Fish Family Pegasidae (Order Gasterosteiformes)." Indo-Pacific Fishes 18 (1989): 1–38.

Pietsch, T. W. "Evolutionary Relationships of the Sea Moths (Teleostei: Pegasidae) with a Classification of Gasterosteiform Families." Copeia 1978, no. 3 (1978): 517–529.

Sorbini, L. "The Cretaceous Fishes of Nardò. 1. Order Gasterosteiformes (Pisces)." Bollettino del Museo Civico di Storia Naturale Verona 8 (1981): 1–27.

Vari, R. P. "Seahorses (Subfamily: Hippcampinae)." Fishes of the Western North Atlantic. Memoirs of the Sears Foundation for Marine Research 1, no. 8 (1982): 173–189.

Vincent, A. C. J. "The Improbable Seahorse." National Geographic 186 (Oct. 1994): 126–140. ——. "Trade in Pegasids Fishes (Sea Moths), Primarily for Traditional Chinese Medicine." Oryx 31, no. 3 (1997): 199–208.

Vincent, A. C. J., and L. M. Sadler. "Faithful Pair Bonds in Wild Seahorses, Hippocampus whitei." Animal Behaviour 50(1995): 1557–1569.

"Project Seahorse." (17 Feb. 2003).

[Article by: Marcelo Carvalho, PhD]

An order of actinopterygian fishes which includes the groups Solenichthyes, Thoracostei, Hemibranchii, Lophobranchii, and Syngnathiformes of other classifications, Members of this order, commonly known as sticklebacks, tube-snouts, snipefishes, pipefishes, and seahorses, may be classified in 3 suborders, 7–9 families, 50–55 genera, and 200 or more species. The group dates from the Eocene.

Common characters include a swim bladder without a duct; pelvic fin, if present, with or without a spine and abdominal to subthoracic in position; pelvic girdle not in contact with the cleithrum; and articulation of the quadrate with the lower jaw in advance of the orbit. Fin spines are present or absent. The snout is commonly produced, the mouth opening at the end of a long tube (see illustration).

Trumpetfish (Aulostomus maculatus). (After D. S. Jordan and B. W. Evermann, The Fishes of North and Middle America, U.S. Nat. Mus. Bull. no. 47, 1900)

Most species are inhabitants of warm seas, but some sticklebacks live in fresh waters of northern continents, and a few tropical pipefishes enter or reside permanently in rivers. See also Actinopterygii.

Gasterosteiformes
Three-spined sticklebacks, Gasterosteus aculeatus
Scientific classification
Kingdom: Animalia Phylum: Chordata Superclass: Osteichthyes Class: Actinopterygii Subclass: Neopterygii Infraclass: Teleostei Superorder: Acanthopterygii Order: Gasterosteiformes
Families
Aulorhynchidae Gasterosteidae Hypoptychidae and see text

Gasterosteiformes is an order of ray-finned fishes that includes the sticklebacks and relatives.

In the Gasterosteiformes, the pelvic girdle is never attached to the cleithra directly, and the supramaxillary, orbitosphenoid, and basisphenoid bones are absent. The body is often partly or completely covered with dermal plates.

The name "Gasterosteiformes" means "bone-bellies". It is derived from Ancient Greek gaster (γαστήρ; "stomach", "abdomen") + ostoun (ὀστοῦν; "bone"). The ending for fish orders "-formes" is derived from Latin and indicates "of similar form".

Contents 1 Systematics 2 Footnotes 3 References 4 External links

Systematics

Often Gasterosteiformes includes the sea horses, pipefishes and their relatives as suborder Syngnathoidei, with the sticklebacks and relatives in the suborder Gasterosteoidei^[1]. In many more recent treatments the traditional placement^[2] as different orders, with the former becoming Syngnathiformes, is used^[3]. There is a growing body of evidence that this is correct; in fact, the two groups do not seem to be particularly close relatives among the Acanthopterygii.

As it seems, the loosely delimited Gasterosteiformes are paraphyletic with the Scorpaeniformes. The more typical members of that group (e.g. scorpionfishes) are apparently closer to the "true" Gasterosteiformes, whereas the keel-bodied flying gurnards (Dactylopteridae) seem actually to belong to the Syngnathiformes clade. It seems that the closest living relatives of the narrowly-delimited Gasterosteiformes are the gunnels (Pholidae) and eelpouts (Zoarcidae), traditionally placed in the massively paraphyletic "Perciformes". These two families, as well as the related Trichodontidae, would then appear to be derived offshoots of the scorpaeniform-gasterosteiform radiation which have apomorphically lost the bone "armour" found in their relatives^[4].

Three families certainly belong to the Gasterosteiformes sensu stricto:

• Aulorhynchidae – tubesnouts and tubenoses
• Gasterosteidae – sticklebacks
• Hypoptychidae – sand eels

The armoured stickleback (Indostomidae) and the Pegasidae (dragonfishes and sea moths) are variously placed with the pipefish or the stickleback lineage. While the Pegasidae are almost certainly Syngnathiformes, the placement of the monotypic former family is essentially unresolved, as it has always been. At least provisionally it is better treated as an acathopterygian order of its own.^[4]

Footnotes

1. ^ E.g. ITIS (2004), Nelson (2006)
2. ^ E.g. McAllister (1968)
3. ^ E.g. FishBase (2005a,b)
4. ^ ^{a b} Kawahara (2008)

References

• FishBase (2005a): Order Summary for Gasterosteiformes. Version of 2005-FEB-15. Retrieved 2008-AUG-19.
• FishBase (2005b): Order Summary for Syngnathiformes. Version of 2005-FEB-15. Retrieved 2008-AUG-19.
• Integrated Taxonomic Information System (ITIS) (2004): Gasterosteiformes (TSN 166361). Retrieved 2006-APR-08
• Kawahara, Ryouka; Miya, Masaki; Mabuchi, Kohji; Lavoue, Sébastien; Inoue, Jun G.; Satoh, Takashi P.; Kawaguchi, Akira & Nishida, Mutsumi (2008): Interrelationships of the 11 gasterosteiform families (sticklebacks, pipefishes, and their relatives): A new perspective based on mitogenome sequences from 75 higher teleosts. Mol. Phylogenet. Evol. 46(1): 224–236. doi:10.1016/j.ympev.2007.07.009 (HTML abstract)
• McAllister, D.E. (1968): Evolution of branchiostegals and classification of teleostome fishes. Bulletin of the Nattional Museum of Canada, Ottawa 221: 1–239.
• Nelson, Joseph S. (2006): Fishes of the World. John Wiley & Sons, Inc. ISBN 0471250317

External links

Wikimedia Commons has media related to: Gasterosteiformes

• Gasterosteiformes entry on Animal Diversity Web

v • d • e Extant actinopterygii orders by subclass Kingdom Animalia · Phylum Chordata · Subphylum Vertebrata · Infraphylum Gnathostomata · Superclass Osteichthyes Chondrostei Polypteriformes · Acipenseriformes Neopterygii Lepisosteiformes · Amiiformes · Osteoglossiformes · Hiodontiformes · Elopiformes · Albuliformes · Notacanthiformes · Anguilliformes · Saccopharyngiformes · Clupeiformes · Gonorynchiformes · Cypriniformes · Characiformes · Gymnotiformes · Siluriformes · Salmoniformes · Esociformes · Osmeriformes · Ateleopodiformes · Stomiiformes · Aulopiformes · Myctophiformes · Lampriformes · Polymixiiformes · Percopsiformes · Batrachoidiformes · Lophiiformes · Gadiformes · Ophidiiformes · Mugiliformes · Atheriniformes · Beloniformes · Cetomimiformes · Cyprinodontiformes · Stephanoberyciformes · Beryciformes · Zeiformes · Gasterosteiformes · Syngnathiformes · Synbranchiformes · Tetraodontiformes · Pleuronectiformes · Scorpaeniformes · Perciformes

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)