Body slender and covered with bony scutes; upper jaw not protrusible; oper-cle with five to seven spines; dorsal and anal fins each with six rays, usually five isolated spines preceding the dorsal fin; three pectoral radials; 22-24 pectoral fin rays; pelvic fin with four soft rays, no spine; gill filaments lobate; subopercle minute and interopercle present; parietals absent; six bran-chiostegal rays; no ribs; usually 21 vertebrae; swim bladder physoclistic. Maximum known length about 3.3 cm SL.
The systematic placement of the family in the Gasterosteoidei follows the conclusions of Britz and Johnson (2002) in their detailed anatomical study.
The first species, Indostomus paradoxus, was described in 1929 from Lake Indawgyi in Upper Myanmar.
One genus, Indostomus, and three species (Britz and Kottelat, 1999b).
Suborder Syngnathoidei. Mouth small, at end of tube-shaped snout (except in the "finless" pipefish Bulbonaricus, whose adults lack even a short tubiform snout); pelvic fins, when present, abdominal; upper jaw not protractile; lachrymal usually present, other circumorbital bones usually absent; ribs absent; anterior 3-6 vertebrae elongate; aglomerular kidney in at least some. Members of the first infraorder—the pegasids, syngnathids, and solenostomids—share a similar-shaped gill filament, a unique lobate gill filament termed the lopho-branch pattern (described by Johnson and Patterson, 1993). In these taxa and Indostomus, the gill filaments have fewer lamellae than in other teleosts, such as members of the infraorder Aulostomoida with the normal elongate gill filaments (described as comblike). These three families, which share a complete body armor of bony plates, may form a monophyletic group (see Johnson and Patterson, 1993, and modifications by Britz and Johnson, 2002, for a description of various characters shared in these groups).
Seven families with 62 genera and about 264 species.
Infraorder Syngnatha. Head and trunk encased in bony plates and tail encircled by bony rings; metapterygoid and postcleithrum absent; gill openings each a small hole on dorsolateral surface behind head; lachrymal large; gill filaments tufted or lobate; posttemporal co-ossified with cranium; hyoid apparatus short, with elongate branchiostegal rays; common feeding mechanism (with interopercle widely separated from reduced subopercle); articular processes of mobile vertebral centra absent (Pietsch, 1978c). In addition, all members have a small toothless mouth.
Superfamily Pegasoidea. T. W. Pietsch in a 1978 study concluded that pegasids are most closely related to the solenostomid-syngnathid lineage. He also believed them to be closely related to the lower Eocene Ramphosus of Italy and Denmark (and recognized the fossil family Ramphosidae in the same superfamily).
Family PEGASIDAE (293)—seamoths. Marine, rarely brackish water; tropical to temperate, Indo-West Pacific.
Body oddly shaped (broad and depressed), encased in bony plates; mouth beneath a long flattened rostrum (formed by fused elongate nasals), with an unusual mechanism for protrusion of the jaws; opercle and subopercle minute (widely separated from the interopercle), preopercle greatly enlarged; dorsal and anal fins short, opposite one another, each with five unbranched soft rays (spinous dorsal fin represented only by a horizontal pterygiophore); pectoral fins relatively large, horizontal, with 9-19 unbranched rays; pelvics abdominal, with one spine and two or three soft rays; caudal fin with eight unbranched rays; caudal peduncle quadrangular; five filamentous branchiostegal rays; supracleithrum absent; three circumorbital bones, lachrymal largest; no swim bladder; 19-22 vertebrae (anterior six of the seven abdominal ones elongate). Maximum length 14 cm, perhaps up to 18 cm, attained in Pegasus volitans. Seamoths occur in coastal waters, up to 150 m in depth.
Two genera, Eurypegasus (two species, with eight or nine tail rings and eyes visible in ventral view) and Pegasus (three species, with 11 or more tail rings and eyes not visible in ventral view), with five species (documented in a 1989 study by W. A. Palsson and T. W. Pietsch).
Superfamily Syngnathoidea. Branchiostegal rays 1-3; no lateral line; anterior three vertebrae elongate.
Family SOLENOSTOMIDAE (294)—ghost pipefishes. Marine; tropical Indo-West Pacific (from South Africa and the Red Sea to Fiji).
Body short, compressed and with large stellate bony plates; two separate dorsal fins, the first with five long feeble spines and the second with 17-22 unbranched soft rays on an elevated base; anal fin with 17-22 unbranched rays; pelvic fins relatively large, with one spine and six soft rays, opposite spin-ous dorsal; gill openings moderately large; females with brood pouch formed by the pelvics (the females brood the eggs, not the males as in syngnathids); circumorbital bones absent; vertebrae 32-34. Maximum length up to 16 cm.
One genus, Solenostomus, with four or five species (Orr et al., 2002).
Family SYNGNATHIDAE (295)—pipefishes and seahorses. Marine and brackish water, some species in freshwater; Atlantic, Indian, and Pacific.
Body elongate and encased in a series of bony rings; one dorsal fin, usually with 15-60 soft rays, anal fin very small and usually with 2-6 rays, and pectoral fin usually with 10-23 rays (the dorsal, anal, and pectoral fins may be absent in adults of some species, and all three are absent in adults of Bulbonaricus); no pelvic fins; caudal fin absent in some; tail (caudal peduncle) may be prehensile and employed for holding on to objects when caudal fin is absent; gill openings very small; supracleithrum absent; kidney present only on right side, aglomerular. Some species are very colorful. Maximum length about 65 cm.
Syngnathids are usually confined to shallow water. Most species occur in warm temperate to tropical waters but some pipefishes range into relatively cool water, occurring from southwestern Alaska to Tierra del Fuego in the Americas. At least 18 species are known only from freshwater (streams and lakes, most in the genus Microphis), about 37 are euryhaline (entering brackish water from either the oceans or rivers or both), and the rest are marine. Males care for the eggs, which are attached to them by the female in a special area in the undersurface of the trunk or tail, which may or may not be developed into
a pouch. Two groups, once given taxonomic rank, may be recognized based on whether the brood organ is on the tail (the Urophori or syngnathines), as in most genera and including seahorses and the ghost pipefishes, or on the trunk (the Gastrophori or doryrhamphines). Some genera such as Acentronura are, to a certain extent, morphological intermediates, if not evolutionary links, between pipefishes and seahorses. The intermediate forms and the various genera of seadragons of Australia, which resemble seahorses but reach a larger size and have leaflike appendages, are placed in the pipefish subfamily.
Two subfamilies with 52 genera and about 232 species.
Subfamily Syngnathinae (pipefishes). Marine and brackish water, some in freshwater.
Fifty-one genera—e.g., Acentronura, Anarchopterus, Bhanotia, Bryx, Bulbonaricus, Campichthys, Choeroichthys, Corythoichthys, Cosmocampus, Doryichthys, Doryrhamphus, Enneacampus, Festucalex, Halicampus, Heraldia, Hippichthys, Leptonotus, Lissocampus, Micrognathus, Microphis, Nerophis, Nannocampus, Penetopteryx, Phyllopteryx, Siokunichthys, Solegnathus, Syngnathoides, and Syngnathus—with about 196 species (Fritzsche, 2003; Fritzsche and Vincent, 2003; Kottelat, 2000a).
Subfamily Hippocampinae (seahorses). Marine.
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