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Polynemidae
Rafinesque 1815
Family
Family
Hierarchy
Hierarchy
General
General
Description
threadfins
AuthorWI
Rafinesque [C. S.]
AuthorNI
Rafinesque
Year
1815
Status
Valid
Notes
Body elongate to moderately deep, compressed. Snout obtusely conical, overhanging. Adipose eyelid (firm transparent gelatinous tissue) covering eye; 5 infraorbitals (3 in <b><i>Parapolynemus&nbsp;</i></b> ). Mouth ventral, near-horizontal and large; lip on upper jaw absent or poorly-developed; maxilla extending beyond level of posterior margin of eye; supramaxilla absent; teeth villiform in broad bands on jaws, vomer, palatines and ectopterygoids (vomerine teeth absent in some species); canine, molariform or incisiform teeth absent. Posterior margin of preopercle serrated (without serrations in <b><i>Parapolynemus&nbsp;</i></b>  and <b><i>Pentanemus&nbsp;</i></b> ); 7 branchiostegal rays, one ray present on epihyal. Two well-separated dorsal fins; first dorsal fin with VIII spines (VII spines in 2 <b><i>Polynemus&nbsp;</i></b>  species); second dorsal fin with I spine and 11 to 18 soft rays; anal fin with III spines and 10 to 18 soft rays (II spines in 2 <b><i>Polynemus&nbsp;</i></b>  species and 24 to 30 soft rays in <b><i>Pentanemus&nbsp;</i></b> ; the last dorsal- and anal-fin soft rays usually split to their base but counted as a single ray); pectoral fins divided into an upper part with 12 to 19 rays joined by membrane and a lower part with 3 to 11separate rays (pectoral filaments) (14 to 16 separate rays in 1 <b><i>Polynemus&nbsp;</i></b>  species); pelvic fin with I spine and 5 soft rays; scaly process (axillary scale) present at base of pelvic fin; caudal fin deeply forked; small scales covering most of dorsal, pectoral, anal and caudal fins; trisegmental pterygiophores absent. Scales weakly ctenoid, extending onto head; lateral line simple, extending from upper end of gill opening to posterior margin of caudal-fin membrane (lateral line bifurcating on caudal-fin base in 5 <b><i>Polydactylus&nbsp;</i></b>  species and divided into 3 on caudal-fin base and membrane in 2 <b><i>Eleutheronema&nbsp;</i></b>  species). Vertebrae 10 precaudal and 14 caudal (15 caudal in <b><i>Eleutheronema&nbsp;</i></b>  and <b><i>Polynemus&nbsp;</i></b> ); supraneural bones 0 to 3.

Polynemids are epibenthic fishes found in the tropical and subtropical waters of all oceans. Most species occur in coastal waters and estuaries, although some (e.g. <b><i>Polynemus&nbsp;</i></b>  species and <b><i>Polydactylus macrophthalmus&nbsp;</i></b> ) live in entirely freshwater rivers. Polynemids generally occur on sandy and muddy bottoms in depths less than 150 m, although juveniles are found in seagrass beds and tidepools. Most polynemids generally feed on a variety of fishes and crustaceans. A few small species (e.g. <b><i>Filimanus&nbsp;</i></b>  species) have numerous gill rakers adapted for plankton feeding. Young stages of most polynemids also feed on plankton, some species later becoming piscivorous with growth. Most polynemids exhibit protandry, their sex changing from male to female with fish growth. Reaches 2 m maximum total length, reported for <b><i>Eleutheronema tetradactylum&nbsp;</i></b> . The genera <b><i>Eleutheronema</i></b>, <b><i>Filimanus</i></b>, <b><i>Galeoides</i></b>, <b><i>Leptomelanosoma</i></b>, <b><i>Parapolynemus</i></b>, Indo-Pacific <b><i>Polydactylus</i></b>, and eastern Pacific <b><i>Polydactylus&nbsp;</i></b>  were revised by Motomura et al. (2001 [ref. 25954]), Feltes (1991 [ref. 14760]), Motomura et al. (2001 [ref. 25384]), Motomura & Iwatsuki (2001 [ref. 25242]), Feltes (1993 [ref. 20316]), Motomura (2002 [ref. 26356]), and Motomura et al. (2002 [ref. 26500]), respectively. A revision of the genus <b><i>Polynemus&nbsp;</i></b>  is in progress by the author (e.g. Motomura & Sabaj 2002 [ref. 26155], Motomura et al. 2002 [ref. 26494], Motomura 2003 [ref. 26829], Motomura & van Oijen in press [ref. 27209]).</i></b>