Body elongate; long dorsal and anal fins; pelvic fins usually present (some Asian species of Channa lack the pelvics), with six rays; no fin spines; cycloid or ctenoid scales; lower jaw protruding beyond upper; suprabranchial organ for air breathing present. Maximum length about 1.2 m.
Distribution maps and descriptive information for the species are given in Courtenay and Williams (2004).
Two genera, Channa (26, synonym Ophicephalus) and Parachanna (3), with about 29 species (Courtenay and Williams, 2004; Courtenay et al., 2004). The species of Channa are found in Asia and those of Parachanna in Africa.
Suborder Caproidei. Nelson (1994) included this taxon in the zeiforms despite evidence suggesting that it showed stronger relationships elsewhere. For example, Rosen (1973a) observed that the caproid caudal skeleton is of percoid type in having three epurals and the parhypural and five hypurals articulating with a terminal half-centrum, whereas the other zeiforms have only one or two epurals and the hypurals fused together into large plates. Subsequently, in a 1984 study, D. E. Rosen suggested that caproids, zeiforms, and tetraodontiforms form a clade. However, Tyler et al. (2003) found in their analysis such a relationship to be ambiguous; it was supported in three of their four analyses but not in the one they considered most rational and best justified. Pending further clarification, I retain the Zeiformes as a preperciform taxon and place the caproids in the perciforms, as supported by Johnson and Patterson (1993), although caproids could be considered preperciform from the study of Tyler et al. (2003).
The fSorbinipercidae, containing Sorbinicapros and Sorbiniperca, two Middle Eocene taxa found at Monte Bolca, Italy, was thought by Bannikov and Tyler (1999) to have sister-group relationships with a clade of caproids + zeiforms +
tetraodontiforms or with a larger clade also including some other percomorphs. As noted above, there are reasons for doubting a caproid, zeiform, and tetraodontiform relationship. In addition, Tyler and Bannikov (2002) described Zorzinichthys from the Eocene of Monte Bolca, Italy, representing a new family, the fZorzinichthyidae, and related to the caproid and sorbinipercidlike clades.
Family CAPROIDAE (488)—boarfishes. Marine; Atlantic, Indian, and Pacific.
Body covered with small ctenoid scales; dorsal fin spines 7-9; anal fin spines two or three; pelvic fin with one spine and five soft rays; caudal fin rounded; distinct sagittal crest; pleural ribs present; vertebrae 21-23. Monophyly of this family is uncertain.
Two subfamilies, two genera, and about 11 species.
Subfamily Antigoniinae. Red-colored fishes with extremely deep and slim bodies (rhomboid shape); most body scales with large elevated ridge, curved posteriorly; dorsal fin with eight or nine spines and 26-38 soft rays; three anal spines, separate from the anal soft rays; 10 branched caudal rays (12 principal rays and total of seven or eight procurrent rays); maxillary process of palatine articulates with anterior end of nasal.
One genus, Antigonia, with about 10 species. In addition, fossil species of Antigonia are known from the Eocene and Miocene. See Nelson (1994) and Parin (2003) for references.
Subfamily Caproinae. Caudal fin with 12 branched rays (14 principal rays and total of two procurrent rays); five distinct hypurals (not fused). Also differ from Zeidae, with which they have a very superficial external similarity, in lacking abdominal spinous plates.
One species, Capros aper, occurring in the Mediterranean Sea and eastern North Atlantic.
Order PLEURONECTIFORMES (Heterosomata) (59)—flatfishes. Adults not bilaterally symmetrical, with one eye migrating to the other side of the cranium; dorsal and anal fins with long bases, dorsal fin base overlapping at least the neurocranium except in Psettodes; body highly compressed, somewhat rounded on eyed side and flat on eyeless side; eyes can protrude above body surface, allowing fish to see when buried in the substrate; usually six or seven branchiostegal rays, rarely eight; body cavity small; adults almost always without swim bladder; scales cycloid, ctenoid, or tuberculate. Variation in caudal fin ray number was discussed by Hoshino (2001a).
This is a very distinctive group. Young flatfishes are bilaterally symmetrical and swim upright, but early in their development, between 5-120 mm but usually 10-25 mm in length, one eye migrates across the top of the skull to lie adjacent to the eye on the other side. They then lie and swim on the eyeless side. The metamorphosis involves a complex modification of skull bones, nerves, and muscles, and it leaves one side of the fish eyeless (lower side) and the other side with two eyes (upper side). The upper side is pigmented, whereas the underside is usually light colored. Asymmetry may also be reflected in other characters such as dentition, squamation, and paired fins. Most species have both eyes on the right side and lie on the left side (dextral) or have both eyes on the left side and lie on the right side (sinistral). In some species both dextral (right-eyed) and sinistral (left-eyed) individuals may occur. Among the latter species, the pleuronectid Platichthys stellatus (the Starry Flounder) is especially interesting because of the varying frequency of dextral to sinistral individuals over its range in the North Pacific. Other members of the family are dextral, but almost all Starry Flounder from Japanese waters are sinistral, while off California the two types are about equal in frequency. As yet there appears to be no convincing argument for a direct adaptive advantage for being sinistral or dextral.
Flatfishes are benthic and carnivorous. Sexual maturity is attained from 1 to 15 years of age. Maximum length almost 3 m in the halibuts; much smaller in most groups.
Common names for flatfishes include flounder, halibut, sole, plaice, dab, sanddab, tonguefish, and turbot; some of these names apply to species in different families. Many species are important in commercial fisheries and are valued as a food source.
Many changes have been made from Nelson (1994). The classification of this order is based largely on Chapleau (1993), Cooper and Chapleau (1998a, b), and Hoshino (2001b). In addition, much information now and in the past has been based on the research of E. H. Ahlstrom, K. Amaoka, D. A. Hensley, and their colleagues. Much taxonomic information is in Desoutter, Chapleau, et al. (2001). The order is thought to be monophyletic (Chapleau, 1993; Berendzen and Dimmick, 2002). Its sister group may be some percoid taxon, but its relationships are essentially unknown.
Caudal fin rays have been used in flatfish systematics, and Hoshino (2001a) established homologies between various rays and discussed the phylogenetic significance of the rays and associated structures. As an example of an earlier study involving caudal fin ray morphology, the bothoid lineage as comprising the Pleuronectinae (Pleuronectidae in this edition), most Paralichthyidae, Scophthalmidae, and most Bothidae was recognized in a 1984 paper by E. H. Ahlstrom and D. A. Hensley. Schwarzhans (1999) documents the recent and fossil otoliths of the order; it contains much useful taxonomic information but lacks a cladistic analysis. Chanet (2003) gave references, including that of his major 1997 cladistic review, to studies on the fossils of this order (in a 1995 paper he placed the Eocene Joleaudichthys in the suborder Pleuronectoidei).
There is general agreement that the Psettodidae are the primitive sister group to other pleuronectiforms (the Pleuronectoidei) (Cooper and Chapleau, 1998; Hoshino, 2001b; Berendzen and Dimmick, 2002) with a monophyletic Citharidae being sister to the remaining pleuronectoids (Hoshino, 2001b). Two major clades are thought to accommodate all other flatfishes, with Scophthalmidae, Paralichthyidae, Pleuronectidae, and Bothidae forming one clade and Paralichthodidae, Poecilopsettidae, Rhombosoleidae, Samaridae, Achiridae, Soleidae, and Cynoglossidae forming the other clade; Tephrinectes (placed here in the Paralichthyidae) was thought to be sister to these two clades by Hoshino (2001b). The Paralichthodidae and Achiropsettidae were not in the cladogram of Hoshino (2001b). The former was placed following Cooper and Chapleau (1998). The Achiropsettidae were placed between Samaridae and Achiridae in Hoshino (2001a); because the clade of Samaridae and the other three families seems strong, I place Achiropsettidae before Samaridae but after the families formerly placed in Pleuronectidae. In order to reflect our current understanding of relationships in the suborder Pleuronectoidei based on Hoshino (2001b:401) and modifications in Chanet et al. (2004:10), I recognize three superfamilies: Citharoidea, Pleuronectoidea (this is what was termed the bothoid lineage in some literature), and Soleoidea. It might be reasonable to also recognize the family Tephrinectidae for the paralichthyid Tephrinectes sinensis as suggested by Desoutter, Chapleau, et al. (2001) and done by Chanet (2003), but I prefer to wait for confirming studies. The molecular study of Berendzen and Dimmick (2002), while in agreement with the higher-level classification, found differences at lower levels that invite further study. Additional comments on possible higher relationships within the order are given below under family Citharidae (see also Cooper and Chapleau, 1998a); future changes are expected. Munroe (2005a,b) discussed the taxonomic and geographic diversity of flatfishes.
About 678 extant species are recognized in approximately 134 genera and 14 families. About 10 species are thought to occur only in freshwater (six achirids, one soleid, and three cynoglossids); another few that are primarily freshwater enter estuaries or marine water, and another 20 species that are normally marine occasionally enter freshwater.
Suborder Psettodoidei. Dorsal fin not extending onto head (to or past eye); anterior dorsal and anal rays spinous; palatine with teeth; basisphenoid present; supramaxilla large; 24 or 25 vertebrae.
Family PSETTODIDAE (489)—spiny turbots. Marine; western Africa and Indo-West Pacific.
Pelvic fins nearly symmetrical, with one spine and five soft rays; mouth large; jaw teeth barbed; gill arches with groups of teeth; eyes sinistral or dextral; pre-opercular margin distinct, not covered with skin; 15 branched caudal fin rays. Maximum length about 60 cm.
One genus, Psettodes, with three species: P. belcheri and P. bennetti from tropical western Africa (eastern Atlantic) and P. erumei from eastern Africa and the Red Sea to the western Pacific (e.g., D. A. Hensley in Carpenter and Niem, 2001).
Suborder Pleuronectoidei. Dorsal fin extending onto head at least to eyes; dorsal and anal fins without spines; palatine without teeth; no basisphenoid; supramaxilla vestigial (in some citharids) or absent; vertebrae 26-70, 10 or more are abdominal.
Superfamily Citharoidea. One family.
Family CITHARIDAE (490)—largescale flounders. Marine; Mediterranean, Indo-West Pacific (Japan to Australia).
Pelvic fins with one spine and five soft rays; pelvic fin bases short; branchioste-gal membranes basically separated from each other; posterior nostril on eyeless side enlarged.
The monophyly of this family has until recently been questioned. The cladis-tic analysis shown in Cooper and Chapleau (1998b) suggested that the dextral Lepidoblepharon is sister to all remaining pleuronectiforms, and the sinistral Citharoides is sister to the remaining pleuronectiforms. The sinistral Citharus was not shown on the cladogram, but the dextral Brachypleura was sister to a clade comprising the four families Scophthalmidae, Paralichthyidae, Bothidae, and Pleuronectidae; this clade along with Brachypleura (termed the bothoid lineage) was sister to all other pleuronectiforms, although Achiropsettidae was not placed in the Cooper and Chapleau (1998) cladogram. Hoshino (2001b) established monophyly for the family based on six synapomorphies and showed that sinistral species and those that are dextral do not form mono-phyletic groups.
Five genera, Brachypleura, Citharoides, Citharus (synonym Eucitharus), Lepidoblepharon, and Paracitharus, with about six species (e.g., D. A. Hensley in Carpenter and Niem, 2001; Hoshino, 2000, 2001b).
Superfamily Pleuronectoidea. Four families.
Family SCOPHTHALMIDAE (491)—turbots. Marine (occasionally in brackish water); northern Atlantic and Baltic, Mediterranean, Black seas.
Eyes sinistral; both pelvic fin bases elongate, mouth large and lower jaw prominent. Maximum length about 100 cm.
Monophyly of this family was confirmed by Chanet (2003), who recognized two subfamilies.
The position of this family is changed from Nelson (1994). Common names for species include turbots, windowpanes, and brills. Only one species occurs in the western Atlantic; the others occur in the northeastern Atlantic area.
Four genera, Lepidorhombus (2), Phrynorhombus (2), Scophthalmus (3, synonym Psetta), and Zeugopterus (1), with about eight species (e.g., Chanet, 2003; Munroe, 2003b).
Family PARALICHTHYIDAE (492)—sand flounders. Marine, rarely in freshwater; Atlantic, Indian, and Pacific.
Eyes in most species sinistral; pelvic fin bases short and nearly symmetrical (but position of bases variable between species); pectoral rays branched. Maximum length about 1.5 m.
A species of Citharichthys and of Pseudorhombus ascends rivers from the ocean in Africa. Also called largetooth flounders. This family may not be mono-phyletic. Hoshino (2001b) found Tephrinectes to be sister to the remaining families (including this one) (see comments under the order concerning the recognition of a separate family for this genus); the osteology of Tephrinectes was given by Hoshino and Amaoka (1998).
The position of this family is changed from Nelson (1994). Paralichthyidae and Pleuronectidae are sister taxa (Hoshino, 2001b).
About 16 genera, Ancylopsetta, Cephalopsetta, Citharichthys, Cyclopsetta, Etropus, Gastropsetta, Hippoglossina, Lioglossina, Paralichthys, Pseudorhombus, Syacium, Tarphops, Tephrinectes, Thysanopsetta, Verecundum, and Xystreurys, and about 105 species (e.g., van der Heiden and Mussot-Perez, 1995; Hoshino and Amaoka, 1998, 1999; K. Amaoka and D. A. Hensley in Carpenter and Niem, 2001; Munroe, 2003b; Khidir et al, 2004).
Family PLEURONECTIDAE (493)—righteye flounders. Marine (occasionally in brackish water, rarely in freshwater); Arctic, Atlantic, Indian, and Pacific.
Eyes almost always dextral; no oil globule in yolk of egg except for two species; origin of dorsal fin above the eyes; lateral line well developed on both sides; pelvic fins symmetrical.
Nelson (1994) and Evseenko (2004) treated this family at the subfamily level, Pleuronectinae. The subfamilies Paralichthodinae, Poecilopsettinae, and Rhombosoleinae, given in Nelson (1994), are now recognized as separate families. Paralichthyidae and Pleuronectidae are sister taxa (Hoshino, 2001b).
Twenty-three genera with about 60 species. The following five subfamilies and the four tribes in the last subfamily are based on the cladistic analysis of Cooper and Chapleau (1998). The commercially important and large halibuts belong to this family.
Subfamily Hippoglossinae. Five genera, Atheresthes, Clidoderma, Hippoglossus, Reinhardtius, and Verasper, with eight species (Cooper and Chapleau, 1998;
Nelson et al., 2004). Cooper and Chapleau (1998) placed species of Atheresthes within Reinhardtius, but Nelson et al. (2004) recognized both genera, as did Orr and Matarese (2000); Nelson et al. (2004) also noted the 2001 molecular study of N. Suzuki, M. Nishida, and K. Amaoka finding that A. evermanni is not closely related to Reinhardtius and supporting the retention of Atheresthes as a valid genus.
Subfamily Eopsettinae. One genus, Eopsetta, with two species (Cooper and Chapleau, 1998).
Subfamily Lyopsettinae. One monotypic genus, Lyopsetta (Cooper and Chapleau, 1998).
Subfamily Hippoglossoidinae. Three genera, Acanthopsetta, Cleisthenes, and Hippoglossoides, with seven species (Cooper and Chapleau, 1998).
Subfamily Pleuronectinae. Thirteen genera and 42 species.
tribe psettichthyini. One monotypic genus, Psettichthys. tribe isopsettini. One monotypic genus, Isopsetta.
tribe microstomini. Six genera, Dexistes, Embassichthys, Glyptocephalus (synonyms Errex and Tanakius), Lepidopsetta, Microstomus, and Pleuronichthys, with 20 species (Cooper and Chapleau, 1998; Orr and Matarese, 2000). Cooper and Chapleau (1998) placed Embassichthys bathybius within Microstomus, but Nelson et al. (2004) recognized both genera, as did Orr and Matarese (2000); however, as Nelson et al. (2004) emphasized, the phylogenetic conclusions of Cooper and Chapleau (1998) in recognizing monophyly of this clade are not in question.
tribe pleuronectini. Five genera, Limanda, Parophrys, Platichthys, Pleuronectes, and Pseudopleuronectes, with 20 species (Cooper and Chapleau, 1998).
Family BOTHIDAE (494)—lefteye flounders. Marine; Atlantic, Indian, and Pacific.
Eyes sinistral; pelvic fin base on eyed side longer than on eyeless side, on mid-ventral line and origin anterior to base on eyeless side; pectoral and pelvic fin rays not branched; pelvic fins without a spine; at least two series of intermuscular bones (termed myorhabdoi); branchiostegal membranes connected; egg with a single oil globule in the yolk (true also of scophthalmids and par-alichthyids). Chanet et al. (2004) demonstrated that the similarity in the ossification of ligaments in bothids and samarids is the result of convergence, not common ancestry.
Twenty genera, Arnoglossus, Asterorhombus, Bothus, Chascanopsetta (synonym Pelecanichthys), Crossorhombus, Engyprosopon, Engyophrys, Grammatobothus,
Japonolaeops, Kamoharaia, Laeops, Lophonectes, Monolene, Neolaeops, Parabothus, Perissias, Psettina, Taeniopsetta, Tosarhombus, and Trichopsetta, with about 140 species (e.g., Hensley and Smale, 1997; Amaoka, Arai, et al., 1997; Amaoka, Mihara, et al., 1997; Amaoka and Imamura, 2000; D. A. Hensley and K. Amaoka in Carpenter and Niem, 2001; Munroe, 2003b; Hensley and Randall, 2003).
Superfamily Soleoidea. Eight families.
Family PARALICHTHODIDAE (495)—measles flounders. Marine; southern Africa.
Origin of dorsal fin before the eyes; lateral line with prominent curve over pectoral fin; vertebrae 30-31; eyed side brownish gray with small dark spots.
Considered a subfamily of Pleuronectidae in Nelson (1994) and Evseenko (2004).
One species, Paralichthodes algoensis of southern Africa (P. C. Heemstra in Smith and Heemstra, 1986:864; Evseenko, 2004).
Family POECILOPSETTIDAE (496)—bigeye flounders. Marine: Atlantic, Indian, and Pacific, primarily in deep water.
Origin of dorsal fin above the eyes; lateral line rudimentary on eyeless side; pelvic fins symmetrical; vertebrae 36-43.
Considered a subfamily of Pleuronectidae in Nelson (1994) and Evseenko (2004).
Three genera, Marleyella (2), Nematops (4), and Poecilopsetta (14), with 20 species (e.g., Guibord and Chapleau, 2001; Hoshino et al., 2001; Munroe, 2003b; Evseenko, 2004).
Family RHOMBOSOLEIDAE (497)—rhombosoleids. Marine; primarily a South Pacific group, occurring mostly around Australia and New Zealand, with one species in the southwestern Atlantic.
Pelvic fins asymmetrical (one on the eyed side may be joined to anal fin); lateral line equally developed on both sides; pectoral radials absent; vertebrae 30-46.
Only Oncopterus darwini occurs in the southwestern Atlantic. Two species of Rhombosolea enter freshwater in New Zealand (McDowall, 1990). Some of the species resemble the Soleidae.
Considered a subfamily of Pleuronectidae in Nelson (1994) and Evseenko (2004).
Nine genera, Ammotretis, Azygopus, Colistium, Oncopterus, Pelotretis, Peltorhamphus, Psammodiscus, Rhombosolea, and Taratretis, with 19 species (e.g., Evseenko, 2004).
Family ACHIROPSETTIDAE (498)—southern flounders. Marine; Southern Hemisphere, Antarctic and subantarctic.
Eyes sinistral; body extremely compressed; pectoral fins rudimentary (juveniles) or absent; no fin spines; lateral line straight; branchiostegal membranes separate. Its relationships are uncertain, but it probably belongs in the clade of the following families.
This family was established by S. A. Evseenko in 1984. For placement in classification, see above under the order.
Four genera, Achiropsetta, Mancopsetta, Neoachiropsetta, and Pseudomancopsetta, with five or six species (P. C. Heemstra in Gon and Heemstra, 1990; Miller, 1993; Evseenko, 1997).
Family SAMARIDAE (499)—crested flounders. Marine, tropical and subtropical; Indo-Pacific, primarily in deep water.
Origin of dorsal fin in front of eyes; lateral line well developed or rudimentary; pelvic fins symmetrical; postcleithra absent (as is also true for the Achiridae, Soleidae, and Cynoglossidae).
Three genera, Plagiopsetta,, Samaris, and Samariscus, with about 20 species (Quero et al., 1989).
Family ACHIRIDAE (500)—American soles. Marine and freshwater; Amphi-American (United States to Argentina).
Eyes dextral; margin of preoperculum represented by a superficial groove; dorsal and anal fins free from caudal fin; right pelvic fin joined to anal fin.
The families Achiridae, Soleidae, and Cynoglossidae form a monophyletic group, with the Achiridae being the primitive sister group to the families Soleidae and Cynoglossidae. These three families have the skin of the lower jaw and interopercle continuous ventrally and covering the isthmus and bran-chiostegals.
About seven genera, Achirus, Apionichthys (synonyms Achiropsis, Pnictes, and Soleonasus), Baiostoma, Catathyridium, Gymnachirus, Hypoclinemus, and Trinectes, with about 33 species (Walker and Bollinger, 2001; Munroe, 2003b; Ramos, 2003a, b).
Family SOLEIDAE (501)—soles. Marine, tropical to temperate seas, primarily Europe to Australia and Japan, entering rivers in Africa (one species in freshwater), Asia, and Australia.
Eyes dextral; margin of preoperculum completely concealed; dorsal and anal fins free from caudal fin or united with caudal; pelvics free from anal fin. The Moses Sole or Speckled Sole, Pardachirus marmoratus, of the Indian Ocean, has a chemical defense against predation. Chapleau and Desoutter (1996) noted that Dagetichthys lakdoensis occurs 1,300 km inland from the Atlantic Ocean in Cameroon.
About 35 genera (e.g., Achiroides, Aesopia, Aseraggodes, Bathysolea, Brachirus, Dagetichthys, Heteromycteris, Liachirus, Microchirus, Monochirus, Pardachirus, Pegusa, Solea, Synaptura, and Zebrias) with about 130 species (Chapleau and Desoutter, 1996; Desoutter and Chapleau, 1997; Quero, 1997; Desoutter, Chapleau, et al., 2001; Desoutter, Munroe, et al., 2001; T. A. Munroe in Carpenter and Niem, 2001; Randall, 2002). Euryglossa, formerly recognized in this family, is an invalid name (Desoutter, Munroe, et al., 2001).
Family CYNOGLOSSIDAE (502)—tonguefishes. Marine (some entering freshwater); tropical and subtropical seas.
Eyes sinistral; margin of preoperculum concealed by skin and scales; dorsal and anal fins confluent with the pointed caudal fin; pelvic fin of eyeless side of four rays along midventral line, linked to anal fin in some, and pelvic girdle and fin on eyed side absent in some; pectoral fins absent (a fine membrane in Symphurus); eyes very small and usually close together; mouth asymmetrical; vertebrae 42-78 (usually 9 or 10 abdominal and 33-66 caudal). Maximum length for most species is less than 30 cm, rarely over 40 cm (up to about 48 cm).
Monophyly for this family and its two subfamilies was established by F. Chapleau in 1988.
Three genera with about 127 species (e.g., Munroe, 1998).
Subfamily Symphurinae. Snout not hooked; mouth terminal and almost straight; lateral line absent on both sides; pelvic fin free from anal fin. Most are in deep water, occurring about 300-1,900 m.
One genus, Symphurus, with about 77 species, found on both sides of the Americas and in the eastern Atlantic and Indo-West Pacific (including Hawaii) (e.g., Munroe, 1998, 2003b; Munroe et al., 2000; T. A. Munroe in Carpenter and Niem, 2001; Krabbenhoft and Munroe, 2003).
Subfamily Cynoglossinae. Snout hooked; mouth inferior and contorted; lateral line(s) well developed, at least on eyed side; pelvic fin confluent with anal fin. Most are shallow-water burrowing forms; about five species are known primarily from rivers, and three may occur in only freshwater, as noted by T. R. Roberts in 1989.
Two genera, Cynoglossus (lips without fringes) with about 50 species and Paraplagusia (lips on eyed side with fringes) with three species, found in the Old World from the eastern Atlantic to the western Pacific (e.g., T. A. Munroe in Carpenter and Niem, 2001).
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