Fishes: A Guide to Their Diversity. Philip A. Hastings
caudal fin heterocercal
4) ten to thirteen flattened branchiostegal rays
5) maxilla included in gape
6) males with prominent ocellus near upper base of caudal fin
ILLUSTRATED SPECIMEN:
Amia calva, SIO 69–491, 138 mm TL
INSET: Head of Amia calva, SIO uncatalogued (ventral view)
TELEOSTEI—Teleosts
The Teleostei has long been recognized as a monophyletic group. Its composition, distinctive features, and relationships have been discussed at length by a variety of authors (e.g., Arratia, 1997, 1999, 2001; de Pinna, 1996; Fujita, 1990; Gosline, 1971; Greenwood et al., 1966; McAllister, 1968; Nelson et al., 2010; Patterson and Johnson, 1995; Wiley and Johnson, 2010; Winterbottom, 1974a). Most extant members have a somewhat to highly mobile premaxilla that is free from the skull, unpaired basibranchial tooth plates, a unique caudal-fin skeleton with elongate uroneurals (modified neural spines), and a number of other features. The extraordinary diversification of the teleosts has been attributed, in part, to a genome duplication event that occurred early in their evolution (Hoegg et al., 2004; Hurley et al., 2007; Meyer and Van de Peer, 2005; Santini et al., 2009). The diversity of the Teleostei is immense, including approximately 96% of all living “fish” species (Nelson, 2006). Several recent studies (e.g., Betancur et al., 2013; Faircloth et al., 2013; Inoue et al., 2001; Ishiguro et al., 2003; Near et al., 2012, 2013) have hypothesized the relationships among the major lineages of teleosts based on molecular data.
Hypothesized phylogenetic relationships of the early lineages of the Teleostei. The traditional hypothesis (left), based on morphology (Nelson, 2006) and supported by Inoue et al. (2003), differs from the recent molecularly based hypothesis (right) of Faircloth et al. (2013) and Chen et al. (2014) in the placement of the Osteoglossomorpha and Elopomorpha.
OSTEOGLOSSOMORPHA—Bonytongues and Mooneyes
The bonytongues and relatives are a broadly distributed early lineage of ray-finned fishes with a substantial fossil record. Their evolution predates the breakup of Gondwana, with extant representatives found in freshwaters of North America, South America, Africa, Asia, and Australia. At least one group, the Notopteridae or Old World knifefishes, also occurs in brackish waters. They are characterized by several internal features (Hilton, 2003; Li and Wilson, 1996; Wiley and Johnson, 2010; Wilson and Murray, 2008) including a unique “shearing bite” between the basihyal and lateral pterygoquadrate teeth (Greenwood et al., 1966). Most species in the group provide parental care to eggs, and in some cases, young (Britz, 2004). Two lineages are recognized within the Osteoglossomorpha: the Osteoglossiformes, with four families (Mormyridae, or elephantfishes, Notopteridae, or Old World knifefishes, Osteoglossidae, or bonytongues, and Gymnarchidae, or African knifefishes), and the Hiodontiformes, with a single family (Hiodontidae, or mooneyes).
OSTEOGLOSSIFORMES—Bonytongues
DIVERSITY: 4 families, 28 genera, 234 species
REPRESENTATIVE GENERA: Arapaima, Chitala, Gymnarchus, Mormyrus, Pantodon
DISTRIBUTION: Circumtropical
HABITAT: Freshwater, rarely brackish, rivers, streams and still waters; tropical; near surface and over soft bottoms
REMARKS: The bonytongues exhibit remarkable variety in form among and within the four included families. The Osteoglossidae can have long dorsal and anal fins and attain a length of more than 2.5 m (Arapaima gigas) or have short dorsal and anal fins with a maximum length of 10 cm (Pantodon buchholzi). The long pectoral fins of P. buchholzi (Freshwater Butterflyfish) allow it to glide over the surface up to 2 m. The Notopteridae have an extremely long anal fin, but a short or absent dorsal fin, and the pelvic fins may be present or absent. The Mormyridae have moderately long dorsal and anal fins, considerable variation in the snout and lower jaw, and in some cases, electric organs. The monotypic Gymnarchidae (Gymnarchus niloticus) has no anal, pelvic, or caudal fins, but also has electric organs. Air breathing has been documented in all four families (Graham, 1997).
REFERENCES: Graham, 1997; Hilton, 2003; Li and Wilson, 1996; Li et al., 1997; Wilson and Murray, 2008; Zhang, 2006.
OSTEOGLOSSIFORM CHARACTERISTICS:
1) glossohyal (tongue bone) usually with teeth
2) pelvic fins abdominal or (rarely) absent
3) premaxilla fixed to skull
4) branched caudal-fin rays usually fewer than 16
5) three to seventeen branchiostegal rays
6) six (or fewer) hypurals
ILLUSTRATED SPECIMENS:
A) Arapaima gigas, SIO 76–343, 809 mm SL (Osteoglossidae—bonytongues)
B) Gnathonemus petersii, SIO 64–228, 118 mm SL (Mormyridae—elephantfishes)
C) Xenomystus nigri, SIO 64–228, 132 mm SL (Notopteridae—featherfin knifefishes)
D) Gymnarchus niloticus, SIO 64–228, 165 mm SL (Gymnarchidae—Aba or African Knifefish)
HIODONTIFORMES : HIODONTIDAE—Mooneyes
DIVERSITY: 1 family, 1 genus, 2 species
REPRESENTATIVE GENUS: Hiodon
DISTRIBUTION: North America
HABITAT: Freshwater; temperate; pelagic in slow-moving rivers and lakes
REMARKS: Mooneyes characteristically have large eyes, their diameter greater than the length of the snout, and silvery or golden bodies. Unlike similar families, in mooneyes the single dorsal fin is located well posterior to the origin of the abdominal pelvic fins. Mooneyes migrate either upstream or to lake shallows in order to spawn. These fishes are visual predators and feed near the surface at night and during low light, primarily on insects, crustaceans, small fishes, frogs, and small mammals. The anal fin is sexually dimorphic, with males having thickened anterior rays.
REFERENCES: Boschung and Mayden, 2004; Britz, 2004; Greenwood, 1970a; Hilton, 2003; Li and Wilson, 1994; Li et al., 1997.
HIODONTIFORM CHARACTERISTICS:
1) single, short-based dorsal fin situated relatively far posteriorly
2) anal-fin base much longer than dorsal-fin base
3) subopercle with a small spine
4) seven to ten branchiostegal rays
5) pelvic fins with seven rays
6) eyes large
ILLUSTRATED SPECIMEN:
Hiodon tergisus, SIO 74–131, 99 mm SL
ELOPOMORPHA
This large group of morphologically diverse fishes is united in sharing a distinctive larval type, the leptocephalus. These ribbon-shaped larvae have small heads and elongate bodies that in some may be as long as 2 m (Böhlke, 1989). At metamorphosis, they shrink in size and take up the general form of their respective lineages. In addition, elopomorphs have numerous branchiostegal rays (15 or more) and teeth on the parasphenoid. The group includes over 850 species classified in five orders, 24 families, and 156 genera. The largest of these orders is the Anguilliformes or true eels, with nearly 800 species. While the monophyly of the Elopomorpha has been questioned