Indian and western Pacific oceans, off southern Africa and Indonesia
HABITAT: Marine; tropical to temperate; continental shelf and continental slope, demersal on deep rocky reefs
REMARKS: The living coelacanths represent a group thought to have become extinct 80 million years ago. An extant member of this unique group of fishes was first discovered in 1938 in the western Indian Ocean, while a second species was first captured by scientists in 1998 in Indonesia (Holder et al., 1999; Pouyaurd et al., 1999). Coelacanths have been and continue to be studied extensively. They are the only vertebrates with an intracranial joint, possibly allowing vertical movement of the head in order to increase the size of the gape. They are piscivorous and utilize an electroreceptive sense to enhance their predation on small fishes. Coelacanths are unusual in having a rectal gland and high levels of urea in the blood. They are internal fertilizers (Smith et al., 1975), may be monogamous (Lampert et al., 2013), and the females give birth to 5–26 well-developed young. Their entire genome was recently sequenced (Amemiya et al., 2013). They are endangered as a result of their low reproductive potential and small geographic range; Latimeria chalumnae is listed as critically endangered by the IUCN. The stories of the discovery of both species are full of drama and intrigue (Nelson, 2006; Smith, 1956; Thomson, 1991).
REFERENCES: Amemiya et al., 2013; Bruton, 1995; Cloutier and Ahlberg, 1996; Forey, 1980, 1991, 1998; Holder et al., 1999; Lampert et al., 2013; McCosker and Lagios, 1979; Musick et al. 1991; Pouyaurd et al., 1999; Smith et al., 1975; Smith, 1940, 1956; Thomson, 1991.
COELACANTHIFORM CHARACTERISTICS:
1) second dorsal, anal, pelvic, and pectoral fins lobe-like
2) first dorsal fin with hollow spines
3) caudal fin diphycercal and in three lobes
4) double gular plate between left and right sides of lower jaw
5) large, bony, cosmoid scales
6) intracranial joint
ILLUSTRATED SPECIMEN:
Latimeria chalumnae, SIO 75–347, 950 mm TL
CERATODONTIFORMES—Lungfishes
DIVERSITY: 3 families, 3 genera, 6 species
REPRESENTATIVE GENERA: Lepidosiren, Neoceratodus, Protopterus
DISTRIBUTION: Sub-Saharan Africa (Protopterus), South America (Lepidosiren), and Australia (Neoceratodus)
HABITAT: Freshwater; tropical to subtropical; benthic to demersal over soft bottoms
REMARKS: The three families of living lungfishes, also called the Dipnoi, have one or two lungs used for either facultative or, in some cases, obligate air breathing (Graham, 1997). The African lungfishes (Protopteridae) are characterized by the presence of slender, elongate pectoral and pelvic fins, small scales, and six gill arches, while the montotypic South American Lungfish (Lepidosirenidae) also has slender pectoral and pelvic fins, small scales, and paired lungs, but only five gill arches. In contrast, the monotypic Australian Lungfish (Ceratodontidae) has paddle-like pectoral and pelvic fins, larger scales, and a single, unpaired lung. The African lungfishes are the sister group of the single species of South American Lungfish, and are placed together in the order Lepidosireniformes by some authors. These two lineages are the sister group of the single extant Australian Lungfish (Ceratodontidae). Nelson (2006) includes all three families in the order Ceratodontiformes. African lungfishes are large, with at least one species reaching lengths up to 1.8 m TL. During the dry season, individuals burrow into the mud and aestivate inside mucous cocoons. The pelvic fins of reproductive males of the South American Lungfish become highly vascularized and feather-like, infusing oxygen into the water where young are developing. Lungfishes are omnivorous, feeding on other fishes, frogs, mollusks, and in some cases, plant material, including seeds.
REFERENCES: Bemis et al., 1987; Cloutier and Ahlberg, 1996; Graham, 1997; Nelson, 2006.
CERATODONTIFORM CHARACTERISTICS:
1) pectoral and pelvic fins slender (A and B) or flattened (C)
2) gular plate absent
3) premaxilla and maxilla absent
4) one or two lungs
5) five or six gill arches
ILLUSTRATED SPECIMENS:
A) Protopterus aethiopicus, CAS 46377, 854 mm TL (Protopteridae—African lungfishes)
B) Lepidosiren paradoxa, CAS 14001–7, 549 mm TL (Lepidosirenidae—South American Lungfish)
C) Neoceratodus forsteri, CAS 18189, 748 mm TL (Ceratodontidae—Australian Lungfish)
ACTINOPTERYGII
Ray-finned Fishes
The Actinopterygii includes approximately 33,000 valid species (Eschmeyer and Fong, 2013) classified by Nelson (2006) in 453 families. They are found in all aquatic habitats occupied by vertebrates and range vastly in body size from a tiny species of the gobiiform genus Schindleria that grows no longer than 1 cm (and ca 0.7 mg) and spends its entire short life in the plankton, to the Oarfish (Regalecus) that grows to over 8 m in length, to the Ocean Sunfish (Mola mola) that weighs up to 2,300 kg. Given this enormous diversity, it is not surprising that the group is difficult to characterize morphologically. Extant actinopterygians have enlarged basal elements in the pectoral fins and fused basal elements in the pelvic fins (Lauder and Liem, 1983; Patterson, 1982). Early lineages (i.e., non-teleosts) have a single dorsal fin (variously lost or divided in many) and ganoid scales (variously lost or modified in most species). Several studies (e.g., Faircloth et al., 2013; Hurley et al., 2007; Inoue et al., 2003; Lauder and Liem, 1983) have examined the relationships among the major lineages of the Actinopterygii.
Hypothesized phylogenetic relationships of the early lineages of actinopterygians (after Faircloth et al., 2013).
Actinopterygii I
Lower Ray-finned Fishes
POLYPTERIFORMES : POLYPTERIDAE—Bichirs
DIVERSITY: 1 family, 2 genera, 12 species
REPRESENTATIVE GENERA: Erpetoichthys ( = Calamoichthys), Polypterus
DISTRIBUTION: Africa
HABITAT: Freshwater; tropical; demersal over soft bottoms
REMARKS: Bichirs are thought to be the sister group of all other actinopterygians, exhibiting many unique characters. All bichirs have lungs, an intestinal spiral valve, a skeleton of mostly cartilage, and a uniquely divided dorsal fin. Pelvic fins are present in most species but absent in one (Erpetoichthys calabaricus). Bichirs are carnivorous and feed on other fishes, mollusks, and crustaceans. They are restricted to Africa, are known to reach lengths of up to 90 cm, and are often seen in the aquarium trade.
REFERENCES:
