Fishes: A Guide to Their Diversity. Philip A. Hastings
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are lipid histotrophs (Musick, 2011; Musick and Ellis, 2005), with gestation periods up to one year.
REFERENCES: Compagno, 2005; de Carvalho et al., 2004; Last and Compagno, in Carpenter and Niem, 1999; Lovejoy, 1996; McEachran, in Fischer et al., 1995; McEachran and de Carvalho, in Carpenter, 2003; Musick, 2011; Musick and Ellis, 2005; Rosenberger, 2001.
DASYATID CHARACTERISTICS:
1) tail extremely long, usually much longer than disc length
2) one or more serrated, venomous spines on tail
3) pectoral fins thinning toward margins
4) dorsal and caudal fins absent
5) fleshy papillae present in mouth
ILLUSTRATED SPECIMENS:
A) Pteroplatytrygon violacea, SIO 72–82, 226 mm DW
B) Himantura uarnak, DE 0508, 345 mm DW
INSET: Spine of Pteroplatytrygon violacea (SIO 74–79)
MYLIOBATIFORMES : GYMNURIDAE—Butterfly Rays
DIVERSITY: 1 genus, 14 species
REPRESENTATIVE GENUS: Gymnura
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine, rarely in freshwater; tropical to warm temperate; continental shelf, benthic on soft bottoms
REMARKS: Butterfly rays are characterized by the unmistakable, wide disc and greatly reduced tail. Jacobson and Bennett (2009) recently reviewed their systematics and synonomized Aetoplatea with Gymnura, recognizing only a single genus. These rays are predatory and feed primarily on benthic invertebrates including crustaceans and bivalves, as well as small bottom fishes. Like other myliobatiforms, butterfly rays are lipid histotrophs (Musick, 2011; Musick and Ellis, 2005).
REFERENCES: Compagno, 2005; Compagno and Last, in Carpenter and Niem, 1999; Jacobson and Bennett, 2009; McEachran, in Fischer et al., 1995; McEachran and de Carvalho, in Carpenter, 2003; Musick, 2011; Musick and Ellis, 2005.
GYMNURID CHARACTERISTICS:
1) disc extremely wide, much wider than long
2) tail greatly reduced
3) venomous spines on tail present or absent
4) dorsal fin reduced or absent
5) caudal fin absent
ILLUSTRATED SPECIMEN:
Gymnura marmorata, SIO 13–237, 215 mm DW (dorsal and ventral views)
MYLIOBATIFORMES : MYLIOBATIDAE—Eagle Rays
DIVERSITY: 7 genera, 44 species
REPRESENTATIVE GENERA: Aetobatis, Manta, Mobula, Myliobatis, Rhinoptera
DISTRIBUTION: Atlantic, Indian and Pacific oceans
HABITAT: Marine; tropical to warm temperate; coastal to oceanic, continental shelf to continental slope, pelagic or demersal over soft bottoms and reefs
REMARKS: The eagle rays are divided into three distinctive groups: the cownose rays (Rhinopterinae), the mantas and devil rays (Mobulinae), and the true eagle rays (Myliobatinae), the latter considered by some (e.g., Compagno, 2005; Naylor et al., 2012) to be a separate family. These fishes can be very large bodied, with Manta birostris, the largest ray in the world, reaching a disc width of over 7 m. Oceanic species filter feed on large zooplankton and small fishes, while coastal species often specialize on benthic invertebrates, especially bivalves. All species are lipid histotrophs (Musick, 2011; Musick and Ellis, 2005), with litters of up to six young; the mantas and devil rays have litters of only one.
REFERENCES: Compagno, 2005; Compagno and Last, in Carpenter and Niem, 1999; de Carvalho et al., 2004; McEachran and de Carvalho, in Carpenter, 2003; McEachran et al., 1998; McEachran and Notarbartolo-Di-Sciara, in Fischer et al., 1995; Musick, 2011; Musick and Ellis, 2005; Notarbartolo-Di-Sciara, 1987.
MYLIOBATID CHARACTERISTICS:
1) head raised above surface of disc
2) eyes and spiracles on sides of head
3) tail slender, often whip-like, usually longer than disc
4) serrated, venomous spine on tail (absent in some)
5) small to moderately sized dorsal fin on base of tail
6) caudal fin absent
ILLUSTRATED SPECIMENS:
A) Myliobatis californica, SIO 50–26B, 720 mm DW
B) Mobula tarapacana, SIO 83–113, 405 mm DW
Osteichthyes
Bony Fishes
The clade Osteichthyes may at first seem misnamed as it includes not only what are readily recognized as “bony fishes” but also the entire lineage of tetrapods. However, Osteichthyes refers to the ancestor and all descendants (i.e., a monophyletic group) of a lineage that is the sister group of the cartilaginous fishes. These two great lineages of fishes differ in several fundamental features, most notably in the composition of their skeleton. Osteichthyans have a bony skeleton while chondricthyans have a skeleton formed entirely of cartilage. In addition, the neurocranium of osteichthyans has evident sutures (sutures are absent in chondrichthyans); their fin rays (if present) are segmented and derived from the dermis (termed “lepidotrichia”), while those of chondrichthyans are unsegmented and epidermal in origin (termed “ceratotrichia”). Finally, osteichthyans typically have a gas bladder or its derivative (lungs in tetrapods), a structure lacking in chondrichthyans. The Osteichthyes comprises two large lineages, the Sarcopterygii, or lobe-finned fishes and tetrapods, and the Actinopterygii, or ray-finned fishes (Stiassney et al., 2004).
SARCOPTERYGII—Lobe-finned Fishes
The Sarcopterygii is a major group of vertebrates that includes the coelacanths, lungfishes, and tetrapods and comprises over 25,000 species. These “lobe-finned fishes” are characterized by the presence of enamel on the teeth, a unique skeletal support for the paired fins (or limbs) that includes a central axis of bone, and autostylic jaw suspension in which the upper jaw is fused with the skull. We treat the two most “fish-like” orders of sarcopterygians, the Ceratodontiformes, or lungfishes, and the Coelacanthiformes, or coelacanths. The tetrapods are not considered here.
COELACANTHIFORMES : LATIMERIIDAE—Coelacanths
DIVERSITY: 1 family, 1 genus, 2 species
REPRESENTATIVE GENUS: Latimeria
DISTRIBUTION: 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),