Fishes: A Guide to Their Diversity. Philip A. Hastings
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genera, 62 species
REPRESENTATIVE GENERA: Aptychotrema, Platyrhinoides, Rhina, Rhinobatos, Zapteryx
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine, rarely entering freshwater; tropical to temperate; continental shelf to continental slope, benthic on soft substrates and rocky reefs
REMARKS: Guitarfishes are elongate batoids with a wedge-shaped head and a wide tail. Their lower caudal-fin lobe is not well defined. In addition to dermal denticles covering the body and fins, they can have enlarged thorn-like spines on the dorsal surface of the snout and the midline of the body and tail. Some authors (e.g., McEachran and Aschliman, 2004; Nelson, 2006) separate them into two or more families, considered here as subfamilies. These include the monotypic Bowmouth Guitarfish (Rhininae), the six species of wedgefishes (Rhynchobatinae), and the six species of thornbacks (Platyrhininae), once considered members of the Myliobatiformes (Nelson, 2006). Guitarfishes feed on a variety of benthic invertebrates, as well as small bony fishes. They are yolk-sac viviparous (Musick, 2011; Musick and Ellis, 2005).
REFERENCES: Compagno, 2005; Compagno and Last, in Carpenter and Niem, 1999; McEachran, in Fischer et al., 1995; McEachran and Aschliman, 2004; McEachran and de Carvalho, in Carpenter, 2003; Musick, 2011; Musick and Ellis, 2005.
RHINOBATID CHARACTERISTICS:
1) body slightly depressed, more shark-like than ray-like, tail essentially an extension of body in most
2) two dorsal fins of equal size, usually widely separated
3) nostrils well anterior and usually not connected to mouth
4) caudal fin well developed
5) jaws protrusible
6) dorsal surface of body and fins covered with dermal denticles
ILLUSTRATED SPECIMENS:
A) Rhinobatos productus, SIO 09–201, 817 mm TL (Rhinobatinae)
B) Platyrhinoidis triseriata, SIO 54–188, 660 mm TL (Platyrhininae)
RAJIFORMES : RAJIDAE—Skates
DIVERSITY: 18 genera, 179 species
REPRESENTATIVE GENERA: Bathyraja, Breviraja, Dipturus, Raja
DISTRIBUTION: Arctic, Atlantic, Indian, and Pacific oceans
HABITAT: Marine (one species occurs in freshwater); tropical to polar; continental shelf to abyssal plain, benthic on soft substrates
REMARKS: The Rajidae is the largest family of chondrichthyan fishes and constitutes approximately 15% of all chondrichthyan diversity (Ebert and Compagno, 2007). Skates exhibit a wide variety of disc shapes and often have sharp dermal thorn-like spines, particularly along the tail. Males can have additional spines near the margins of the pectoral fins. Their phylogenetic relationships have been studied by Ebert and Compagno (2007) and McEachran and Dunn (1998) and their biology was reviewed by Ebert and Sulikowski (2008). Skates are predatory, generally feeding on a wide variety of benthic invertebrates and bony fishes. They are oviparous (Musick, 2011; Musick and Ellis, 2005), laying rectangular, keratinoid egg cases, commonly known as “mermaid’s purses.”
REFERENCES: Compagno, 2005; Ebert and Compagno, 2007; Ebert and Sulikowski, 2008; Last and Compagno, in Carpenter and Niem, 1999; McEachran, in Fischer et al., 1995; McEachran and de Carvalho, in Carpenter, 2003; McEachran and Dunn, 1998; Musick, 2011; Musick and Ellis, 2005.
RAJID CHARACTERISTICS:
1) conspicuous, strong rostral cartilage extending from cranium
2) usually two dorsal fins, positioned posteriorly on tail
3) pelvic fins with two lobes or occasionally with a single lateral lobe
4) thorn-like spines usually present on dorsal surface (at least along midline of tail)
5) caudal fin generally reduced
ILLUSTRATED SPECIMEN:
A) Raja stellulata, SIO 61–513, 654 mm DW (dorsal view)
B) head of Raja stellulata, SIO 61–513 (ventral view)
MYLIOBATIFORMES—Stingrays
The stingrays include eight families, 27 genera, and 220 species. The distinguishing character of this group is the serrated, often venomous spine located on the tail of most species. The sixgill stingrays (Hexatrygonidae) are characterized by six gill openings and an extremely elongate snout; the river stingrays (Potamotrygonidae) are restricted to South American freshwaters. The round stingrays (Urolophidae) are morphologically similar to the American round stingrays (Urotrygonidae, described below), but occur exclusively in the western Pacific. The Deepwater Stingray (Plesiobatidae) and the river stingrays also resemble the American round stingrays. Along with the urotrygonids, three additional families (Myliobatidae, Gymnuridae, and Dasyatidae) are described below. Their phylogenetic relationships were studied by Dunn et al. (2003) and Aschliman et al. (2012).
REFERENCES: Aschliman et al., 2012; de Carvalho et al., 2004; Dunn et al., 2003.
MYLIOBATIFORMES : UROTRYGONIDAE—American Round Stingrays
DIVERSITY: 2 genera, 17 species
REPRESENTATIVE GENERA: Urobatis, Urotrygon
DISTRIBUTION: Western Atlantic and eastern Pacific oceans
HABITAT: Marine, occasionally in freshwater; tropical to warm temperate; continental shelf, benthic on soft bottoms
REMARKS: The well-developed caudal fin, tail of moderate length, and serrated, venomous spines distinguish American round stingrays from nearly all other rays except the Urolophidae. The closely related urolophids (round stingrays) are restricted to the western Pacific Ocean, while the Urotrygonidae are a New World group (McEachran et al., 1996). American round stingrays are predators, feeding primarily on benthic crustaceans and bottom fishes. These rays are lipid histotrophs (Musick, 2011; Musick and Ellis, 2005).
REFERENCES: Compagno, 2005; McEachran, in Fischer et al., 1995; McEachran and Aschliman, 2004; McEachran and de Carvalho, in Carpenter, 2003; McEachran et al., 1996; Musick, 2011; Musick and Ellis, 2005.
UROTRYGONID CHARACTERISTICS:
1) tail relatively thick at base, its length approximately equal to disc length
2) one or more serrated, venomous spines on tail
3) disc more or less circular
4) caudal fin well developed
5) dorsal fins absent
ILLUSTRATED SPECIMEN:
Urobatis concentricus, SIO 65–297, 180 mm DW
MYLIOBATIFORMES : DASYATIDAE—Whiptail Stingrays
DIVERSITY: 8 genera, 88 species
REPRESENTATIVE GENERA: Dasyatis, Himantura, Neotrygon, Taeniura, Urogymnus
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine to freshwater; tropical to temperate; continental shelf to continental slope, normally benthic over soft bottoms but one species oceanic (pelagic)
REMARKS: The long, whip-like tail and serrated, venomous spines distinguish whiptail stingrays from nearly all other rays. Like other chondrichthyan fishes, whiptail stingrays are predatory, feeding primarily on benthic invertebrates. Some marine species are euryhaline,