Family PRISTIDAE (44)—sawfishes. Marine (rarely occurring in freshwater and ascending rivers), circumtropical, continental shelves; Atlantic, Indian, and Pacific.
Snout produced in a long flat blade with teeth on each side (teeth of equal size and embedded in deep sockets); barbels absent; body somewhat sharklike, although the head is depressed; two distinct dorsal fins and a caudal fin. Maximum length over 6 m.
Two genera, Anoxypristis (1) and Pristis (4-7), with about seven species (de Carvalho and McEachran, 2003; Compagno, 1999, 2005).
Order RAJIFORMES (15)—skates. Caudal fin moderately well developed, reduced, or absent; tail extremely slender; dorsal fins 0-2; most with prickles or thorns (derived from placoid scales) on skin, often with a row along mid-line of back; claspers long, slender, and depressed distally. Oviparous, with eggs encased in horny capsule with four long tips.
Members of this order were placed in the suborder Rajoidei with the same three families in the 1994 edition. McEachran and Aschliman (2004) recognized only two families, the Rhinobatidae and Rajidae, with the two rhinid genera being listed as incertae sedis because of their uncertain relationships (see below under Rhinidae). McEachran and Konstantinou (1996) discuss the taxonomic occurrence and variation of alar and malar thorns in skates.
For a discussion of the terms "skates and rays" see above under Cohort Batoidea.
Four families, 32 genera, and 285 species.
Family RHINIDAE (45)—bowmouth guitarfishes. Marine, continental shelves; IndoWest Pacific.
Body intermediate between sharklike and skatelike (family called "sharkrays" in Compagno, 2005); caudal fin large, bilobed; origin of first dorsal over or in front of pelvics; snout and anterior part of head broadly rounded, with deep indentation separating it from pectoral-fin origin. Maximum total length at least 270 cm.
Rhina and Rhynchobatus (see next family) were placed together in family Rhinidae in Nelson (1994) and Compagno (1999), but the latter recognized the family in its own order, Rhiniformes. It was recognized that there was only weak evidence that the two genera formed a monophyletic group. McEachran and Aschliman (2004) suggested that Rhina and Rhynchobatus are successive sister groups of the remaining rajiforms, and placed the two genera as incer-tae sedis, until they could be examined in better detail, under the order Rajiformes. The present treatment in placing them in separate families follows Compagno (2005), who placed them in separate suborders, somewhat reflecting the view of McEachran and Aschliman (2004).
One monotypic genus, Rhina (Compagno, 2005; Compagno and Last, 1999).
Family RHYNCHOBATIDAE (46)—wedgefishes. Marine, continental shelves; eastern Atlantic (off Africa) and Indo-West Pacific.
Body intermediate between sharklike and skatelike; caudal fin large, bilobed; origin of first dorsal over or in front of pelvics; snout and anterior part of head broadly angular and wedge-shaped, with shallow indentation separating it from pectoral-fin origin. Maximum total length at least 300 cm. See family Rhinidae above for systematic notes.
One genus, Rhynchobatus, with four species (Compagno, 2005; Compagno and Last, 1999).
Family RHINOBATIDAE (47)—guitarfishes. Marine (rarely entering estuaries and freshwater), tropical to temperate, continental shelves and uppermost slopes; Atlantic, Indian, and Pacific.
Body intermediate between sharklike and skatelike; tail stout, not definitely marked off from body; two distinct dorsal fins and a caudal fin, the latter not bilobed; origin of first dorsal behind pelvics; denticles over body form a row on midline of back; tail without spine.
Compagno (1999) recognized this family, along with two other (herein placed in the Myliobatiformes), in the order Rhinobatiformes. McEachran and Aschliman (2004) followed here; note that monophyly of the family and placement relative to Rajidae are uncertain.
Four genera, Aptychotrema (3), Rhinobatos (including Acroteriobatus and Glaucostegus, 35), Trygonorrhina (1), and Zapteryx (3), with 42 species (Compagno, 1999, 2005; Last, 2004; Last et al., 2004).
Family RAJIDAE (48)—skates. Marine, tropical to polar seas, shallow to deep-water; Atlantic, Indian, and Pacific.
Caudal fin moderately well developed, reduced, or absent; tail extremely slender; weak electric organs derived from caudal muscles; dorsal fins 0-2; most with prickles on skin, often with a row along midline of back. Eggs encased in horny capsule with four long tips. Maximum total length about 2.5 m.
The Arhynchobatinae (softnose skates) and the rajines Anacanthobatis and Cruriraja, are recognized as separate families from Rajidae by Compagno (1999, 2005), the Arhynchobatidae (softnose skates) and Anacanthobatidae (legskates), respectively. They are classified here following McEachran and Aschliman (2004), in whose cladogram Anacanthobatis and Cruriraja form a monophyletic group but one which is nested within the Rajinae. McEachran and Dunn (1998) give a detailed analysis of rajid interrelationships.
Subfamily Rajinae (hardnose skates). Fifteen genera, Amblyraja (10), Anacanthobatis (10), Breviraja (6), Cruriraja (8), Dactylobatus (2), Dipturus (31, with many undescibed species), Fenestraja (8), Gurgesiella (3), Leucoraja (12), Malacoraja (3), Neoraja (5), Okamejei (14), Raja (12, and 15 or so additional valid species currently in Raja, but probably requiring new genera, based on McEachran and Dunn, 1998, and Compagno, 1999, 2005), Rajella (15), and Rostroraja (1), with at least 155 species, and many undescribed species (Compagno, 1999, 2005; McEachran and Last, 2004).
Subfamily Arhynchobatinae (softnose skates) . Eleven genera, Arhynchobatis (1), Atlantoraja (3), Bathyraja (43), Irolita (1), Notoraja (at least 6), Pavoraja (at least 2), Psammobatis (8), Pseudoraja (1), Rhinoraja (13), Rioraja (1), and Sympterygia (4), with at least 83 species (Compagno, 1999, 2005; Stevenson et al., 2004; Diaz de Astarloa et al., 2004).
Order MYLIOBATIFORMES (16)—stingrays. Monophyly of this taxon is recognized after McEachran and Aschliman (2004). There has been strong support for monophyly of this order as well based on the earlier works of Nishida (1990), Lovejoy (1996), and McEachran et al. (1996). Platyrhinids and Zanobatus are thought to form successive sister taxa to the myliobatoids (McEachran and Aschliman, 2004). Most members have enlarged brain development. Ten families with 27 genera and 183 species
Family PLATYRHINIDAE (49)—thornbacks. Marine, continental shelves; tropical to cool-temperate, North Pacific (off Asia and North America, in Mexico and California).
Round or heart-shaped pectoral disc; long, stout shark-like tails with two large dorsal fins well anterior on the tail; strong thorns (derived from placoid scales) on dorsal surface of the disc and tail.
The family was redefined by de Carvalho (2004b) and the newly described Late Cretaceous fossil Tethybatis, known from articulated remains from Italy, was placed within it.
Two genera, Platyrhina (2, the fanrays) and Platyrhinoidis (1), with three species (Compagno, 1999, 2005; Compagno and Last, 1999).
Family ZANOBATIDAE (50)—panrays. Marine; tropical, eastern Atlantic (off Africa) and possibly Indian.
Similar in appearance to the Platyrhinidae.
One genus, Zanobatus, with possibly two species (Compagno, 1999, 2005).
Suborder Myliobatoidei. Monophyly of this clade has been further established by de Carvalho et al. (2004). They recognized this group, at the ordinal level (Myliobatiformes) following Compagno (1973), as having numerous synapomorphies such as a serrated caudal spine and lacking thoracic ribs. They present a revised classification but agree with many past conclusions, e.g., Hexatrygonidae is sister to the remaining taxa and the families Gymnuridae and Myliobatidae (the pelagic stingrays) are sister groups; for an example of differences, see below under Dasyatidae. The fossil record, extending primarily from the Paleocene to the Miocene but known from the Early Cretaceous to the Quaternary, is reviewed by de Carvalho et al. (2004); fossils include the freshwater Asterotrygon and Heliobatis (the latter in its own family, Heliobatidae) of the Eocene Green River Formation of Wyoming.
The de Carvalho et al. (2004) paper is a highly informative model study. It very nicely showed the problems that exist in studying elasmobranch phy-logeny, where there is much character conflict, and cladogram results are sensitive to changes in character coding. These are the same problems that exist in many studies of fishes but are not usually made transparent.
Family HEXATRYGONIDAE (51)—sixgill stingrays. Marine, continental and insular slopes; Indo-West Pacific (South Africa to Hawaii).
Six gill openings and six gill arches; snout elongate, thin (depressed), translucent; no supraorbital crests on cranium; spiracles large, well behind eyes, with external flaplike valve (the spiracle of other rays is closed by an internal valve); brain very small, posteriorly placed in large cranial cavity; tail with one or two serrate spines; disc longer than broad; nostrils wide apart, anterior nasal flaps short, not joined to form a broad nasal curtain that reaches the mouth.
McEachran et al. (1996) placed Plesiobatis and Urolophus (they included Trygonoptera as a synonym) in this family as incertae sedis.
Probably only one valid species, Hexatrygon bickelli, described in 1980 (Smith and Heemstra, 1986; Compagno, 1999, 2005).
Family PLESIOBATIDAE (52)—deepwater stingrays. Marine; continental and insular slopes, Indo-West Pacific (South Africa to Hawaii).
Nasal curtain incompletely united, not reaching the mouth (true also for Hexatrygon, which has six gill arches). Maximum length 2.7 m (Smith and Heemstra, 1986).
This family (as Plesiobatididae) was established by Nishida (1990) for the species Plesiobatis daviesi, recognized prior to that in the genus Urotrygon. For alternate family placement see Hexatrygonidae above and Urolophidae below. The family is recognized here as done in the 1994 edition until analysis involving more species better clarifies relationships of the one included species. The common name for family in Compagno (1999, 2005) is giant stingarees. One species, Plesiobatis daviesi (Compagno, 1999, 2005).
Family UROLOPHIDAE (53)—round stingrays. Marine, continental shelves and upper slopes; western Pacific.
Disc less than 1.3 times as broad as long; caudal fin small but well-developed; dorsal fin present in some species (e.g., Trygonoptera, of Australia); tail moderately long with a barbed spine.
The family Urolophidae was formerly recognized as also including Urobatis and Urotrygon (e.g., by Nelson, 1994, although Urobatis was not listed but was regarded as a synonym of Urolophus, by Nelson et al., 2004, and by Compagno, 1999). McEachran et al. (1996) placed Urobatis and Urotrygon of North, Central, and South America and species of Urolophus from the same area, in their own family, the Urotrygonidae, and this is followed here. However, McEachran et al. (1996) regarded Indo-Pacific Urolophus as incertae sedis in the Hexatrygonidae and did not recognize the family Urolophidae. Subsequently, McEachran and Aschliman (2004) recognized the family but, unlike here, as also including the species Plesiobatis daviesi; de Carvalho et al. (2004) included only the following two genera. Family members are also known as stingarees.
Two genera, Trygonoptera (4) and Urolophus (20), with at least 24 species (Compagno, 2005; Seret and Last, 2003).
Family UROTRYGONIDAE (54)—American round stingrays. Marine, tropical to warm temperate, continental shelves; western Atlantic and eastern Pacific.
Disc not more than 1.3 times as broad as long; tail slender and about as long as disc length, without dorsal fin but with one or more long, poisonous spines; caudal fin distinct.
This family, as noted above, was included in the Urolophidae in Nelson (1994).
Two genera, Urobatis (6) and Urotrygon (10), with 16 species (Compagno, 2005).
Family DASYATIDAE (Trygonidae) (55)—whiptail stingrays. Marine (continental and insular shelves and uppermost slopes, one species oceanic), brackish, and freshwater, tropical to warm temperate; Atlantic (including the Mediterranean Sea), Indian, and Pacific.
Disc not more than 1.3 times as broad as long; no caudal fin; tail long (distance from cloaca to tip much longer than breadth of disc), very slender to whiplike, without dorsal fin but tail with one or more long, poisonous spines; caudal fin absent.
A few species of Dasyatis and Himantura and Pastinachus sephen occur in tropical to warm-temperate rivers and lakes. Pteroplatytrygon violacea, often placed in Dasyatis, is oceanic. McEachran and Aschliman (2004) provisionally recognized only three genera in the family, placing Pastinachus and Urogymnus, as well as Dasyatis kuhlii as incertae sedis in the superfamily Dasyatoidea, as were the IndoWest Pacific species of Himantura as incertae sedis (the two amphi-American species of Himantura were placed within the Potamotrygonidae). The study of de Carvalho et al. (2004) placed the dasyatid genera Dasyatis, Himantura, Pastinachus (but not included in their analysis), Pteroplatytrygon, and Taeniura as incertae sedis at a node sister to the clade comprising Gymnuridae and Myliobatidae; the family Dasyatidae was thus not recognized. Compagno (2005) anticipates that species of Taeniura and the two Western Hemisphere species of Himantura may belong in the Potamotrygonidae (see also Potamotrygonidae below).
Six genera, Dasyatis (at least 38, synonyms include Trygon and Urolophoides), Himantura (at least 23, but see above note), Pastinachus (1, synonym Hypolophus), Pteroplatytrygon (1), Taeniura (3), and Urogymnus (2), with at least 68 species (Compagno, 1999, 2005).
Family POTAMOTRYGONIDAE (56)—river stingrays. Freshwater; South America (Atlantic, including Caribbean, drainage).
Long, median, anteriorly directed process from the pelvic girdle; angular cartilages present (except Paratrygon), within hyomandibular-Meckelian ligament;
adaptation to freshwater as evidenced by rectal gland (used for salt secretion) reduced and low urea concentration in body fluids. Most species are quite colorful on the dorsal surface. A detailed study was given by de Carvalho et al. (2004). Maximum length over 100 cm.
Additional species may belong in this family that are here retained in the Dasyatidae pending further research to clarify their relationships. The species in question are the three marine species of Taeniura, occurring in the eastern Atlantic (and Mediterranean) and Indo-West Pacific, and two marine species of the large genus Himantura, H. pacificus (Pacific off Central America and northern South America) and H. schmardae (Atlantic off southern North America and northern South America) which were placed in the Potamotrygonidae by Lovejoy (1996) and followed by McEachran et al. (1996). However, McEachran and Aschliman (2004) retained Taeniura in the Dasyatidae (see also above under Dasyatidae). The taxon Potamotrygonidae was regarded as a subfamily of Dasyatidae in Nelson (1994). Eocene fossils of this family are known, and de Carvalho et al. (2004) and Brito and Deynat (2004) hypothesized that the family arose in the Late Cretaceaous or Early Tertiary.
Three genera, Paratrygon (1), Plesiotrygon (1), Potamotrygon (at least 18), with 20 species (Rosa, 1991; de Carvalho et al., 2003; Compagno, 1999, 2005).
Family GYMNURIDAE (57)—butterfly rays. Marine; tropical to temperate, continental shelves, Atlantic, Indian, and Pacific.
Disc extremely broad (more than 1.5 times as broad as long); dorsal fin and tail spines present (and poisonous) or absent; tail short (distance from cloaca to tip much shorter than breadth of disc); no caudal fin.
Possibly two genera, Aetoplatea (2) and Gymnura (at least 9), with at least 11 species (Compagno, 1999, 2005).
Family MYLIOBATIDAE (58)—eagle rays. Marine; tropical to warm temperate, continental and insular shelves to offshore but not oceanic, Atlantic, Indian, and Pacific.
Distinct but small dorsal fin present; most species with one or more long poisonous spines on tail; no caudal fin; head elevated above disc; eyes and spiracles lateral on head; gill openings about length of eye to much longer; tail much longer than disc; small dorsal fin; pectoral fins reduced or absent opposite the eyes, but with an anterior subdivision that unites below the tip of the snout forming a subrostral lobe. Some are famous for their ability to leap high into the air from the water.
Monophyly of this family is recognized in McEachran et al. (1996), although they gave it as a subfamily of Dasyatidae, and in de Carvalho et al. (2004) and McEachran and Aschliman (2004). Although available evidence suggests that the Myliobatinae as given below are paraphyletic, the three subfamilies given below (accorded family status in Compagno, 1999, 2005) are recognized as given in Nelson (1994) because of their phenetic distinctiveness, until more species are used in a cladistic analysis. Three subfamilies, seven genera, and 37 species.
Subfamily Myliobatinae (eagle rays). Anterior face of cranium nearly straight; subrostral fin not incised.
Four genera, Aetobatus (3), Aetomylaeus (4), Myliobatis (at least 11), and Pteromylaeus (2), with at least 20 species (Compagno, 1999).
Subfamily Rhinopterinae (cownose rays). Marine; tropical to warm temperate, continental shelves, Atlantic, Indian, and Pacific. Anterior face of cranium concave; subrostral fin incised (bilobed).
One genus, Rhinoptera, with at least seven species (Compagno, 1999, 2005).
Subfamily Mobulinae (devil rays). Marine; tropical to warm temperate, inshore and oceanic, Atlantic, Indian, and Pacific.
Members of this family are the only living vertebrates with three pairs of functional limbs. The cephalic pair assist in feeding and are the anterior subdivision of the pectorals.
Some mantas grow to a width of about 6.1 m and a weight of more than 1,360 kg; largest members of the superorder (and, like the Whale Shark and Basking Shark, are zooplanktophagous, straining their food out of the water).
Two genera, Manta (perhaps 1, Manta) and Mobula (9, devil rays), with about 10 species (Compagno, 1999, 2005).
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