Читать книгу Fishes: A Guide to Their Diversity - Philip A. Hastings - Страница 13
ОглавлениеChondrichthyes
Cartilaginous Fishes
The cartilaginous (or chondrichthyan) fishes are a major group that includes 14 orders and more than 1,200 living species. These fishes are distinguished by a skeleton made entirely of cartilage, and a neurocranium with no sutures. Their teeth are derived from placoid scales and are replaced serially. Their fin rays, termed ceratotrichia, are usually soft and somewhat flexible, are always unsegmented, and are developmentally epidermal. They have a well-developed electroreceptive sense, with numerous pores of the ampullae of Lorenzeni often evident, especially surrounding the mouth. Males have pelvic-fin claspers for use in mating, as all species of chondrichthyan fishes have internal fertilization. Some groups are oviparous, releasing protective keratinized egg cases in which embryos develop. Others retain developing embryos within the body of the female, where they develop solely from nutrition supplied in the egg (yolk-sac viviparity). Still others supplement the nutrition of the embyos in an astounding variety of ways (Musick, 2011), including mucous and lipid secretions from the uterine lining (mucoid and lipid histotrophy), additional eggs released by the mother that are ingested by the embryos (oophagy), and transfer of nutrients from the mother to the embryo via a placenta (placental viviparity; Hamlett et al., 2005). Interestingly, Musick and Ellis (2005) concluded that the primitive condition in chondrichthyans is yolk-sac viviparity, from which all other forms, including oviparity, evolved. Most chondrichthyan species are marine, although some can enter freshwater and a very small number are restricted to freshwater. Cartilaginous fishes usually have a high concentration of urea in their blood relative to bony fishes, in order to maintain osmotic balance with seawater. The biology of sharks and rays has been summarized by several researchers including Carrier et al. (2012), Hamlett (2005), and Klimley (2013).
This monophyletic group is sister to all other living jawed vertebrates, the Osteichthyes, a group that includes the ray-finned fishes and lobe-finned fishes. While comprising only approximately 3% of fish species diversity, this group includes more than 15% of fish orders, implying a high level of fundamental differences in morphology among relatively few species. There are two distinct evolutionary lines of chondrichthyan fishes, the Elasmobranchii (sharks, skates, and rays) and the Holocephali (chimaeras or ratfishes). Among these fishes, the elasmobranchs include 96% of the diversity, while the Holocephali comprises only 4%. The Batoidea (skates and rays) account for 54% of the total chondrichthyan diversity, leaving 42% to the Selachii (shark-like species).
Hypothesized phylogenetic relationships of the major lineages of the Chondrichthyes (after Aschliman et al., 2012).
HOLOCEPHALI—Chimaeras
This chondrichthyan lineage includes one extant order, described below, that is the sister group to the Elasmobranchii (Lund and Grogan, 1997).
CHIMAERIFORMES—Chimaeras
The Chimaeriformes includes three families, six genera, and approximately 50 species of generally deep-sea predators characterized by a single gill opening and an upper jaw fused to the neurocranium (holostylic jaw suspension). The plownose chimaeras (Callorhinchidae) are restricted to the Southern Hemisphere, while the longnose chimaeras (Rhinochimaeridae) and the shortnose chimaeras (Chimaeridae) are more widespread. As their common names imply, the shortnose chimaeres have a blunt snout, the longnose chimaeras have long, pointed snouts, and the plownose chimaeras have long, hook-shaped snouts. One member of the latter family (Callorhinchus milli) has become a model organism for comparative genomics because of its relatively compact genome (Venkatesh et al., 2007; Tan et al., 2012). The shortnose chimaeras, detailed below, are the most speciose lineage in this group. Many of the characteristics described for them apply to the other families as well.
REFERENCES: Grogan and Lund, 2004; Grogan et al., 1999; Lund and Grogan, 1997; Patterson, 1965; Tan et al., 2012; Venkatesh et al., 2007.
CHIMAERIFORMES : CHIMAERIDAE—Ratfishes, Shortnose Chimaeras
DIVERSITY: 2 genera, 38 species
REPRESENTATIVE GENERA: Chimaera, Hydrolagus
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine; tropical to temperate; lower continental shelf to bathyal, demersal usually over soft substrates
REMARKS: Ratfishes, one of two major groups of chondrichthyan fishes, are characterized by a lack of a stomach and the presence of separate anal and urogenital openings. They are deep-sea predators with tooth plates for crushing hard-bodied prey such as benthic mollusks and crustaceans. Ratfishes are oviparous and produce keratinoid egg cases with a long, pointed end and small hooks that anchor them to the substrate.
REFERENCES: Compagno, in Carpenter and Niem, 1998; Didier, in Carpenter, 2003; Didier, 2004; Lund and Grogan, 1997; Patterson, 1965.
CHIMAERID CHARACTERISTICS:
1) body elongate with a whip-like tail, body usually naked
2) one external gill opening, anterior to pectoral fin
3) pectoral fins broad and wing-like
4) two dorsal fins: the first high with an erectile spine, the second low with a long base
5) mouth inferior
6) conspicuous lateral-line canals on snout
7) males with a club-like clasper on top of head
8) pelvic claspers bi-lobed
9) spiracles absent
ILLUSTRATED SPECIMENS:
A) Hydrolagus colliei, SIO 49–121,134 mm TL (tip of tail missing)
B) Hydrolagus colliei, SIO 85–73, 448 mm TL (lateral view of head)
C) Hydrolagus colliei, SIO 85–73, 448 mm TL (frontal view of head)
ELASMOBRANCHII—Sharks and Rays
The Elasmobranchii, with 12 extant orders of sharks and rays, is the sister group to the Holocephali. In contrast to that group, elasmobranchs have five to seven separate gill openings, and the upper jaw is not fused to the neurocranium (amphistylic or hyostylic jaw suspension). Additionally, males of this group lack a cephalic clasper organ. The phylogenetic relationships of elasmobranchs, although intensively studied by numerous researchers using a variety of data sets including morphology, molecular data, and the fossil record, have been controversial (e.g., Maisey, 2012; Naylor et al., 2005; Shirai, 1996). Among the main contentious issues have been questions about the monophyly of the sharks (the Selachii) as a group, and the monophyly of the rays (the Batoidea) as a group. Naylor et al. (2005) and more recently Aschliman et al. (2012) concluded that these groups are reciprocally monophyletic, that is, each is monophyletic and they are sister groups, sharing a unique common ancestor. Naylor et al. (2012) recently summarized information on the valid species of elasmobranchs.
SELACHII—Sharks
The Selachii includes all species of sharks and is characterized by lateral gill openings and pectoral fins separate from the head (Nelson, 2006). This group includes 518 species, classified in eight orders, 35 families, and over 100 genera (Compagno, 1984a, 1984b, 2005; Compagno et al., 2005; Eschmeyer and Fong, 2013; Naylor et al., 2012). Phylogenetic relationships of sharks have been hypothesized by several researchers (e.g., de Carvalho, 1996; Naylor et al., 2005; Shirai, 1996; Vélez-Zuazo and Agnarsson, 2011), including Maisey et al. (2004), who recognized two major lineages, the Squalomorphii and the Galeomorphii.
Hypothesized phylogenetic relationships of the Selachii (sharks) after Maisey et al. (2004) and Musick and Ellis (2005).
HETERODONTIFORMES : HETERODONTIDAE—Bullhead Sharks
DIVERSITY: 1 genus, 9 species
REPRESENTATIVE GENUS: Heterodontus
DISTRIBUTION: Indian and Pacific oceans
HABITAT: Marine; tropical to warm temperate; continental shelf (one species on continental slope), benthic to demersal including shallow rocky or coral reefs
REMARKS: Members of the family of bullhead sharks are characterized by their distinctive dorsal fins and blunt snouts. They are usually nocturnal and generally feed on benthic invertebrates and occasionally on small fishes. Bullhead sharks are oviparous (Musick, 2011; Musick and Ellis, 2005) and produce distinctive screw-shaped, keratinoid egg cases.
REFERENCES: Compagno, 2001, 2005; Compagno, in Carpenter, 2003; Compagno and Niem, in Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; Musick, 2011; Musick and Ellis, 2005.
HETERODONTIFORM CHARACTERISTICS:
1) five external gill slits, two to three behind pectoral-fin origin
2) two dorsal fins, each with a broad-based spine
3) crests above eyes
4) eyes without a nictitating membrane
5) spiracles small
6) nostrils and mouth connected by a groove
ILLUSTRATED SPECIMEN:
Heterodontus francisci, SIO 64–33, 765 mm TL
INSET: Lower jaw of Heterodontus francisci (SIO 60–23, 865 mm TL) showing anterior rows of pointed teeth and posterior rows of pavement-like teeth.
ORECTOLOBIFORMES—Carpet Sharks
The carpet sharks comprise seven families, 14 genera, and 42 species of mostly benthic sharks, noted for sitting perfectly still on the bottom of the ocean. Their nostrils have barbels and are connected to the relatively small mouth by a groove. The wobbegongs (Orectolobidae) are sit-and-wait predators and have a head covered in skin flaps, cryptic coloration, large spiracles, and large fang-like teeth. Their phylogenetic relationships were studied by Goto (2001) and Corrigan and Beheregaray (2009). Two families (Ginglymostomatidae and Rhincodontidae) are described in more detail below. The remaining families (Parascyliidae, Brachaeluridae, Hemiscyliidae, and Stegostomatidae) include relatively few species and occur in the tropical Indo-West Pacific.
REFERENCES: Corrigan and Beheregaray, 2009; Goto, 2001.
ORECTOLOBIFORMES : GINGLYMOSTOMATIDAE—Nurse Sharks
DIVERSITY: 1 family, 3 genera, 3 species
REPRESENTATIVE GENERA: Ginglymostoma, Nebrius, Pseudoginglymostoma
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine; tropical to subtropical; continental shelf, benthic on shallow reefs and adjacent sandy areas
REMARKS: Nurse sharks are characterized by their brownish coloration and by dorsal fins located far back on the body. They are generally nocturnal and can be observed resting in small groups on the reef or sandy surfaces during the day. The small mouth with a large oral cavity is capable of suction-feeding benthic invertebrates and small fishes. Nurse sharks are yolk-sac viviparous (Musick, 2011; Musick and Ellis, 2005).
REFERENCES: Compagno, 2001, 2005; Compagno, in Carpenter, 2003; Compagno, in Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; Musick, 2011; Musick and Ellis, 2005.
GINGLYMOSTOMATID CHARACTERISTICS:
1) five small gill openings (slits), fifth slit nearly overlapping fourth
2) dorsal fins without spines, positioned posteriorly on body
3) mouth short, subterminal, not extending to level of eyes
4) eyes without nictitating membrane
5) spiracles small, located just behind eyes
6) nostrils with barbels
ILLUSTRATED SPECIMEN:
Ginglymostoma cirratum, SIO 64–229, 521 mm TL (dorsal view)
ORECTOLOBIFORMES : RHINCODONTIDAE—Whale Sharks
DIVERSITY: 1 genus, 1 species
REPRESENTATIVE GENUS: Rhincodon
DISTRIBUTION: Atlantic (absent from Mediterranean), Indian, and Pacific oceans
HABITAT: Marine; tropical to warm temperate; usually epipelagic but occasionally mesopelagic or neritic
REMARKS: While the Whale Shark is distinguished by its huge size (the largest fish on Earth), it feeds on planktonic organisms and fish eggs, using its long, thin gill rakers for filter feeding. Its brain anatomy was studied by Yopak and Frank (2009). The Whale Shark is yolk-sac viviparous (Musick, 2011; Musick and Ellis, 2005), but, curiously, produces keratized egg capsules that hatch within the female. These enormous fishes are highly fecund compared to other members of the Chondrichthyes; one female caught by fishermen held 300 pups. In many areas, the Whale Shark has been overfished; it is considered “vulnerable” by the IUCN (2013) and it has been given protected status by many nations.
REFERENCES: Compagno, 2001, 2005; Compagno, in Carpenter, 2003; Compagno, Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; Musick, 2011; Musick and Ellis, 2005; Yopak and Frank, 2009.
RHINCODONTID CHARACTERISTICS:
1) body covered in yellow or white spots
2) head broad and flattened
3) snout short, mouth nearly terminal, anterior to small eyes
4) mouth and gill openings especially large
5) spiracles small
6) longitudinal ridges on body of adults
ILLUSTRATED SPECIMEN:
Rhincodon typus, SIO 85–20, 601 mm TL (dorsal and lateral views)
LAMNIFORMES—Mackerel Sharks
The mackerel sharks have two dorsal fins without spines, an anal fin, five gill slits (the last two often above the pectoral fin), eyes without a nictitating membrane, a large mouth that extends well behind the eyes, and small spiracles usually present behind the eyes. This distinctive lineage includes only 15 species, classified in ten genera and seven families, indicating a high level of morphological diversity among a small number of closely related species. For example, the Basking Shark (Cetorhinidae) and the Megamouth Shark (Megachasmidae) are large-bodied filter feeders, while the White Shark (Lamnidae) is one of the ocean’stop predators. The Goblin Shark (Mitsukurinidae), characterized by an elongate snout, and the Crocodile Shark (Pseudocarchariidae), which has extremely large eyes, are generally found in deeper water. The sand tiger sharks (Odontaspididae) are some of the few sharks that have exposed teeth when the mouth is closed, giving them a ferocious appearance. In contrast with the otherwise similar Carcharhiniformes, members of the Lamniformes do not have a nictitating membrane protecting the eyes. The phylogenetic relationships of lamniforms have been studied by a number of workers (e.g., Compagno, 1990; Naylor et al., 1997; Shimada, 2005; Shimada et al., 2009), while variation in their caudal-fin anatomy was documented by Kim et al. (2013). Lamniforms have an unusual reproductive mode in which developing embryos eat eggs (oophagy) and sometimes other embryos (Musick, 2011; Musick and Ellis, 2005) produced by the mother. The thresher sharks (Alopiidae) and the mackerel sharks sensu stricto (Lamnidae) are further described below.
REFERENCES: Compagno, 1990, 2001; Kim et al., 2013; Musick, 2011; Musick and Ellis, 2005; Shimada, 2005; Shimada et al., 2009.
LAMNIFORMES : ALOPIIDAE—Thresher Sharks
DIVERSITY: 1 genus, 3 species
REPRESENTATIVE GENUS: Alopias
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine; tropical to temperate; neritic to epipelagic
REMARKS: Thresher sharks use their long, whip-like caudal fin to disable small pelagic fishes and squids during feeding (Kim et al., 2013). Like mackerel sharks, at least one species (Alopias vulpinus) has the ability to maintain a higher body temperature than ambient seawater (Sepulveda et al., 2005). Thresher sharks are oophagous (Musick, 2011; Musick and Ellis, 2005), giving birth to small numbers of relatively large pups. These sharks support limited commercial fisheries.
REFERENCES: Compagno, 2001, 2005; Compagno, in Carpenter, 2003; Compagno, in Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; Kim et al., 2013; Musick, 2011; Musick and Ellis, 2005; Sepulveda et al., 2005.
ALOPIID CHARACTERISTICS:
1) upper lobe of caudal fin long and whip-like, equaling length of body
2) mouth subterminal, relatively small
3) second dorsal fin and anal fin small, pectoral fins large
4) caudal peduncle with a precaudal pit
5) gill slits small, fourth and fifth above pectoral-fin base
ILLUSTRATED SPECIMEN:
Alopias vulpinus, SIO 64–804, 1,448 mm TL
LAMNIFORMES : LAMNIDAE—Mackerel Sharks
DIVERSITY: 3 genera, 5 species
REPRESENTATIVE GENERA: Carcharodon, Isurus, Lamna
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine; tropical to temperate; neritic to epipelagic
REMARKS: Mackerel sharks are strong-swimming, large-bodied predators that prey mainly on fishes, birds, marine mammals, and cephalopods. These sharks are one of a few groups of fishes known to have body temperatures higher than their surroundings, allowing them to remain active in very cold water (Bernal et al., 2001). Mackerel sharks are oophagous (Musick, 2011; Musick and Ellis, 2005) and give birth to large, well-developed pups. For example, newly born White Shark pups can be up to 1.3 m long (Domeier, 2012). The White Shark is responsible for a number of attacks on humans each year (Domeier, 2012). Some laminid species support commericial fisheries.
REFERENCES: Bernal et al., 2001; Compagno, 2001; Compagno, in Carpenter, 2003; Compagno, in Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; Domeier, 2012; Musick, 2011; Musick and Ellis, 2005.
LAMNID CHARACTERISTICS:
1) second dorsal fin much smaller than first dorsal fin
2) caudal fin nearly symmetrical (approaching lunate)
3) caudal peduncle strongly depressed with a lateral keel and precaudal pit
4) mouth large, extending past level of eyes
5) gill openings large
6) teeth large
7) gill rakers absent
ILLUSTRATED SPECIMEN:
A) Isurus oxyrinchus, SIO 55–85, 875 mm TL (dorsal view)
B) head of Isurus oxyrinchus, SIO 55–85 (lateral view)
LAMNIFORM DIVERSITY:
A) PSEUDOCARCHARIIDAE—crocodile sharks: Pseudocarcharias kamoharai, SIO 97–221, 952 mm TL
B) MEGACHASMIDAE—megamouth sharks: Megachasma pelagios, SIO 07–53, 2,150 mm TL
C) MITSUKURINIDAE—goblin sharks: Mitsukurina owstoni, SIO 07–46, 1,150 mm TL
CARCHARHINIFORMES—Ground Sharks
The ground sharks comprise the most speciose order of sharks, with eight families, approximately 50 genera, and at least 287 species. More than half of the species are small-bodied cat sharks (Scyliorhinidae and Proscylliidae), named for their horizontally elongate eyes. The false cat sharks (Pseudotriakidae) are characterized by a deep groove anterior to their elongate eyes, while the monotypic Barbled Houndshark (Leptochariidae) has notably long labial furrows and nostrils with barbels. The weasel sharks (Hemigaleidae) are characterized by their wavy, upper caudal-fin lobe. The Carcharhiniformes as a group are difficult to characterize, but all included species have two dorsal fins without spines, an anal fin, five gill slits (last one to three positioned over the pectoral fin), and a large mouth extending behind the eyes (Compagno, 1988). In contrast with the similar Lamniformes, the eyes of most carcharhiniforms are protected by a nictitating membrane and most species lack spiracles. Three families (Carcharhinidae, Sphyrnidae, and Triakidae) are described in more detail below.
REFERENCES: Compagno, 1988, 2001.
CARCHARHINIFORMES : TRIAKIDAE—Hound Sharks
DIVERSITY: 9 genera, 47 species
REPRESENTATIVE GENERA: Galeorhinus, Mustelus, Triakis
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine, occasionally in river mouths; tropical to temperate; coastal to continental slope, demersal over rocky reefs and soft substrates
REMARKS: Hound sharks are moderately sized (to 2.4 m) and feed on benthic and midwater invertebrates and fishes. Some species specialize on crustaceans and others on cephalopods. Hound sharks are either yolk-sac viviparous or placental viviparous (Musick, 2011; Musick and Ellis, 2005) and produce litters with as many as 52 pups. Their phylogenetic relationships were studied by Lopez et al. (2006).
REFERENCES: Compagno, 1988, 2001, 2005; Compagno, in Carpenter, 2003; Compagno and Niem, in Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; Lopez et al., 2006; Musick, 2011; Musick and Ellis, 2005.
TRIAKID CHARACTERISTICS:
1) mouth small, subterminal, snout long
2) dorsal-fin base well anterior to pelvic fins
3) eyes oval with nictitating membranes
4) fourth and fifth gill slits over pectoral-fin base
5) nostrils with flaps, often broad, not barbel-like
ILLUSTRATED SPECIMEN:
Triakis semifasciata, SIO 62–213, 1,035 mm TL (dorsal and lateral views)
CARCHARHINIFORMES : CARCHARHINIDAE—Requiem Sharks
DIVERSITY: 12 genera, 60 species
REPRESENTATIVE GENERA: Carcharhinus, Galeocerdo, Prionace, Rhizoprionodon
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine and occasionally freshwater; tropical to temperate; neritic to epipelagic to demersal over reefs and adjacent soft substrates
REMARKS: Requiem sharks are medium to large (up to 7.4 m) predators and are well known for their occasional migrations into freshwater (sometimes exceeding 1,000 km). Species in this family are among those most commonly encountered by divers and sport fishers, and several have been known to attack swimmers. The Bull Shark, Tiger Shark, and Oceanic Whitetip Shark are responsible for most human fatalities. Requiem sharks are generalist predators, taking a wide variety of prey. While some species are yolk-sac viviparous, most species are placental (Musick, 2011; Musick and Ellis, 2005). Some species are highly fecund: the Blue Shark (Prionace glauca) is known to have litters of up to 100 pups.
REFERENCES: Compagno, 1988, 2001, 2005; Compagno et al., 2005; Compagno et al., in Fischer et al., 1995; Compagno and Niem, in Carpenter and Niem, 1998; Garrick, 1982; Musick, 2011; Musick and Ellis, 2005; Naylor, 1992.
CARCHARHINID CHARACTERISTICS:
1) mouth large, subterminal
2) caudal peduncle with a precaudal pit
3) eyes with nictitating membrane
4) dorsal fin with lateral undulations along posterior margin
5) spiracles usually absent
6) nasal grooves and barbels absent
ILLUSTRATED SPECIMEN:
Galeocerdo cuvier, SIO 66–44, 1,310 mm TL
CARCHARHINIFORMES : SPHYRNIDAE—Hammerhead Sharks
DIVERSITY: 2 genera, 9 species
REPRESENTATIVE GENERA: Eusphyra, Sphyrna
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine; tropical to warm temperate; continental shelf and seamounts, neritic or demersal over reefs and soft bottoms
REMARKS: Their characteristic hammer-shaped heads distinguish these sharks from all other fishes. This unusual feature increases capabilities of both vision and the electromagnetic sense and also improves maneuverability. The phylogenetic relationships of hammerheads were studied by Naylor (1992) and Lim et al. (2010). Hammerheads are top predators that feed on bony fishes, sharks and rays, and squids and other invertebrates. Unlike most sharks, hammerheads often form large schools near seamounts during the day, likely dispersing to hunt individually at night. They are viviparous, with yolk-sac placentas (Musick, 2011; Musick and Ellis, 2005). Hammerheads are particularly vulnerable to overfishing and are often captured as bycatch in longline and net fisheries.
REFERENCES: Compagno, 1988, 2005; Compagno, in Carpenter, 2003; Compagno, in Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; Gilbert, 1967; Lim et al., 2010; Musick, 2011; Musick and Ellis, 2005; Naylor, 1992.
SPHYRNID CHARACTERISTICS:
1) head flattened and broad, hammer-shaped
2) eyes and nostrils near ends of hammer-like extensions
3) mouth relatively small, subterminal
4) usually one or two gill slits above pectoral-fin base
5) spiracles absent
ILLUSTRATED SPECIMEN:
A) Sphyrna zygaena, SIO 64–528, 1,035 mm TL (dorsal view)
B) head of Sphyrna zygaena, SIO 64–528 (lateral view).
HEXANCHIFORMES—Six-gill Sharks
The hexanchiforms were once thought to be the most primitive extant shark group, but recent research (e.g., Naylor et al., 2005; Vélez-Zuazo and Agnarsson, 2011) has shown them to be allied with the squaliform and related sharks. This group is characterized by six or seven gill slits, a single, spineless dorsal fin originating posterior to the origin of the pelvic fins, a large mouth, and small spiracles, which are located above and well posterior of the eyes. The Hexanchiformes comprises two families, four genera, and six species. The two species of frill sharks (Chlamydoselachidae) have a terminal mouth and the first pair of gill slits meeting across the throat. The cow sharks (Hexanchidae) are described in more detail below.
REFERENCES: de Carvalho, 1996; Naylor et al., 2005; Shirai, 1996; Vélez-Zuazo and Agnarsson, 2011.
HEXANCHIFORMES : HEXANCHIDAE—Cow Sharks
DIVERSITY: 3 genera, 4 species
REPRESENTATIVE GENERA: Heptranchias, Hexanchus, Notorynchus
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine; tropical to temperate; continental shelf to slope, occasionally deeper, usually demersal over soft or rocky bottoms
REMARKS: The cow sharks are known for their numerous gill slits (six or seven), and each of the four species is found over a broad geographic range. These sharks are yolk-sac viviparous (Musick, 2011; Musick and Ellis, 2005) with two species known to have litters of over 100 pups. Hexanchids feed on a variety of prey, from squids, crustaceans, and small bony fishes to elasmobranchs, seals, and small cetaceans. Some species are utilized both for their meat and liver oil, and they often are displayed in public aquariums.
REFERENCES: Compagno, in Carpenter, 2003; Compagno and Niem, in Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; Musick, 2011; Musick and Ellis, 2005; Shirai, 1992a, 1996.
HEXANCHID CHARACTERISTICS:
1) six to seven long gill slits, all anterior to the pectoral fins
2) teeth of lower jaw compressed, wide, and serrated
3) anal fin smaller than dorsal fin, originating posterior to origin of dorsal fin
4) mouth inferior
5) distinct, subterminal notch in caudal fin
6) pectoral fins larger than pelvic fins
ILLUSTRATED SPECIMEN:
Hexanchus griseus, SIO 74–176, 838 mm TL (dorsal and lateral views)
ECHINORHINIFORMES : ECHINORHINIDAE—Bramble Sharks
DIVERSITY: 1 family, 1 genus, 2 species
REPRESENTATIVE GENERA: Echinorhinus
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine; tropical to temperate; continental shelf to slope, benthic or demersal over soft bottoms
REMARKS: The bramble sharks, so-called because of their large denticles, were formerly placed in the Squaliformes, but recent authors have them independent of that group, and possibly closely related to the sawsharks (Vélez-Zuazo and Agnarsson, 2011). Both species have a broad geographic range, but they are rarely seen. These sharks are yolk-sac viviparous (Musick, 2011; Musick and Ellis, 2005), with one female E. cookei recorded with a litter of 114 pups; E. brucus is known to have up to 26 pups. Bramble sharks feed on bony fishes, small chondrichthyans, crustaceans, octopods, and squids, and E. brucus occasionally is utilized in fisheries.
REFERENCES: Compagno, in Carpenter, 2003; Compagno and Niem, in Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; de Carvalho, 1996; Musick, 2011; Musick and Ellis, 2005; Vélez-Zuazo and Agnarsson, 2011.
ECHINORHINIFORM CHARACTERISTICS:
1) many skin denticles large and thorn-like, in various places on body
2) two relatively small dorsal fins, positioned posteriorly, spines absent
3) all five gill slits anterior to pectoral fin
4) anal fin absent
5) head broad and depressed
6) spiracles small, well posterior to eyes
ILLUSTRATED SPECIMEN:
Echinorhinus cookei, SIO 60–378, 1,700 mm TL.
INSET: Close-up of skin showing thorn-like denticles
SQUALIFORMES—Dogfish Sharks
The dogfish sharks include six families, at least 24 genera, and 130 species. Some authors (e.g., Compagno, 2005; Ebert, 2003; Eschmeyer and Fong, 2013) also include the two species of bramble sharks (Echinorhinidae) among the squaliforms, but others (e.g., de Carvalho, 1996; Vélez-Zuazo and Agnarsson, 2011) place the bramble sharks in their own order. Both groups are characterized by the lack of an anal fin, presence of spiracles, and the location of all five gill slits anterior to the origin of the pectoral fin. Among the squaliforms, the gulper sharks (Centrophoridae) and the lantern sharks (Etmopteridae) are characterized by two dorsal fins, each with a single grooved spine, and by very large eyes. The lantern sharks usually have light organs along the ventral aspect of the body. Some species of sleeper sharks (Somniosidae) have dorsal-fin spines while others do not, and all species are characterized by abdominal ridges between the pectoral and pelvic fins. The roughsharks (Oxynotidae) are easily distinguished by their triangular body (in cross section) and their large, sail-like dorsal fins. The dogfish sharks sensu stricto (Squalidae) and the kitefin sharks (Dalatiidae) are described below.
REFERENCES: de Carvalho, 1996; Vélez-Zuazo and Agnarsson, 2011.
SQUALIFORMES : SQUALIDAE—Dogfish Sharks
DIVERSITY: 2 genera, 30 species
REPRESENTATIVE GENERA: Cirrhigaleus, Squalus
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine; tropical to temperate; continental shelf to continental slope and seamounts, coastal, demersal over soft bottoms
REMARKS: Dogfish sharks have strong dorsal-fin spines, some of which are venomous. Some species commonly form large, social schools that are known to attack and dismember large prey. All dogfishes are yolk-sac viviparous (Musick, 2011; Musick and Ellis, 2005), and one species, Squalus acanthias, has extremely large eggs and a gestation period of up to two years. This low reproductive potential, together with their propensity for forming large schools, makes dogfishes quite vulnerable to overfishing, particularly given their importance as a commercially exploited group of sharks (IUCN, 2013).
REFERENCES: Compagno, 2001, 2005; Compagno, in Carpenter, 2003; Compagno and Niem, in Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; Musick, 2011; Musick and Ellis, 2005; Shirai, 1992a.
SQUALID CHARACTERISTICS:
1) two dorsal fins, each with a strong, smooth spine
2) caudal peduncle with lateral keels and a precaudal pit
3) all five gill slits usually anterior to pectoral-fin base
4) spiracles large
5) anal fin absent
6) nictitating membrane absent
ILLUSTRATED SPECIMEN:
Squalus suckleyi, SIO 08–138, 740 mm TL
SQUALIFORMES : DALATIIDAE—Kitefin Sharks
DIVERSITY: 6 genera, 10 species
REPRESENTATIVE GENERA: Dalatius, Isistius, Squaliolus
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine; tropical to temperate; continental shelf to continental slope, coastal to oceanic, epipelagic to bathypelagic
REMARKS: Kitefin sharks are some of the smallest of all sharks; species in the genus Squaliolus reach maximum sizes of only 22–28 cm TL. These cigar-shaped sharks generally eat small fishes, squids, and crustaceans, but the highly specialized cookiecutter sharks (Isistius spp.) attack much larger prey, removing bite-sized pieces from live marine mammals and large-bodied fishes. Kitefin sharks are yolk-sac viviparous (Musick, 2011; Musick and Ellis, 2005) and probably use their ventral light organs to achieve countershading, decreasing their visual profile from below.
REFERENCES: Compagno, 2005; Compagno, in Carpenter, 2003; Compagno and Niem, in Carpenter and Niem, 1998; Compagno et al., 2005; Musick, 2011; Musick and Ellis, 2005; Shirai, 1992a.
DALATIID CHARACTERISTICS:
1) two dorsal fins, without spines, or with a spine in the first dorsal fin only
2) luminous organs usually present along ventral surface
3) caudal fin with a pronounced notch
4) spiracles large
5) anal fin absent
6) nictitating membrane absent
ILLUSTRATED SPECIMENS:
A) Squaliolus aliae, DE 0508, 117 mm TL
B) Isistius brasiliensis, SIO 69–345, 470 mm TL
INSET: Flank of Oarfish (Regalecus russelii, SIO 13–259) with multiple wounds caused by Isistius brasiliensis.
SQUATINIFORMES : SQUATINIDAE—Angel Sharks
DIVERSITY: 1 family, 1 genus, 22 species
REPRESENTATIVE GENUS: Squatina
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine; tropical to temperate; continental shelf to continental slope, benthic on soft substrates
REMARKS: These distinctive sharks resemble rays in many respects, but unlike rays, their pectoral fins are not attached to their heads. In keeping with their benthic lifestyle, their well-developed spiracles are used for respiration, and there are barbels associated with their nostrils. Angel sharks are ambush predators that rely on crypsis to attack their unsuspecting prey (Fouts and Nelson, 1999). They are one of only a few groups of sharks that have protrusible jaws and are capable of producing strong negative pressure for suction feeding. Angel sharks are yolk-sac viviparous (Musick, 2011; Musick and Ellis, 2005). Shirai (1992b) studied their phylogenetic relationships.
REFERENCES: Compagno, 2001, 2005; Compagno, in Carpenter, 2003; Compagno and Niem, in Carpenter and Niem, 1998; Compagno et al., 2005; Fouts and Nelson, 1999; Musick, 2011; Musick and Ellis, 2005; Shirai, 1992b.
SQUATINIFORM CHARACTERISTICS:
1) body strongly depressed, ray-like
2) pectoral fins separate from head
3) eyes dorsal
4) two dorsal fins, roughly equal in size, positioned posteriorly
5) spiracles large
6) caudal peduncle with strong, lateral keels
7) anal fin absent
ILLUSTRATED SPECIMEN:
Squatina californica, SIO 65–305, 435 mm TL (dorsal view)
PRISTIOPHORIFORMES : PRISTIOPHORIDAE—Saw Sharks
DIVERSITY: 1 family, 2 genera, 7 species
REPRESENTATIVE GENERA: Pliotrema, Pristiophorus
DISTRIBUTION: Atlantic, Indian, and Pacific oceans (excluding eastern Pacific)
HABITAT: Marine; tropical to temperate; continental shelf to slope, benthic on soft substrates
REMARKS: Saw sharks, so named because of their saw-like snouts, are superficially similar to the sawfishes (Pristiformes), but differ in having the pectoral fins separate from the head, lateral gill slits, and long barbels on the ventral side of the rostrum. These sharks are yolk-sac viviparous (Musick, 2011; Musick and Ellis, 2005) and have litters of 7–17 pups. The large rostral teeth lie flat until after birth. The one species of Pliotrema, P. warreni, is unusual in having six gill slits. These sharks feed on small fishes, crustaceans, and squids, and occasionally are utilized as food fishes.
REFERENCES: Compagno, 1984a; Compagno, in Carpenter and Niem, 1998; Compagno, in Carpenter, 2003; Compagno, 2005; Compagno et al., 2005; Musick, 2011; Musick and Ellis, 2005.
PRISTIOPHORIFORM CHARACTERISTICS:
1) snout extremely long, depressed, with rows of lateral and ventral teeth
2) barbels long, ventral and anterior to nostrils
3) all five (or six) gill slits lateral and usually anterior to pectoral fin
4) spiracles large
5) lateral ridge on caudal peduncle
6) anal fin absent
7) head depressed, body cylindrical
ILLUSTRATED SPECIMEN:
Pristiophorus japonicus, SIO 92–164, 1,128 mm TL (dorsal view)
BATOIDEA—Skates and Rays
The Batoidea includes over 650 species of skates and rays that are classified in four orders, 17 families, and over 70 genera. They are characterized by a variety of features including a dorso-ventrally flattened head and body, enlarged pectoral fins contiguous with the head, mouth and gill slits opening on the ventral side of the head, and eyes and spiracles placed on the dorsal side of the head. The monophyly of this group is well established (Aschliman et al., 2012; McEachran and Aschliman, 2004; McEachran et al., 1998; Naylor et al., 2005) and the group has long been recognized under a variety of names including the Hypotremata, Batidoidimorpha, and Rajiformes sensu lato (Nelson, 2006).
Hypothesized phylogenetic relationships of the Batoidea (rays) after (left) McEachran and Aschliman (2004) and (right) Aschliman et al. (2012).
TORPEDINIFORMES—Electric Rays
There are four families, 11 genera, and 67 species of electric rays, characterized by a nearly circular disc, electric organs located on the pectoral fins, and a completely naked body (without denticles or spines). The Narcinidae is described in more detail below.
REFERENCES: McEachran and Aschliman, 2004
TORPEDINIFORMES : NARCINIDAE—Numbfishes
DIVERSITY: 4 genera, 31 species
REPRESENTATIVE GENERA: Benthobatis, Diplobatis, Discopyge, Narcine
DISTRIBUTION: Atlantic, Indian and Pacific oceans
HABITAT: Marine; tropical to warm temperate; continental shelf to continental slope, benthic on soft substrates
REMARKS: Numbfishes use their electric organs for both defense and feeding. They can be distinguished from the similar torpedo electric rays (Torpedinidae) by their similarsized dorsal fins (first fin larger in torpedo rays), relatively smaller caudal fin, and thin (rather than thick) outer margin of the pectoral-fin disc. Numbfishes prey on benthic invertebrates and small fishes, using their protrusible mouths to provide suction for removing organisms from soft sediments. Numbfishes are yolk-sac viviparous (Musick, 2011; Musick and Ellis, 2005).
REFERENCES: Compagno, 2005; de Carvalho et al., in Carpenter and Niem, 1999; McEachran, in Fischer et al., 1995; McEachran and de Carvalho, in Carpenter, 2003; Musick, 2011; Musick and Ellis, 2005.
NARCINID CHARACTERISTICS:
1) two dorsal fins of equal size, positioned posteriorly
2) mouth slot-shaped, jaws protrusible
3) pectoral fins thin around outer edges
4) caudal fin and dorsal fins similar in size
5) lobes of caudal fin continuous
ILLUSTRATED SPECIMEN:
Narcine brasiliensis, SIO 67–89, 300 mm TL
PRISTIFORMES : PRISTIDAE—Sawfishes
DIVERSITY: 1 family, 2 genera, 7 species
REPRESENTATIVE GENERA: Anoxypristis, Pristis
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine and occasionally in freshwater; tropical; continental shelf and coastal, demersal and benthic on soft substrates
REMARKS: The remarkably large rostral blade with teeth on either side distinguishes sawfishes from all other fishes except sawsharks, from which they can be differentiated by their absence of barbels and by their pectoral fins being connected to the head. These impressive predators use their “saw” for disabling swimming prey or digging for buried prey in soft sediments. Sawfishes are known to enter freshwater, with some individuals captured more than 1,000 km upriver, and are known to reproduce in at least one freshwater lake (Thorson, 1976). Sawfishes are yolk-sac viviparous (Musick, 2011; Musick and Ellis, 2005). All seven species are listed as critically endangered by the IUCN (2013) as a result of overfishing (sawfishes are especially susceptible to gill-nets) and habitat degradation.
REFERENCES: de Carvalho, 2003; Compagno, 2005; Compagno and Last, in Carpenter and Niem, 1999; McEachran and de Carvalho, in Carpenter, 2003; Musick, 2011; Musick and Ellis, 2005; Thorson, 1976.
PRISTIFORM CHARACTERISTICS:
1) snout elongate, blade-like, with single row of large teeth on each side
2) body large and shark-like, with anterior margin of pectoral fins attached to head
3) nostrils well anterior and not connected to mouth
4) spiracles large
5) two large dorsal fins of equal size, widely separated
6) barbels absent
ILLUSTRATED SPECIMEN:
A) Pristis pectinata, UAZ uncatalogued, 940 mm to end of broken snout (dorsal view)
B) head of Pristis pectinata, UAZ uncatalogued (ventral view)
RAJIFORMES—Skates
The skates are the most diverse order of chondrichthyan fishes, with 361 species and over 30 genera in four families. Their disc is diamond- or heart-shaped, and the dorsal surface of the tail has one or more longitudinal rows of thorns but no stinging spine. Skates have large, well-developed spiracles that usually contain visible pseudobranchs.
REFERENCES: Aschliman et al., 2012; McEachran and Aschliman, 2004.
RAJIFORMES : RHINOBATIDAE—Guitarfishes
DIVERSITY: 11 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, entering freshwater. Whiptail stingrays 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
