Drawing of four sharks from: http://www.mun.ca/biology/scarr/Fig28-07.gif

CLASS CHONDRICHTHYES

Sharks and their relatives have a skeleton of prismatic calcified cartilage.  The dermal covering is of minute denticles that are tooth-like in structure.  They have separate gill slits, well-developed, paired appendages (pectoral and pelvic fins), usually two dorsal fins, an anal fin, and a heterocercal caudal fin.  The mouth is subterminal and the teeth are not fused to the jaws but are replaced through the life of the animal.  They have no swim bladder or lungs.  Many have a spiral valve in the intestine, a structure that greatly lengthens the absorptive surface.  Many have pelvic claspers and internal fertilization.  The class has two subclasses: Elasmobranchii and Euchondrocephali.

Upper Devonian to the present.

SUBCLASS ELASMOBRANCHII

Most sharks fall into this subclass.  They have five to seven separate gill slits.  The dorsal fins and spines are rigid.  Males do not have accessory copulatory organs on the head (as do the Holocephali).  The skin is covered with placoid scales.  The teeth are numerous and not fixed to the jaws but rapidly replace those that have fallen out.  They may have ribs and spiracles.

Devonian to the present

ORDER UNNAMED+

FAMILY CLADOSELACHIDAE

Tail symmetrical but internally heterocercal.  Skin nearly without scales. Large pectoral fins.  Dorsal fins with spines.

Upper Devonian

Cladoselache

ORDER SYMMORIDA+

FAMILY SYMMORIIDAE

Body similar to that of Cladoselache but without dorsal fin spines and with whip-like appendages on the pectoral fins.

Carboniferous

Denaea

FAMILY FALCATIDAE

Shark resembling a dogfish with bizarre large spines emerging from the back above the pectoral girdle and bent over the head.  These seem to have been part of the sexual mating display of the mature male sharks, because those with spines also had claspers.

Carboniferous

Falcatus

FAMILY STETHACANTHIDAE

These sharks resembled falcatids except that a spine-brush complex emerged from the dorsum. 

Carboniferous

Stethacanthus, Akmonistion.

ORDER EUGENODONTIFORMES+

Also called the edestids, these sharks are known almost exclusively by their tooth whorls.  The spiraled tooth whorl was between the lower jaws and worked against teeth in the upper jaw.  Only fragmentary remains of skeletal material remain except for Fadenia, which had a long dorsal fin and lived in swampy ponds.

Carboniferous to Permian

Fadenia, Helicoprion, Sarcoprion

ORDER PETALODONTIFORMES+

These were stubby sharks with stout pavement like teeth used for crushing prey, likely mollusks, corals, or other shelled invertebrates.  They also had armor plates around the mouth that likely served to protect against abraision.

Carboniferous to Permian

Janassa, Belantsea.

ORDER XENACANTHIFORMES+

Dorsoventrally depressed freshwater sharks with an elongate diphycercal tail and a ling spine just behind the head.  There was a low elongate dorsal fin.  The ventral fins were typically shark like, and they seem to have had claspers.

Devonian to Triassic

Xenacanthus.

ORDER CTENACANTHIFORMES+

Poorly preserved fish do show quite modern looking that support the two dorsal fins on their leading edges. Cladodont teeth; animals up to 2.5 meters long

Middle Devonian to Triassic

FAMILY UNNAMED

Acronemus, Carinacanthus.

FAMILY CTENACANTHIDAE

Upper Devonian to Mississippian

Ctenacanthus, Goodrichthys

FAMILY BANDRINGIDAE

Freshwater; elongate snout.

Pennsylvanian

Bandringa.

FAMILY PHOEBODONTIDAE

Middle Devonian to upper Triassic

Phoebodus

ORDER HYBODONTIFORMES+

These sharks had a heterocercal tail and large pectoral fins.  Dorsal fins were supported by anterior spines.  Sluggish swimmers, they were the dominant sharks in the Jurassic.  Devonian?

Carboniferous to upper Cretaceous

FAMILY HYOBODONTIDAE

Hybodus, Acrodus, Asteracanthus, Hamiltonichthys, Lissodus, Lonchidion, Palaeobates, Polyacrodus, Pseudodalatias, Ptychodus, Steinbachodus, Tribodus.

THE NEOSELACHII

SUPERORDER GALEOMORPHI

With anal fin

ORDER UNNAMED

FAMILY PALEOSPINACIDAE

Lower Triassic to Paleocene

Nemacanthus, Paleospinax, Paraorthacodus, Synechodus.

ORDER HETERODONTIFORMES

Bullhead sharks. Two dorsal fins, each with a spine.  Head with crests above the eyes.  5 gill slits; first two largest.  Spiracle present but small.  Eyes without nictitating fold.  Nostrils connected to the mouth.  Oviparous, screw-shaped eggs.

FAMILY HETERODONTIDAE

Marine; tropical to warm temperate; continental shelf (0-275m).  Maximum length 1.6m.

Heterodontus.

ORDER ORECTOLOBIFORMES

Carpet sharks, whale sharks.  Two dorsal fins, not spines.  Five gill slits and spiracles; eyes without nictitating membrane.  Nostrils longitudinal.  Most with barbels.

SUBORDER PARASCYLLOIDEI

Spiracle minute; no gill filaments.  Last (5^th) gill opening large.

FAMILY PARASCYLLIDAE

Collared Carpet Sharks.  Marine; tropical to temperate; coastal (1-137m; Australia to Japan).

Cirrhoscyllium, Parascyllium.

SUBORDER ORECTOLOBOIDEI

Spiracles moderate to large with gill filaments.  Fifth gill opeming moderate in size.

FAMILY BRACHAELURIDAE

Blind Sharks.  Marine; tropical to temperate continental shelf (0-137m).  Western south Pacific.  Spiracles large; nasal barbels long.  Maximum length to 1.2m.

Brachaelurus, Heteroscyllium.

FAMILY ORECTOLOBIDAE

Wobbegongs.  Marine; tropical to warm temperate on continental shelf (0-110m).  Western Pacific ( Australia to Japan ).  Head and body dorsoventrally flattened; mouth terminal; skin flaps on sides of the head and long barbels.  Spiracle large; fang like anterior teeth.  Maximum length 3.2m.

Orectolobus, Eucrossorhinus, Sutorectus.

FAMILY HEMISCYLLIDAE

Bamboo Sharks.  Marine; tropical and subtropical continental shelves (0-100m).  Madagascar to Japan and Australia .  Barbels short; spiracles large; anal fin rounded.  Maximum length 1m.

Hemiscyllium, Chiloscyllium.

FAMILY STEGOSTOMATIDAE

Zebra Sharks. Marine, tropical inshore.  From Red Sea to Japan .  Spiracles moderate in size and behind the eyes.  Caudal fin long.

Stegostoma.

FAMILY GINGLYMOSTOMATIDAE

Nurse Sharks. Marine, tropical tropical inshore (0-100m). Northern USA to Brazil; Africa, Inian Ocean, Australia, to Japan; and Mexico to Peru.  Spiracles small and behind the eyes; nostrils with barbels (long to short); with groove around nostrils.  4^th and 5^th gill slits almost overlapping.  Maximum length 3m.

Ginglymostoma, Nebrius, Pseudoginglymostoma.

FAMILY RHINCODONTIDAE

Whale Sharks. Marine; tropical to warm temperate; coastal to open ocean (0-700m); circumglobal.  Mouth very large and terminal; gill openings very large; gill rakers elongate; plankton feeders.  Teeth reduced but numerous.  Spiracles small.  Maximum length 12m (but over 14 and maybe 18m).  The world’s largest fish.

Rhincodon.

ORDER LAMNIFORMES

Mackerel sharks.  Two dorsal fins without spines.  5 gill slits; spiracles usually present.  Eyes without nictitating membrane or barbels.  Mouth large and extends well behind the eyes.  Spiral valve appears as a stack of rings.

FAMILY CRETOXYRHINIDAE

Known mainly by teeth.

Lower Cretaceous to Paleocene.

Credotus, Cretoxyrhina, Leptostyrax, Paraisurus, Protolamna.

FAMILY OTODONTIDAE

Known mainly by teeth.

Paleocene to Pliocene.

Carcharocles, Otodus.

FAMILY ANACORACIDAE

Known mainly by teeth.

Lower to upper Cretaceous.

Pseudocorax, Squalicorax.

FAMILY ODONTASPIDAE

Sand Tiger sharks. Marine, tropical to temperate; continental to deep ocean (1-1600m)Found in the Atlantic, Pacific, and Indian Oceans.  All gill slits in front of the pectoral fins; caudal fin with short ventral lobe.  Maximum length 4.1m.

Cretaceous to present.

Eugomphodus, Carcharias, Odontaspis.

FAMILY MITSUKURINIDAE

Goblin sharks.  Marine, outer continental slopes and seamounts (100-1300m).  France to South Africa ; Japan to Australia and New Zealand ; Southern California .  Snout very elongate and like a flattened blade.  (to depths of 1000m).  Jaws very protrusible.  Caudal fin long but very small ventral lobe. 

Lower Cretaceous to present.

Mitsukurina, Anomotodon, Scapanorhynchus.

FAMILY PSEUDOCARCHARIIDAE

Crocodile sharks. Marine, tropical to subtropical, inshore (rarely) to oean ocean and global ( Brazil ; Cape Verde to South Africa ; spotty in Indian Ocean to Australia and New Zealand ; much of the open Pacific, including Hawaii to North and South America . (0 to 590m)..  Eyes very large.  Gill slits extend to dorsal surface.  Moderate lower lobe to caudal fin.  Maximum length 1.1m.

Pseudocarcharias.

FAMILY MEGACHASMIDAE

Megamouth sharks.  Marine, tropical to warm temperate, coastal (as shallow as 5m) and opean ocean (8-166m); circumtropical?  Elongated head, almost the length of the trunk.   Mouth very large and terminal.  Snout broadly rounded.  Gill slits moderately long but not extending to the dorsal part of the head.  Teeth small in many rows.  Gill rakers of a unique of fingerlike dermal papillae.  Maximum length 5.5 m.  Large filter-feeding sharks discovered only in 1976.

Megachasma.

FAMILY ALOPIIDAE

Thresher sharks. Marine; tropical to cold temperate; coastal to opean ocean (0-500m).  Atlantic , Indian, and Pacific oceans.  Upper lobe of caudal fin very long and curving like a scythe, and about as long as the rest of the shark’s body.  Gill slits short and mouth small.  Maximum length 5.7m.

Alopias.

FAMILY CETORHINIDAE

Basking sharks.  Marine; warm temperate to cool temperate.  Continental shelves and possibly to the open ocean. Atlantic , Mediterranean Sea , Indian, and Pacific.  Gill slits very large and extend to the dorsum of the head.  Large mouth with many small teeth.  Gill rakers elongate and hair-like.  Filter feeder.  Maximun length may be up to 15+m.

Cetorhinus.

FAMILY LAMNIDAE

Mackerel sharks. Marine, tropical to cool temperate. Continental shelves to open ocean (0-1200m).  Atlantic , Indian, and Pacific.  Gill slits large, extending just to dorsum of the head.  Teeth few but large; no gill rakers.  Caudal fin lobes nearly equal.  Maximum length 6m (the extinct megalodon had a length of 11-20m).

Carcharodon, Isurus, Lamna.

ORDER CHARCHARHINIFORMES

Ground sharks.  Most with two dorsal fins, both without spines.  Anal fins present.  5 gill slits.  No gill rakers.  Eyes with nictitating membrane.  Usually no spiracles.

FAMILY SCYLORHINIDAE

Cat sharks.  Marine, temperate to tropical; contintental shelves.  Global distribution in Atlantic , Indian and Pacific.  Nictitating membranes rudimentary; spiracles present.  Intestine with spiral valve.  Maximum length 1.6m.

Apristurus, Asymbolus, Atelomycterus, Bythaelurus, Cephaloscyllium, Cephalurus, Galeus, Halaelurus, Haploblepharus, Holohalaelurus, Parmaturus, Pentanchus, Poroderma, Schroederichtys, Scyliorhynus.

FAMILY PROSCYLLIIDAE

Finback Cat sharks.  Marine, continental slopes.  North Atlantic , western Indian, western to central Pacific.  Nictitating membranes rudimentary.  Spiracles present.  Many tooth rows; posterior teeth comb-like.  Spiral valve.  Maximum length 2.9m.

Proscyllium, Ctenacis, Gollum (some species), Eridacnis.

FAMILY PSEUDOTRIAKIDAE

False Cat sharks. Marine; continental slopes; North Atlantic, western Indian, and central Pacific.  First dorsal fin low and long.  Nictitating membranes rudimentary; spiracle large; many tooth rows; posterior teeth comb-like.  Spiral valve.  Maximum length 2.9m.

Gollum, Pseudotriakis.

FAMILY LEPTOCHARIIDAE

Barbled Hound Sharks. Marine; African continental shelf in eastern Atlantic .  Labial furrows long and nasal flaps formed into barbels.  Internal nictitating membranes; spiracles present but small.  Intestine with spiral valve.  Maximum length 8.2m.

Leptocharias.

FAMILY TRIAKIDAE

Hound Sharks. Marine, though sometimes in freshwater; tropical to cool temperate; continental shelves, slopes and islands; circumglobal..  Long labial furrows; anterior nasal flaps not barbell-like.  Spiracles present and intestine with spiral valve.  Maximum length 2.4m.

Scylliogaleus, Triakis, Mustelus, Cazon, Furgaleus, Galeorhinus, Gogolia, Hemitriakis, Hypogaleus, Iago.

FAMILY HEMIGALEIDAE

Weasel Sharks. Marine; continental shelves; eastern tropical Atlantic and Indo-west Pacific.  Dorsal fin undulated; precaudal pit.  Nictitating membranes internal; small spiracles; labial furrows long; intestine with spiral valve.  Maximum length 2.4m.

Chaenogaleus, Hemigaleus, Hemipristis, Paragaleus.

FAMILY CARCHARHINIDAE

Requiem Sharks. Marine and sometimes in freshwater; tropical and warm-temperate; continental slopes and open ocean; some in rivers and lakes; circumglobal in Atlatic, Indian and Pacific oceans.  Dorsal fin undulated; precaudal pit; spiracles usually absent; nictitating membranes internal;intestine with scroll valve, not spiral valve.  Maximum length 7.4m.

Charcharinus, Galeocerdo, Glyphis, Isogomphodon, Lamiopsis, Loxodon, Nasolamia, Negaprion, Prionace, Rhizoprionodon, Scoliodon, Triaenodon.

FAMILY SPHYRNIDAE

Hammerhead Sharks.  Marine; tropical to warm temperate on continental shelves in the Atlantic , Indian, and Pacific oceans.  Distinctive, latera extensions of the head making eyes and nasal openings farther apart than in any other shark group.  Spiracles absent.  Maximum length 6.1m.

Eusphyra, Sphyrna.

SUPERORDER SQUALOMORPHI

Sharks with orbitostylic jaw articulation.

ORDER HEXANCHIFORMES (NOTIDANOIDEI)

Six-gilled Sharks.  One dorsal fin and spineless; anal fins; six to seven gill slits; no nictitating fold; spiracles small.  The fossil record to lower Jurrassic (some teeth from the Devonian have also been assigned to this order).

FAMILY CHLAMYDOSELACHIDAE

Frill Sharks.  Marine; continental slopes and sometimes on continental shelves; scattered over the oceans: western North Atlantic, eastern Atlantic , southwestern Indian, western Pacific, and eastern Pacific.  Six gill slits; mouth terminal; teeth with three cusps.  Lateral line canal open; body elongate.  Maximum length 1.9m.

Chlamydoselachus.

FAMILY HEXANCHIDAE

Cow Sharks. Marine; temperate to tropical, shelves and slopes of continents and islands; circumglobal in the Atlantic , Indian, and Pacific oceans.  Six to seven gill slits; mouth ventral; teeth in upper and lower jaws different.  Lateral line open.  Maximum length 4.7m.

Hexanchus, Heptranchias, Notorhynchus.

ORDER ECHINORHINOFORMES

Bramble Sharks. The order has a single family.

FAMILY ECHINORHINIDAE

Bramble Sharks.  Marine; cool to warm temperate water on continental shelves, slopes, island margins and sea mounts.  Atlantic, western Indian, and Pacific oceans.  Both dorsal fins spineless; first dorsal fin far back on the body (arising over pelvic fin, which is larger than second dorsal fin).  Caudal fin without a notch.  Body covered with coarse denticles; teeth similar in both jaws.  Last gill slit larger than the others.  Spiracle very small and behind the eye.  Lateral line open.  Maximum length up to 2m.

Echinorhinus.

ORDER SQUALIFORMES

Dogfish Sharks.  Two dorsal fins, with or without spines; no anal fins; five gill slits; spiracles present; lower nictitating membrane absent; lateral line canal

FAMILY SQUALIDAE

Dogfish Sharks.  Marine; cool temperate to tropical; circumglobal on continental shelves, slopes, island margins, and sea mounts; Atlantic , Pacific, and Indian oceans.  Both dorsal fins with spines that are not grooved; teeth on lower jaw slightly larger than those of the upper jaw.  Upper precaudal pit; caudal peduncle with lateral keels.

Squalus, Cirrhigales.

FAMILY CENTROPHORIDAE

Gulper Sharks. Marine; warm temperate to tropical; outer sleves and slopes of continents and islands; Atlantic , Indian, and western Pacific oceans.  Both dorsal fins with spines, both of which are grooved.  Teeth in lower jaw larger than those of upper jaw; precaudal pits and lateral keels absent.

Centrophorus, Deania.

FAMILY ETMOPTERIDAE

Lantern Sharks.  Marine; tropical to temperate; slopes of continents and islands; rarely open ocean; Atlantic , Indian, and Pacific oceans.  Both dorsal fins with grooved spines; caudal fin with notch; luminous organs present.  Maximum length less than 90cm.

Aculeola, Centroscyllium, Etmopterus, Miroscyllium, Trigonognathus.

FAMILY SOMNIOSIDAE

Sleeper Sharks.  Marine; Arctic to sub-Arctic; Slopes of continents and islands; some oceanic; Atlantic, Indian, and Pacific oceans.  Dorsal fins without spines, or small if present; lateral ridge present on abdomen between pectoral and pelvic fins; luminous organs present.

Centroscymnus, Centroselachus, Proscymnodon, Scymnodalatias, Scymnodon, Somniosus, Zameus.

FAMILY OXYNOTIDAE

Rough Sharks. Marine; shelves and slopes of continents and islands; eastern Atlantic (including Mediterranean), western Atlantic , and western Pacific.  Body high and compressed, triangular in crossection; dorsal fins high, each with a spine; the first dorsal fin is far forward; lateral ridge present on body; skin very rough; luminous organs present.

Oxynotus.

FAMILY DALATIIDAE

Kitefin Sharks. Marine; tropical to temperate; shelves and slopes of continents and islands, some in open ocean; Atlantic , Indian, and Pacific oceans.  Dorsal fins usually without spines; luminous organs present.  This includes some of the smallest known sharks (only about 25cm).

Dalatias, Euprotomicroides, Euprotomicrus, Heteroscymnoides, Isistius, Mollisquama, Squaliolus.

ORDER PROTOSPINACIFORMES+

This group is sister to the Hypnosqualeans (remaining squalomorphs, squatinids, and pristiophorids). 

Upper Jurrasic of Bavaria

FAMILY PROTOSPINASIDAE

Protospinax.

ORDER SQUATINIFORMES

Angel Sharks. Body flattened like the skates and rays.

FAMILY SQUATINIDAE

Angel Sharks. Marine; temperate to tropical; shelves and slopes of continents; Atlantic , southwestern Indian, and Pacific oceans.  Body ray-like; eyes dorsal; spineless dorsal fins; large mouth (almost terminal) with barbels; no anal fin.  Maximum length 2m.

Squatina.

ORDER PRISTIOPHORIFORMES

Saw Sharks.

FAMILY PRISTIOPHORIDAE

Saw Sharks. Marine, sometimes in estuaries; temperate to tropical; shelves and slopes of continents and islands; western Atlantic ; southwestern Indian and western pacific oceans.  Body sharklike; snout elongate as a long saw-like structure with teeth on each side; one pair of barbels; no dorsal fin spines; no anal fin; large spiracles.  Maximum length 1.4m.

Pliotrema, Pristiophorus.

SUPERORDER BATIDIOMORPHA (=SUBDIVISION BATOIDEA

The Rays and Skates.  Gill slits ventral and spiracles large which function as primary water intake while the animal is on the bottom; body dorso-ventrally flattened with very large pectoral fins; no nictitating membrane; teeth pavement-like.

ORDER TORPEDINIFORMES

Electric Rays. Powerful electric organs; eyes small or absent; caudal fin well-developed.

FAMILY TORPEDINIDAE

Torpedo Electric Rays.  Marine; shelves and slopes of continents and islands; Atlantic, Mediterranean , Indian, and Pacific oceans. Body forming a truncate disc; slender mouth and reduced rostrum.  Two subfamilies, each with a single genus.

Torpedo Rays: Torpedo.

Coffin Rays: Hypnos.

FAMILY NARCINIDAE

Numbfishes. Marine; tropical to warm temperate; shelves and slopes; Atlantic , Indian, and Pacific oceans. Body dosc-like and rounded anteriorlly; jaws stout; rostrum present; one or two dorsal fins.  Two subfamilies.

Numbfishes: Benthobatis, Diplobatis, Discopyge, Narcine.

Sleeper Rays: Crassinarke, Heteronarke, Narke, Temera, Typhlonarke.

ORDER PRISTIDAE

Sawfishes. One family.

FAMILY PRISTIDAE

Marine and esturine, sometimes ascending rivers; circumtropical; continental shelves; Atlantic , Indian, and Pacific oceans.  Body shark-like but with a depressed head.  Rostrum elongate into a flat blade with similar-sized teeth on the outer margins; no barbels; with two dorsal fins and caudal fin.  Maximum length 6m.

Anoxypristis, Pristis.

ORDER RAJIFORMES

Skates.  Caudal fin variable; tail slender; many of the placoid scales elaborated into prickles and thorns; Oviparous; eggs in a horny case with 4 long horns.

FAMILY RHINIDAE

Bowmouth Guitarfishes.  Marine, continental shelves; west Pacific.  Caudal fin large and bilobed; first dorsal fin above or in front of pelvic fins.  Front of the head broadly rounded with a deep indentation that separates the head from the pectoral fins.  Maximum length 270cm.

Rhina

FAMILY RHYNCHOBATIDAE

Wedgefishes.  Marine; continental shelves; eastern Atlantic , Indian and western Pacific.  Tail stout and not distinct from rest of the body; two dorsal fins and caudal fin (not bilobed).  First dorsal behind the pelvic fins;  tail without a spine.

Aptychotrema, Rhinobatos, [Acroteriobatus, Glaucostegus], Trygonorrhina, Zapteryx.

FAMILY RAJIDAE

Skates.  Marine; tropical to polar seas; shallow to deep water; Atlantic , Indian, and Pacific oceans.  Caudal fin variable (well-developed to absent); tail very slender; electric organs (weak); dorsal fins 2-none.  Eggs in horny capsule with four long spines.  Maximum length 2.5m. This family has two subfamilies.

Hardnose Skates: Amblyraja, Anacanthobatis, Breviraja, Cruriraja, Dactylobatus, Dipturus, Fenestraja, Gurgesiella, Leucoraja, Malacoraja, Neoraja, Okamejei, Raja, Rajella, Rostroraja.

Softnose Skates.  Arhynchobatis, Atlantoraja, Bathyraja, Irolita, Notoraja, Pavoraja, Psammobatis, Pseudoraja, Rhinoraja, Rioraja, Sympterygia.

ORDER MYLIOBATIFORMES

Stingrays.  Three suborders and ten families.

SUBORDER PLATYRHINOIDEI

FAMILY PLATYRHINIDAE

Thornbacks.  Marine; shelves of continents; tropical to cool temperate; north Pacific.  Round or heart-shaped anterior disc; tail shark-like; strong thorns.

Late Cretaceous to present.

Platyrhina, Platyrhinoidis, Tethybatis+.

SUBORDER ZANOBATOIDEI

FAMILY ZANOBATIDAE

Panrays.  Marine; tropical; eastern Atlantic ocean .  They resemble the thornbacks.

Zanobatus.

SUBORDER MYLIOBATOIDEI

Rays with no thoracic ribs and having a serrated caudal spine.

Early Cretaceous to the present.

FAMILY HEXATRYGONIDAE

Sixgill Stingrays.  Marine.slopes of continents and islands; Indian, western Pacific oceans.  Six gill slits; rostrum elongate; large spiracles; tail with one or two spines; short nasal flaps.

Hexatrygon, [Plesiobatis, Urlolophus, Trygonoptera].

FAMILY PLESIOBATIDAE

Deepwater Stingrays. Marine; slopes of continents and islands; Indian, western Pacific oceans. Nasal curtain united, not reaching the mouth; six gill arches.  Maximum length 2.7m.

Plesiobatis.

FAMILY UROLOPHIDAE

Round Stingrays.  Marine, upper slopes and shelves of western Pacific ocean .  Disc less than 1.3 times as wide as long; caudal fin small; dorsal fin present; tail long with barbed spine.

Trygonoptera, Urolophus.

UROTRYGONIDAE

American Round Stingrays. Marine; tropical to warm temperate; shelves of continents; western Atlantic and eastern Pacific.  Disc not more than 1.3 times as wide as long;tail slender and as long as the disc; no dorsal fin; distinct caudal fin; one or two barbed spines.

Urobatis, Urotrygon.

FAMILY DASYATIDAE

Whiptail Stingrays. Mainly marine, some into brackish and freshwater; upper slopes and shelves of continents and islands; brackish and freshwater, one species oceanic; tropical to warm temperate; Atlantic (including Mediterranean ), Indian, and Pacific oceans.  Disc not more than 1.3 times as broad as long; no caudal fin; long tail;; no dorsal fin but with one or two barbed spines.

Dasyatis, Himantura, Pastinachus, Pteroplatytrigon, Taeniura, Urogymnus.

FAMILY POTAMOTRYGONIDAE

River Stingrays. Freshwater; South America .  Most are colorful on the dorsal surface; long, anteriorly-directed process from the pelvic girdle; rectal gland reduced.

Paratrygon, Potamotrygon, Plesiotrygon.

FAMILY GYMNURIDAE

Butterfly Rays.  Marine; tropical to temperate; shelves of continents; Atlantic , Indian, and Pacific oceans.  Disc very wide (1.5 times as wide as long); dorsal fin and tail spines present or absent; no caudal fin.

Aetoplatea, Gymnura.

FAMILY MYLIOBATIDAE

Eagle Rays.  Marine; tropical to warm temperate; shelves of islands and continents; Atlantic , Indian, and Pacific oceans.  Small, dorsal fin; most with poisonous spines on tail; no caudal fin; head elevated above disc; eyes and spiracles lateral; small dorsal fin; some with anterior lobe of pectoral fin making appendages on either side of the mouth.  Three subfamilies.

Eagle Rays: Aetobatus, Aetomylaeus, Myliobatis, Pteromylaeus.

Cownose Rays: Rhinoptera.

Devil Rays: Manta, Mobula.

SUBCLASS EUCHRONDROCEPHALI (=SUBTERBRANCHIALIA, HOLOCEPHALI)

Fishes in this subclass have gill covers over their four gill slits; so, they have only one opening from the outside.  They have no spiracle.  The teeth have been reduced to grinding plates in the extant and many extinct forms.  Also, living holocephalans have the upper jaw fused to the chondrocranium.  They have no cloaca and the living holocephalans have naked skin, that is, their skin has no placoid scales (though they may be found in some extinct taxa).  They have no stomach or ribs.  Males have structures on their heads that are used in copulation in addition to claspers.  

Upper Devonian to present

SUPERORDER PARASELACHIMORPHA+

Dentition similar to selachians.  Palatoquadrate fused to cranium.  Some had cuboidal scales that grew throughout life.

ORDER ORODONTIFORMES

FAMILY ORODONTIDAE

Hercynolepis, Orodus.

ORDER PETALODONTIFORMES

FAMILY BELANTSEIDAE

Belantsea, Ctenoptychius.

FAMILY JANASSIDAE

Janassa.

FAMILY PETALODONTIDAE

Polyrhizodus.

FAMILY PRISTODONTIDAE

ORDER INIOPTERYGIFORMES+

Large heads, rounded tails, and large pectoral fins that seem to have been adapted to flapping for propulsion in the water.

Pennsylvanian Period

FAMILY INIOPTERYGIDAE

Iniopteryx, Promyxele.

FAMILY SIBYRHYNCHIDAE

Sibyrhynchus.

ORDER DEBEERIIFORMES

These fish appear to be intermediate between chimeroid and typical selachians.  The postcranial skeleton is chimeroid while the teeth (heterodont dentition) appears to be selachian.

Upper Mississippian

Debeerius, Heteropetalus.

ORDER EUGENEODONTIFORMES

This order holds an uncertain position.

FAMILY AGASSIZODONTIDAE (INCLUDING HELICOPRIONIDAE)

FAMILY CASEODONTIDAE

Fadenia, Ornithoprion.

FAMILY EDESTIDAE

Lestrodus.

FAMILY EUGENEODONTIDAE

Bobbodus, Gilliodus.

SUPERORDER HOLOCEPHALIMORPHA (HOLOCEPHALI)

Dentition of several flat grinding plates; usually with a dorsal fin spine.

ORDER PSAMMODONTIFORMES+

Identification based on tooth plates.

Upper Devonian to Mississippian

FAMILY PSAMMODONTIDAE

Lagarodus, Psammodus.

ORDER COPODONTIFORMES+

Description based only on tooth plates.

Mississippian through Pennsylvanian

Copodus.

ORDER SQUALORAJIFORMES

Body dorsoventrally flattened.

Lower Jurassic

FAMILY SQUALORAJIDAE

Squaloraja.

ORDER CHONDRENCHELYIFORMES+

Long, tailless body, very much like an eel.  The paired fins also were small.  Some skull elements were fused. Males had claspers.

Lower Carboniferous (Mississippian?)

FAMILY CHONDRENCHELYIDAE

Chondrenchelys, Harpagofututor, Platyxystrodus.

ORDER MEASPIFORMES+

Lower Carboniferous (Mississppian?) to upper Permian

FAMILY DELTOPTYCHIIDAE

Deltoptychius.

FAMILY MENASPIDAE

Menaspis.

FAMILY TRAQUAIRIIDAE

Traquairius.

ORDER COCHLIODONTIFORMES+

Identified on the basis of tooth and dental plate morphology.

Upper Devonian to Permian

FAMILYCOCHLIODONTIDAE

Cochliodus, Deltodus, Poecilodus, Sandalodus

FAMILY PSEPHODONTIDAE

Psephodus.

ORDER CHIMAERIFORMES (HOLOCEPHALIFORMES)

The chimeras. Long pointed tail and relatively large pectoral fins.  Dentition reduced to a few crushing pavements. Skull elements fused.

SUBORDER ECHINOCHIMAEROIDEI+

Had dermal cranial armor and no frontal claspers.

Mississippian

FAMILY ECHINOCHIMAERIDAE

Echinochimaera.

SUBORDER MYRIACANTHOIDEI+

Upper Triassic to Jurassic

FAMILY CHIMAEROPSIDAE

Chimaeropsis.

FAMILY MYRIACANTHIDAE

Acanthorhina, Agkistracanthus, Halonodon, Myriacanthus.

SUBORDER CHIMAEROIDEI

Two dorsal fins; mouth inferior.  Water for gas exchange taken in through the nostrils.

Lower Jurassic to present

FAMILY CALLORHINCHIDAE

The plownose chimeras.  Found on the continental shelves of the southern hemisphere.  Snout elongate and hook-like.  Tail heterocercal.

Fossil history to the Jurassic.

Callorhinchus, Brachymylus+, Ischyodus+, Pachymylus+, Edaphodon+.

FAMILY RHINOCHIMERIDAE

Longnose chimeras. Deep ocean and continental shelves of the Atlantic , Indian, and Pacific Oceans.

Helodus, Deltoptychius, Ischyodus.