1. Lancelets Amphioxiformes: Branchiostomatidae * branchio = gill (G)
* stom = mouth (G)

2. Hagfishes
Myxiniformes: Myxinidae
myxin = slime (G)

3. Lampreys Petromyzontiformes: Petromyzontidae
petra = stone (L) + myzo = to suckle (G) + odontos = teeth (G)

4. Elasmo-sources Bulleted lists and cladogram that follow ref:
Martin, R. Aidan.  2003. 
ReefQuest Centre for Shark Research Home. 
World Wide Web Publication,

5. Chimaeras Chimaeriformes: Chimaeridae
Gill cover over the four gills, leaving a single opening on each side of the head
palatoquadrate (upper jaw) is usually fused to the cranium
no spiracle opening behind the eye
branchial (gill) basket mostly beneath the neurocranium (posterior part of the cranium that encases the brain)
teeth relatively few (one pair in the lower jaw and two pairs in the upper), occurring as mineralized grinding plates
tooth plate replacement is slow
no cloaca, but with separate anal and urogenital openings
skin in adults 'naked' (without dermal denticles)
no stomach or ribs
males - in addition to the pelvic claspers - have an accessory clasping organ on the head

6. Chimaeras Chimaeriformes: Chimaeridae
* single gill opening rather than multiple

7. Carpet Sharks Orectolobiformes two, spineless dorsal fins
a very short, transverse mouth that is well anterior to the eyes
specialized nostrils, with prominent barbels and nasoral grooves connecting the nostrils to the mouth corners in most forms
spiracles small to very large, located below the eye
most with small gill slits, with the fourth overlapping the fifth and behind origin of the pectoral fin
most species have a caudal fin with an upper lobe that is more-or-less in line with the main body axis (not tilted upward, as in most other sharks) and a poorly-developed lower lobe; the order's scientific name translates roughly to "stretched-out lobe", in reference to the tail type characteristic of the group
13 genera in 8 families
Note: Whale Sharks, the only fully pelagic orectolobid,
are exceptions to many of these rules.

8. Carpet Sharks Orectolobiformes: Ginglymostomatidae – Nurse Sharks
ginglymo = hinge (G) stom = mouth (G)

9. Carpet Sharks Orectolobiformes: Stegostomatidae – Zebra Sharks
Stegos = roof, house, from; stegein = to cover (G) stoma = mouth (G)

10. Carpet Sharks Orectolobiformes: Rhincodontidae – Whale Sharks
Greek, rhyngchos = snout, muzzle + Greek, odous, odontos = tooth, teeth
rhyngchos = snout, muzzle (G) + odous, odontos = tooth, teeth (G)

11. Requiem Sharks Carchariniformes
two dorsal fins (except in the scyliorhinid Pentanchus profundicolus, which has only one), without spines
anal fin present
five gill slits, with the last one to three over the pectoral fin base
eyes with nictitating fold or membrane (moveable lower eyelid)
intestinal valve of spiral or scroll type
found in virtually every marine habitat, many species occur in estuarine areas and a few make use of freshwater habitats as well; they range from coastal areas to the open ocean, in temperate to tropical zones of the Atlantic, Pacific, and Indian oceans
at least 49 genera in 9 families (possibly as many as 60 genera in 14 families)

12. Requiem Sharks Carchariniformes: Scyliorhinidae – Cat Sharks
Greek, skylla = a shark + Greek, rhinos = nose
skylla = a shark (G) + rhinos = nose (G)

13. Requiem Sharks Carchariniformes: Triakidae – Hound Sharks
Triakis = thrice (G)

14. Requiem Sharks
Carchariniformes: Carcharinidae – Requiem Sharks, Tiger Sharks, Reef Sharks
karcharos = cutting, sharp, also a kind of shark (G) + rhinos = nose (G)

15. Requiem Sharks Carchariniformes: Sphyrnidae – Hammerhead Sharks
sphyr = hammer (G)

16. Mackerel Sharks Lamniformes two dorsal fins, without spines
anal fin present
five pairs of gill slits, either entirely in front of the pectoral fin base or with the last two above the pectoral base
spiracles usually present, small and behind eyes
eyes without nictitating membrane
mouth subterminal, jaws extending well behind the eyes
upper teeth well differentiated along the jaws forming the so-called "lamnoid dental pattern" which features enlarged anterior teeth, slightly to much smaller intermediate teeth, large lateral teeth, followed by much smaller posterior teeth
intestinal valve of ring type
exclusively marine, in coastal to open-ocean environments; they inhabit cold temperate to tropical zones of the Atlantic, Pacific, and Indian Oceans
10 genera in 8 families

17. Mackerel Sharks Lamniformes: Lamnidae – Mackerel Sharks
lamna = shark (G)

18. Mackerel Sharks Lamniformes: Cetorhinidae – Basking Shark
cetus = whale, marine monster (L) + rhinos = nose (G)

19. Mackerel Sharks Lamniformes: Odontaspididae – Sand Tiger Shark
odont = teeth (G) aspid = viper (G)

20. Dogfish Sharks Squaliformes five pairs of gill slits
two dorsal fins, often with a spine along the leading edge; the first dorsal originates in front of pelvic fin origins
lack of an anal fin 
many species are bioluminescent to some degree
ovoviviparous 
exclusively marine; most species are strongly bottom oriented, although many mesopelagic forms undertake nightly vertical migrations; a successful and widely distributed group, dogfishes inhabit coastal and oceanic waters, mostly in cool temperate to deep tropical waters in both hemispheres, but ranging from the Antarctic to the Arctic
22 genera in 6 families

21. Dogfish Sharks Squaliformes: Squalidae – Dogfishes
squaleo, squalidus = with rough skin (L)

22. Dogfish Sharks (Squaliformes: Somniosidae) – Sleeper Sharks
Now Squaliformes: Dalatiidae
dalos, -ou = torch (G)

23. Skates & Rays (Batoids)
Rajiformes: Pristidae now Pristiformes:Pristidae
snout saw-like with equal-sized, strongly-embedded teeth along margin; nasal barbels absent
body shark-like
two distinct dorsal fins and a caudal fin
ovoviviparous
mostly marine, although the largetooth sawfish (Pristis microdon) ascends some rivers in Australia and New Guinea
2 genera (Pristis and Anoxypristis) in the family Pristidae
prist = sawed (G)

24. Skates & Rays
Rajiformes: Pristidae – Sawfishes
prist = sawed (G)

25. Skates & Rays Rajiformes: Torpedinidae
or Torpediniformes: Torpedinidae
rounded snout and pectoral disc
large, kidney-shaped electrogenic organs (derived from branchial musculature) at base of pectoral fins
body thick and flabby, with soft, loose skin
eyes small to obsolete (four species are blind)
0 to 2 dorsal fins, depending upon species
caudal fin well developed
ovoviviparous
exclusively marine, inhabiting temperate to tropical zones of the Atlantic, Pacific, and Indian oceans
11 genera in 4 families

26. Skates & Rays Rajiformes: Torpedinidae – Electric rays
torped = numb, paralysis (L)

27. Skates & Rays Rajiformes: Rajidae snout pointed
pectoral disc usually rhomboid
tail slender, set off from pectoral disc
caudal fin moderately well developed, reduced or absent; weak electrogenic organs at base of tail stalk (derived from caudal peduncle muscles)
0 to 2 dorsal fins
most with enlarged, thorn-like denticles ('bucklers') on skin, often with a row along midline of back 
oviparous 
almost exclusively marine; a few species live in shallow waters close to shore, but most live in deep water, on soft bottoms along continental margins, down to feet (3 000 metres) or more 
26 genera in a single family (Rajidae), divided into 2 subfamilies

28. Skates & Rays
Rajiformes: Rajidae – Skates
Raja = ray (L)

29. Skates & Rays Order Myliobatiformes: Stingrays - 178 species
pectoral disc rhomboid, oval, or triangular in outline, elaborated into gracefully-shaped wings in some forms 
tail moderately stout to very slender 
caudal fin and a single dorsal fin are variably present or absent, depending on species 
most species have one or more saw-edged spines or stings on the dorsal surface of the tail (the sting is a modified dermal denticle, sheathed with poisonous tissue and used as a defensive weapon)
most forms have five pairs of gill slits, but members of the family Hexatrygonidae have six
ovoviviparous 
temperate to tropical zones of the Atlantic, Pacific, and Indian oceans; most species are marine, but some enter brackish or fresh waters and the river stingrays (family Potamotrygonidae) are exclusively freshwater inhabitants, having lost the ability to osmoregulate in the sea 
33 genera in 10 families

30. Skates & Rays
Rajiformes: Dasyatidae – Stingrays
dasys = hair (G)

31. Skates & Rays Rajiformes: Gymnuridae – Butterfly Rays
gymnos = naked (G) + uro = tail (G)

32. Skates & Rays Rajiformes: Myliobatidae – Eagle Rays
myleys = mill, millstone (G) + batis = ray (G)

33. Skates & Rays (Rajiformes: Mobulidae – Manta Rays)
Now lumped with Myliobatidae

34. Coelacanth Coelacanthiformes: Coelacanthidae – Coelacanths
coel = hollow (G) acanth = spine (G)

35. Lungfish Lepidosireniformes: Protopteridae – African Lungfish
pro = before, in front of (G) + pteron = fin (G)

36. Reedfishes & Bichirs Polypteriformes: Polypteridae – Bichir
poly = many (G)
pteri = fin (G)

37. Sturgeons & Paddlefishes
Acipenseriformes:
Acipenseridae – Sturgeons
acipenser = sturgeon (L)

38. Sturgeons & Paddlefishes
Acipenseriformes: Polyodontidae – Paddlefishes
poly = many (G) odont = teeth (G)

39. Gars Semiontiformes: Lepisosteidae – Gars
lepis, -idos = scale (G) + osteon = bone (G)

40. Bowfin Amiiformes: Amiidae
amia = A kind of fish, probably the perch or the bonito (G)

41. Bonytongues Osteoglossiformes: Osteoglossidae – Bonytongues
osteon = bone (G) + glossa = tongue (G) + forma = shape (L)

42. Bonytongues Osteoglossiformes: Pantodontidae – Butterflyfishes
pan = all (G) + odous = tooth, teeth (G)

43. Bonytongues Osteoglossiformes: Notopteridae – African Knifefishes
noton = back (G) + pteron = wing, fin (G)

44. Bonytongues Osteoglossiformes: Mormyridae – Elephantnose Fishes
mormyros = a kind of fish (G)