Shark Species and Taxonomic
Information
This Knowledge Base,
provided by Marine Themes, is not intended to be an authority
on taxonomic order. The following information was correct
at time of publication but, no doubt, has since changed and
will change yet again. It is intended to provide a basic knowledge
of some of the more "obvious", though not necessarily
common, animal species found in our database.
Fish species can be divided into three distinct
groups: Osteichthyes (fishes with a bony skeleton), Chondrichthyes
(fish with cartilage skeleton) and Agnatha (jawless fish i.e.
Hagfish). Sharks, Rays and Chimaeras are Chondrichthyans,
all having a skeleton made of cartilage, a substance similar
in structure to your ears or nose. The Chondrichthyans are
further broken up into two groups: Elasmobranchs (sharks and
rays) and Holocephali (chimaeras or ghost sharks and spookfish).
Elasmobranchs are then divided into two groups: Selachii (sharks)
and Batoidea (rays).
Sharks and rays are primarily differentiated
by their gill slits. Sharks always have their gills originating
on the sides of the head (even if they do terminate, at times,
under the head) while rays always have their gill slits under
the head. Rays are mostly flattened in profile and may have
spines on the tail. Some ray species are similar to sharks,
with rounded bodies and shark-like dorsal fins and tail, and
some sharks are ray-like with flattened bodies. However, the
gill placement is always a determining feature.
There are eight distinct orders of sharks:
Hexanchiformes:
Frilled, Sixgill & Sevengill Sharks
Squaliformes:
Dogfish or Dogsharks
Heterodontiformes:
Hornsharks or Bullhead Sharks
Orectolobiformes:
Carpetsharks
Lamniformes:
Mackerel Sharks
Carcharhiniformes:
Groundsharks
Squatinaformes:
Angelsharks
Pristiophoriformes:
Sawsharks
Some may argue that there are at least ten,
splitting the Hexanchiformes and putting the Frilled Shark
into Chlamydoselachiformes and taking the Bramble Sharks out
of the Squaliformes order and creating the Echinorhiniformes
family.
The distinctive features of each group are,
in part:
Hexanchiformes: All have 6 or 7 gills (all
other species have 5). Single spineless dorsal and anal fins.
2 families.
Squaliformes:
No anal fin. Two dorsal fins (often with spines). 7 families.
Heterodontiformes:
Anal fin present, both dorsal fins have spines. 1 family.
Orectolobiformes:
Anal fin, two spineless dorsal fins. Barbels on nostrils.
7 families.
Lamniformes:
Anal fin, two spineless dorsal fins, mouths reach back behind
eyes, no nictitating eyelid. 7 families.
Carcharhiniformes:
Anal fin, two spineless dorsal fins, mouths reach back behind
eyes, nictitating eyelid. 8 families.
Squatinaformes:
No anal fin, two dorsal fins without spines set well back
near the tail. Flattened ray-like body. 1 family.
Pristiophoriformes:
Sawsharks are distinctive with a long snout edged with sharp,
straight teeth. 1 family.
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