2 Sharks: The Animal Answer Guide
ras) have evolved during their 400-million-year history. It is also worth re-
membering that these answers are the result of careful research conducted
by shark biologists over the decades.
The chondrichthyan fishes include several groups whose names can
sometimes be confusing at first. The table provides a quick listing of terms
applied to the different groups of these related but diverse fishes and the
traits they share.
Glossary of terms used with chondrichthyan (sharklike) fishes
Batoids Skates, rays, guitarfishes, and sawfishes
Cartilage Non-bony but calcified skeletal material
Claspers Paired cartilage-supported male reproductive organs derived from
pelvic fins
Chimaeras Odd relatives (Holocephali) of the elasmobranchs; also known as
ratfishes, rabbitfishes, and ghost sharks
Chondrichthyans All sharklike fishes, including selachian sharks, batoid skates and
rays, and chimaeras
Denticles The scale type in sharklike fishes; technically, they are enamel-
covered structures and are referred to as placoid scales
Elasmobranchs Sharks, skates, and rays (but not chimaeras) with a slightly calcified
cartilaginous skeleton, internal fertilization via modified pelvic fins,
rows of replaceable teeth embedded in the connective tissue of jaws
rather than in the jaw “bones” themselves, and scales (denticles)
modified from tooth forerunners
Gill slits External gill openings, typically five but as many as seven in
elasmobranchs, one in chimaeras
Guitarfishes A family of elongate rays with pronounced, pointed snouts
Rajiforms The order of batoids made up of guitarfishes and skates
Rays Several families of batoids that bear live young and have a long,
whiplike tail, often with poisonous barbs
Sawfishes A family of large, elongate rays with very pronounced, tooth-
studded snouts
Sawsharks A family of small, elongate sharks with very pronounced, tooth-
studded snouts
Selachians The group of elasmobranchs that includes sharks and sawsharks but
not the batoid skates and rays
Skates A family of rajiforms that lay eggs in cases (“mermaid purses”) and
have a thick tail with two small dorsal fins and a tail fin
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