Class Chondrichthyes
General Overview
· Cartiligenous fishes
· Three subclasses
o Sharks (elasmobranchi)
o Skates & Rays (elasmobranchi)
o Chimaeras
Habitat
· Water Habitat
· Primarily salt water (oceans)
o Reefs (common)
o Coastal Areas (common)
o Estuaries
o Open ocean (not as common)
o Muddy/sandy bottom (primarily skates & rays)
o Deep ocean (primarily chimaeras)
· Freshwater (rare)
o Large river systems - primarily in South America
o Many species are unique to only one river system
o Freshwater sharks are very rare, only 6 documented species
o Freshwater rays are more common and are often electric rays
Feeding Mechanisms
· Most sharks have large jaws that help them actively hunt prey
o Teeth often give a clue as to what they eat
o Jaws can detach from the skull, allowing for larger bites
o Hundreds of teeth are arranged in rows, constantly replacing old teeth
· Rays have a flattened and flexible snout
o Snout allows them to grub for food
o Teeth are plates that are designed to crush food such as mollusks
· Some are filter feeders
o Basking shark, megamouth shark, manta ray
· Well developed sensory organs help locate prey
o Olfactory
o Electroreception
§ Lateral line
o Eyesight
Reproduction
· Sexual
· Males (including sharks, rays, chimaeras) have claspers that hold him in place during mating
o Males can be very aggressive, surrounding a female and preventing her escape
o Males will often bite during courtship
· Females
o Have two uteruses
o Female rays have been known to store sperm until conditions are favorable for bearing young
o Pregnant females have been known to migrate to more favorable areas for young
o Rarely, mothers will protect young for a shortened period of time
· Young
o Are miniature adults - there is no larval stage
o Eggs
§ Tough, leathery, attached to substrate
o Live birth
§ Litters are of a small size
§ Pups fight within the womb; only the strongest is born
§ No placental - only a yolk
· When yolk is depleted, mother supplies nutrition
Unique Characteristics
· Senses are very well developed
o Olfactory senses
o Inner ear
§ Provides balance
§ Also allows hearing underwater
o Electroreception
§ Ampulae of Lorenzini
§ Lateral line
o Touch + taste
§ “Bite & Spit” theory
· Skin is covered in tiny scale-like structures called denticles (feels like sandpaper!)
o Offers protection
o Reduces drag
· Gas exchange occurs at the gills for sharks
· Skates and rays have spiracles in addition to gills
o Because skates & rays lie still at the bottom, and because the gills are located on the underside, the gills are poorly ventilated
Sharks
· Not all sharks are of the classic fusiform shape
o Wobbegong
· Today sharks are threatened by overfishing as a result of sport, fear (“Jaws”), and food
· The sharkfin business is destroying shark populations - the fins are cut off and the animal is thrown back into the ocean to die
Skates & Rays
· Body is flattened, with enlarged pectoral fins forming a disc
· The jaw is also flattened, often with fused teeth that are better suited to crushing and grinding
· Also has filter feeders: manta ray
· Spiracles
· Males also have claspers
· Stinging spine
· Some rays house electrical organs
Chimaeras
· Primitive group, poorly understood
· Taxonomy is debated
· Consists of ratfishes, rabbitfishes, and elephantfishes
· Live at extreme depths
· Feed on mollusks and other invertebrates
· Large pectoral fins to help them glide, large eyes, long whiplike tail
· Dorsal fin occasionally features a poisonous spine, depending on the species
Sources
· Book: “The Nature Company Guides: Sharks & Rays” by multiple authors: Tricas, Deacon, Last, McCosker, Walker, Taylor
· Book: “Smithsonian Institution: Animal” Edited by David Burnie & Don E. Wilson
· Wikipedia: http://en.wikipedia.org/wiki/Holocephali
· Wikipedia: http://en.wikipedia.org/wiki/Chondrichthyes
· Seaworld.org: http://www.seaworld.org/animal-info/info-books/sharks-&-rays/anatomy.htm
DONE