Chondrichthyes

Holocephali:Chimera Chimaeras are cartilaginous fish in the order Chimaeriformes. They are related to the sharks and rays, and are sometimes called ghost sharks, ratfish (not to be confused with the "rattails"), or rabbitfishes. Chimaeras live in temperate ocean floors and grow up to two meters long. Like other members of the class Chondrichthyes, chimaeras have a skeleton constructed of cartilage. Their skin is smooth and lacks scales, and their color can range from black to brownish gray. For defense, most chimaeras have a venomous spine located in front of the dorsal fin. Chimaeras resemble sharks in some ways: they employ claspers for internal fertilization of females and they lay eggs with leathery cases. They differ from sharks in that their upper jaws are fused with their skulls; they have separate anal and urogenital openings; and they lack the many sharp and replaceable teeth of sharks, having instead a few large permanent grinding tooth plates. In some classifications the chimaeras are included (as subclass Holocephali) in the class Chondrichthyes of cartilaginous fishes; in other systems this distinction may be raised to the level of class. Chimaeras also have some characteristics of bony fishes. There are about forty species in six genera and three families:

The Chondrichthyes or Cartilaginous fishes jawed fish with paired fins, paired nostrils, scales, two-chambered hearts, and skeletons made of cartilage rather than bone. Animals from this group have a brain weight relative to body size that comes close to that of mammals, and is about ten times that of bony fishes. A spiracle is found behind each eye on most species. Their digestive systems have spiral valves (allows for better digestion and more mineral absorption). With the exception of Holocephali, they also have an anus. As they do not have bone marrow, red blood cells are produced in the spleen and special tissue around the gonads. They are also produced in an organ called Leydig's Organ which is only found in cartilaginous fish. There are exceptions: the mormyrid bony fish have a relative brain size comparable to humans. One of the explanations for their relatively large brains is that the density of nerve cells is much lower than in the brains of bony fishes, making the brain less energy demanding and allowing it to be bigger.

ELASMOBRANCHII sharks, rays, & skates Elasmobranchii have no swim bladders Five to seven pairs of gill clefts which open individually to the exterior Rigid dorsal fins and small placoid scales Widely distributed throughout tropical and temperate waters

Chondrichthyes Internal Anatomy Cartilaginous endoskeleton instead of bone. No lungs or swim bladder - buoyancy is maintained mainly by large reserves of liver oil. Respiration by means of five to seven pairs of gills with separate and exposed gill slits, no operculum. Circulatory system includes a two chambered heart and the system is closed.

Digestive system - intestine is short but spiraled so that nutrient absorption increases. Unlike fish, sharks and rays reproduce like mammals. They have internal fertilization. Oviparous (egg hatches outside) Ovoviviparous (egg hatches inside, young “born alive”) Viviparous (live bearing)

Chondrichthyes: Reproduction & Behavior

Sharks (Reproduction) Sexually dimorphic (differences between male and female bodies) Mating: Male shark will follow female shark closely, then bite female pectoral fin. The male then inserts his claspers into the female’s cloaca. Fertilization occurs internally. Either lay eggs or give live birth

Rays and Skates (Reproduction) Rays display internal fertilization They give birth to live young Skates lay flat, rectangular eggs enveloped by a leathery shell

Sharks (Behavior) Some sharks can be highly social, remaining in large schools Others are solitary, and live benthic lives Complex migratory patterns Highly territorial Threat display to ward off potential predators (consists of exaggerated swimming movements)

Rays and Skates (Behavior) Most species live on the sea floor Rounded teeth for crushing bottom dwelling species for food Only a few species live in the open sea (Manta rays) Manta rays feed on plankton