Class Chondricthyes chimaeras, sharks, rays The cartilaginous fishes Most primitive living vertebrates that have: –complete vertebra –movable jaws –paired appendages

Chondricthyes Most are predacious, some such as the whale shark is a filter feeder. None have a swim bladder –adapted to bottom dwelling –Or predators in water column

Placoid scales- scales with spiny points –are modified anterior to form replaceable rows of teeth- resemble teeth of higher vertebrates –originate from same tissues as teeth Other types of scales include: –primitive bony fishes- Ganoid Scales –more advanced bony fishes Ctenoid scales- Cycloid scales Chondricthyes characteristics

Paired pectoral and pelvic fins; - pelvic fins in males modified as "claspers" two median dorsal fins Chondricthyes characteristics

Types of tails in fishes: –heterocercal tail- most primitive form; spinal column turns up (dorsad) in fin –diphycercal tail- spinal column goes straight into fin –homocercal tail- fin located behind spinal column Chondricthyes characteristics

Nostrils (nares)- - not connected to mouth cavity; - have two nasal sacs. Spiral valve in intestine; - increases surface area & efficiency of digestion. Notochord persists Heart is two chambered; - atrium & ventricle Chondricthyes characteristics

respiration done by 5-7 pairs of gills No swim bladder or lung. Fairly well developed brain; –with 10 pairs of cranial nerves; –well developed olfactory bulbs Chondricthyes characteristics

Sexes separate; gonads paired; have a cloaca; development one of three types: –oviparous - i.e., lay eggs –ovoviviparous- eggs retained in uterus without attachment to female –viviparous- eggs attach and get nutrients directly from female. Some sharks possess uteri with very primitive placentas Chondricthyes characteristics

Three types of kidneys in vertebrates: –pronephritic kidney: functional kidney of adult hagfishes, and the embryos of some higher vertebrates –mesonephritic kidney: functional kidney of sharks and bony fishes; collecting duct is the Wolffian Duct, also carry sperm. –metanephritic kidney: functional kidney of birds reptiles and mammals; is drained by a ureter. Chondricthyes characteristics

Lateral line system; –vibrations and currents in water Ampullae of Lorenzini –Electromagnetic forces Chondricthyes characteristics

Digestive tract well developed: - mouth - pharynx - esophagus - stomach - liver - pancreas - intestine - spiral valve rectal gland- –functions in regulating salt content of blood Chondricthyes characteristics

Ancestor of these fishes evolved in freshwater –Sea water is hyperosmotic (i.e., salt conc. of blood less than that of seawater) so they have a problem of losing water from there tissues. to prevent water loss they retain nitrogenous wastes in blood; –this elevates salt conc. in blood to be slightly higher than sea water, –and therefore they will not lose water passively; –rectal gland helps keep this balance Chondricthyes characteristics

Features that are more advanced than Agnathans (Cyclostomates) –Scales –2 pairs of lateral fins –moveable jaws –enamel covered teeth –3 semicircular canals (inner ear)- agnathans had two –paired reproductive organs and ducts Chondricthyes characteristics

Features that make them more primitive than boney fishes: –Cartilage –placoid scales –separate gill clefts –spiracle to pharynx –no air bladder Chondricthyes characteristics

Interesting trivia about sharks –Have very large livers 20% of body weight can be liver oil- called squalene; –use as fuel for long term swimming or cruising. –Squalene important commercially in Japan as a cosmetic and aphrodisiac. Chondricthyes characteristics