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

Chondricthyescharacteristics

• Paired pectoral and pelvic fins;

• - pelvic fins in males modified as "claspers"

• two median dorsal fins

Chondricthyescharacteristics

• 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

Chondricthyescharacteristics

• 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

Chondricthyescharacteristics

• 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

Chondricthyescharacteristics

• 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

Chondricthyescharacteristics

• 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.

Chondricthyescharacteristics

• Lateral line system; – vibrations and

currents in water

• Ampullae of Lorenzini– Electromagnetic

forces

Chondricthyescharacteristics

• Digestive tract well developed:

• - mouth- pharynx- esophagus- stomach- liver- pancreas- intestine- spiral valve

• rectal gland-– functions in regulating salt

content of blood

Chondricthyescharacteristics

• 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

Chondricthyescharacteristics

• 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

Chondricthyescharacteristics

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

Chondricthyescharacteristics

• 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.

Chondricthyescharacteristics