class chondricthyes chimaeras, sharks, rays the cartilaginous fishes most primitive living...
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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