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Superclass Agnatha

Classes Myxini and Cephalaspidomorphi

Characteristics of Superclass Agnatha

lack a jaw; no paired fins; no scales; persistent notochord

Class Myxini


Characteristics of Class Myxini

teeth on tongue; naked skin; fibrous and cartilaginous skeleton; 2 chambered heart (ventricle, atrium) & accessory hearts; pronephric & mesonephric kidney; no stomach; nervous system (no cerebellum, eyes degenerate, 10 pairs of cranial nerves); no larval stage- direct development

Characteristics of Class Cephalaspidomorphi

no jaws (mouth with circular sucker like structure with lots of teeth); pineal eye (third eye for orientation); persistent notochord; cartilaginous skeleton; two median fins, no paired appendages; two-chambered heart (blood with specialized cells- leucocytes, nucleated erythrocytes); gills as adults; mesonephritic kidney; brain with 10 cranial nerves; small cerebellum; poikilothermic (cold blooded)

Class Chondricthyes

chimarras, sharks, rays-- The cartilaginous fishes; most primitive living vertebrates that have a complete vertebra, movable jaws, and paired appendages

Chordate characteristics of Class Chondricthyes

Persistent notochord w/cartilaginous skeleton; dorsal hollow nerve cord protected in cartilaginous skeleton; heterocercal post-anal tail; 5-7 gill arches; thyroid gland (?)

Characteristics of Class Chondricthyes

Paired pectoral and pelvic fins; Pectoral and Pelvic girdles; pelvic fins in males modified as "claspers"; two median dorsal fins

Placoid scales

scales with spiny points; are modified anteriorly to form replaceable rows of teeth- resemble teeth of higher vertebrates-- these originate from the same tissues as teeth

Other characteristics of Class Chondricthyes

Spiral valve in intestine (increases surface area & efficiency of digestion); two-chambered heart (atrium & ventricle); well developed brain with 10 sets of cranial nerves and well developed olfactory bulbs

Locomotion in Class Chondricthyes

No swim bladder or lung (can't rest suspended in water column, must swim); heterocercal tail: provides thrust & lift; paired fins: provide lift

Reproduction in Class Chondricthyes

Dioecious; gonads paired, internal fertilization; development one of three types (oviparous, ovoviviparous, viviparous)

Oviparous development

lay eggs

Ovoviviparous development

eggs retained in uterus without attachment to female

Viviparous development

eggs attach and get nutrients directly from female

Three types of kidneys in vertebrates

pronephritic, mesonephritic, metanephritic

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

Sensory Systems

Nostrils (nares): not connected to mouth cavity; have two nasal sacs; lateral line system: vibrations and currents in water; Ampullae of Lorenzini: electromagnetic forces

Digestive tract

Well developed; mouth, pharynx, esophagus, stomach, liver, pancreas, intestine w/spiral valve

Osmoregulation in Chondricthyes

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 their tissues-- to prevent water loss they retain nitrogenous wastes in blood; this elevates solute conc. in blood to be slightly higher than sea water and therefore they will not lose water passively

Advances over Agnathans

2 pairs of lateral fins; movable jaws; enamel-covered teeth; scales; 3 semicircular canals (inner ear)- agnathans had two; paired reproductive organs and ducts

Features Primitive to Bony Fishes

Cartilage skeleton; placoid scales; separate gill clefts- no operculum; spiracle to pharynx; no air bladder

Superclass Osteichthyes

bony fishes

Two subclasses in Superclass Osteichthyes

Actinopterygii (ray-finned fishes); Sarcopterygii (lobe-finned fishes)

Class Actinopterygii

bony dermal scales: ganoid, cycloid and ctenoid; notochord- persists in some, absent in others; bony skeleton & paired fins; well developed skull with 60 bones; homocercal tail; operculum covering gills- more effective respiration; 2 chambered heart, 4 pairs of aortic arches

Swim Bladders

Most Actinopterygii have a swim bladder; some have lost it-- probably evolved from lungs of primitive bony fishes

Functions of swim bladders

Can maintain position in water column w/o expending much energy; a buoyancy device

Ancestral swim bladders

were attached to the esophagus by a pneumatic duct through which air is gulped or expelled; some fish such as trout have this type of bladder

Advanced swim bladders

separate from the esophagus; gas is added by the gas gland and its rete mirabilis (the "wonderful net") and absorbed from the bladder by the ovale

Osmoregulation in Actinopterygii

mesonephritic kidney; freshwater fishes are hyperosmotic to environment- tend to gain water, lose salt; kidney produces dilute urine to eliminate excess water; gills pump salts from water to blood; marine fishes are hypoosmotic to sea water- tend to gain salt and lose water; swallow water and unwanted salts are disposed of in two ways: salt excretion by gills; salt voided with feces

Reproduction in Actinopterygii

Sexes separate; fertilization usually external- most oviparous, some ovoviviparous; some species, such as wrasses, change sexes in their lifetime

Two types of breeding migration

Anadromous, catadromous

Anadromous migration

migrating from salt water to freshwater to reproduce; spend adult life in sea; ex. salmon (born in freshwater then migrate to sea when reach adulthood migrate back to spawning grounds)

Catadromous migration

migrating from freshwater to salt water to reproduce; spend adult life in freshwater; ex. eels (born in Sargassum Sea migrate to rivers)

Feeding in Fishes

Carnivorous, herbivorous, omnivorous, filter feeders, scavengers

Fish Mouth Morphology

Allows diverse feeding niches; position of mouth: terminal, subterminal, dorsal, ventral

Class Sarcopterygii

Have a fleshy lobe at base of paired fins- precursor of appendage to support body; diphycercal tail; includes lungfishes, coelacanth

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