Agnatha & Early Fish

Describe, from the earliest to latest event, the early fish timeline:

vertebrates split from urochordata cambrian, gnatha split from agnatha early Silurian, actino split from sarco late silurian

What are the placoderms? What clade are they from?

armored fishes from gnathostomes

Describe the placoderms (6 features):

heavy dermal armor on heady/middle, gnathal plates instead of teeth, part bone-cartilage skeleton, first paired appendages, nostril & eyes dorsal, Devonian extinction

What are Chondrichthyes? To what clade do they belong?

cartilaginous fish, gnathostomes

Describe Chondrichthyes (6 features):

cartilage in skeleton, cartilage replaces notochord, pectoral & pelvic fins connected ventral but not spinal, tooth-like placoid scales, ampullae of Lorenzini, no swim bladder

What are Ampullae of Lorenzini?

electroreceptive organ in snout that detects water movement

Which Chondrichthyes doesn’t have a notochord replaced with cartilage?

holocephali

What are Osteichthyes? To what clade do they belong?

bony fishes & tetrapods, gnathostomata

Describe Osteichthyes (7 characters):

largest clade of late Silurian, bone replaces cartilage skeleton, dermal boned skull roof, operculum, & fin supports, swim bladder, truth enamel/dentin teeth

What are the 7 clades of agnatha?

osteostraci, pteraspidomorphi, cyclostomata, petromyzontida, myxini conodonta, anaspida

Agnatha 4 Characteristics:

no jaws or paired appendages, cartilaginous endoskeleton, 1 median nostril, 2 semicircular canals

What are the Osteostraci? To what clade do they belong?

extinct jawless armored fishes, agnatha

Describe the Osteostraci:

extinct, large bony headshield with lateral-line-like canal, paired pectoral & unpaired pelvic, hypocercal tail, single median nasohypophyseal

What is a hypocercal tail?

asymmetrical, larger lobe on bottom

What is a nasohypophyseal?

nostril-like, not a true nostril

Are pectoral, pelvic, or both fin types paired in Osteostraci?

just pectoral

What are Pteraspidomorphi? How do they differ from Osteostraci?

extinct jawless armored fishes, have no paired fins but osteostraci have paired pectoral

What are the 3 traits of Pteraspidomorphi?

head & body covered in dermal bony plates, no paired fins, median fins

What is the clade Cyclostomata? What clade does it belong to?

living lamprey & hagfish, agnatha

What are the 5 traits of Cyclostomata?

about as old as tetrapods, no jaws or paired fins, 1 median nostril, thin tissue regulates water flow, 7 gill pouches & no perculums

What are the two important taxa of Cyclostomata?

petromyzontida (lamprey) & myxini (hagfish)

What are Petromyzontida? What clades do they belong to?

lampreys, are agnathan & cyclostomatas

What are the 5 features of Petromyzontida?

no jaws dermal bones or paired fins, eel-like bodies, circular mouth discs, keratin tooth plates, semelparous life cycle

What is a semelparous life cycle?

1 reproductive cycle before death

Describe the feeding strategies of Petromyzontida:

most aren’t parasites, filter feeders, some don’t eat as adults

What are Myxini? What clades do they belong to?

hagfish, agnathan & cyclostomata

What are the 5 features of Myxini?

elongated body, no scales jaws paired fins, produce defensive slime, isosmotic blood, scavengers/detritivores

What are Conodonta? To what clade do they belong?

conodonts, belong to agnatha

Describe the 10 features of Conodonta:

extinct cambrian to triassic, tooth-like parts made of phosphate, soft bodies, notochord, myomere muscle, eyes, fins, no jaws, move independently of water currents, stem vertebrates

What is a stem-vertebrate?

extinct, branch off line leading to modern verts

What are Anaspida? To what clade do they belong to?

lighter armored fishes, agnatha

What are the 8 features of Anaspida?

extinct, streamlined body w/o heavy armor, rhomboid scales, no large headshields, 6-15 gill openings, hypocercal tail, no paired fins, agile midwater swimmers