agnathans
Fish without jaws
Agnathans are jawless fish—the most primitive vertebrates, lacking the hinged jaws that characterize most fish and all land animals.
The group includes lampreys and hagfish, the only jawless fish surviving today, though fossils reveal many extinct forms.
The term comes from Greek words meaning "without jaw." Agnathans represent an early branch in vertebrate evolution.
Jawless parasitic fish
- hagfishJawless, slime-producing marine fish
- suctionPulling via pressure difference
- mouthOral opening
- cartilageFlexible connective body tissue
teeth · rasping · funnel · tongue · keratin · feeding · attachment · host
Earliest Paleozoic period
- PaleozoicEarly complex-life epoch
- OrdovicianPaleozoic geological period
- SilurianPaleozoic period, mid-range
- fossilsPreserved ancient organism traces
extinct · ancestors · ancestral · phylogeny · cladistics · basal · primitive · origins
Embryonic axial support structure
- cartilaginousComposed of flexible connective tissue
- soft-bodiedLacking internal skeleton
- dorsalOf the back
- bilateralInvolving two parties
symmetry · ectothermic · larvae · metamorphosis · sensory · barbels · eyeless · degenerate
lamprey
Jawless parasitic fish
cartilage · teeth · rasping · funnel · tongue · keratin · feeding · attachment · host · blood
Cambrian
Earliest Paleozoic period
- PaleozoicEarly complex-life epoch
- OrdovicianPaleozoic geological period
- SilurianPaleozoic period, mid-range
fossils · extinct · ancestors · ancestral · phylogeny · cladistics · basal · primitive · origins · paleontology
notochord
Embryonic axial support structure
- cartilaginousComposed of flexible connective tissue
- soft-bodiedLacking internal skeleton
- dorsalOf the back
bilateral · symmetry · ectothermic · larvae · metamorphosis · sensory · barbels · eyeless · degenerate · skull
marine
Relating to the sea
- freshwaterNon-saline aquatic environment
- anadromousMigrating upstream to breed
- deep-seaOf ocean depths
benthic · oceanic · sediment · burrowing · nocturnal · temperate · Atlantic · Pacific · rivers · streams