Agnathan fish Flashcards
(25 cards)
What are the key features of extant agnathans?
No jaws, paired fins, or true teeth; single nostril; cartilaginous skeleton; persistent notochord; smooth scale-less bodies; pore-like gill openings.
What classes are included in Agnatha?
Myxini (hagfish), Petromyzontida (lampreys), and extinct groups like Pteraspids and Ostracoderms.
Describe the features of hagfish.
Elongated, scaleless, eel-like; deep-sea scavengers; produce slime; no vertebrae; can tie themselves in knots for leverage.
What is the lifecycle of a lamprey?
Anadromous: larvae (ammocoetes) are suspension feeders; adults may become parasitic; reproduce in freshwater.
How do adult lampreys feed?
Use keratinised teeth and suction to attach; tongue rasps at host tissue.
How did jaws evolve?
From skeletal supports of pharyngeal slits; evolved once in vertebrates. Allowed development of teeth and paired appendages.
What were placoderms?
Extinct jawed fish with bony armour; both predators and bottom feeders; dominated marine/freshwater from 420–359 mya.
What subclasses exist in Chondrichthyes?
Elasmobranchii (sharks & rays) and Holocephali (chimaeras/ratfish).
Describe features of sharks (Elasmobranchii).
Heterocercal tail, placoid scales, rows of replaceable teeth, spiral valve, internal fertilisation, oily liver for buoyancy.
How do sharks detect prey?
Olfaction, lateral line (vibrations), vision (close range), ampullae of Lorenzini (bioelectric fields).
What are the reproductive modes in Chondrichthyes?
- Oviparous: eggs laid (e.g., zebra shark)
- Ovoviviparous: eggs hatch inside, nourished by yolk
- Viviparous: placenta nourishes embryo (e.g., hammerhead)
What are characteristics of rays and skates?
Flattened bodies, bottom-dwellers, specialized pectoral fins.
What are features of Holocephali (chimaeras)?
Flat crushing plates instead of teeth, deep-sea dwellers, upper jaw fused to cranium.
What are general features of bony fish?
Endochondral bone, operculum, swim bladder, monophyodont teeth, paired fins.
What are chondrosteans?
Primitive ray-finned fishes with ganoid scales and heterocercal tails (e.g., sturgeons).
What are neopterygians?
Intermediate group including bowfins and gars—swim bladder for respiration, ambush predators.
What are teleosts?
Modern ray-finned fishes—symmetrical homocercal tail, thin flexible scales (cycloid, ctenoid), highly diverse fins.
Key features of lobe-finned fish?
Fleshy, lobed fins; lungs and gills; coelacanths and lungfish; precursors to tetrapods.
What group gave rise to tetrapods?
Rhipidistia—a group of sarcopterygians.
What muscle structure do fish use for movement?
Myomeres—zigzag muscle bands.
What are the five types of body/caudal fin locomotion?
- Anguilliform (e.g., eels)
- Sub-carangiform
- Carangiform
- Thunniform
- Ostraciiform (tail only)
What is the function of the swim bladder?
Regulates buoyancy in bony fishes by controlling internal gas volume (Boyle’s Law: P₁V₁ = P₂V₂).
Different types of swim bladders?
- Physostomous: pneumatic duct connects to gut (gulp/expel air)
- Physoclistous: gas exchange with blood via ovale and gas gland (more advanced)
What are catadromous fish?
Live in freshwater, migrate to sea to spawn (e.g., eels).
