L8 - Agnathans and Fish Flashcards
What is the subphylum vertebrata?
Cranium (protects brain). Vertebral column (bone and/or cartilage). Highly developed tripartite brain. Forebrain - olfaction, midbrain - vision, hindbrain - hearing. Development of neural crest (involved in the formation of part of the head.
What are the Agnathous?
No Jaws
Super class Agnatha
Class - Myxini, pteraspidomorphi, petromyzontida.
What are the Gnathostomate?
Jaws present
Superclass Gnathostomata
Class - Placodermi, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, Mammalia.
What are the early vertebrates?
Conodonts (500-150mya). Fossilised ‘teeth’ of conodonts. Astrapis, a pteraspid ostracoderm ca. 450mya.
What are the Agnathous - No Jaws (Superclass Agnatha?
Features of extant (living) agnathans. No jaws; instead the mouth is a simple cup surrounded by either tentacles or an adhesive disc with ‘teeth’. True (i.e. socketed, heterodont) teeth are absent. Paired fins are absent, single nostril. Scale-less smooth body (but lots of mucous). Skeleton of cartilage (not bone). Persistent notochord. Pore-like gill openings along side of body.
What are the Superclass Agnatha?
Conventional classification of the agnathous vertebrates. Class myxini (hagfishes), the pteraspids and other ostracoderms (pteraspidomorphi or diplorhina). Class petromyzontida (monorhina).
What are the class Myxini?
Part of the Agnathous, hagfish about 20 species; 300mya. Elongate, scaleless eel-like bodies. Entirely marine, deep water. Scavengers and predators. Produce large amounts of slime. Can tie itself in knots to increase leverage.
What are the class Pterapsids?
Found in cambrian deposits from 540-350mya. Shielf made of dermal bone. Fed by scoop like action of head shield.
What are the class Ostracoderms?
Not a monophyletic group. Possessed heavy bony armour-plating over the head. Small scales, dominated freshwater systems. Probably sediment feeders. Appeared 470 mya, extinct 359mya.
What are the class Petromyzontida (lampreys)?
About 38 species. Elongate, scale-less eel-like bodies. Found in fresh and saltwater. Toothed funnel-like sucking mouth. Larvae called ammocoetes (suspension feeders). All are anadromous. Some parasitic as adults.
What is the infraclass Gnathostomes?
Jaws evolved from skeletal supports of the pharyngeal slits. Evolved once in vertebrate history, in addition to opposing jaws, living gnathostomes: teeth, paired appendages, modifications to ear.
What are the class Placoderms?
Armoured placoderms - earliest gnathostomes in fossil record. Dominated marine and freshwater habitats. Bottom feeders and predators. Appear 420mya, extinct 359mya.
What are the class Chondrichthyes, subclass Elasmobranchii (sharks and rays)?
The largest and most diverse subclass of chondrichthyes. Cartilaginous fishes. Sharks : most streamlined fast swimmers, heterocercal tail, placoid scales, rows of ever-growing teeth, jaw not fused, spiral valve in intestine for absorption, large fatty liver aids buoyancy. Prey initially identified using large olfactory organs. Mechanoreceptors in the lateral line system sense low-frequency vibration from far away. Vision is important at close range. Bioelectric fields surrounding their prey detected using electroreceptors in the ampullae of Lorenzini
What are the class Chondrichthyes, subclass Elasmobranchii (sharks and rays)? What do all chondrichthyes have?
Internal fertilisation, males have claspers. Oviparous species (e.g. zebra shark) lay large yolky eggs soon after fertilisation. Some lay eggs in a capsule called a ‘mermaids purse’.
What are the class Chondrichthyes, subclass Elasmobranchii (sharks and rays)? Oviparous vs Viviparous species?
Oviparous species: embryo retained in the uterus nourished by yolk - no placenta (e.g. great white shark). Viviparous species: embryo receives nourishment through a placenta (e.g. hammerhead shark). Some receive additional nutrition by eating eggs & siblings. Parental care ends as soon as eggs laid or young are born. Pups born with full set of teeth.
What are the class Chondrichthyes, subclass Elasmobranchii (sharks and rays)? How many species?
Around 500 species, skates and rays specialised for bottom dwelling. Common skate (Dipturus batis), Manta ray (Manta birostris).
What are the class Chondrichthyes, subclass Holocephali (chimaeras or ratfishes)?
About 50 species. A second subclass is composed of a few dozen spp; the chimaeras, or ratfishes. Flat plates instead of teeth, upper jaw fused to cranium, largely confined to deep oceans. Plough-nosed (Callorhinchus mili)
What are the class Teleostomi, class Acanthodii?
Spiny sharks share features with bony fishes and cartilaginous fishes.
What are the superclass osteichthyes (bony fishes)?
> 28,000 species. Endochondral bone replaces the cartilage during development. Operculum - bony flap protects four or five gill pairs. Monophyodont teeth. Most have two sets of jaws. A swim bladder is present for buoyancy (and respiration in some). Not a monophyletic group. Moray eel.
External features of fish?
Operculum, lateral line, spinous dorsal fin, soft dorsal fin, caudal fin, anal fin, pelvic fins, pectoral fin.
What are the superclass osteichthyes (bony fishes), class Actinopterygii (ray-finned fishes)?
> 23,600 species. Ray-finned fishes contain all the familiar bony fishes. These fins, supported mainly by long, flexibe rays are modified for maneuvering, defense, and other functions.
What are the superclass osteichthyes (bony fishes), class Actinopterygii (ray-finned fishes)? What are the three subclasses?
Chondrosteans, Neopterygians, Teleosts
What are the superclass osteichthyes (bony fishes), class Actinopterygii (ray-finned fishes)? What are the chondrosteans
Heterocercal tail, ganoid scales. Atlantic sturgeon: 27 species, europe, asia, NA, freshwater/coastal marine, many anadromous. Bichir: 11 species, africa, freshwater. American paddlefish: 2 species, NA and china, mostly scaleless, elongate snouts & electroreceptors.
What are the superclass osteichthyes (bony fishes), class Actinopterygii (ray-finned fishes)? What are the Neopterygians?
Bownfins & Gars. Bowfins: 1 species, NA, freshwater, large rivers. Short heterocercal fin. Swim bladder capable of respiratory function. Gars: 7 species, mostly central america, freshwater, uniquely elongated snout, lurking ambush predators.
What are the superclass osteichthyes (bony fishes), class Actinopterygii (ray-finned fishes)? What are the Teleosts?
Changes in fins - increased maneuverability and speed. Symmetrical, homocercal tail - allows increased speed. Approximately 20,800 species, worldwide. Thinner and lighter cycloid and ctenoid scales - greater flexibility. Fins diversified for a variety of functions: camouflage, communication, complex movements, streamlining.
What are the class sacropteygii (lobe-finned fishes)?
Include 2 species of coelacanths and 6 species of lungfishes. All early sarcopteygians had lungs, gills and a heterocercal tail. Developed continuous flexible around tail. Some lungfishes can live out of the water for long periods of time. Rhipidistia is a group of sarcopterygians that were thought to be extinct, until rediscovered alive and well in 1926. This lineage gave rise to all the tetrapods
How do fish move in water?
Fishes use trunk and tail musculature to propel them through the water. Musculature is composed of zigzag bands called myomeres. Flexible fishes like eels use a serpentine movement. Fast swimmers are less flexible. Many swimmers are streamline with grooves so their fins can lie flat
What is body/caudal fin locomotion?
There are 5 types of locomotion in fishes, based on how much of their body is moved to produce forward movement. Anguilliform, sub-carangiform, carangiform, thunniform, ostraciiform
What happens in anguilliform fish?
The whole body moves in a sinusoidal ‘wave’.
What happens in ostraciiforms?
Only the tail fin itself moves, whilst the body remains still.
What are the other 3 like?
The 3 intermediate forms of body movement are grades between these two extremes.
Buoyancy in fish?
Unlike the elasmobranchs, bony fish (telosts) use a gas-filled space to regulate buoyancy - swim bladder. Fish must be able to regulate gas inside the swim bladder. At depth, the gas will compress and the fish will sink. As it rises to the surface, the gas will expand and the fish will rise faster. Boyle’s law P1V1 = P2V2. Gas may be removed or added in two ways.
What is buoyancy in physostomous fishes?
More primitive fishes, have a pneumatic duct that connects the swim bladder and the esophagus. Air can be expelled through the duct. Gas must be secreted into the swim bladder from the blood, although some species can gulp air to fill the swim bladder.
What is buoyancy in physoclistous fishes?
More derived, e.g. advanced telosts. Pneumatic duct absent. Gas must be absorbed by blood from the highly vascularised ovale (aka Rete mirabile). Gas is excreted into the swim bladder from the blood at the gas gland
Migration?
Freshwater eels are catadromous, they enter the ocean as adults, migrate to a spawning area where they spawn & then die. Larvae make their way back to the streams. Anadromous salmon spend their lives at sea, returning to freshwater to spawn.
