L8 - Agnathans and Fish

Question 1

What is the subphylum vertebrata?

Answer 1

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.

Question 2

What are the Agnathous?

Answer 2

No Jaws
Super class Agnatha
Class - Myxini, pteraspidomorphi, petromyzontida.

Question 3

What are the Gnathostomate?

Answer 3

Jaws present
Superclass Gnathostomata
Class - Placodermi, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, Mammalia.

Question 4

What are the early vertebrates?

Answer 4

Conodonts (500-150mya). Fossilised ‘teeth’ of conodonts. Astrapis, a pteraspid ostracoderm ca. 450mya.

Question 5

What are the Agnathous - No Jaws (Superclass Agnatha?

Answer 5

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.

Question 6

What are the Superclass Agnatha?

Answer 6

Conventional classification of the agnathous vertebrates. Class myxini (hagfishes), the pteraspids and other ostracoderms (pteraspidomorphi or diplorhina). Class petromyzontida (monorhina).

Question 7

What are the class Myxini?

Answer 7

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.

Question 8

What are the class Pterapsids?

Answer 8

Found in cambrian deposits from 540-350mya. Shielf made of dermal bone. Fed by scoop like action of head shield.

Question 9

What are the class Ostracoderms?

Answer 9

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.

Question 10

What are the class Petromyzontida (lampreys)?

Answer 10

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.

Question 11

What is the infraclass Gnathostomes?

Answer 11

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.

Question 12

What are the class Placoderms?

Answer 12

Armoured placoderms - earliest gnathostomes in fossil record. Dominated marine and freshwater habitats. Bottom feeders and predators. Appear 420mya, extinct 359mya.

Question 13

What are the class Chondrichthyes, subclass Elasmobranchii (sharks and rays)?

Answer 13

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

Question 14

What are the class Chondrichthyes, subclass Elasmobranchii (sharks and rays)? What do all chondrichthyes have?

Answer 14

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’.

Question 15

What are the class Chondrichthyes, subclass Elasmobranchii (sharks and rays)? Oviparous vs Viviparous species?

Answer 15

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.

Question 16

What are the class Chondrichthyes, subclass Elasmobranchii (sharks and rays)? How many species?

Answer 16

Around 500 species, skates and rays specialised for bottom dwelling. Common skate (Dipturus batis), Manta ray (Manta birostris).

Question 17

What are the class Chondrichthyes, subclass Holocephali (chimaeras or ratfishes)?

Answer 17

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)

Question 18

What are the class Teleostomi, class Acanthodii?

Answer 18

Spiny sharks share features with bony fishes and cartilaginous fishes.

Question 19

What are the superclass osteichthyes (bony fishes)?

Answer 19

> 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.

Question 20

External features of fish?

Answer 20

Operculum, lateral line, spinous dorsal fin, soft dorsal fin, caudal fin, anal fin, pelvic fins, pectoral fin.

Question 21

What are the superclass osteichthyes (bony fishes), class Actinopterygii (ray-finned fishes)?

Answer 21

> 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.

Question 22

What are the superclass osteichthyes (bony fishes), class Actinopterygii (ray-finned fishes)? What are the three subclasses?

Answer 22

Chondrosteans, Neopterygians, Teleosts

Question 23

What are the superclass osteichthyes (bony fishes), class Actinopterygii (ray-finned fishes)? What are the chondrosteans

Answer 23

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.

Question 24

What are the superclass osteichthyes (bony fishes), class Actinopterygii (ray-finned fishes)? What are the Neopterygians?

Answer 24

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.

Question 25

What are the superclass osteichthyes (bony fishes), class Actinopterygii (ray-finned fishes)? What are the Teleosts?

Answer 25

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.

Question 26

What are the class sacropteygii (lobe-finned fishes)?

Answer 26

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

Question 27

How do fish move in water?

Answer 27

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

Question 28

What is body/caudal fin locomotion?

Answer 28

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

Question 29

What happens in anguilliform fish?

Answer 29

The whole body moves in a sinusoidal 'wave'.

Question 30

What happens in ostraciiforms?

Answer 30

Only the tail fin itself moves, whilst the body remains still.

Question 31

What are the other 3 like?

Answer 31

The 3 intermediate forms of body movement are grades between these two extremes.

Question 32

Buoyancy in fish?

Answer 32

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.

Question 33

What is buoyancy in physostomous fishes?

Answer 33

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.

Question 34

What is buoyancy in physoclistous fishes?

Answer 34

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

Question 35

Migration?

Answer 35

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.