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Phylum Chordata FISH!

SP Vertebrata Largest subphylum: ~42000 species in 7 classes. Larger size and activity led to more highly developed nervous system and other characteristics. Major characteristics: • Notochord is replaced with vertebrae • All have a cartilaginous or bony skeleton (endoskeleton) • High degree of cephalization • Brain is protected by a cranium • Well developed 2-4 chambered heart • Closed circulatory system

SP Vertebrata: the amniotic egg

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Figure 34.6 One hypothesis for the evolutionary relationships among the chordates The age of Fishes: Devonian period 420-360 Million Years Ago (MYA)

28-32,000 species: more than any other group of vertebrates Freshwater species 39% Temperature range -2 to +44

Fish Diversity - 1 -

Number of families 445 Seven largest families Represent 30% of all species

Fish Diversity - 2 -

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4 classes, 1 of which is extinct: •  Agnatha (jawless) ~60 species •  Placoderms (extinct) •  Chondrichthyes (sharks, rays and chimeras)

•  Osteichthyes (bony fish)

Class Agnatha – the jawless fish

• Evolved during the Cambrian ~530 MYA

• Many, including ostracoderms (armoured plates), became extinct during the devonian - about 370 MYA

Cl. Agnatha: jawless vertebrates • About 55 species extant today: hagfish and lampreys. Have a cartilaginous skeleton, no paired fins, 2 chambered heart

• Hagfish are the only marine vertebrates that don’t osmoregulate

• Lampreys have a larval stage

• Neither has a stomach!

Hagfishes - Mixini 30-35 species Live deep – scavengers No real stomach Slime! No scales Young develop directly from eggs Only marine - isoosmotic - no osmoregulation They have a skull but no vertebral column (but a notochord)

http://www.youtube.com/watch?v=pmaal7Hf0WA

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Hagfish eat rotting and decaying animals in the deep sea

They can tie themselves in knots!

Lampreys

About 40 species Osmoregulate - found in freshwater and ocean - parasitic Larval stage called ammocoete Ammocoetes undergo metamorphosis Ammocoetes are filter feeds

Lampreys

Hematophagus feeders as adults – suck blood and fluids – anticoagulant in their saliva

Keratinized ‘teeth’

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Cl. Placoderma: armored fishes

Evolved during the Silurian: ~440 MYA Extinct. 410-350 MYA Major innovations: diversification of lifestyle and nutrients: • Hinged jaws – allowed active predation.

• Paired fins – enhanced swimming ability

Figure 34.8 The evolution of vertebrate jaws

Cl. Chondrichthyes: sharks, rays and chimeras

• Appeared about 400 MYA • 12 orders, 45 families, 800 species, half are rays, ~ 350 sp sharks • They have paired fins and biting jaws. • Cartilaginous skeletons: means they have to be big and most are. •Many use fat (not air) for buoyancy

Buoyancy: oils and fats – often concentrated in the liver

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Cl. Chondrichthyes: sharks, rays and chimeras

Other adaptations: • Body shapes-stiff fins • Ventilation of gills • Feeding • Sensory systems - lateral line and ampulae of

lorenzini • Osmoregulation - salty! urea • Reproduction

Ovovivipary - ‘live birth’ from eggs Vivipary - placental - live birth Ovipary - lay eggs

Cl. Osteichthyes: bony fishes • Bony fish and Cartilaginous fish probably both arose from the placoderms – but took very different trajectories.

Osteichthyes arose about 415 MYA:

Lobe-finned fishes (lungfish and ceolocanths) – these gave rise to the tetrapods (amphibians etc…)

Ray-finned fishes

Cl. Osteichthyes: bony fishes • 19 orders, 206 families (25,000 species) • gill cover = operculum • fin rays – bony spines that are connected by a membrane = flexible, for swimming • teeth fused to jawbone • swim bladder in many • Mucus to reduce drag and protect • Diversity of form and size!

External anatomy of a fish Caudal Fin

Pectoral Fin

Anal Fin

Dorsal Fin 1 or 2

Pelvic Fin

Gill cover: Operculum

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Modified fins

Dorsal fin

Pelvic fins

Pelvic fin

Modified fins

Anal fin

Modified fins

Caudal fin

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Other modifications Fish body form Laterally compressed Dorso-ventrally compressed ‘other’

Fish body form Fish body form

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Laterally compressed Dorso-ventrally compressed (rays)

Laterally compressed!

Fusiform: speedy Shapes

Eel-shaped

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Odd shapes Feeding: suck, pick, bite, slurp, filter feed, grind,

graze. No chewing…wrong teeth •  Generalists •  Specialists

Filter feeders

Filter feeders

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Biters: pursuit Feeding Suction Feeding

slurpers Protrusible jaw

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Pickers Ambush!

Grazers – key to many healthy ecosystems! Color: disruptive, camoflauge, advertise,

countershading

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Reproduction – live bearing viviparous Surfperch

Live birth from eggs inside the female – ovovivipary

nests Brooding – nesting ‘on the body’

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Seahorses and pipefish are brooders

Usually in this group it’s the males…

Broadcasting – sending eggs and sperm into the water column

Fish respire with a complex arrangement of gills to increase surface area, along with counter current blood flow

Respiration

Aerial respiration

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Sensory: •  Sight •  Pressure (lateral

line) •  Electromagnetic

fields (ampulae of lorenzini)

•  Chemosensory – ‘smell’

•  Otolith – ear bones - balance

schooling

Buoyancy Oils Air/gas Hydrofoil lift

Symbiosis:�mutualism – both benefit�parasitism – only one benefits and one is compromised�Commensalism – one benefits and the other is neutral

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Cleaning stations Thermal regulation

Figure 34.13 The Devonian radiation of fishes

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Lungfish

• Fleshy fins • Primitive lungs • Aestivate

Coelocanth: Latimeria

Figure 34.14 The origin of tetrapods Figure 34.21x Turtle