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10/22/13 Phylum Chordata FISH! SP Vertebrata SP Vertebrata: the amniotic egg 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 1 10/22/13 Figure 34.6 One hypothesis for the evolutionary relationships among the chordates The age of Fishes: Devonian period 420-360 Million Years Ago (MYA) Fish Diversity - 1 - 28-32,000 species: more than any other group of vertebrates Freshwater species 39% Temperature range -2 to +44 Fish Diversity - 2 - Number of families 445 Seven largest families Represent 30% of all species 2 10/22/13 4 classes, 1 of which is extinct: • Agnatha (jawless) ~60 species • Placoderms (extinct) • Chondrichthyes (sharks, rays and chimeras) • Osteichthyes (bony fish) 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! Class Agnatha – the jawless fish • Evolved during the Cambrian ~530 MYA • Many, including ostracoderms (armoured plates), became extinct during the devonian - about 370 MYA 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 3 10/22/13 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’ 4 10/22/13 Figure 34.8 The evolution of vertebrate jaws 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 Cl. Chondrichthyes: sharks, rays and chimeras Buoyancy: oils and fats – often concentrated in the liver • 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 5 10/22/13 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 • 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 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 External anatomy of a fish Caudal Fin Dorsal Fin 1 or 2 Gill cover: Operculum • swim bladder in many Anal Fin Pectoral Fin • Mucus to reduce drag and protect • Diversity of form and size! Pelvic Fin 6 10/22/13 Modified fins Dorsal fin Pelvic fins Pelvic fin Modified fins Anal fin Modified fins Caudal fin 7 10/22/13 Other modifications Fish body form Fish body form Laterally compressed Dorso-ventrally compressed ‘other’ Fish body form 8 10/22/13 Laterally compressed Dorso-ventrally compressed (rays) Laterally compressed! Fusiform: speedy Shapes Eel-shaped 9 10/22/13 Odd shapes Feeding: suck, pick, bite, slurp, filter feed, grind, graze. No chewing…wrong teeth • Generalists • Specialists Filter feeders Filter feeders 10 10/22/13 Biters: pursuit Feeding Suction Feeding Protrusible jaw slurpers 11 10/22/13 Pickers Grazers – key to many healthy ecosystems! Ambush! Color: disruptive, camoflauge, advertise, countershading 12 10/22/13 Surfperch Reproduction – live bearing viviparous nests Live birth from eggs inside the female – ovovivipary Brooding – nesting ‘on the body’ 13 10/22/13 Seahorses and pipefish are brooders Broadcasting – sending eggs and sperm into the water column Usually in this group it’s the males… Respiration Aerial respiration Fish respire with a complex arrangement of gills to increase surface area, along with counter current blood flow 14 10/22/13 Sensory: • Sight • Pressure (lateral line) schooling • Electromagnetic fields (ampulae of lorenzini) • Chemosensory – ‘smell’ • Otolith – ear bones - balance 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 15 10/22/13 Cleaning stations Thermal regulation Figure 34.13 The Devonian radiation of fishes 16 10/22/13 Lungfish Coelocanth: Latimeria • Fleshy fins • Primitive lungs • Aestivate Figure 34.14 The origin of tetrapods Figure 34.21x Turtle 17