Subphylum Vertebrata – Early Fishes and Extant Jawless Fishes Subphylum Characteristics (all present in lamprey’s ammocoete larvae; most also with vertebrae): cranium, chambered heart, tripartite brain with pituitary gland, paired sense organs, paired pronephric kidneys, liver with gallbladder, and pancreatic tissue Early Fishes (fishes = all non-tetrapod vertebrates ; present by early Cambrian) Ostracoderms: armored, jawless fishes; included heterostracans (lacked paired fins), osteostracans (with paired fins), and anaspids (streamlined); all extinct by end of Devonian Conodonts: only known from tooth-like fossils until impressions discovered in 1980s Placoderms: heavily armored, jawed fishes (early Gnathostomes); extinct at Devonian Acanthodians: fins with spines; ancestors of today’s bony fishes; extinct at Permian Agnathans (Extant Jawless Fishes) Hagfishes (Class Myxini): marine scavengers and predators; exude copious amounts of mucous when disturbed; knotting behavior; fishery for eel- skin products Lampreys (Class Petromyzontida): suck on stones to maintain position and for building nests; marine forms are anadromous (spawn in streams); parasites (invasion of Great Lakes led to collapse of fisheries)

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Table 23.1

Fig. 24.1

Fig. 24.2

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Fig. 24.3

Fig. 24.4

Fig. 24.5

Fig. 24.6

Cartilaginous Fishes – Diversity and Taxonomy Class Chondrichthyes (cartilaginous skeleton with chondrocranium and jaws; mineralized teeth, scales, and spines) Subclass Elasmobranchii: sharks, skates, and rays (~937 species; most marine) Order Carcharhinoformes: incl. catsharks (largest family); smoothhounds; requiem sharks (incl. reef sharks, hammerheads, blue, bull, and tiger sharks) Order Lamniformes: incl. mackerel sharks (white, mako); thresher sharks (long tail); sandtiger sharks; basking and megamouth sharks (filter feeders) Order Squaliformes: dogfish sharks; incl. many deep-sea families (gulper and lantern- sharks, cookie-cutter shark); sleeper, Greenland, and pygmy sharks Order Hexanchiformes: include frilled, sixgill, and sevengill sharks Order Squatinoformes: angelsharks; ambush predators Order Heterodontiformes: bullhead sharks (incl. horn shark); diet includes sea urchins Order Orectolobiformes: wobbegongs; carpetsharks (incl. bamboosharks, many popular aquarium species); nurse, zebra, and whale sharks (largest fish) Order Pristiophoriformes: sawsharks; saw used for prey capture Order Rajiformes (skates): ray-like body lacking stinger; many deep-sea species; electrogenic organs in tail (used for communication) Order Myliobatiformes (rays): most with venomous barb on tail; include bat rays, eagle rays, electric rays, mantas; some freshwater species Subclass Holocephali: chimaeras (ratfishes); deep-sea, bioluminescent, venomous spines; upper jaws fused to cranium; “living fossils”

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Fig. 24.7

Figs and 24.13

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Sharks and Stingrays – Form and Function External Anatomy Most with streamlined bodies and countershading; placoid scales (dermal denticles) reduce drag; paired fins (pectoral fins provide hydrodynamic lift, attached to head in rays; pelvic fins with two claspers in males, allowing sperm transfer); 5-7 gill slits (spiracles in benthic forms); multiple rows of teeth (not rooted in jaw) Sense Organs and Sensory Reception Eyes large, with tapetum lucidum in nocturnal forms; many with nictitating membrane; nostrils for chemoreception; lateral-line system of neuromasts for detection of near-field water movements (rays with additional internal/ closed canals); hearing attuned to pulsed, low-frequency sounds (e.g., struggling fish); ampullae of Lorenzini concentrated around head, detect electrical fields emitted from prey and magnetic fields (local, global) Internal Anatomy Large, oily liver provides buoyancy; efficient spiral valve intestine; rectal gland (aids kidney in excretion); lamnid sharks are warm blooded (with proximal arteries, red muscle, rete mirabile, & ram-gill ventilation) Reproduction: some sharks and all skates oviparous (lay egg cases), many ovoviviparous, some viviparous (with placenta); some with oophagy and/or oviphagy in uterus; late age of maturity and low fecundity (“K-selected”)

Fig. 24.8

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Sharks and Stingrays – Behavior, Ecological Importance, and Human Interactions Behavior (see sensory reception notes in previous slide) Feeding: many feed during twilight periods (crepuscular); teeth sharp for piscivores, flattened in rays, serrated edges with white, bull, and tiger sharks; electroreception helps guide bites; upper jaw not attached to skull (protrusion possible) Mating: males bite females (have thicker skin) during copulation; young often develop in coastal wetlands; no parental care (females may refrain from eating in nurseries) Movements: may use local and global magnetic fields as cues (ex. scalloped hammerheads in Sea of Cortez); vertical migrations with many (ex. megamouth) Ecological Importance (a healthy ocean has sharks in it ) Sharks are usually top predators; affect population structures of fish and invertebrate prey (ex. crash of Atlantic large sharks led to increase in small shark species) Human Interactions Shark Attack: severe injuries with white, tiger, bull, and oceanic white-tip sharks; white sharks attack silhouettes of pinniped prey, ensanguinate prey after initial strike by dragging underwater, often reject humans after initial bite; oceanic white-tip sharks may seldom feed and may attack anything edible when located (ex. U.S.S. Indianapolis) Sharks and Cancer: sharks resistant to mutagens; cartilage pills sold as a result of best-selling books and anti-angiogenic qualities of cartilage (clinical trials have disproved value) Over-fishing and Conservation: especially a result of fin and cartilage trades; some species and areas protected; ecotourism popular among divers (ex. shark and ray feeding dives)