Subphylum Vertebrata – Early Fishes and Extant Jawless Fishes

1. 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 kidneys, liver with gallbladder, and pancreatic tissue • Early Fishes (present by early Cambrian) • Ostracoderms: armored, jawless fishes; extinct by end of Devonian • Placoderms: heavily armored, jawed fishes; extinct at Devonian • Agnathans (Extant Jawless Fishes) • Hagfishes: marine scavengers and predators; exude copious amounts of mucous when disturbed; knotting behavior; fishery for eel- skin products • Lampreys: 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)

2. Figure 5-79

3. 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; requiemsharks (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”

4. 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 tapetumlucidum 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, retemirabile, & 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”)

5. Figure 5-83

6. Figures 5-82 and 5-84

7. 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)

8. Figure 5-85