Subphylum Vertebrata – Early Fishes and Extant Jawless Fishes

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)

Fig. 23.13

Table 23.1

Fig. 24.1

Fig. 24.2

Fig. 23.14

Fig. 23.15

Fig. 23.17

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; 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”

Fig. 23.16

Fig. 24.7

Figs. 24.12 and 24.13

Fig. 24.14

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”)

Fig. 24.8

Fig. 24.10

Fig. 24.11

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)

Subphylum Vertebrata – Early Fishes and Extant Jawless Fishes