Transcript Subphylum Vertebrata – Early Vertebrates and

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)
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Hagfishes: marine scavengers and predators; exude copious amounts of
mucous when disturbed; knotting behavior; fishery for eelskin 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)
Figure 5-79
Cartilaginous Fishes – Diversity and Taxonomy
 Class Chondrichthyes (cartilaginous skeleton with chondrocranium and
jaws; mineralized teeth, scales, and spines)
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Subclass Elasmobranchii: sharks, skates, and rays (~937 species; most marine)
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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 lanternsharks, 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”
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”)
Figure 5-83
Figures 5-82 and 5-84
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)
Figure 5-85