Vertebrate Zoology Chapters 6&7 Chondrichthyes PDF

Chondrichthyes Chapters 6 & 7  Megalodon Largest shark Pre-birth cannibalism  Chondrichthyes: The Cartilaginous Fish Divided into 2 groups: Elasmobranchii and Holocephali Elasmobranchii have multiple gill openings on each side of head Have independently mobile upper...

Chondrichthyes Chapters 6 & 7  Megalodon Largest shark Pre-birth cannibalism  Chondrichthyes: The Cartilaginous Fish Divided into 2 groups: Elasmobranchii and Holocephali Elasmobranchii have multiple gill openings on each side of head Have independently mobile upper jaw Includes sharks, rays and skates Sharks are torpedo-shaped with 5-7 gill openings on each side of the head Rays and skates are dorsoventrally flattened with 5 pairs of gill openings on ventral surface  Chimaera Chondrichthyes: The Cartilaginous Fish Holocephali has undivided appearing head due to single external gill opening and gill slits covered by an operculum Includes chimaeras, rabbitfishes, ratfishes, and ghost sharks Fishlike body with long flexible tail Some have big eyes and broad tooth plates like a rabbit Ratfish Phylogeny of Cartilaginous Fishes  ~ 970 extant species Synapomorphies: Cartilaginous chondrocranium, jaws, gill arches, vertebrae, fin supports Bony tissues: fin spines, teeth, scales (dermal in origin) Lost the plates seen in acanthodians, but have an exoskeleton of placoid scales composed of dentine, enameloid, and bone Distinctive Male pelvic fins modified into claspers Characters of Broad wing-like pectoral fins that generate “lift” when animal swims forward Large lipid-filled liver that keeps them neutrally Chondrichthyes buoyant Retain nitrogenous compounds for osmotic regulation in marine environment https://www.youtube.com/watch?v=4HGNqFdaD34 Phylogenetic Relationships of Extant Chondrichthyans Chondrichthyan Skeleton Made of hydroxyapatite Same as bone, but mineralized differently Forms cartilage (the flexible material you can feel in your nose and ears) Only their teeth and the vertebrae in some groups are calcified Tooth Replacement by Chondrichthyans Chondrichthyan teeth are not embedded in the jaw like bony fish Teeth form in a whorl where teeth are replaced as they wear down and fall out Skeletons break down after death since made of cartilage Teeth are made of bone, so fossils are teeth Chondrichthyan Jaws Primitive chondrichthyans had autodiastylic jaws - upper jaw was firmly attached to the cranium Primitive elasmobranchs has amphistylic jaws - anterior end attached to the cranium, posterior end supported by the hyomandibular arch Extant elasmobranchs have hyostylic jaws - upper jaw can be extended and retracted during feeding Extant chimeras have holostylic jaws - upper jaw is fused to the cranium and lower jaw pivots Incredible Close-Up Sharks Biting and Grabbing the Bait Compilation - YouTube  Chondrichthyan Skin Placoid scales - bony, spiny projections with an enamel- like covering Same structure as their teeth Referred to as dermal denticles (dermal=skin, denticle=teeth) Slanted toward the tail of the shark and help direct the flow of water around the shark's body, reducing friction Stroking a shark from head to tail, its skin feels smooth to the touch, but stroking it from tail to head, the skin feels like sandpaper A shark can inflict wounds on potential prey by breaking the creature's skin with its scales Placoid scales do not increase in size as the fish grows, instead new scales are added between older scales Chondrichthyan Scales Each placoid scale consists of a flattened rectangular base plate which is embedded in the fish, and variously developed structures, such as spines, which project posteriorly on the surface Composed of a vascular inner core of pulp, a middle layer of dentine and a hard enamel-like outer layer of vitrodentine  Bioluminescence Photopores produce light on the sharks’ bodies Illuminate spines and break up the appearance of their body Lantern sharks: The Lantern Shark Glows in the Dark | Alien Sharks - YouTube Viper dogfish: Glow-in-the- Dark Sharks - YouTube Biofluorescence Have molecules in their skin that can only be seen under special light Absorb blue light and transform it to green Probably used in communication between the sexes Swellsharks: The Neon Green Swell Shark - YouTube  Subclass: Elasmobranchii - Sharks, rays, skates ~937 extant species, most marine Synapomorphies: Ventral mouth, upper jaw not fused to chondrocranium (protrusible) Skin with placoid scales 5 to 7 pairs of gills, leading to exposed gill slits Lateral Line No swim bladder – liver contains squalene (oil) Digestive system with J-shaped stomach & intestine with spiral valve Some species are viviparous with a 2-yr gestation period (longest known for any vertebrate) Have lateral line to detect vibrations Elasmobranchii ~ 45% of elasmobranchs are sharks, sawfishes, guitar fishes, etc. Jaws moveably articulated to the braincase (chondrocranium) by ligaments Fusiform body shape; most with a heterocercal tail dorsal (epichondral) lobe much longer than ventral (hypochondral) lobe Very keen olfactory sense (2/3 of brain area) Detect 1 drop of blood/100,000,000 drops of water (100x human)  Sharks (Selachii) Galeomorphii - (mostly) large sharks Squalomorphii - usually smaller Great white sharks – carnivorous sharks that live in the deep sea Cow sharks – largest of group, 5m Hammerhead sharks – carnivorous Angel sharks – 1.5-2m Whale sharks – largest, surface filter feeder Spiny dogfish – 1.5m Basking sharks – largest, surface filter Green lantern shark – cold, deep feeder water, 23cm Megamouth sharks – largest, deep filter Cookie-cutter sharks – cold, deep feeder water, 0.5m Mako sharks – smaller, 3-4m Horn sharks – smaller, 1-1.5m  Size Range of Sharks Figure 7.5 Representative extant sharks Galeomorphii Great White Shark 5-6m Bonnethead Shark 4m Longnose Angel Shark Sawshark 1.5m 1.25m Squalomorphii  Chemoreception Swimming noses Concentrations as low as 1 part per 10 billion Migratory and deep-sea species have Chemoreception large olfactory lobes and Coral reef species have small olfactory Mechanoreception lobes Mechanoreception Possess lateral line that detects turbulence and vibrations Some sharks have a nictitating membrane (“3rd eyelid”) Thin, tough membrane or inner eyelid that covers the eye and protects it from abrasion, mainly when feeding or Shark Vision encountering another shark. Sight probably plays an important role for many shark species when focusing in on their food Focus is achieved by moving entire lens forward or back via muscles inserting directly on the lens Great vision at low light intensities Most sharks feed at dusk or in deeper water They have more rods than cones in their retinas Tapetum lucidum behind retina - Platelike crystals of guanine that act like mirrors and reflect light back through the retina to increase the number of photons that are absorbed Reflects light back thru retina to re-stimulate rods in dim light Electroreception Ampullae of Lorenzini - most sensitive receptors in animal kingdom In sharks, sensors are located in small pores in the head & face, detect electric fields of other animals (produced by muscle activity) – detect these impulses & can locate prey buried in sand  Membranous labyrinth or “inner ear”, a group of ducts and sacs, filled with endolymph made of mostly sea water Membranous labyrinth Also detects water-born vibrations via the endolymphatic duct, which carries vibrations from surface to the inner labyrinth A pair of these are enclosed in the otic capsules on either side of the chondrocranium; 3 semicircular canals are at right angles to each other – detect motion in 3 spatial planes Sacculus contains otoliths (granules of CaCO3) that shift slightly when animal changes direction or receives vibrations; this triggers hair cells & signals brain Inner ear is used for hearing and balance/equilibrium Predatory Behavior Usually attack familiar prey immediately, but circle unfamiliar prey Also, opportunistic feeders, eat dead or weakened animals During the last moments when attacking their prey, the shark is basically blind and most likely relies on other senses such as electroreception and smell. The pupil can change shape, but the lens is spherical & rigid Thermoregulation Majority of sharks are poikilothermic, but a few pelagic species (Mako Shark) are homeothermic (Swordfish, etc.) Top – Mako shark Middle – Swordfish Bottom – Great White Shark Ecology Apex predators that are key components of marine food webs Sharks – Apex Predators Proposed Mechanism of Top-Down Control by Apex-Predator Sharks  Regional Heterothermy Occurs in mackerel sharks (Lamnidae) such as the shortfin mako shark and the great white shark Countercurrent heat exchange throughout the body A network of blood vessels capture heat produced in their muscles as they swim More blood vessels take cold water from the gills toward the muscles, which warms it It then moves to the vessels that go to the eyeballs and warms them up, which probably helps them see better in dim light Also helps them swim into deep water and cold water at the poles  Teeth are replaceable, form Feeding up to 20 rows deep inside of jaws 20,000 teeth may be replaced in lifetime of one shark Sharks are either carnivorous (eating fish or mammals) or planktivorous (filter feeders) Inanimate objects are commonly recovered from their stomachs (metal objects, plastics, etc.) Teeth Shapes and Functions Mechanisms of prey capture include biting, ramming, and suction Teeth held in place by collagen Reproduction Spotted dogfish pelvic fins modified as claspers, which egg case when paired form an intromittent organ; fertilization is internal Oviparity – ova deposited as eggs in a sac-like membrane (30% of sharks and rays - ancestral) Viviparity – ova hatched internally, but some nutrition to embryos is supplied by mother via umbilical connection; mother gives birth to fully developed babies (~30% of viviparous species have a placenta) Lecithotrophy – A yolk supplies nourishment to the embryo Matrotrophy – Mother supplies the energy Clutch size: 2 – 40 “pups”; Gestation: 9 – 24 months  Copulation by the Whitespotted Bamboo Shark (Chiloscyllium plagiosum) (A) The siphon sacs beneath the male’s pelvic fins, visible here as the bulge at the ventral area of the male (arrow), have been inflated with seawater, and the male has grasped the female’s right pectoral fin. (B) The right clasper of the male is bent at a 90º angle to his body and is inserted into the female’s cloaca (arrow). The male’s siphon sacs have nearly been emptied. Batoidea > 50% of elasmobranchs are rays and skates Sting rays, electric rays, mantas, etc. Dorsoventrally flattened, with enlarged pectoral fins attached to their heads, used for locomotion Ventral gill openings, water intake through enlarged dorsal spiracles Whip-like tail in sting rays, with saw-toothed venomous spine Batoidea (superorder of Elasmobranchii) Usually bottom-dwellers Ambush hunters - rest on the sea floor and cover themselves with sand to await prey Mouth is often extremely protrusible, suck prey from the substrate Flat teeth that crush prey The largest rays, manta rays, filter feed plankton Figure 7.11 Representative extant skates and rays Cownose Spotted Stingray Eagle Ray Common Sawfish Whipray (freshwater)  Skates vs. Rays Most (but not all) skates have a circular or rounded body shape while rays are kite-shaped Most skates have a thick tail without spines; rays have a whiplike tail, sometimes with venomous spines Skates are oviparous (mermaid’s purse); rays are viviparous (nonplacental)  Electric Rays Specialized muscles on either side of the head of electric rays can deliver a severe shock to stun prey Electric rays are ambush hunters during the day - surge upward from the sand, engulf prey in their pectoral fins and stun them At night, they hover in the water above the sand and descend on fish below them, stunning them  Synapomorphies: Subclass: Holocephali operculum – bony plate covering gill arches Chimaeras ~50 extant species, all upper jaw is solidly fused to braincase (holostylic) marine some with a tenaculum (“clasper”) on the forehead skin without scales of any kind teeth modified into crushing plates  Live just off the seafloor (500 m or more) Chimaeras Usually < 1 m long Feed on sea anemones, jellyfish, small fish, crustaceans, & mollusks Life histories are poorly known Take 10-12 years to reach maturity Only reproduce 1x per year, only have a few young Oviparous Females lay 2 eggs simultaneously, with several pairs laid each season Takes 6-12 months for the embryo to hatch Chimaera have 3 forms: Shortnose, Longnose, and Plownose