Elasmobranch Biology,Elasmobranch: Any of numerous fishes of the class Chondrichthyes, characterized by a cartilaginous skeleton and placoid scales and including the sharks, rays, and skates.,FLORIDA PROGRAM FOR SHARK RESEARCH Florida Museum of Natural History,鲨鱼-软骨鱼类生物,Topics,Basic Morphology Senses Digestion system Circulatory system Osmoregulation Reproduction system Evolutionary adaptations,There are approximately 400 described species of sharks. Additionally, there are around 400 species of batoids (rays and skates).,When did sharks first appear?,Sharks and their ancestors first appeared in the late Silurian/early Devonian, or around 400 million years ago. Sharks predate dinosaurs by 200 million years.,Body Plan,Stingrays vs. Skates,Whats the difference?,Stingray Fins,Skate Fins,Pectoral,Pelvic,Pectoral,Pelvic,Dorsal,Caudal,Spiracle,Spiracle,Stingray vs. Skate,Most have venomous spine,No spine present,Stingray Tail,Spine,Dorsal fin-fold,Anal fin-fold,Reproduction: Aplacental viviparity (live birth).,Reproduction: Oviparous (lay eggs).,Stingray vs. Skate,Can be very large in size.,Usually smaller in size.,Stingray vs. Skate,Stingray vs. Skate,In general have thinner tails,Can have very thick tails,Elasmobranch Senses,Elasmobranch Senses Olfactory (Smell):,Highly acute sense of smell Used to locate food or potential mates Paired openings with or without a connection to the mouth Not used for respiration,Lack external ears Good sense of hearing especially in the lower frequency range Often first sense to detect prey from a distance,Elasmobranch Senses,Sound:,Elasmobranch Senses Pressure:,Sharks, like other fish, have a lateral line system that can detect pressure waves in the water. Sense struggling prey,Shark eyesight will vary by species but most have good visual acuity Sharks have both rods (light/dark) and cones (color) Retina posses a “tapetum lucidum”,Elasmobranch Senses Vision:,Elasmobranch Senses Electric:,Electrosensory system: “Ampullae of Lorenzini” Allows for detection of weak electric fields given off by prey organisms or potential mates,Digestion,Shark Digestion,Large Liver up to 25% of body weight. Short Gut long passage rate Spiral Valve intestine increase surface area,Circulatory System,Four chamber heart: sinus venosus, atrium, ventricle, and conus arteriosus. One direction of flow: Heart Gills Body Ectotherms/Endotherms,Osmoregulation,Sharks are slightly hyperosmotic to sea water Retain urea and TMAO Results in slight but continuous influx of water Excess water is excreted by the kidney Most sharks are stenohaline,Reproduction,Male Sharks,Male Reproductive System,Both testes functional Seasonal reproduction cycle Sperm stored in seminal vesicles Both claspers functional,Warning! Graphic images ahead. Viewer discretion is advised.,Female Sharks,Modes of Reproduction Oviparous:,Oviparous species, eggs are released into the environment Females select sites to deposit eggs 40% of all Shark species and all skates are oviparous,Modes of Reproduction Aplacental viviparity:,Females retain developing embryos in utero Embryos nourished with yolk and then “histotroph”, or ovulated eggs (oophagy) or siblings (embryophagy) All rays are aplacental viviparous with histotroph,Modes of Reproduction Placental viviparity:,Females retain embryos in utero Embryos nourished through yolk and then through a placental connection 10% of shark species are placental viviparous Appendiculae,Female Reproductive System,One functional ovary in most viviparous species Seasonal reproductive cycle Fertilization in nidamental gland,Nidamental,Stomach,Ovary,Female Anatomy,Female Anatomy,Ovary,Nidamental Glands,Uteri,Liver,Uteri,Pregnant Sandbar Shark Carcharhinus plumbeus,Placental Embryos,Parturition,Shark Mating,Shark Mating,One clasper will rotate 90 and will be inserted into the females cloaca,Clasper will expand cartilaginous spurs to anchor in the female,Shark Mating,Mating Scars,Evolutionary Adaptations,Evolutionary Adaptations,Placoid Scales = decrease drag,Evolutionary Adaptations: Teeth,Large Liver and cartilaginous skeleton helps with buoyancy,Evolutionary Adaptations,Hammerhead Sharks,The unique head (cephalophoil) provides several advantages,Increase lift, maneuvering Electrosensory Olfactory Feeding,Stingray Spines,Stingray Spines,Questions,?,