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Elasmobranch Biology

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. Topics. Basic Morphology

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Elasmobranch Biology

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  1. 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

  2. Topics • Basic Morphology • Senses • Digestion system • Circulatory system • Osmoregulation • Reproduction system • Evolutionary adaptations

  3. There are approximately 400 described species of sharks. • Additionally, there are around 400 species of batoids • (rays and skates).

  4. 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.

  5. Body Plan

  6. Elasmobranch Senses

  7. Elasmobranch SensesOlfactory (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

  8. Elasmobranch Senses Sound: • Lack external ears • Good sense of hearing especially in the • lower frequency range • Often first sense to detect prey from • a distance

  9. Elasmobranch SensesPressure: • Sharks, like other fish, have a lateral line system that can detect pressure waves in the water. • Sense struggling prey

  10. Elasmobranch Senses Vision: • 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”

  11. Elasmobranch SensesElectric: • Electrosensory system: “Ampullae of Lorenzini” • Allows for detection of weak electric fields given off by prey organisms or potential mates

  12. Digestion

  13. Shark Digestion • Large Liver • up to 25% of body weight. • Short Gut • long passage rate • Spiral Valve intestine • increase surface area

  14. Circulatory System • Four chamber heart: sinus venosus, atrium, ventricle, and conus arteriosus. • One direction of flow: Heart Gills Body • Ectotherms/Endotherms

  15. 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

  16. Reproduction

  17. Male Sharks

  18. Male Reproductive System • Both testes functional • Seasonal reproduction cycle • Sperm stored in seminal vesicles • Both claspers functional

  19. Warning!! Graphic images ahead. Viewer discretion is advised.

  20. Female Sharks

  21. Modes of ReproductionOviparous: • Oviparous species, eggs are released into the environment • Females select sites to deposit eggs • 40% of all Shark species and all skates are oviparous

  22. Modes of ReproductionAplacental 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

  23. Modes of ReproductionPlacental viviparity: • Females retain embryos in utero • Embryos nourished through yolk and then through a placental connection • 10% of shark species are placental viviparous • Appendiculae

  24. Female Reproductive System • One functional ovary in most • viviparous species • Seasonal reproductive cycle • Fertilization in nidamental • gland

  25. Female Anatomy Nidamental Ovary Stomach

  26. Female Anatomy Uteri Ovary Liver NidamentalGlands Uteri

  27. Pregnant Sandbar Shark Carcharhinus plumbeus

  28. Placental Embryos

  29. Parturition

  30. Shark Mating

  31. Shark Mating

  32. Shark Mating • One clasper will rotate 90º • and will be inserted into • the female’s cloaca • Clasper will expand • cartilaginous spurs to • anchor in the female

  33. Mating Scars

  34. Evolutionary Adaptations

  35. Evolutionary Adaptations • Placoid Scales = decrease drag

  36. Evolutionary Adaptations: Teeth

  37. Evolutionary Adaptations • Large Liver and cartilaginous skeleton helps with buoyancy

  38. Hammerhead Sharks • The unique head (cephalophoil) provides several advantages • Increase lift, • maneuvering • Electrosensory • Olfactory • Feeding

  39. Questions ?

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