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Just Being Crabby…

Just Being Crabby…. Maia McGuire Florida Sea Grant Extension Agent. Arthropods. “Jointed foot” animals Have exoskeleton made of cuticle/chitin Animals have to shed their skeleton as they grow (molting) Have highly-developed brain, some have well-developed eyes (color vision)

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Just Being Crabby…

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  1. Just Being Crabby… Maia McGuire Florida Sea Grant Extension Agent

  2. Arthropods • “Jointed foot” animals • Have exoskeleton made of cuticle/chitin • Animals have to shed their skeleton as they grow (molting) • Have highly-developed brain, some have well-developed eyes (color vision) • Most are gonochoric

  3. Horseshoe crabs • Most closely related to spiders and scorpions • Very ancient species • 4 species of horseshoe crabs worldwide, but only one in North America (from Maine to the Yucatan peninsula)

  4. Horseshoe crab anatomy • Have 6 pairs of legs (1 pair modified as feeding appendages); first pair of walking legs is modified in males • Several pairs of claws • “Book gills” help in swimming

  5. Horseshoe crab feeding • Scavengers—crawl along the sea floor in shallow areas looking for clams and worms or other food items • Use senses of touch and smell to find food

  6. Horseshoe crab biology • Well-developed circulatory system • Copper-based blood (hemocyanin) • Compound eyes, as well as other light and chemical-sensing organs • Gonochoric • Mature males have modified “claws” on first pair of legs—used for clasping female’s shell

  7. Horseshoe crab reproduction • Spawning is in late spring • Females crawl out of the water onto the beach; males grab onto females and fertilize eggs as they are laid • Pastel green eggs are important food for shorebirds (red knots) • Eggs hatch in about 2 weeks • Lifespan is about 19 years

  8. Horseshoe crabs and people • “Blue blood” of horseshoe crabs is used to test human medicines for bacterial contamination (it will clot) • Vision research has been conducted using horseshoe crabs’ optical nerves • Chitin from horseshoe crab shells is used to coat surgical sutures www.horseshoecrab.org

  9. Activity • Horseshoe crab models (DE Sea Grant; NJ Sea Grant)

  10. Crustaceans • Subphylum of Arthropods • Crabs, lobsters and shrimp • 5 pairs of legs; 2 pairs of antennae • Back shell is often called the “carapace” • Cuticle may be calcified • Gonochoric; most have planktonic larvae that go through several molts • Generally have compound eyes

  11. Crustaceans molt • Crustaceans cannot add to their shell—when they outgrow it, they separate the shell at the back of the carapace and crawl out of it. • They have a new, soft shell which they stretch by taking in water. • They hide for a few days until the new shell hardens, then release the water and have room to grow.

  12. www.1cro.com

  13. Molt or dead? • Molts have clear eye capsules (dead crabs have black eyes) • You can separate the carapace from the rest of the shell on moist molts (once they have dried out, this will not be possible • Old dead crabs will STINK! Molts will not smell.

  14. Crabs—male or female? Images from www.bluecrab.info

  15. Crabs on the beach—ghost crab

  16. Ghost crabs • In the same family as fiddler crabs • Get to be about 2” across the carapace • Feed on coquina clams and mole crabs; also eat sea turtle eggs and hatchlings • Can change color to provide camouflage • Must keep their gills moist • Nocturnal

  17. Ghost crab burrows • May be up to 4 feet deep • Crabs may close the entrance to the burrow on hot days • Burrows are usually above the high tide line

  18. Crabs on the beach—mole crabs • Sometimes also called “sand fleas” • Live buried in the sand in the swash zone • Get to be about 1” in length • Pale grey in color, egg-shaped • No claws • Feed by filtering plankton using their antennae, which they stick out of the sand. www.jaxshells.org

  19. Crab shells on the beach 

  20. Fiddler crabs • Different species—some found on the beach, some in the saltmarsh • Males have one large claw, one small • Males wave their claw to attract females • Large claw can be on the right or left

  21. Fiddler crabs • Live in burrows that can be about a foot deep • Burrows may be inter-connected • If frightened, a fiddler crab will withdraw into any nearby burrow • Crabs use a large ball of mud to seal up the burrow at high tide • Small mud balls outside the burrows are the result of feeding activity

  22. midcoast.tamu.edu

  23. Activity • Crabs (Monterey Bay Aquarium) • Walk like a Decapod-ian (UGA, CrabEcology)

  24. Barnacles • Only sessile (fixed in place) crustaceans • Two types: acorn-style (look like a volcano) and goose-neck • Use feathery “legs” to filter plankton out of the water

  25. Acorn barnacles • Be careful of the sharp edges of these barnacles’ shells!

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