Invertebrates Arthropoda

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Arthropods Arthropods make up the largest phylum of animals –1 million known and several million undiscovered Of all the animals on earth, ¾ are arthropods Largest group of arthropods by far are the insects The vast majority of marine arthropods are crustaceans – arthropods adapted for life in the water –Barnacles, shrimps, lobsters, crabs, and many unfamiliar animals

Arthropod Body Plan The arthropod body is segmented and bilaterally symmetrical In addition to flexible, segmented body arthropods have jointed appendages such as legs and mouth parts Another characteristic of arthropods is an exoskeleton made of chitin, a tough polysaccharide (C 8 H 13 NO 5 ) To grow, arthropods must molt their exoskeleton –A new shell develops under the old one prior to molting

Subphylum Crustacea Crustaceans – 68,000 known species, as many as 150,000 undiscribed Most are marine Small crustaceans are everywhere: in the plankton, on the bottom, among sediments, on and in other animals, and among seaweeds –Copepods, barnacles, amphipods, isopods, krill

Parasitic isopod

Decapods Decapods (10 legs) –Shrimps, lobsters, and crabs Around 10,000 species Largest group of the crustaceans Largest crustaceans in size Many are prized as food and are of great commercial importance

Decapod Body Plan Decapods have 5 pairs of legs, the first of which is usually modified into claws Decapods also have 3 pairs of maxillipeds –Sorting and pushing food into mouth A carapace covers the cephalothorax The rest of the body is the abdomen (part of shrimp and lobster people eat – tail)

Crayfish / Crawfish

Nervous System and Behavior The nervous system of the structurally simplest crustaceans is ladder-like, but more centralized in decapods Crustaceans have a small, relatively simple brain. Well developed sensory organs Compound eyes

Red King Crab NMFS research biologists Sara Persselin and Brad Stevens display one of 32 red king crabs collected in waters around Kodiak Island for use in a collaborative effort to rebuild Kodiak's red king crab stocks. The research program is aimed at hatching and rearing red and blue king crabs in a large-scale hatchery setting.

Horseshoe Crabs The horseshoe crab is the only surviving member of class merostomata which is highly represented in the fossil record The 5 species of horseshoe crab are not true crabs but “living fossils,” not unlike forms that became extinct long ago Horseshoe crabs possess the rare ability to regrow lost limbs, in a manner similar to sea stars.

Horseshoe crab vision

Medical research and testing Horseshoe crabs are valuable as a species to the medical research community, and in medical testing. The above-mentioned clotting reaction is used in the Limulus Amebocyte Lysate (LAL) test to detect bacterial endotoxins in pharmaceuticals and to test for several bacterial diseases. LAL is obtained from the animals' blood. Horseshoe crabs are also used in finding remedies for diseases that have developed resistances to penicillin and other drugs. Horseshoe crabs are returned to the ocean after bleeding. Studies show that blood volume returns to normal in about a week, though blood cell count can take two to three months to fully rebound. A single horseshoe crab can be worth $2,500 over its lifetime for periodic blood extractions.

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Class Insecta Insects are distinguished from other arthropods by having only 3 pairs of legs They are the most diverse group of animals on earth, but are rare in the sea

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