Arthropods

• Arthropoda


  Phylum of animals, largest phylum with over 1 million known species and several million remaining undiscovered
• Arthropods


  • Segmented body
  • Bilaterally symmetrical
  • Jointed appendages; legs and mouthparts
  • Non-living external exoskeleton composed of chitin
  • Undergo molting (ecdysis) to grow
• Crustacea


  Phylum that includes barnacles, shrimps, lobsters, crabs, and a huge variety of less familiar animals
• There are approximately 68,000 known species of crustaceans
• Crustaceans


  • Specialized for life in water because they possess gills to obtain Oxygen
  • Have two pairs of antennae
• Copepods


  Extremely abundant and important in the plankton, some are parasitic and simplified in appearance
• Barnacles


  Filter feeders that usually live attached to surfaces, including living surfaces like whales and crabs, have a body part called cirri that allows filtering of water, some have become highly parasitic
• Amphipods


  Small crustaceans with a curved body that is flattened sideways, most under 2 cm in length, with a head and tail that typically curve downward
• Isopods


  About the same size as amphipods, but easily identifiable because the main part of the body has legs that are similar to each other and the body is dorsoventrally flattened and thus has a flat back
• Krill or euphausiids


  Planktonic, shrimp-like crustaceans up to 6 cm long, most are filter feeders that feed on diatoms and other plankton
• Decapoda


  The largest group of crustaceans, includes shrimps, lobsters, and crabs, many are prized as food and are of great commercial importance
• Hermit crabs


  Not true crabs, are scavengers that hide their long, soft abdomens in empty gastropod shells
• True crabs


  Have a small abdomen tucked under the compact and typically broad cephalothorax, the abdomen is visible as a flat, V-shaped plate in males and expanded and U-shaped in females for carrying eggs
• Crustacean feeding and digestion

  • Filter feeding is very common in copepods and many of the small planktonic crustaceans
• Crustacean nervous system and behavior

  • Crustaceans have a small, relatively simple brain but well-developed sensory organs, most have compound eyes consisting of a bundle of up to 14,000 light-sensitive units grouped in a mosaic
• Horseshoe Crabs


  The only surviving members of a group (class Merostomata) that is widely represented in the fossil record, they are "living fossils" not unlike forms that became extinct long ago, they live on soft bottoms in shallow water and have a distinctive horseshoe-shaped carapace that encloses a body with five pairs of legs
• Sea Spiders


  Only superficially resemble true spiders, have four or more pairs of jointed legs stretching from a small body, and a large proboscis with the mouth at the tip used to feed on soft invertebrates such as sea anemones and hydrozoans, most common in cold waters but occur throughout the oceans