ARTHROPODS

ARTHROPOD CHARACTERISTICS  Largest phylum of animals  Most marine arthropods are crustaceans  Body is segmented, bilaterally symmetrical  Jointed appendages  Exoskeleton made of chitin  Molt (shed exoskeleton)  small

CRUSTACEANS  68,000 known species  Most marine  Have gills  2 pairs of antennae  Examples; copepods, barnacles, amphipods, isopods, krill, shrimp, lobster, crabs

BIOLOGY OF CRUSTACEANS  Filter feeding smaller crustaceans Use bristles on appendages to gather particles Use appendages in some for sucking and piercing Stomach has chitinous teeth  Predators- decapods Stomach is two chambered; digestive enzymes Extracellular digestion; have anus

 Open circulatory system  Gill exchange gases  Simple brain; but well developed sensory organs Compound eyes Keen sense of smell Communicate with signals

REPRODUCTION & LIFE HISTORY  Separate sexes  Internal fertilization  In decapods, females carry their eggs in their pleopods or swimmerets  Most have planktonic larvae

SMALL CRUSTACEANS  COPEPODS: planktonic; use mouthparts to filter and capture food Some parasitic

 Barnacles- filter feeder; live attached to surfaces; body enclosed with heavy calcareous plates; have feathery filtering appendages called cirri

 AMPHIPODS- have a curved body that is flattened sideways Under ¾ in Head and tail typically curve downward Ex: whale lice, beach hoppers 5000 species Beach hopper

 ISOPODS- similar in size to amphipods but have legs that are similar to each other and the body is dorsoventrally flat (flat back) Pill bugs (land) Fish lice

Giant deep sea isopod

 KRILL OR EUPHAUSIIDS- shrimp-like crustaceans; up to 2.5”; planktonic; head is fused with some of the body segments to form a carapace Most filter feeders Polar waters Deep water Main food source for large marine mammals

DECAPODS  Shrimps, lobsters, and crabs  species  Largest group of crustaceans  Five pairs of legs or perapods 1 st which is the heavier- the claw or cheliped  3 pairs of maxillipeds- close to the mouth; used for eating  Well-developed carapace and encloses the cephlathorax (fused head and thorax)  abdomen

 Shrimps and lobsters Laterally compressed bodies with elongated abdomens Shrimps are scavangers-some are cleaners Some burrow in muddy bottoms Lobsters are mostly nocturnal; scavangers and predators; Hermit crabs (they are not true crabs) are scavangers; hide in snail shells

Giant lobster Mantis shrimp

OTHER MARINE ARTHROPODS  HORSESHOE CRABS 5 living species Last of the class Merostomata; “living fossils” Live on soft bottoms in shallow water 5 pairs of legs

 SEA SPIDERS 4 or more pairs of jointed legs w/small body Large proboscis w/mouth at the tip used to feed on small invertebrates Cold water

 Insects 3 prs of legs as an adult Rare in the sea  Most live on water’s edge or high tide mark Marine water strider