Arthropoda

• Describe specific examples of how insects communicate with each other
• Phylum Arthropoda


  • Describe the characteristics of members
  • Discuss its basic physiology
  • Identify representative species
• Arthropods


  • Shelled creatures; "the insects of the sea"
  • Mostly aquatic, mostly marine
  • Inhabit most waters of the earth: ocean, arctic, freshwaters, high mountain creeks and lakes, thermal springs, brine waters
  • Many are at the base of aquatic food chains part of zooplanktons
• Arthropods


  • Only a few are terrestrial
  • Some crustaceans live for several decades
  • Some molt throughout life
  • Some crustaceans are quite colorful; blue, red, orange, yellow
  • Many are bioluminescent

  
• Arthropod body plan


  • Abdomen usually with pairs of jointed appendages on most segments
  • Most crustaceans can cast off legs or pinchers to escape predators and later regrow them
  • Functions: sensory, feeding, defense, walking, swimming, reproduction and respiration
  • Many are biramous appendages
• Arthropod body form


  • The body is divided into a cephalothorax, abdomen and tail (telson)
  • 2 pairs of antennae
  • Often have carapace extending over the abdomen and gills
  • Most with compound eyes
• Cephalothorax


  Feeding and sensory appendages
• Abdomen


  • 5 or more pairs of walking legs including chelipeds (pinchers)
  • Segmentation is most apparent
• Telson (tail)


  Has its own paired appendages (uropods) that with the telson form a finlike tail
• Arthropod movement


  • Most appendages are biramous
  • Voluntary (striated) muscle tissue arranged in antagonistic groups
  • One of the branches usually have a gill attached at its base
  • Flexors & extensors
• Arthropod feeding and digestion

  • Use jaw-like mandibles as the main feeding structures; also maxillae and maxillipeds
  • Have a well-developed digestive system: cardiac stomach with gastric mill for grinding, pyloric stomach for sorting, digestive gland secretes digestive enzymes
• Arthropod respiration


  • In small crustacea: no special organs
  • In larger crustacea: respiration is usually by feathery gills
  • Exchange across body surface
  • In some sides of carapace form gill chambers that enclose gills
• Arthropod circulation


  • Open Circulatory System
  • Hemolymph is pumped through 2 or more arteries for distribution
  • Dorsal heart in hemocoel
  • Heart has ostia (holes) to draw in hemolymph (blood)
  • Hemolymph may be bluish, reddish or colorless
• Arthropod nervous system


  • 2 pairs of ganglia around the esophagus supply sense organs of the cephalothorax
  • Double ventral nerve cord with a pair of ganglia in each segment along the rest of the body
  • Most have compound eyes and simple eyes (ocelli)
  • Chemoreceptors (taste) on mouthparts
  • Crustaceans uniquely have 2 pairs of antennae
  • Statocysts for orientation
  • Tactile hairs and spines spread over body
• Arthropod communication


  • Hearing: communication by sound, make underwater noises to communicate
  • Light emitting organs & communication by light, many crustaceans have light-emitting organs (photophores) that use luciferase to produce light
• Arthropod endocrine system


  Hormones help to control: Body coloration by chromatophore/pigment cells, Molting/ecdysis, Heart rate, Blood sugar levels, Sexual development
• Arthropod excretion


  • Nitrogen wastes are excreted through skin (if no gills)
  • No malpighian tubules
  • Located in the ventral part of the head anterior to the esophagus or through gills & antennal glands/green glands
  • Coxal glands modified nephridia at base of legs in some chelicerates
  • In some aquatic species nitrogen wastes are excreted through skin or through gills
• Arthropod reproduction and development

  • Mostly dioecious
  • Larva → metamorphosis → adult, often with a complete change in feeding and lifestyles
  • Few groups reproduce parthenogenetically
  • Nymph → juvenile → adult
• Origin and evolution of arthropods

  Arthropods show many similarities to certain segmented worms: 1. Metamerism with a tendency for segments to become specialized, 2. Similar nervous system with paired ganglia in each segment, 3. Some have the same type of excretory system, 4. Spiral cleavage in primitive members, 5. Mesoderm derived from 4D blastomere