Annelida - Oligochaeta - Lumbricidae - Earthworm (Lumbricus terrestris). Head end. Digestive system. Relatively simple, straight digestive tract. Small oral cavity opens into larger pharynx. Aquatic species feature everted pharynx; mucus covered muscular disk collects particles onto adhesive pad; earthworm sucks food through. Pharynx opens into narrow tubular esophagus that expands into gizzard, or Lumbricidae's crop