Possible Clues:

• Shellfish — one consumed by a friend of Pickwick
• Mollusc, one often encountered in gardens
• Poisonous plant with blue flowers
• [Mollusk]
• Poisonous plant — edible marine snail
• Bat in jeopardy, along with European mollusc
• Sort of blue colour around elevated cable, live on the outside
• Purple-blue shade or the flower it's named after
• This plant may be poisonous -- peril I knew about
• Ornamental plant