Flame cells and Malpighian tubules are excretory organs found in different groups of organisms. Let's discuss each organ and its corresponding group of organisms in detail.

a) Flame cells in insects:
- Flame cells are excretory cells found in the excretory system of insects.
- These cells are responsible for removing excess water and waste products from the insect's body.
- They are named flame cells due to their appearance under a microscope, resembling flickering flames.
- Flame cells consist of a bulbous structure with a tuft of cilia that create a flow of fluid.
- The fluid collects waste materials and carries them out of the insect's body through specialized ducts.
- In insects, flame cells are connected to a network of tubules called the Malpighian tubules.

b) Malpighian tubules in arthropods:
- Malpighian tubules are excretory organs found in arthropods, which include insects, spiders, and crustaceans.
- These tubules are responsible for maintaining the osmotic balance, removing nitrogenous waste, and conserving water.
- They are long, thread-like structures located in the posterior region of the arthropod's digestive system.
- Malpighian tubules extract waste products and excess water from the surrounding hemolymph (insect blood) and transport them to the intestine.
- From the intestine, the waste products are eliminated from the body through the rectum.
- The main function of Malpighian tubules is to regulate the composition of the hemolymph and remove nitrogenous waste, such as uric acid.

Therefore, the correct answer is (a) insects and arthropods, respectively.
Flame cells are found in insects, while Malpighian tubules are found in arthropods, which include insects as a subgroup. These organs play a crucial role in excretion and maintaining the osmotic balance in their respective organisms.

Platyhelminthes and athropoda