Due to the very few annelid species currently proven, any Annelid proving is strongly encouraged. It is however particularly encouraged to be sure about species identification, and annelid species can be difficult to determine without biological expertise.
Potentially interesting species of Clitelatta could be members of the Enchytraeidae, the ice worms, which live in glaciers and die at higher temperatures and the Americobdellidae, an order of leeches which hunt earthworms. The worlds largest known leech, Haementeria ghilianii can be upto 18 inches long, live 20 years and can inject its proboscis upto 15 cm into the hosts skin[i]. Another leech, Coratobranchus mestrovi, is a cave dwelling, transparent and has several appendages, appearing to be predatory.
Some interesting polychaete species for proving could be[ii] Alvinella pomojana, the hydrothermal vent worms, some of the most heat tolerant organisms in the world and one which lives off of sulphur fixing bacteria , Osedax species, or the bone worms which decompose whale bones in the deep ocean, Hesiocaca methanicola, which derives energy from methane deposits and Lamelibrachia luymesi, a cold water worm which may live to be over 250 years old. Hesiocaeca methanicola is a species of iceworm that inhabit methan hydrate deposits and feed off of bacteria that metabolise those hydrates[iii]. One family, the Amphinomidae are called the fireworms and cause itching and pain when handled due to a secretion of complanine from the worm chaetae[iv]. Another species, Eunice aphroditois is a voracious predator, often slicing its prey in half due to the fury of its attack.
Any species of Echiurians or Sipunculata would be excellent candidates for proving due to the near complete lack of representatives from this phyla in the material medica. One Echiuran, Bonella viridis has already been potentised and would be quite easy to effectively prove. One group of Echiurians, the Thalassematidae can alter their body shape incredibly, and rarely maintains the same shape for long[v].
[i] Anonymous. Online Document Accessed March 12th 2015. http://invertebrates.si.edu/Features/stories/haementeria.html
[ii] I would like to thank the Wikipedia page on Polychaetes for these suggestions. Accessed March 3rd 2015. http://en.wikipedia.org/wiki/Polychaete
[iii] Fisher et al. Methane Ice Worms: Hesiocaeca methanicola Colonizing Fossil Fuel Reserves. Naturwissenschaften. April 2000, Volume 87(4) Pp 184-187.
[iv] Nakamura et al. Complanine, an inflammation-inducing substance isolated from the marine fireworm Eurythoe complanata. Org. Biomol. Chem. 6 (12): 2058–2060.
[v] Online Document. Accessed March 12th 2015. http://mucholderthen.tumblr.com/post/65748522495/a-morphing-marine-worm-a-truly-weird-animal.