What could better express a malacologist's love on Valentine's Day than a box of love darts painstakingly isolated from scores of Helix aspersa* sacrificed in the name of love (and science)?
During mating of hermaphrodite land snails, each partner places a spermatophore, a bag of spermatozoa (sperm cells), in their partner's bursa copulatrix (BC). The spermatophore is digested in the BC and only a small fraction of the spermatozoa escapes to the higher parts of the female reproductive system to fertilize the partner's eggs.
Diagrammatic representation of the reproductive organs of a pulmonate snail. All pulmonates are hermaphrodites, but not all of them have darts. P, penis; D, dart; S, dart sac; V, vagina; MG, mucus glands; BC, bursa copulatrix; G, genital opening. Original by Koene, copy from Schilthuizen.
The so-called love darts are sharp needles of calcium carbonate that are stored one at a time in a special bag-like organ, the dart sac, and thrust inside the body of a snail's partner during mating. Studies have demonstrated that darts transfer mucus from the mucus glands (MG), which, probably by reducing sperm digestion in the BC, increases fertilization success of the sperm.
*Also known as Cantareus aspersus.
Recent papers on love darts:
Schilthuizen, M. 2005. The darting game in snails and slugs. TRENDS in Ecology and Evolution 20:581-584.
Joris M. Koene & Satoshi Chiba. 2006. The Way of the Samurai Snail. American Naturalist 168:553-555. copy and movie on Koene's web page