Trematode: A Penis-Eating Parasite

Last May I found two isopods in the mouth of the Indian Meckeral I bought back from the market. And several weeks ago Carl Zimmer posted an excellent piece about this tongue-eating parasites.

Today, I'm going to write about another parasite that eats not the tongue, but--get ready to cringe, guys--phallus.

Fortunately for us men these parasites prefer the penis of a type of sea snail called whelk.

A whelk. Image: http://en.wikipedia.org

Tremadotes are small parasitic flatworms that use molluscs as their intermediate hosts to reach their definitive host, the vertebrates. And once they end up in a molluscs, for instance a whelk, they will start chomping away the entire whelk gonad while waiting for a fish, for example an Atlantic cod, to devour the whelk.

In April 2000, a group of scientists from Canada decided to evaluate the impact of the parasites on the population of whelks in the northern gulf of St. Lawrence. The study--led by scientist Francoise Tetreault--involved collecting and dissecting 600 whelks and looking at their gonads, and compared the size of their gonads with the distribution of parasites.

The researchers discovered that there were 23% female and 15% male whelk whose gonads were affected. The parasite infected the digestive system as well, but 97% of the infected whelks had their gonads covered by 90% of the parasite.The parasite munched away a large portion of the male penis and changed the once bright color of the female gonad into pale grey.

Picture (B) shows an uninfected whelk. Its penis is labelled as "P".
Picture (D) shows an infected whelk. Look at the "P", and the whelk's sad face.
Awwww.... 

Picture (A) shows the gonad(G) and digestive system(DG) of a female whelk.
Pciture (B) shows the pale grey gonad of an infected female whelk.

Luckily for us there is no parasite that loves eating human penis. As for the whelks, they can only watch helplessly as the trematode feasts on their manhood.
Sucks to be a male whelk.

Malcolm
info: Tetreault, F., Himmelman, J., & Measures, L. (2000). Impact of a Castrating Trematode, Neophasis sp., on the Common Whelk, Buccinum undatum, in the Northern Gulf of St. Lawrence Biological Bulletin, 198 (2) DOI: 10.2307/1542529