"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift
January 24, 2010
January 24 - Enteroxenos oestergreni
Let's say you are dissecting some sea cucumbers and you come across this thing (see photo) - what do you think it is? Is it a worm? No - In fact, it is a snail! You have just found Enteroxenos oestergreni - a species of parasitic gastropod that lives inside the body cavity of sea cucumbers. Evolution has done away with all its apparently superfluous organs like its digestive system, gills, heart, nervous system, and reducing it down to just the bare essentials of a parasite - reproductive organs. The only morphological clue that this organism is a gastropod are its larval stages (veligers), which look like tiny, delicate snails - just like that of many other marine snails. However, after it enters the sea cucumber host, it eventually transforms into the worm-like adult form. An adult E. oestergreni is essentially a long stringy sac of eggs, just floating in the coelomic fluid of its host.
See the original paper here.
Contribution by Tommy Leung.