Fish Beware – A New Species of Parasite is Discovered

Drawing of  Lethacotyle vera.

Drawing of Lethacotyle vera.

The world is full of creepy crawlers; some are harmless bugs while others are blood sucking parasites. Adding to the list of parasites this month is one identified in a recent PLOS ONE article, Lethacotyle vera n. sp, a new species of fish parasite, found in the South Pacific. Lethacotyle vera is part of the class Polyopisthocotylean monogenean, which are tiny (less than 1-cm long), parasitic flatworms that live on fish gills.

For any type of ectoparasite (parasites that live outside their host’s body) staying attached to their host is an important ability. One of the most notable features of Polyopisthocotylea is their multiple sucking clamps that allow them to keep their position on the fish. These clamps are found on the haptor, a body part developed specifically for attaching. Some parasites in this group can have hundreds of clamps as part of their haptor. In fact, Polyopisthocotylea literally translates to ‘many sucker-cups at the rear’. Thank goodness they only like fish!

However, there is one rare species discovered 60 years ago, Lethacotyle fijiensis, that appears to be clamp-less. The only available specimen for study is the one shown in the picture below.

The only available specimen of L. fijiensis

The only available specimen of L. fijiensis.


This close up below shows you what L. fijiensis actually looks like. The clamp-less haptor is the oblong protrusion on the very left end.


Close up of L. fijiensis

Because only four specimens of L. fijiensis have ever been found, and because having clamps is a major distinguishing feature of monogeneans, many researchers have assumed that L. fijiensis was incorrectly identified as clamp-less, and that these specimens probably lost their clamps through mishandling of the specimens by people.

In an attempt to verify the true nature of L. fijiensis, the authors went in search of additional specimens in the Pacific, where it was originally discovered. While they were unable to find any, they instead unearthed a hereto-undiscovered close relative, which they named Lethacotyle vera (vera is Latin for true, meaning that the genus Lethacotyle, is indeed real).

Haptor and Hooks

As it turns out L. vera is also a monogenean without clamps. The main physical difference between L. vera and L. fjiensis is the length in the male reproductive organ. The authors noted that L. vera has flaps on its haptor that are covered in many ridges, as well as hooks. A drawing of the haptor with its ridges and hooks can be seen in part F in the image to the right.


The authors sequenced the DNA from two of the eighteen specimens. The extracted DNA showed that the genetic information in L. vera is unique from all other known monogeneans. Then, in an effort to determine why L. fijiensis and L. vera don’t have the typical clamps of their family, they compared the ratio of clamp-to-body surface area in 120 different monogenean species. They found that members of the monogenean family to which L. vera and L. fijiensis belong, protomicrocotylids, had consistently the smallest clamp-to-body ratio. Additionally, many other species of polyopisthocotylean monogeneans had lateral flaps with ridges on their haptors.

From this observation, the authors concluded that in the family protomicrocotylids, their clamps are in fact slowly disappearing, and that in the specific case of L. fijiensis, the clamps have completely disappeared. The authors suggest that flaps can also hold onto the host, and that this process is assisted by the ridges and hooks along the flaps.

The discovery of a new species is always exciting, and as the case of L. vera shows us, can lead to insights about the larger family of related organisms. Read more about new species at PLOS ONE, such as this orchid or this Indonesian owl.

Citation: Justine J-L, Rahmouni C, Gey D, Schoelinck C, Hoberg EP (2013) The Monogenean Which Lost Its Clamps. PLoS ONE 8(11): e79155. doi:10.1371/journal.pone.0079155

Image 1 Credit: doi:10.1371/journal.pone.0079155.g001

Image 2 Credit: doi:10.1371/journal.pone.0079155.g002

Image 3 Credit: doi:10.1371/journal.pone.0079155.g007