August 23 - Lobatostoma manteri

Lobatostoma manteri is a species belong to a group of parasitic worm call the Aspidogastrea. The aspidogastreans are a very ancient group of parasitic flukes and are the sister group to the far more numerous and diverse digenean trematodes. In contrast to the digeneans which have a 3-host life-cycle (or variations on such), aspidogastreans only have 2 hosts in their life-cycle with the larval stage living in a mollusc and the adult living inside the gut of fishes. Unlike their digenean cousins, aspidogastreans do not asexually multiply within the mollusc host.

Lobatostoma manteri itself can be found on many tropical islands on the Great Barrier Reef of Australia. The definitive host for Lobatostoma is the Snubnosed Dart, Trachinotus blochi, from which the parasite's eggs are shed into the surrounding water. Marine snails become infected when they ingest the eggs and the larvae hatch from the eggs then develop into juvenile stages within the snail, which are in turn eaten by the Snubnosed Dart. L. manteri is very host-specific to this fish host because only that particular species of Dart has the well-developed pharyngeal plates (special teeth found in the throat of some species of fish) necessary to crack the hard shells of snails.

While it is a popular (and misguided) belief that the evolution of parasitism results in a lost of morphological complexity, this is a misconception, as the lost of certain sensory organs (such as eyes) which not necessary for navigating within the body of the host are replaced by the evolution of other sensory systems which are more appropriate for such an environment. Lobatostoma manteri has a complex and extensive nervous system, and the surface of the larval stage is dotted with over 8000 sensory receptors, with the adult (which grows to 4 mm in length) estimated to be covered in 20000-40000 receptors!

Contributed by Tommy Leung.