Below is one of the first ever recorded high-speed video sequences of Inermia vittata, a zooplanktivore from the tropical western Atlantic. We are using its first live appearance in the lab to see how the feeding kinematics of Inermia compare with that of other reef fishes. Watch how far that upper jaw projects forward!
[youtube=http://www.youtube.com/watch?v=WOQ3US92Tt0]
One common name for this fish is the bonnetmouth, named after the appearance of the protruded mouth. Like other reef zooplanktivores, Inermia appears qualitatively to be specialized at picking prey from the water column. As you can see in the video, the mouth reaches forward, closing the distance to the prey while preparing to pull the prey closer with suction.
The evolutionary relationship of Inermia to other species has been tricky to resolve because it is very similar in appearance and behavior to other zooplanktivores such as fusiliers (Lutjanidae). However, molecular analysis shows Inermia to be nested within the grunts (Haemulidae), which typically feed on benthic invertebrates. A look at the pictures below will show how much different Inermia appears from a typical grunt and how similar it looks to the distantly-related fusilier.
Our new star, Inermia vittata
A fusilier, nested within the snappers (Lutjanidae)
A close relative of Inermia
Why does Inermia look so different from a typical grunt, and why does it look so similar to a distantly related species? Perhaps the feeding mechanisms captured in these videos can help to resolve this evolutionary anomaly.