Before the lockdown, while at the Museum's new Beyond Shells exhibit, I caught one of the Wedge Sea Hares, Dolabella auricularia (Lightfoot, 1786), taking a break from munching on seaweed, and scraping the plexiglass tank wall with its radula, probably to nibble on microalgae. The radula, the light-colored, horseshoe-shaped structure in the photo, is the main feeding organ in a gastropod mollusk. The photo also shows the beginning of the alimentary canal (the darker cavity on top of the radula). The oral disk, that oval-rounded, fleshy "muzzle" surrounding the mouth, is about 20 mm (about 0.8 inch) in diameter.
As seen better in the second illustration (below), the radula consists of many rows of elongated, cutting teeth that look like whitish filaments in the images. Sea hares (family Aplysiidae) feed on seaweeds of different kinds, and the Wedge Sea Hare, a species from Indo-West Pacific region, is no exception. In sea hares, the radula is deployed for “seaweed mowing” by the animal, pretty much like one would roll up the cuff of a long-sleeve shirt, but just one fold. The teeth are located inside the “sleeve,” and rolling the sleeve inside-out deploys the teeth for action. A series of complex moves of the radula clip the seaweed and bring the food fragments to the alimentary canal. The illustration below shows an attempt at two steps of that sequence.
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