Feeding by Broom and Brush: A Unique Prey-Capture Organ in Flagellophora apelti (Nemertodermatida)

In live specimens of the nemertodermatidan Flagellophora apelti Faubel and Dörjes, 1978, a peculiar organ looking like a fascicle of bristles-and so called a broom organ by its discoverer-occupies the front third or so of the body. The animal can extrude the organ to splay the bristles in a fan-like array, each bristle having an adhesive tip. Described first by light histology as a bundle of flagella, this organ can be seen by transmission electron microscopy to be actually a bundle of exceedingly long necks of glands. Bodies of the glands sat well behind the brain, and the necks reached forward through the brain and folded back to a small bulb where they emerged into a canal. Protrusion of the organ would involve unfolding of the necks, projection of the bulb through a pore at the rostral end of the canal, and eversion of the bulb to form a knob-like point from which the gland necks radiate. Confocal microscopy of specimens stained for F-actin showed the muscles that drive protrusion and retraction and cell junctions that anchor the necks at the bulb, and we propose mechanisms through which these motions can be produced. The animal's rostrum had many other glands besides those of the broom organ, including a set forming a brush-like protruberance immediately ventral to the pore of the broom organ, and it likely plays a role in processing prey captured by the broom. Longitudinal muscles of the ventral body wall were specialized into strong bands that could serve to transfer the prey, then, to a facultative mouth.