A novel cilia-based feature within the food grooves of the ctenophore Mnemiopsis mccradyi Mayer

Abstract

We describe a novel compound ciliary structure (g-cilium) from the food groove of the lobate ctenophore Mnemiopsis mccradyi. G-cilia are small, flat compound ciliary organelles that are oriented with their tips pointing toward the mouth. Typically three to four rows of g-cilia line the inner surface of the tentacular groove, which together with the transport groove, make up the food groove. G-cilium cells are ∼11.4 μm long and ∼4.2 μm wide at the g-cilium base. The g-cilium itself is ∼3.4 μm long and tapers to a flat, sharp tip. G-cilia are not motile but are surrounded by many hundreds of smaller, actively motile cilia that beat with orally-directed effective strokes. G-cilia contain ∼50 conventional `9+2' cilia embedded in a fibrous core that arises from the cell body. In addition, g-cilia contain mitochondria, thousands of small membrane-bounded vesicles and rod bacteria. G-cilia basal bodies are anchored by large, strongly-banded rootlets that extend approximately the entire length of the cell. G-cilia may have organizational, sensory and/or secretory function within the feeding apparatus. Their placement strongly suggests that they play critical roles in feeding. They may enhance the efficiency of prey capture and so contribute to M. mccradyi's well-known voracious appetite. By enhancing prey capture they probably play a critical role in the capacity of this organism to follow prey dynamics, so contributing to dense blooms in mid-late summer in coastal regions.