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

We describe a novel compound ciliary structure (g-cilium) from the food gro ove of the lobate ctenophore Mnemiopsis mccradyi. G-cilia are small, flat c ompound ciliary organelles that are oriented with their tips pointing towar d 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 u p the food groove. G-cilium cells are similar to 11.4 mum long and similar to4.2 mum wide at the g-cilium base. The g-cilium itself is similar to3.4 m um long and tapers to a flat, sharp tip. G-cilia are not motile but are sur rounded by many hundreds of smaller, actively motile cilia that beat with o rally-directed effective strokes. G-cilia contain similar to 50 conventiona l '9+2' cilia embedded in a fibrous core that arises from the cell body. In addition, g-cilia contain mitochondria, thousands of small membrane-bounde d vesicles and rod bacteria. G-cilia basal bodies are anchored by large, st rongly-banded rootlets that extend approximately the entire length of the c ell. G-cilia may have organizational, sensory and/or secretory function wit hin 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 enhan cing prey capture they probably play a critical role in the capacity of thi s organism to follow prey dynamics, so contributing to dense blooms in mid- late summer in coastal regions.