The predator is an adult female of Oithona plumifera (Copepoda, Cyclopoida) of about 600 µm prosome length and the prey a protozoon Strobilidium sp. (Ciliata) of 40 µm width. The genus Oithona is an ambush predator which only occasionally relocates i.e. it remains motionless in the water sinking very slowly. This predator uses its numerous setae positioned in 3-D on its first antennae (A1, length of 1 mm) to locate the oncoming prey which is moving in 1 dimension, and monitor its path. The setae on the A1 range in length from 300 to 500 µm. As the prey moves at about 5 mm s-1 the predator knows what to do: It waits until the ciliate is right in front of its feeding appendages and then, with a sudden leap at a velocity of 58 mm s-1, captures the ciliate with its extended cephalic appendages. This capture process is too fast to be recorded at 60 frames s-1. The event shown is at 50 % of the actual velocities.
An adult female of Oithona plumifera is sinking very slowly while a ciliate (Strobilidium sp.) is circling off the tips of the setae of the first antennae (A1). As the ciliate is moving in 2-D the predator appears to require some time to actually locate it despite the fact that the female’s setae are oriented in 3-D. However, as the ciliate cannot perceive the presence of the slowly sinking predator, its fate is sealed as the female knows what to do.
Movies 1 and 2 are partly shown and discussed in Jiang and Paffenhöfer (2008, Mar Ecol Prog Ser 373:37-52).
A late nauplius of the calanoid copepod Eucalanus pileatus (about 0.6 mm body length) is offered the diatom Rhizosolenia alata (about 30 µm width, about 250 µm length). This diatom and this copepod genus, including its offspring, are regularly occurring in cold, nutrient-and phytoplankton-rich Gulf Stream intrusions on the U.S. southeastern continental shelf. The nauplii of E. pileatus create a continuous feeding current with their second antennae and mandibles, displacing water towards themselves. They perceive phytoplankton cells in this current by chemosensory and, using their cephalic appendages individually, direct such cells to their mouth. At the same time they orient such elongated cells in a manner that they can be ingested without being broken, as shown in the sequence of this movie. These processes are documented in detail by Paffenhöfer and Lewis for E. pileatus and E. crassus (1989, Mar Ecol Prog Ser 57:129-136). The period of cell perception to complete ingestion lasts about 1 second. The sequence shown here was obtained by fastening a cat hair in the back of the nauplius, and the cat hair held by a forceps in position while the observation was made at 250 frames s-1 with a 16 mm camera.