setae. The uniramous maxillae (or second maxillae) follow, bearing a palisade of slender, long setae
that are the final food-capturing screen. These setae extend anteriorly from the limb base, pointing to
the posterior opening of the mouth. They can be raked by the endite comb of the maxillules. Last
come the uniramous maxillipeds, which are involved in feeding-current generation and also grasp
large prey and lift them toward the mouth. Now you are ready.The cycle of limb movements is as follows (Fig. 7.3): the second antennae move
forward and the maxillipeds move backward, advancing water one “step” toward the
ventral side from the surrounding volume. A ventral-to-dorsal sweep of the
mandibular palp then advances it laterally and dorsally, just past the end of the
maxilla. The sequence repeats, moving water toward and around the body in a series
of definite, individual steps. The limb motion abruptly stops when a particle of food
(or in some cases any particle) approaches the animal. Then the maxillae swing
laterally with a spreading of the setae. The flow replacing the water moved aside
carries the particle between the extended setae of the maxillae, which then close over
it. The setae are pulled closer to the body wall and closer together, squeezing the
“viscous” water out through the spaces between the setules. Water does not move
anteriorly parallel to the setae of the maxillae because the maxillules move posteriorly
at the same time, closing the anterior gap. Koehl and Strickler term maxillary particle
capture a “fling and clap”. There is also a sequence of reverse moves that can push
water out of the space between the maxillae when a particle is to be rejected. In some
movie sequences, it appears that particles are simply sucked into the mouth at this
point. The esophagus has striated muscles attaching its walls to internal skeletal
elements, and those muscles could suddenly pull it open, sucking in water and
particles close to the mouth. Larger particles, such as small animal prey, are probably
combed from the maxilla by the stiff bristles on the medial lobe of the maxillules just
below the body. Those then push the meal through the medial space between the
labial palps, which close the posterior side of the mouth, and between the toothed
mandibular gnathobases (the jaws) that meet under the labrum below the mouth.
Fig. 7.3 Particle capture by Eucalanus pileatus, side views left, end views right; dark
line is marker dye stream. In (a) and (b), antennae have moved apart, drawing water
toward the mouth area, then around to the sides. In (c) and (d), a particle (circle) is
sensed and the maxillae swing out to surround it and draw it between them. In (e) and
(f), the maxillae close and squeeze water out from around the particle.
(^) (After Koehl & Strickler 1981.)