actinotrocha


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actinotrocha

[‚ak·tə·nō′trō·kə]
(invertebrate zoology)
The free-swimming larva of Phoronis, a genus of small, marine, tubicolous worms.
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Actinotrochas can ingest large dinoflagellates and other prey that are large relative to the width of the tentacle (Lebour, 1922; Herrmann, 1976).
Videorecordings were of actinotrochas from the northeastern Pacific Ocean.
Though different in form, actinotrochas from the plankton off Plymouth and those from Friday Harbor and Bodega Harbor used the oral hood in a similar way.
When actinotrochas had ingested many particles, more particles passed the tentacles without a hood lift, and when they were disturbed, there were more hood lifts without the presence of a particle.
Lengths of cilia of actinotrochas of Phoronopsis viridis at the 14-tentacle stage were measured from video images.
The actinotrochas appear to have two active responses to particles, with the ciliary one acting before the hood lifts.
The actinotrochas do have laterofrontal cilia (Hay-Schmidt, 1989), but our videorecorded images were insufficiently clear for direct observation of sieving by those cilia.
Other measured velocities were slower and overlapped estimates for transport by cilia alone on animals with ciliary bands like those of actinotrochas. These estimates are 1.2 mm [s.sup.-1] for a particle transported down the arm of a pluteus (Hart and Strathmann, 1994), about 0.7 mm [s.sup.-1] in the food groove of the hemichordate Planctosphaera pelagica (Hart et al, 1994), and 0.75 to 1.55 mm [s.sup.-1] for transport down a bryozoan's tentacle (Strathmann, 1982).
The actinotrochas may capture prey larger than those available to other larvae with similar ciliary bands.
The maximum clearance rate of actinotrochas depends on diversion of a particle and a small quantity of surrounding water from the much larger volume of water that flows within range of its sensors.
Adult forms also provide no close analogue to the hood lift of actinotrochas. Tentacle flicks by adult bryozoans aid transport of particles toward the mouth (Strathmann, 1982), but this does not appear to be a suction mechanism.