Actinotrocha


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Ac`ti`not´ro`cha


n. pl.1.(Zool.) A peculiar larval form of Phoronis, a genus of marine worms, having a circle of ciliated tentacles.
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The actinotrocha is the feeding larval form of the lophophorate phylum Phoronida.
The phoronid actinotrocha differs strikingly from both spiralian and deuterostome larval forms in its large, mobile, and muscular oral hood, present throughout growth and development of the larva [ILLUSTRATION FOR FIGURE 1 OMITTED].
When an actinotrocha lifted and lowered its oral hood in rapid succession, a particle moved proximally with each lift and distally with each lowering [ILLUSTRATION FOR FIGURE 5 OMITTED].
The largest particle found in the stomach of an actinotrocha of P.
The actinotrocha might achieve a faster swimming and feeding current by additional propulsion from its telotroch, a posterior ring of longer cilia (Nielsen, 1987).
Although differences in body organization prevent exact comparisons of body size, some echinoplutei with 6 to 8 arms are similar to this actinotrocha in both body length and ciliary band length (McEdward, 1984, 1986).
A functional and structural equivalent of the oral hood is unknown for the larval forms most closely resembling the actinotrocha. In the larvae of bryozoans, enteropneusts, and echinoderms, muscular movements pass food through the gut after it has been concentrated in the oral cavity by cilia (Strathmann, 1971, 1973; Strathmann and Bonar, 1976).
Reported examples include flexing of the chaetopterid larval body to ingest a mucous net (Werner, 1953), and capture of animal prey by tentacles of magelonid larvae (Wilson, 1982), but these structures and activities do not resemble the action of the actinotrocha's oral hood.
The action of the actinotrocha's oral hood in feeding explains a prominent and peculiar feature of a distinctive larval form.
Previous accounts of feeding by actinotrochas have focused on the operation of the lateral, laterofrontal, and frontal ciliary tracts on the tentacles.