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Feeding Behavior in the Hawaiian Zoanthids Palythoa and Zoanthus

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Title:Feeding Behavior in the Hawaiian Zoanthids Palythoa and Zoanthus
Authors:Reimer, Amada A.
Date Issued:Oct 1971
Publisher:University of Hawai'i Press
Citation:Reimer AA. 1971. Feeding behavior in the Hawaiian zoanthids Palythoa and Zoanthus. Pac Sci 25(4): 512-513.
Abstract:Palythoa psammophilia Walsh & Bowers and Zoanthus pacificus
Walsh & Bowers are two subtropical, subtidal zoanthids closely related phylogenetically
but widely different in their feeding methods. Palythoa is a predator that
feeds on zooplankton, particularly crustaceans. Of a vast array of items offered to
Zoanthus in the laboratory, only small pieces of freshly killed or frozen fish elicited
positive feeding responses. In natural situations Zoanthus has never been observed
to feed.
Palythoa polyps capture live prey with their tentacles and use these to hold the
prey against the peristome. Very few nematocysts are discharged and they do not
paralyze the prey. The behavioral response called "tentacle protrusion" allows the
polyps to capture additional prey while ingesting one just caught. The optimum
density of zooplankton, which causes the fastest response and largest capture, was
found to be 200 Artemia per m^3. This represents approximately 10 times the zooplankton
density calculated for the natural environment of Palythoa.
After the food has been obtained, either by capture (Palythoa) or seizure of
items (Zoanthus), both animals show the same complex and orderly series of steps
which is called the feeding reaction and consists of the following: (1) Lip formation.
A group of tentacles seizes the food, the edge of the disc carrying these tentacles
first contracts, then rises up and turns inward, thereby folding tentacles and
food toward the mouth; (2) Mouth opening. Upon contact with the food, the
mouth borders separate and the food is swallowed; and (3) Ingestion response.
Food disappears in the coelenteron and the borders of the mouth close over it.
Appears in Collections: Pacific Science Volume 25, Number 4, 1971

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