Robertson Scheltema R S Adams F W (2 results)

In the Hawaiian Islands, Philippia (Psilaxis) radiata (Reding) lives in sand or rubble near the hermatypic stony coral Porites lobata Dana, and emerges to feed at night on the polyps, Other species of Philippia (Psilaxis) probably have the same mode of life with corals. Philippia (Psilaxis) veliger larvae are abundant in tropical and subtropical oceanic plankton distant from any potential shallow-water hosts, and are dispersed great distances by near-surface currents. Duration of the pelagic larval stage is between several weeks and 6 months or longer. Metamorphosis, involving loss of the 4-lobed velum, initial growth of the teleoconch, and other changes, can precede contact with a host and is induced by capture from the plankton. Newly settled Philippia quickly attain a stage of arrested growth and can remain alive without feeding for several months . At this stage the postlarvae presumably crawl in search of hosts, and failure to find hosts doubtless causes the high mortality observed. Experiments at Woods Hole, Massachusetts, with newly metamorphosed P. (Psilaxis) krebsii (March), obtained as larvae from plankton in the Sargasso Sea, together with the ahermatypic coral Astrangia danae Agassiz, reveal physical problems for Philippia in assuming the adult mode of life with other corals. Young Philippia showed no ability to detect Astrangia except by touch. Young Philippia lacked immunity to Astrangia nematocysts but were not seriously injured by them . The young gastropods are however, subject to predation by this coral. Most contacts with the living tissues of Astrangia caused a Philippia to be promptly drawn through the mouth and ultimately digested. The large protoconchs of Psilaxis would preclude their being swallowed by hermatypic corals such as Porites, with polyps smaller than those of Astrangia. Proboscis eversion and feeding were not observed in young P. krebsii. 11 pp., 7 figs, gr. 8.