Semper's (zoanthid) larvae: pelagic life, parentage and other problems

Semper's larvae were obtained from <300 out of <similar to>1800 plankton ro ws taken in the world's oceans (1964-1993). Zoanthellae (larvae of Sphenopi dae) occurred at 217 stations acid zoanthinae (larvae of Zoanthidae) at 86. the two larval types showing distributions clearly delimited by a minimum sea temperature (similar to 22 degreesC for zoanthellae, similar to 18 degr eesC for zoanthinae: a statistically significant difference, P<0.001). Leng th of formalin-fixed zoanthellae was <similar to>2-8.6 mm and of zoanthinae similar to1.5-5.9 mm. Endodermal zooxanthellae were present in 9/24 zoanth inae but in no zoanthellae (of 19). Three larvae contained all endo-commens al/parasitic amphipod. Septa were externally visible in larger zoanthinae a nd were counted in transverse sections of other larvae, a majority of which (both kinds) had 12 septa, the normal maximum. The pattern was brachycnemi c in 40/43 larvae and anomalous (but nonmacrocnemic) in three. If macrocnem ic genera reproduce by Semper's larvae. they; should have been represented in such a large sample. The distribution of adult Epizoanthus was examined: many species are deep sea (recorded down to similar to 5000 m) but shallow -water species are relatively plentiful in, for example, the Adriatic and N orth Seas. No Semper's larva has ever been recorded from either, Some Paraz oanthus species also occur in shallow water, especially associated with wes tern Atlantic reef sponges. If they produce Semper's larvae, these have nev er been found, It is probable that macrocnemic zoanthids settle from planul ae that do not develop into recognizable zoanthellae or zoanthinae.