Holoplanktonic Mollusca (Gastropoda: Pterotracheoidea, Janthinoidea, Thecosomata and Gymnosomata) from the Pliocene of Pangasinan (Luzon, Philippines)

Fifteen samples taken from interbedded sandstone, siltstone and claystone of Pliocene age, underlying the Bolinao Limestone, at the localities Anda, Roxas and Tiep (Pangasinan, Luzon, Philippines), were analysed for holoplanktonic gastropods; they have yielded 50 species (16 Heteropoda, one Janthinidae, and 33 Pteropoda, the latter consisting of 30 Euthecosomata, two Pseudothecosomata and one Gymnosomata). Faunal diversity between the localities sampled is restricted and explained by differences in sample size and/or preservation. The time interval represented by all samples taken together is postulated to have been brief. Fifteen new taxa (= 30% of the total number of encountered holoplanktonic molluscan species) are erected; Atlanta lingayanensis sp. nov., A. richteri sp. nov., A. seapyi sp. nov., Heliconoides sondaari sp. nov., Striolimacina andaensis sp. nov., Hyalocylis marginata sp. nov., Cavolinia baniensis sp. nov., C. perparvula sp. nov., C. shibatai sp. nov., Diacavolinia pristina sp. nov., Diacria italica Grecchi, 1982 f. fissicostata f. nov., D. microstriata sp. nov., D. paeninsula sp. nov., D. philippinensis sp. nov. and Sphaerocina convolvula sp. nov. Calibration with vertical ranges of holoplanktonic molluscan species as now known enables an age assignment for the Pangasinan assemblages of Pliocene (Piacenzian). A number of species, in particular Atlantidae (Heteropoda), were so far known only from Quaternary or extant assemblages. Comparisons with published data for Japan allow the conclusion that the Philippine assemblages are coeval with the Takanabe Member (Miyazaki Group) in Miyazaki Prefecture (southwest Japan), a unit which incidentally has yielded far fewer species. The absence of bathypelagic holoplanktonics, as well as littoral benthic species indicate an epi- to upper mesopelagic setting, with depth ranges extending to a maximal depth of c. 200 to 300 m.