Five new species of Olivoidea are described based on molecular and morphological evidence: four shallow subtidal Ancilla from Madagascar and Papua New Guinea, and one deep water (500-600 m) Calyptoliva from the Tuamotus. The sympatric – but not syntopic - Ancilla morrisoni and A. kaviengensis, from New Ireland province, are morphologically cryptic, differing mostly in shell colour, but are molecularly distinct. The sympatric – and possibly syntopic - Ancilla atimovatae and A. lhaumeti, belong to a species flock from southernmost Madagascar;  A. atimovatae is conchologically nearly indistinguishable from A. ventricosa, but differs markedly in radular morphology. Calyptoliva was previously known only from the Coral Sea; C. bbugeae is the first representative of the genus to yield molecular data. The new Ancilla are described based on sequenced holotypes; the type material of the new Calyptoliva includes a sequenced paratype.

The genus Retimohnia McLean, 1995 is revised based on conchology, radular morphology, foregut and stomach anatomy. Ten previously described species are recognized as valid: R. frielei (Dall, 1891), R. bella (Ozaki, 1958), R. vernalis (Dall, 1913), R. clarki (Dall, 1907), R.hondoensis (Dall, 1913), R.micra (Dall, 1907), R. sordida (Dall, 1907) comb. nov., R. robusta (Dall, 1913), R. caelata (Verrill et Smith, 1880), R. acadiana García, 2008. two species are described as new: R. lussae sp. nov, and R. mcleani sp. nov. R.japonica (Dall, 1913) is reduced to a junior synonym of R. micra, R. clementina (Dall, 1919) considered as a junior synonym of R clarki. Five species are excluded from the genus. Lectotypes designated for Mohnia frielei, Mohnia vernalis, Mohnia sordida, Mohnia clarki.

The validity of Astarte inaequilatera (Filatova in Scarlato, 1981) (Bivalvia: Astartidae) is substantiated. It is a Pacific, widely-distributed boreal species, earlier synonymized with the subtropical, Japanese-Korean Astarte hakodatensis Yokoyama, 1920. A. hakodatensis differs from A. inaequilatera by the crenulated inner ventral margin of the shell, lack of undulating commarginal ribs (only growth marks are present), radial threads, and strongly produced anterior margin. The shell is thicker and darker, with a dark brown periostracum. A. inaequilatera usually has a yellow-brownish to olivaceous periostracum. A. hakodatensis differs from Astarte montagui (Dillwyn, 1817) by the crenulation of the inner margin and a smaller size. Detailed synonymies of both species are compiled for the first time. Taxonomic and faunal comments on the Astartidae of the Russian Far Eastern seas are provided.

The polyplacophoran genus Hanleya contains two similar species in the Northeast Atlantic, H. hanleyi (Bean in Thorpe, 1844) and H. nagelfar (Lovén, 1846), which were primarily differentiated by dramatic difference in size but also in part by distribution and minor morphological and ecological features. The question of whether these two names represent two species or whether H. nagelfar is merely a name for H. hanleyi that have grown to extraordinary size, has been raised repeatedly since 1865. The problem was protracted by inaccessibility of the type specimen for the senior species name, and a lack of material collected near the type locality of H. hanleyi, both issues which we resolved in the course of this study. We examined the details of valves, girdle armature, and radula in specimens of Hanleya hanleyi from the Mediterranean Sea and Scotland. The similarity of relevant features among small specimens of H. hanleyi and H. nagelfar from Scotland, the Mediterranean Sea, Norway and Newfoundland Bank and the type specimen of Hanleya hanleyi suggests the two species are synonymous. Hanleya nagelfar is a junior synonym of H. hanleyi. Finally we note the eggs of H. hanleyi contain an unusual large drop of lipid that may increase their floatation. We propose that the eggs and larvae of H. hanleyi have an extended pelagic distribution and this extended dispersal period may connect populations from bathyal habitats in the slope of Newfoundland Bank via surface currents of the Gulf Stream System to northward and eastward in the Atlantic ocean.