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ABSTRACT We describe, for the first time, egg masses and larval developmental mode of a recently described Antarctic philinoid snail, Waegelea antarctica. Egg masses resembled the gelatinous, attached masses of many temperate philinoid species and contained very large offspring that hatched as developmentally advanced veligers with many juvenile features. Like other Antarctic heterobranch egg masses, development in the masses of W. antarctica appeared to be largely synchronous despite low internal oxygen levels. Hatched larvae could both swim and crawl, and we did not observe metamorphosis over several days. Molecular barcoding using cytochrome c oxidase subunit I (COI) showed an almost perfect (<0.002% difference) match between our specimens from McMurdo Sound in the Ross Sea and a single sequence from a specimen collected >8,000 km away in the Weddell Sea, suggesting either high realized larval dispersal or a recent range expansion. We also describe the egg mass of the related Antarctophiline alata (identified using COI barcoding) from the Ross Sea, which differed from published descriptions in having considerably smaller embryos.