Higher level relationships within the Gastropoda are difficult to determine, in part due to the paucity of identified synapomorphic characters. Larval shell hydrophobicity may be a useful additional character for gastropod family systematics. A survey of 57 species indicates that larval shell hydrophobicity is common or ubiquitous in pyramidellids, opistho-branchs, and marine pulmonates but is unknown in patellogastropods, vetigastropods, and caenogas-tropods. The taxonomic distribution of hydrophobic larval shells is consistent with the hypothesis that it is a heterobranch synapomorphy. Unfortunately the condition in key ‘lower’ heterobranchs such as architectonicids and valvatoids is unknown.