Neolepetopsidae, a new docoglossate limpet family from hydrothermal vents and its relevance to patellogastropod evolution

Six new species of limpets from hydrothermal vents at spreading centres, hydrothermal vents on seamounts, or cold sulphide seeps are described in three new genera in the new family Neolepetopsidae. Anatomy is detailed separately by V. Fretter (1990). The family is considered to be a living descendant of the Palaeozoic‐Mesozoic family Lepetopsidae (proposed herein), based on Lepetopsis Whitfield, 1882. Both families are placed in the new superfamily Lepetopsacea, new suborder Lepetopsina, order Patellogastropoda. New genera and species are: Neolepetopsis , type species N. gordensis , from the Gorda Ridge, and three additional species: N. densata , from an active sulphide chimney near 12°N on the East Pacific Rise, N. verruca from a sulphide chimney near 21° N on the East Pacific Rise, and N. occulla from hydrothermal vents on the caldera floor of Green Seamount near 21° N; Eulepetopsis , type species E. vitrea , from hydrothermal vents at the Galapagos Rift and the East Pacific Rise near 21°, 13°and 11°N; Paralepetopsis , type species P. floridensis , from cool, hypersaline, sulphide seeps at the base of the continental slope off the west coast of Florida. Inclusion in Patellogastropoda is indicated by plesiomorphic characters: symmetrical shell lacking coiled phase, no epipodium in adult, single dorsally arched jaw, docoglossate dentition with a licker below the tip of the radula, both left and right kidney, and gonad discharging through right kidney. The radula differs from that of other patellogastropods in having the denticle caps delicate and non‐mineralized, the shafts articulating with shafts and cusps of adjacent teeth in the row and with those in adjacent rows, and in having some capacity for longitudinal bending. The rachidian is well developed; the first two pairs of lateral teeth are regarded as homologues of the inner lateral teeth of Patella ; the third lateral tooth is larger than the others and is considered a modified pluricuspid tooth; there are two pairs of plate‐like marginals. Tooth morphology differs in each genus but all have a very long second lateral with a strong mid‐shaft nub to articulate with the overhanging edge of the pluricuspid. The neolepetopsid radula is interpreted as close to that of the patellogastropod archetype except for its lack of mineralization and reduction in the number of marginal teeth. The radula in living docoglossate outgroups (chitons and monoplacophorans) is mineralized and the teeth are articulating. Articulating teeth are therefore regarded as plesiomorphic in patellogastropods. I speculate that articulating teeth may have been characteristic of Palaeozoic and early Mesozoic patellogastropods and that the non‐articulating, straight‐shafted and rapidly replaced teeth of extant Patellina may have arisen in the Mesozoic, a time at which patellogastropods of modern appearance underwent a radiation in shallow‐water habitats.