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Recovery, behaviour and evolutionary implications of live Monoplacophora


THE Monoplacophora are molluscs with bilateral serially repeated structures1. Their shells occur among the oldest mineralised hard parts in the early Cambrian, and because they are traceable from there only to the mid-Devonian they had been considered extinct2,3. However, in 1957 Lemche4 reported an extant species in the deep sea. By 1972 six further extant species and several taxonomically unassigned specimens had become known from abyssal depths5–10, showing that the Monoplacophora continued to exist in post-mid-Devonian time in the deep sea. These finds also established that such molluscs are widely distributed on the deep-sea floor5–10. Two specimens were obtained about 1,800 m deep, but all others came from between 3,000 and 6,500 m (refs 5–10). McLean has reported a new, minute species obtained from cobbles at depths of 174, 229 and 388 m on the Cortes Ridge off southern California11,12. He is assigning it to the genus Vema. This is the first record of an extant monoplacophoran which, like early Palaeozoic species, inhabits shallow bathyal depths and, like some Silurian species, occurs on a hard substrate13. I report here the recovery of live specimens of this monoplacophoran.

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    Lemche, H. & Wingstrand, K. G. Galathea Rep. 3, 9 (1959).

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    Lemche, H. Nature 179, 413 (1957).

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    Horny, R. Sbornik Ustredniho Ustavu Geologickeho, Praha 28, 7 (1963).

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