Pyramidellid Protoconchs, Eggs, Embryos and Larval Ecology: An Introductory Survey
2012
Robertson, Robert
Major papers on pyramidellid protoconchs, larval development, and larval ecology are reviewed, partly with illustrations. Larval shell coiling (including hyperstrophy and heterostrophy) is discussed. A-, B-, and C-type protoconchs are figured and distinguished. Those of species in the Baltic and northwestern France have been used to infer modes of larval development. The reliability of many of these inferences is questioned. Egg, embryo, and veliger morphologies, functions and terminologies are then discussed, including confusions of the terms “egg” and “capsule.” The pigmented mantle organ or gland (“PMO”) is briefly reviewed. Previously published data on the eggs and larvae of Brachystomia “scalaris” (Macgillivray, 1843), of“Turbonilla” cummingi Hori and Okutani, 1997, and of “Odostomia columbiana Dall and Bartsch, 1907”, are reviewed in detail with some new interpretations. In the first of these species, egg size variation is possibly salinity-induced and may cause variation in mode of development. Alternatively, different species may be involved. In the second named species, lecithotrophy straddles intracapsular metamorphosis sympatrically. In the third species, some of its unusual features may have been induced by low temperatures. “Mid-water metamorphosis” is then discussed. It is concluded that species with A-type protoconchs may be constrained to planktotrophy.
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