Marine Invertebrate Larvae: A Study in Morphological Diversity


T.C. Lacalli, University of Saskatchewan


image: Cyphonautes
image: Actinotroch

Lophophorates (phoronids, brachiopods and bryozoans) are puzzling for combining features of both protostomes and deuterostomes. In terms of larval organization, this is seen in the presence of a preoral hood with cilia that beat towards the mouth, like a prototroch, while bands posterior to the mouth, typically arrayed on tentacles or ridges, beat away from the mouth. Current molecular data allies the lophophorates with spiralians (together they form the Lophotrochophora), which suggests the postoral band is probably a derived feature, perhaps precociously developed from the tentacles of the adult at some time in the past. There are numerous examples of this kind of heterochronic borrowing among marine larvae; the process is known as adultation. Two lophophorate larvae are illustrated here, the actinotroch (phoronids) and the cyphonautes (bryozoans). Their common organization is evident in that either is easily converted into the other, simply be expanding or reducing the preoral hood as shown in the following sequence.


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