Unionoida

bivalve order

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July 14, 2026

Quick Summary

The Unionoida are a large order of freshwater mussels, belonging to the subclass Palaeoheterodonta. These bivalves are characterized by equivalve shells that can vary in shape and sculpture. A notable feature of their life cycle is a parasitic larval stage, known as glochidia, which infect fish before developing into adult mussels.12

The Unionoida are found globally, with a significant presence in North America. Their shells have historically been used for button making due to their pearly nacreous interior. These mussels play a crucial role in freshwater ecosystems by filtering water and serving as a food source for other aquatic life.12

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bivalve
Annotated classification
Order Unionoida Large, equivalve, varying from round to elongate and with equally variable sculpture; shell of outer prismatic layer and inner layers of nacre; hinge schizodont; dimyarian; ctenidia eulamellibranch with either 1 or both demibranchs functioning as an incubatory marsupium; ovoviviparous; parasitically larviparous; freshwater; some cemented…
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Order Unionoida Large, equivalve, varying from round to elongate and with equally variable sculpture; shell of outer prismatic layer and inner layers of nacre; hinge schizodont; dimyarian; ctenidia eulamellibranch with either 1 or both demibranchs functioning as an incubatory marsupium; ovoviviparous; parasitically larviparous; freshwater; some cemented…
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