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# of Described Species: First Appearance: Habitats: Exclusively Marine Shapes: Feeding Types: Deposit feeders |
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| The protobranchs are mostly small-sized bivalalves with the hinge typically composed of many similar, small teeth (taxodont condition). Notably, they include the so-called nut shells (Nuculidae). They differ from other bivalves in that their large labial palps are used in deposit feeding and the gills used only for respiration (most bivalves use their gills for filter-feeding). This group is entirely marine and the interior of the shell is nacreous in some families. | All protobranchs are shallow burrowers. One group, the Solemyidae, farm symbiotic bacteria in their gills for food and have a very reduced gut. There are about 10, mostly small-sized families in all. Many are only found in deepwater. |