Protobranchia

<p>Protobranchia is a <a href="/facts/Subclass_(biology)/a7MrgFu3">subclass</a> of <a href="/facts/Bivalve/IQDxHVc8">bivalve</a> <a href="/facts/Mollusc/1elgknsQ">molluscs</a>.  It contains the extant <a href="/facts/Order_(biology)/GKLJvIpt">orders</a> <a href="/facts/Nuculanida/oCf9ycwJ">Nuculanida</a>, <a href="/facts/Nuculida/coIM2cRu">Nuculida</a>, and <a href="/facts/Solemyida/H0Iryo3P">Solemyida</a>.
</p><p>These are deep water clams of a small and primitive order with a taxodont hinge (composed of many similar, small teeth), generally with a central ligament pit, large labial palps which are used in deposit feeding and the <a href="/facts/Gill/FWgM3Jp8">gills</a> used only for respiration, the anterior and posterior <a href="/facts/Adductor_muscles_(bivalve)/Bf7KxQPU">adductor muscles</a> are nearly equal in size, a foot which is divided sagittally and longitudinally with papillate margins. The <a href="/facts/Foot_(mollusc)/1elgknsQ">foot</a> in Protobranchia clams is without a true <a href="/facts/Byssus/7heAVVFr">byssus</a> gland, although they frequently have a <a href="/facts/Analogous_organ/dd0L8z4R">nonhomologous</a> byssal gland in the heel. The byssal gland in these clams does not produce threads as in <a href="/facts/Pteriomorphia/jjnmhu0I">Pteriomorphia</a>.
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Protobranchia open-in-new

Protobranchia