Prodissoconch

In species which have a veliger or swimming larval stage which hatches out of egg capsules (uncommon in bivalves), there are two parts to the prodissoconch.

[1] The prodissoconch I valves of the larval bivalve mollusc are thin, smooth and translucent, and generally appear during the first 24 hours of life.

Smooth valves continue to grow symmetrically and a gently sloping umbo projects from the middle of the hinge line.

[2] During metamorphosis, the veliger, depending on species, may secrete an attachment structure called a byssus that anchors it to the substratum.

Some species spend considerable time searching for an ideal habitat before metamorphosing, but others may settle on the nearest suitable substrate.