The transistional stage between the trochophore and the veliger larva of Tridacna squamosa Lamarck, including shell formation and initial organogenesis, is described. Calcification of the Prodissoconch I begins before formation of the organic component of the shell is completed, and proceeds in a pattern which reinforces the maximum stress areas of the shell, allowing the early onset of the larval escape behavior. Evidence is presented which suggests that the orientation of the mineral crystals in the larval shells is determined by an organic component of the shell and not by an active process of the clam during calcification.

The orientation of mineral crystals in Tridacna squamosa larval shells is determined by an organic component, rather than an active process of the clam during calcification.

Calcification of the first larval shell of Tridacna squamosa (Tridacnidae: Bivalvia)

Key Takeaway: The orientation of mineral crystals in Tridacna squamosa larval shells is determined by an organic component, rather than an active process of the clam during calcification.