razor clam
蟶 centers on a specific shellfish: the razor clam. It is a narrow, elongated bivalve that lives buried in sand.
蟶 combines the insect radical 虫 (used for shellfish and creeping creatures) with 聖, which likely provides the sound テイ. The character was created to name the razor clam.
The insect radical 虫 often appears in characters for shellfish and small creatures. The right side 聖 suggests something holy or pure, but here it mainly gives the sound. Picture a holy razor clam, perfectly straight and pure, buried in the sand.
For テイ, imagine a razor clam shaped like the letter T, and you take a break for tea (ティー) while digging for it: tea -> テイ.