I think you are talking about two transparent lines on the back of squid. Those are two thick nerve fibers of squid. Connected to the nerve nodes of the head.

The nerve fibers of fresh squid are elastic. If dried squid is raised in alkaline water, nerve fibers are just like plastic.

Extended data

Appearance characteristics:

There are a pair of developed gills around the mouth on both sides of the head. It often moves in the middle and upper layers of shallow water, and the vertical movement range is above 100 meters. The slender body is a long cone, which feeds on krill, sardines, whitebait and small male fish, and is also the prey of fierce fish. Eggs are matured in batches and produced in batches. Eggs are wrapped in gelatinous egg sheaths, and each egg sheath contains several to hundreds of eggs according to different species. The amount of eggs laid by different species also varies greatly, ranging from several hundred to tens of thousands.