Not sure exactly what you're talking about, but a squid can certainly appear torpedo shaped when swimming and also possesses a triangular shaped fin on the posterior end (the end opposite the arms and tentacles).
Squid
A zygobranch is a mollusc whose gills are developed on both sides of the body and the renal organs are paired.
Molluscs don't need ridgid body forms, since they live in protective rigid shells.
Delta referred to as the triangular-shaped body of water that forms where a streams enters a larger body of water.
The visceral mass is the collective term for the non-muscular portions of a mollusc's body containing the internal organs.
heart
the male has triangular body
mantises head is a triangular shape body looks like a rectangle.
The triangular one is called a Balalaika. There are several rounded ones by different names.
All molluscs are ectothermic; this means that their body temperatures are the same as the surrounding temperature. So if a mollusc is in a pond that is 60F, its body will be 60F. Later in the day, if the pond gets up to 75F, then the molluscs body temperature will rise to 75F as well.
it diaganaly triangular movement
That triangular area is called a delta. It's named after a triangular shaped letter of the Greek alphabet.Note: A river that empties into a lake is most often known as the headwaters if it is the primary water source for body of water= or = tributary.
Mollusks are invertebrate animals. This means they have no vertrebral column, or back bone.