"it moved" moving
"Their long ribbon-like fins "
could be worded better... maybe something like:
Their frontmost and rearmost ribbon-like fins have changed into four short and highly mobile fins to allow the organism to more easily maneuver in its open water home. Meanwhile the other ribbon-like fins have changed into a selection of movement sensitive quills toward the rear of the body, to detect motion through the water, and to deter predators. The tips of the quills are dark and hardened.
The body is divided into two distinct pieces. The rear has a well-defined exoskeleton where the majority of the organs are located. The front section which is mainly mouth, crop, and stomach is supported by flexible but firm semi-external notochord-like structure of both living cells and cuticle. This supporting structure extends all the way to the front of the body where it rings the toothless mouth and provides an anchor point for the muscles that control the front fins, pincers, and eye nubs."
"The eyes" ... they
"On either side of the mouth are very sharp and hard pincers that carry a venomous bite, these weapons are essentially the only means that this organism has for subduing prey." -
Hard pincers on either side of the mouth carry a venomous bite and are essentially the only means for the Quilled Wigglemaw to subdue its prey.
"species is met than the couple up" - "species is met, they"