Alien Paleontology

The large central creature lived in the open ocean. It is suspected that it washed into shallow waters when it died. In life it swam upside down in the current. Its front "arms" hold a system of filters that are cleaned by a pair of tongue-like appendages. Its main body is covered in armor studs.

fig 1: A small parasite that lives on its hosts feeding arms. A flat shell protects 3 gripping arms, 3 swimming limbs, and a proboscis.

fig 2: A spiral shelled bottom dweller. A series of gills/feeding arms extend from small holes in the shell. It holds on to its rocky habitat with a suction cup. when threatened, it pulls its shell down to the rocks.

for 's spec challenge