Actinoceramus
Actinoceramus is an extinct genus of fossil saltwater clams, marine pteriomorphian bivalve molluscs. These bivalves were facultatively mobile infaunal suspension feeders.
Actinoceramus sulcatus marks the oldest appearance of well-developed radial folds, though the functional significance is still under debate. The wide range of localities and abundance of fossils coupled with an ease of identification leads scientists to consider this genus the most "successful" marine bivalve of the Late Cretaceous.