Although skeletal muscle fatigues fairly rapidly, clams have a protein called paramyosin that allows them to sustain contractions for up to a month. What might be the role of paramyosin at the molecular or cellular level, which results in this peculiarity?
Older papers initially presumed that it was part of a mechanism called "catch" in invertebrates like molluscs which is a "sustained contraction." However, paramyosin was also found in insects. There is a very detailed review on invertebrate muscle from 2008 that you should read through (or, you know, search through) points out that recent evidence has shown that paramyosin is not involved in catch; that review also has this to say on the subject (emphasis added):