Carcharadon Astra: Red Tithe

aka Space Sharks............really?
It's a fun read, but they make them seem like a mash-up of Ultramarines, Black Rage Blood Angels, and Void Dragons all in one, cuz not just a multiple of chapters need to have whacky genetic flaws, they need to add one more.
They Space Sharks start turning in to *SURPRISE!* sharks, over time, or shark-like anyway, with the skin, black empty eyes, etc.
The author also goes so far as to ret-con the Space Sharks being preset during the tail end of the Unification Wars!

The only redeeming factors in this book is that there are thinly veiled suggestions that the Space Sharks may be related to one of the lost primarchs (2 or 11), or, they may be the descendants of a loyal offshoot of the Night Lords.