I've had a vague interest in historical knitting and textiles for a while now, and I've been reading up on it lately - expect a few more articles in the future about some things I find interesting.
When you mention sea silk to a knitter, one thing comes to mind - Seacell, a type of rayon derived from seaweed, and the Hand Maiden yarn containing it. Sea Silk is a much-coveted yarn among knitters, but it takes its name from a much more precious fiber from the past.
A glove knitted from byssus yarn
The term byssus is an unfortunately vague term, because it has been used historically to refer to a number of fine fibers including flax (linen), cotton, and silk - etymologically, it takes its name from a root meaning 'white' - but presently, byssus is a specific type of fiber which comes from, of all things, mollusks.
The tuft of fine silky filaments by which molluscs of the genus Pinna and various mussels attach themselves to the surface of rocks; it is secreted by the byssus-gland in the foot. 'These filaments have been spun, and made into small articles of apparel.. Their colour ranges from golden yellow to rich brown; they also are very durable.. The fabric is so fine that a pair of stockings may be put in an ordinary-sized snuff-box'" [William Beck's 1886 The Draper's Dictionary]
The pinna mussel and its 'beard'
Though it's all but forgotten today, byssus (also referred to as sea silk or sea wool) was a highly prized fiber in antiquity. Some have speculated it is the inspiration behind Jason's golden fleece. The fiber is meant to be extremely similar to silk, only even finer. When you think about it, it makes a bit more sense: even though we're used to thinking of furry animals as sources of fiber, silk comes from moths, so why not silk from mussels as well?