If you read any of my books, particularly Pursuing The Strange & Weird:A Naturalists Viewpoint, I expanded my previous research on possible unidentified sea creatures.
David Rains Wallace https://en.wikipedia.org/wiki/David_Rains_Wallace, in Neptune's Ark: from Ichthyosaurs to Orcas (University of California Press, 2007), p XIX:
"On many days when I see harbor porpoises, countless half-dollar-sized Velella hydroids, jellyfish relatives with transluscent white sails and iridescent violet-blue bodies litter the beaches -doubtless a coincidence, but odd. Unidentified cetaceans pass offshore of the murre rock, showing taller dorsal fins than the porpoises. Unexplained dark shapes and splashes occur. Point Resistance may be just a bedroom of the Pacific, but so many things lurk in that Neptunian mansion that there is no knowing what might slip in. When the air is clear, a notorious haunt of monsters looms to the west..."
The 10th August 1741 sighting of an unidentified sea creature by Georg Wilhelm Steller (who gave his name to the Steller's Sea Cow) and his crew is also dealt with (pp. XX- XXI)
I would suggest everyone to check out the news page and the videos and other info there.
Also, I encourage people to check out the Monterey Bay Aquarium Research Institute (MBARI) You Tube channel https://www.youtube.com/channel/UCFXww6CrLAHhyZQCDnJ2g2A where you can find known and unknown (small) species they film during the course of their work (even if I do not approve of capturing live speciments for killing and dissection).