While on a completely unrelated mission to find out more information about the Portuguese man o'War, I found some amazing illustrations of siphonophorae. Kunstformen der Natur, "Art Forms of Nature", was written by Ernst Haeckel and published in 1900. I can't read German, but I assume it was very informative. The illustrations in this text are so stunning they beg to be hung up on a wall, used as the front of a card, or incorporated into a scrapbook page.
This type of illustration is particularly suited to crafts for men and boys because of the intricate scientific detail and the lack of girly hearts and stars. Not that they wouldn't look good in a young girl's bedroom (they most certainly would!!), but finding starting images for crafts intended for men can be hard. You can get a quick look at the images via Google's image search, but downloading them from the main Kuntsformen der Natur site will yield better looking prints. I've included a few of the renderings I found particularly interesting below. This book is in the public domain, so have fun using the images for a variety of crafts and decorations. It isn't limited to sea creatures: there are many kinds of living organisms illustrated.