Errr, no. Is there any type of RL critter or even cryptid that this is related to?
Well it's been compared to the
Hook Island Sea Monster, which shares a tadpole like shape, stripes, and liking for tropical waters with the Yellow Belly.
I vaguely remember reading a translation of Heuvelmann's book with a description of the Hook Island monster, but don't recall anything about the Yellow Belly. The Hook Island monster is likely to be a hoax (see the article I linked to), but that doesn't make any difference to our "monster" version.
Since we've got so little to work with, I'm inclined to adopt some points of the Hook Island monster - eyes on top of the head, an apparently toothless mouth with a white interior, partially buried in sand.
To me that suggests it's a passive hunter that sucks prey into its mouth. The large head could indicate it's a filter feeder instead, but the fact it has eyes atop its head and was observed partly covered in sand implies it's a creature that lies on the sea bed (or the lightless depths of the sea) and looks upwards for food items that pass above and in front of its head.
For our conversion, how about taking a Common Whale, adding the Aquatic subtype, giving it a single Bite with increased damage for its attack, then making it
slightly more interesting by giving it a "suction attack" based on Swallow Whole?
I'm sure we've already given a sea beastie an attack of that type, I just need to find it!
Ah, here's what I was thinking of - the Vortex Maw we used in the conversions of our large Labyrinthodonts like
Mastodonsaurus. Which incidentally was a real-life creature who's head was compared to the Hook Island Horror's:
Vortex Maw (Ex): A mastodonsaurus can open its mouth so quickly that it creates a powerful suction. All creatures within a 15-foot cone must make Strength checks opposed by the mastodonsaurus's Strength check (+8 for a standard mastodonsaurus), with the same modifiers as a bull rush. If the mastodonsaurus beats a creature's Strength check result, it pulls the victim 5 feet closer to its jaws. For each 5 points by which its check result is greater than a victim's check result, the mastodonsaurus pulls the victim an additional 5 feet closer. The victim provokes attacks of opportunity if it is moved.
It'll need to have Improved Grab and Swallow Whole as well, to gulp down victims it's sucked to its mouth.
Hmm, how about running with the throwaway 'late-surviving, limbless mastodonsauroid' and 'it could be “some kind of gigantic eel-like selachian”' lines in Darren Naish's article and make our conversion amphibious, or literally an Amphibian. That's a Tetrapod we don't have in our sea monster collection yet!
Even with the Amphibious trait, I'd think it'd be helplessly immobile out of water and probably die if beached, slowly being crushed by its own weight.
But you've always seemed to have a lot of interest in and knowledge of cryptids.
