I have been asked to clarify my position on long-necked sea monsters because some readers have seen me speaking of long-necked sea lions while in other places I speak of a more Plesiosaurian-shaped Longnecked Sea-Serpent. The answer is that in checking the statistics of Heuvelmans' Longneck category I found evidence of two distinct subcategories, whereas on the other hand in checking Dinsdale's reconstruction of the Loch Ness Monster I found his model to be sound, and very much the same as Champ, Patagonian Plesiosaurs, and other such creatures world-wide. The Hoy-type long-necked sea lion is specified in two target areas of the world, the one around Scotland and Ireland, and the other around Tasmania, Southern Australia and New Zealand. In both areas stray may go into freshwater on occasion (Bunyips and Costello's Phucas) The larger Plesiosaur-shaped Longnecks are cosmopolitan and must have a good range of temperature tolerance exactly comparable to leatherback turtles. The larger section of Sea-serpent sightings in Heuvelmans' book which deal with the Longnecked creature (which basically also absorbs the Merhorse category, except that the Merhorse category also contains distinctive sets of mistaken observations averaged in with the rest of the reports: my original analysis did not take into consideration swimming moose offshore which now look to be common mistakes in Scandinavia, New England and the Northwest Coastal area) Dinsdale has reports which specify that it has a tail, and Sanderson's and Gould's reconstructions are close to Dinsdale's (and my own identikit reconstruction)
At the current time I am using the two parts of Heuvelmans' Linnean binomial term "Megalotaria longicollis" as provisional generic names for the two subgroupings, Megalotaria for the Hoy-type longnecked sea lions and Longicollis (Longneck) to name the larger creature that is repeated more often and world-wide. I had insisted that the name for the latter be "Megophias" after Oudemans' usage, but arguments with several others have convinced me that name was given in mistake and cannot be said to definitivly describe anything more than a series of indefinite and probably mistaken observations.
So herewith I include a comparison of the long-necked sea lion Megalotaria and the Plesiosaur-shaped Longicollis done as mockups of representative photos from the internet. The inset shows the Arthur Grant land sighting drawing from Tim Dinsdale's Loch Ness Monster. The two photos are to approximate scale to one another: the sea lion type is of a size comparable to a walrus but the Plesiosaur-shaped creature is said to grow to twice this indicated size, at least (the upper end of the size range is uncertain because so many of the largest-size estimates are clearly exaggerated. But 40-50 feet is commonly stated and 60 feet or more at sea)