The modern Clan MacLarens clan history and heraldry is riddled with fiction and errors. Here is one example. The earliest account of the legend that the MacLarens came from a race of mermaids is from 'McIan's Costumes of the Clans of Scotland' by James Logan and Robert McIan, 1846. You probably have a copy on your coffee table.
In 1781 John MacLaurin Lord Dreghorn 1734-1796 became the clan chief the McLaurins. John's coat of arms heraldry included two Britons as supporters on each side of the shield, depicting what I believe to be St. Moluag's staff. The one that Naill Livingstone of Bachuill possesses. MacLea/Livingstone and McLaurin/McLaren YDNA is similar by the way.
At some point in the early 1800's, a heraldic artist depicted John MacLaurin Lord Dreghorn's coat of arms with two 'Tritons' instead of 'Britons", apparently misreading the written description of John MacLaurin's COA's, as you can see below.
In the 1840's, so-called Scottish historian James Logan mistook the 'Tritons' for 'Mermaids', they are similar in appearance and apparently he did not bother to double check John MacLaurin's COA's written description.
Logan and MacIan published the following.
"There is a traditional origin given of the Mac Laurins, with reference to a mermaid, which is among the most puerile of the many similar legends; but it was sufficient to induce the heralds to assign armorial bearings, allusive to the fancied occurance, when the eminent Lord Dreghorn, who claimed the chief ship, applied, in 1781, for matriculation of these family honours in the Lyon College of Arms." James Logan, 'McIan's Costumes of the Clans of Scotland' by James Logan and Robert McIan, 1846. You probably have a copy on your coffee table.
The Britons mistook for Tritons, then mistook for Mermaids, and now it is legend, etched in glossy full colour.