The merrow or murúch is an Irish form of mermaid that has been heavily influenced by the European tradition of women with fish tails, which can also be seen in some versions of the Fin Folk tales. Stories are typically of the attractive female form with the male form, when discussed, usually considered ugly. This is used to justify the merrow’s interest in human males.
Rangers with second sight have identified the typical attributes of a merrow – scaly skin, membrane between fingers and toes, green hair, sharp green teeth, fondness for dancing, attachment to humans – in the spirit form of the Otherworld subspecies of European seabass (Dicentrarchus labrax), which only cross into our reality in particular places off the West coast of Ireland. However, the tradition appears to have been carried to the English West coast where the same characteristics can be used to describe Jenny Greenteeth, a less benevolent creature that drowns unsuspecting children and eats them.
This subspecies is proof that Otherworld denizens can cross while at sea and undersea. Despite the submarine program, there is yet to be any data gathered to suggest that people from our reality can cross in the other direction underwater, although crossing at sea has been proven (see Imrama and Isle of Apples).