Mr Blight, in his “Week at the Land’s End,” speaking of the church in the adjoining parish, Zennor, which still remains in nearly its primitive condition, whereas Morva church is a modern structure, says—“Some of the bench ends were carved; on one is a strange figure of a mermaid, which to many might seem out of character in a church.” (Mr Blight gives a drawing of this bench end.) This is followed by a quotation bearing the initials R. S. H., which, it is presumed, are those of the Rev. R. S. Hawker, of Morwenstow:—
“The fishermen who were the ancestors of the Church, came from the Galilean waters to haul for men. We, born to God at the font, are children of the water. Therefore, all the early symbolism of the Church was of and from the sea. The carvure of the early arches was taken from the sea and its creatures. Fish, dolphins, mermen, and mermaids abound in the early types, transferred to wood and stone.”
Surely the poet of “the Western Shore” might have explained the fact of the figures of mermaids being carved on the bench ends of some of the old churches with less difficulty, had he remembered that nearly all the churches on the coast of Cornwall were built by and for fishermen, to whom the superstitions of mermen and mermaidens had the familiarity of a creed.
ZENNOR folks tell the following story, which, according to them, accounts for a singular carving on a bench-end in their Church.
Hundreds of years ago a very beautiful and richly attired lady attended service in Zennor Church occasionally—now and then she went to Morvah also;—her visits were by no means regular,—often long intervals would elapse between them.
Yet whenever she came the people were enchanted with her good looks and sweet singing. Although Zennor folks were remarkable for their fine psalmody, she excelled them all; and they wondered how, after the scores of years that they had seen her, she continued to look so young and fair. No one knew whence she came nor whither she went; yet many watched her as far as they could see from Tregarthen Hill.
She took some notice of a fine young man, called Mathey Trewella, who was the best singer in the parish. He once followed her, but he never returned; after that she was never more seen in Zennor Church, and it might not have been known to this day who or what she was but for the merest accident.
One Sunday morning a vessel cast anchor about a mile from Pendower Cove; soon after a mermaid came close alongside and hailed the ship. Rising out of the water as far as her waist, with her yellow hair floating around her, she told the captain that she was returning from church, and requested him to trip his anchor just for a minute, as the fluke of it rested on the door of her dwelling, and she was anxious to get in to her children.
Others say that while she was out on the ocean a-fishing of a Sunday morning, the anchor was dropped on the trap-door which gave access to her submarine abode. Finding, on her return, how she was hindered from opening her door, she begged the captain to have the anchor raised that she might enter her dwelling to dress her children and be ready in time for church.
However it may be, her polite request had a magical effect upon the sailors, for they immediately “worked with a will,” hove anchor and set sail, not wishing to remain a moment longer than they could help near her habitation. Sea-faring men, who understood most about mermaids, regarded their appearance as a token that bad luck was near at hand. It was believed they could take such shapes as suited their purpose, and that they had often allured men to live with them.
When Zennor folks learnt that a mermaid dwelt near Pen-dower, and what she had told the captain, they concluded—it was, this sea-lady who had visited their church, and enticed Trewella to her abode. To commemorate these somewhat unusual events they had the figure she bore—when in her ocean-home—carved in holy-oak, which may still be seen.
From Wikipedia, a slightly different version about The Mermaid of Zennor:
There is a local legend about a mermaid in Zennor.
Matthew Trewhella was a good-looking young man with a good voice. Each evening Matthew would sing the closing hymn at the church in Zennor, solo. A mermaid living in neighbouring Pendour Cove was enchanted by the music. She dressed in a long dress to hide her long tail and walked a bit awkwardly to the church. Initially, she just marvelled at Matthew's singing before slipping away to return to the sea. She came every day, and eventually became bolder, staying longer. It was on one of these visits that her gaze met Matthew's, and they fell in love. However, the mermaid knew she had to go back to the sea or die. As she prepared to leave, Matthew said, "Please do not leave, who are you, where are you from?" The mermaid told him that she was a creature from the sea and that she must go back. Matthew was so love-struck that he swore he would follow her wherever she went. Matthew carried her to the cove and followed her beneath the waves, never to be seen again. It is said that if you sit above Pendour Cove at sunset on a fine summer evening you might hear Matthew singing faintly on the breeze.
At St. Senara Church there is a carved bench-end over 600 years old showing the mermaid (which, arguably, might have inspired the Sue Monk Kidd novel, The Mermaid Chair).