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.
Source: Traditions and Hearthside Stories of West Cornwall, Vol. 2, by William Bottrell, , at sacred-texts.com