as far as erotic artists are concerned, there are three types of mermaid tails... 1: from the waist down (common mermaid literature), 2: from below the navel [(bellybutton) less common, but more enticing], and 3: from below the pelvis/ass (least common, but extremely erotic/sexy)...... personally, i think the last one was created to make human-mermaid intercourse possible... some artists combine the last two, in where the tail starts beneath the navel, but the pussy is exposed......