Sally and the Wicked Jelly Fish

Once the lovely Sally swam
  through salty swells of sea.
With tresses jetsam garlanded,
  the picture of a mermaid she.

Her skin translucent like a pearl
  made minnows all dart up to peek;
and one bold tiny briny shrimp
  contrived to drift against her velvet cheek.

They schooled about her flashing silver,
  and formed a wild living cape
the likes of which no earthly queen,
  or airy goddess ever trailed from her nape.

Now there lurked amongst the water's gloom
  a sea creature most malevolent.
It was an ugly jelly fish
  whose mind was murky and of evil bent.

He spied our sweetest Sally,
  and so highly did he rate her,
that he turned a jealous red,
  and resolved forthwith to mate her!

Sally raced unknowing through the foam,
  till coming on a yacht of pine,
she breached for show, and waved;
  but fouled dangling from a line.

So delicately she hung
suspended for all to see in air
that even the soaring petrel
did soon desire an affair.

But the gracious bird withheld
  and only thought of doing well.
So gallantly he pecked the twine
  and strove to cut her to the swell.

Our undulating denizen,
  seeing his anticipated chance,
quivered to a spot beneath her
  well suited for his advance.

He spread out his cruel appendages,
  and though he feigned to float most amorous,
The color of his thoughts infused
  his tendrils with a blue most poisonous.

Alas for mermaid Sally,
  the fragile line went tattering.
She plunged again into the waves,
  and with a splash sent minnows scattering.

The evil beast caught her in his arms,
  and then intimately on tender skin
he laid his softest kisses,
  and tried to lure her into sin.

Then further to excite her,
  he held her stricken to his bold caress;
while lavishly he fingered her,
  and sought the spots most likely to transgress.

The minnows turned horrified as one
  to watch ribbons laid round her pretty ass;
to see stripes lashed across her breasts -
  the marks of burning whips in pitiless harass

Sparing nothing, he teased her nipples;
  and searching deep for a cry of ecstasy,
the devil stung her lovely lips apart,
  and quite by chance uncovered her dark fantasy.

At this she broke into submission,
  and ceased to struggle in his arms.
And at last he saw that he might look upon
  that most beguiling of her charms.

At the pinnacle of her awful plight
  Sally smiled in generous measure.
For in the heart of her distress
  she found her sinful pleasure.

***

(Thanks to champangne1982 for several improvements)