From The Enigma
NPL Magazine - Oct. 2014
LIRATH (adapted)

1. The answers to this flat are two "tongue-twister" words.

A crab is famous for its lack of
    generosity.
A lobster's not magnanimous, as any-
    one can see.
The oyster's altruistic bent is utterly
    unknown,
Yes, _ _ _ _ _ _ _ _ _ are _ _ _ _ _ _ _
With the things they call their own.

2. The two answer words to this flat have the same first five letters.

The barracuda's famous for its generosity.
A marlin is magnanimous, as anyone
    can see.
The mahimahi's altruistic tendencies
    are known,
A _ _ _ _ _ _ _ _ though is quite _ _ _ _ _ _
    with all the things he calls his own.

Answers:

1. SHELLFISH - SELFISH
2. STINGRAY - STINGY