King Conch & Sand Dollar
2004
Nemo & Coral
2003
Cosmo & Miss Cosmopolitan
2004, 2006
Mr. Martini & Miss Martini
2006
Nemo & Coral
2003
Treat & Trixie
2006
Jambalaya & Etouffee
2006
Clint & Casey Cowgirl
2006
Driver & Putter
2008
Dr. Fish & Nurse Nettle
2006
Santa's Helper & Santa Baby
2007
Ziggy & Sunshine
2008
Surfer Dude & Surfer Girl
2006, 2007
Officer Ripped & Siren
2009, 2010
Touchdown & Cheerleader
2008
Aqua & Aquatini
2007
Rum Runner & Bloody Mary
2008
Candy Cane & Peppermint
2009
Bride & White Bride Tuxedo
2009, 2010
Jack O'Lantern & Willamina
2010
Zircon & Zirconia
2010
Dr. Turnencoff & Nurse Feel Better
2010
Other Ornament Counterparts
Groom & White Groom
2009
Flyboy & Regina
2012
Bones & Sabrina
2010
Cajun & Beignet
2010
Surf & Wave
2012
Aquarius & Capricorn
2012
Stud & Rhinestone
2010
Muscle Beach & Luscious Lucy
2013
Scotch & Soda
2012
Mr. Champagne & Miss Champagne
2012
Swabbie & Marina
2013
Jackie & Michelle
2013
Fifty & Ana
2013
Mr. Mertini & Miss Mertini
2014
Stripes & Stars
2013
Spark & Flame
2013
Nautilus & Nautica
2016
Happy Together & Pearl Girls
2014
Aloha & Mai Tai II
2014
Bruce & The Stylist
2009
While collecting the ornaments over time, the company definitely paired some of the mermen with mermaid counterparts. Not all of them came out at the exact same time, but one can tell there were counterparts nonetheless.
There are others that were the basic same ornament, but made differently with skin tone changes different colors, or other slight variations then renamed. These pictures show the differences on these particular items:
Mermen & Mermaid Counterparts
Duplicates
Sebastian & Scarlett
2014
Island Queen & Caribbean Queen
2004
Mickey & Maude Manatee
2004
Twirley Shirley White/Black
2009
Lady Chablis & Lady Ebony
2009
Bahama Mama & Mai Tai
2004
Poseidon & Atlantis
2003, 2004
King Neptune & King Neptune II
2007, 2013
Tonic & Gin
2012
Jingle & Bell
2013
Father & Mrs. Chrismouse
2004
Maisee & Manny Manatee
2004
Splash & Splish
2003
Alfred & Agnes Alligators
2006
Inkie & Pinky
2008
Nancy Nurse Shark & Dr. Feelgood
2004
Einswine & Mu Shu
2004
Felisha, Lace & Leather
2007, 2006
Miss Flo & Freddie
2003
Felipa & Felipe
2003
Harry & Harriet The Hermit Crabs
2012, 2006
Janis & Purple Haze
2008
Biceps & Mr. Mussel
2009
Cabernet & Claret
2003, 2008
Trition
2013
Jackpot & Slot Queen
2015
Santa Daddy II & Santa Baby II
2016
Mr. Selfie & Miss Snap
2016
Ginger Snap & Snicker Doodle
2016
Carmen Orig & Carmen (New)
2003