There is no seahorse emoji. Unicode's list, version 18.0, has 18 marine animals, Spouting whale to Oyster, and no seahorse. Seahorse emoji copy and paste here means stand-ins: a wave and a horse face first, then 46 more.
Read the full guide
What to paste instead
The closest single emoji is Tropical fish, because a seahorse is a bony fish. The closest outline is the black chess knight, a horse's head and neck by Wikipedia. Search reads Unicode names and CLDR search words, so poseidon finds Trident emblem.
Which stand-ins arrive intact
Ten of the 18 single emoji carry Emoji 0.6, the oldest label in Unicode's list. Coral, 14.0, and Jellyfish, 15.0, are the newest and the likeliest to land as empty boxes on an older phone. Five of the six text drawings are plain ASCII, both seahorses included, while the four hieroglyphs need a font that has them.
Tips
The chess knights and 桷馬 are ordinary text, not emoji: try them where a field strips emoji out.
The Text style switch acts on one tile, Fish, the only emoji here with a text form.
Roll call copies six reef emoji at once. For a shoal of one fish, the emoji repeater goes to 10,000.
Questions and answers
Is there a seahorse emoji?
No. Unicode's emoji names never mention a seahorse, and CLDR files nothing under the word. The nearest is a horse face beside a fish: Wikipedia gives the hippocampus of Greek myth the upper body of a horse and the lower body of a fish.
Did a seahorse emoji ever exist, or get removed?
Not in Unicode. Its stability policy says an encoded character is never removed, and no version has had a seahorse. Wikipedia's false memory article lists the emoji among memories many people share, and its Emoji article records one in a 1988 Japanese word processor manual.
What is a seahorse called in other languages?
Chinese and Japanese write 桷馬, sea plus horse (hΗimΗ in Mandarin, umiuma or kaiba in Japanese), and Korean ν΄λ§ comes from the same characters. Japanese tatsu no otoshigo begins with the word for dragon. Hippocampus is Ancient Greek: hΓppos, horse, and kΓ‘mpos, sea monster.
π‘BlowfishU+1F421. CLDR gives it three search words: animal, blowfish and fish. Emoji 0.6.
πFishU+1F41F. The plain fish. The only emoji on this page with a text form, so the Text style switch changes this one and nothing else. Emoji 0.6.
π΄Horse faceU+1F434. The horse half. By Wikipedia a seahorse's head and neck are what bring the horse to mind. Emoji 0.6.
ππ΄Sea horse, the long wayWater wave, then horse face. Unicode has no seahorse emoji, so this spells one: sea, then horse. Chinese, Japanese and Korean write the animal the same way, sea plus horse.
π¦ShrimpU+1F990. Not a fish, and no relation. CLDR files it under shellfish and small, and small is the part it shares: Wikipedia calls seahorses small marine fish. Emoji 3.0.
π Tropical fishU+1F420. A seahorse is a bony fish, so this is the nearest relative on offer. CLDR files it under fish and tropical. Emoji 0.6.
πWater waveU+1F30A. The sea half. Unicode files it under sky and weather; CLDR files it under ocean. Emoji 0.6.
Show all 47 stand-ins (40 more)
Neighbours on the reef 8
πͺΈCoralU+1FAB8. Something to hold on to. CLDR files it under reef, and also under climate and change. One of the newer ones, so an older phone may show an empty box. Emoji 14.0.
π¦CrabU+1F980. CLDR files it under Cancer and zodiac, and never under sea or ocean. Emoji 1.0.
π¬DolphinU+1F42C. Filed under ocean, beach and flipper. Emoji 0.6.
πͺΌJellyfishU+1FABC. The newest emoji on this page. CLDR gives it 15 search words, aquarium and ouch among them. Emoji 15.0.
π¦LobsterU+1F99E. Filed under seafood, claws and bisque, which tells you where CLDR thinks it is going. Emoji 11.0.
πOctopusU+1F419. Filed under ocean and creature. Emoji 0.6.
πSpiral shellU+1F41A. Filed under sea, beach and conch. Emoji 0.6.
π¦SquidU+1F991. Filed under mollusk, and under food. Emoji 3.0.
Horses and legends 4
πDragonU+1F409. One Japanese name for the seahorse begins with the word for dragon: tatsu no otoshigo. Wiktionary puts it down to their resemblance to dragons. Emoji 1.0.
πHorseU+1F40E. The whole horse, where Horse face is only the head. Emoji 0.6.
π±Trident emblemU+1F531. Filed by CLDR under poseidon and trident. For the mythological end of the page. Emoji 0.6.
π¦UnicornU+1F984. The horse that did get in without existing. CLDR gives it two search words: face and unicorn. Emoji 1.0.
Single characters 8
βChess knight, blackU+265E Black chess knight. The nearest single character to the outline. By Wikipedia the knight is carved as a horse's head and neck, and a seahorse's head and neck bring a horse to mind.
βChess knight, whiteU+2658 White chess knight. The same piece in outline. Plain text, so it takes the colour of the words around it.
πHieroglyph fishU+1319C Egyptian hieroglyph K002. Described by Unicode as a fish, with a species: Labeobarbus bynni.
πHieroglyph horseU+130D7 Egyptian hieroglyph E006. Unicode describes it as a horse, about to rear, front legs nearly vertical. It shows as an empty box where no font has hieroglyphs.
π‘Hieroglyph puffer fishU+131A1 Egyptian hieroglyph K007. Described by Unicode as a fahaka puffer fish. A blowfish, several writing systems earlier.
πHieroglyph ripple of waterU+13216 Egyptian hieroglyph N035. Described by Unicode as a ripple of water. A wave, in one zigzag.
馬Horse, in one Han characterU+99AC CJK unified ideograph-99AC. Unihan defines it as horse. Mandarin mΗ, Japanese uma. The second half of the word for seahorse.
ζ΅·Sea, in one Han characterU+6D77 CJK unified ideograph-6D77. Unihan defines it as sea, ocean. Mandarin hΗi, Japanese umi. The first half of the word for seahorse.
One-line text seahorses and fish 6
<><The same fish, heading left
><(((*>Longer fish with scales, plain ASCII
><>Fish in three keystrokes, plain ASCII
>°)))彑Fish with a brush-stroke tail
@}}}o=Seahorse on its side, our own attempt: curled tail, armour, snout
=o{{{@The same seahorse, facing left
Seahorse in Chinese, Japanese, Korean and Greek 4
αΌ±ΟΟΟΞΊΞ±ΞΌΟΞΏΟSeahorse in Ancient Greek (hippΓ³kampos): horse plus sea monster
γΏγγγͺγγ·γ΄Seahorse in Japanese (tatsu no otoshigo). The name begins with the word for dragon
桷馬Seahorse in Chinese and Japanese: sea plus horse (hΗimΗ, umiuma or kaiba)
ν΄λ§Seahorse in Korean, from the same sea and horse
Seahorse combos 10
βπKnight at sea: the chess knight and a wave
π΄ππ₯Carrying the eggsHorse face, then water wave, then egg. The male does it. Wikipedia: up to 1,500 eggs, carried for 9 to 45 days.
ππDragon of the seaWater wave, then dragon. After the Japanese name tatsu no otoshigo, which starts with the word for dragon.
π΄πHippocampusHorse face, then fish. The mythological one. Wikipedia has it with the upper body of a horse and the lower body of a fish, which is this, read left to right.
πͺΈπ΄πHolding on to the reefCoral, then horse face, then water wave. A seahorse has a prehensile tail, and Wikipedia says it swims extremely poorly. Hence the grip.
π π‘π¦ππͺΌπͺΈRoll callTropical fish, then blowfish, then shrimp, then octopus, then jellyfish, then coral. Everyone is here. One absence noted.
ππ΄π΄πSide by sideWater wave, then horse face 2 times, then water wave. Courting seahorses swim side by side holding tails, according to Wikipedia.
ππ΄πSlowest fish in the seaWater wave, then horse face, then snail. By Wikipedia no fish moves slower than the dwarf seahorse: about 5 feet an hour.
π¦ππ¦Tide poolCrab, then spiral shell, then shrimp. The rest of the beach.
ππ΄πWearing the coronetCrown, then horse face, then water wave. The crown-like spine on a seahorse's head is called a coronet.