What is a group of Seahorses called?

A group of seahorses is commonly called a Herd. Other collective nouns you may see include Shoal and School.

A world beneath the ocean's surface exists, where graceful creatures known as seahorses reside. Within this watery kingdom, seahorses display an astonishing sense of togetherness, captivating the minds and hearts of all who witness them. While encountering a solitary seahorse is not uncommon, it is in the collectives where their extraordinary nature truly shines. A perfect description for a collective noun that encompasses these delicate creatures is a "mermaid", resembling the mythical beauties from ancient folklore. When assembled together, seahorses imprint an image of enchantment as they swim gracefully in synchrony, their tails intertwining like fine pieces of calligraphy invoking harmony. Wrapping their delicate bodies around one another, acting as lightly swaying ornaments, seahorses form merry congregations akin to harmonizing choruses seen in musical performances. Furthermore, the breathtaking sight of seahorses swinging gently through the undulating currents as a collective reveals them to embody a "rainfall". Coral reefs and seagrass meadows ceaselessly meet these mythical beings during their aquatic voyage, pausing for a moment to appreciate their collective unity, resembling suspended droplets that shower life upon the humble ocean floor. Another perfectly fitting collective noun for seahorses is a "cosmos". Just like the vastness of space, shimmering with radiant colors from distant constellations, so too do coral reefs painted with the vivid hues of seahorses' vibrant array. Spotting groupings and gatherings of seahorses scattered throughout this symbolic universe unravels a delightful tapestry vivid with visions of celestial strokes, highlighting the essence of cosmic harmony adorning the underwater world. In conclusion, collective nouns portraying the brotherhood and togetherness of seahorses encompass some of the wonders offered by nature. Whether likened to mermaids, forming a melody in a harmonious symphony, reflecting raindrops delicately descending upon the ocean floor, or mirroring a cosmic tableau of vibrant constellations, seahorses prove to be fascinating creatures weaving stories of unity through their extraordinary existence.