No, seahorses do not bury themselves. Chances are they have died and have been consumed by something in your aquarium. If there is rock it is possible they are hiding in the nooks and crannies. However, many pipefish species are difficult to maintain, so in all likelihood they have perished.
Pipefish do not have large fins, making them slow swimmers. Pipefish have prehensile tails for grabbing and holding onto plants.
Yes, a pipefish is in fact a fish. They are part of the order syngnathiformes, which contains seahorses, pipefish and seadragons.
Broadnosed pipefish was created in 1758.
Spotted pipefish was created in 1810.
Worm pipefish was created in 1835.
Dusky pipefish was created in 1882.
Darkflank pipefish was created in 1871.
Schultz's pipefish was created in 1953.
Ocellated pipefish was created in 1953.
Lesser pipefish was created in 1855.
Barred pipefish was created in 1882.
Pelagic pipefish was created in 1827.