Hippocampinae

[2] All seahorse and pygmy pipehorse species have a prehensile tail (a character shared with some other syngnathids),[4] a fully enclosed brood pouch, a short head and snout angled ventrally from the abdominal axis, and no caudal fin.

[7] The subfamily Hippocampinae is named after the seahorse genus Hippocampus, which is derived from the Ancient Greek ἱππόκαμπος (hippokampos), a compound of ἵππος, "horse" and κάμπος, "sea monster".

Due to the morphologically intermediate nature of the pygmy pipehorses between pipefishes and seahorses, the taxonomic placement of this group remains contentious, and three different classifications have been proposed for the subfamily Hippocampinae.

[9] An alternative explanation for the evolution from pygmy pipehorse to seahorse is based on the finding that a vertically bent head is more efficient in capturing prey because it increases the animal's strike distance, which is considered particularly useful in tail-attached sit-and-wait predators.

[3] Independent geological confirmation of the genetic data would require finding a fossil site from the Oligocene in which seahorse-like pygmy pipehorses are present, but seahorses are not.

Kyonemichthys rumengani , one of several small syngnathids discovered in the West Pacific in recent years
A simplified reconstruction of the evolution of seahorses from a pipefish-like ancestor based on a combination of genetic data, fossils and the body structure of living species. Although some species have become extinct, the major stages of evolution are still represented in living species. The timing of only two evolutionary events is known with some certainty: the evolution of the first pipefishes and the evolution of seahorses. The placement of the pipefish-like pygmy pipehorses has yet to be confirmed by genetic data.