The diverse, distinctive and charismatic seahorse genus Hippocampus

Presented by Graham Short

Research Associate, Ichthyology and 2020-21 AMF/AMRI Visiting Collection Fellowship recipient, Australian Museum Research Institute; Research Associate, Ichthyology California Academia of Sciences, San Francisco; and, Research Associate, Ichthyology, Burke Museum, Seattle.

Seahorses (genus Hippocampus) belong to the family Syngnathidae and are arguably one of the most distinctive and charismatic fish in existence. Members of this family, also comprising the pipefish, pygmy pipehorses, and seadragons, are uniquely characterised by a tubular snout ending in a fused jaw that enables suction feeding, male brood pouch and pregnancy, prehensile tail, and cryptic morphology and behaviour.

A total of 46 species of seahorses have been described, including 14 in the last 20 years, and range in size from as small as a lentil to as large as a banana. The largest seahorse species is Hippocampus abdominalis, which can reach more than 35 cm and lives in the temperate waters off Southern Australia and New Zealand. In contrast, the smallest seahorse, the pygmy seahorse H. satomiae from Indonesia, is only 12 mm in length. The eight species of Indo-Pacific pygmy seahorses share many external morphological features with the larger (non-pygmy) seahorses but they differ dramatically in size, the number of gills, and location of egg brooding on the body in males.

Despite the notable morphological differences between the two groups of seahorses, taxonomic publications have yet to comprehensively classify them. As a 2021/21 AMF/AMRI Visiting Collection Fellow, Graham's research used computed tomography (CT) imaging to study and compare the skeletal features of non-pygmy and pygmy seahorses. Graham documented some surprising morphological differences that strongly support placing members of Hippocampus into many distinct genera.