[Ichthyology • 2026] Hippocampus amandavincentae • A New Species of Spiny Seahorse (Syngnathiformes: Syngnathidae) from Indian Ocean, with Redescription of H. histrix and H. jayakari

 

The thorny seahorse, Hippocampus histrix Kaup, 1856, has long been treated as a single, widely distributed species ranging from the Red Sea and western Indian Ocean to the western Pacific. Morphological and molecular evidence now demonstrate that this broad concept encompasses at least three diagnosable species. Examination of Indian Ocean specimens combined with mitochondrial COI sequence analysis reveals a new lineage herein described as Hippocampus amandavincentae sp. nov., based on material from southeastern India and corroborated by published sequences from Madagascar, Mozambique, the Seychelles, and the northern Red Sea. The new species is diagnosed by a shorter snout, five coronet spines, and spines present on all principal trunk and tail ridges. A published COI sequence from the northern Red Sea places H. amandavincentae in apparent sympatry with Hippocampus jayakari Boulenger, 1900, in that region, indicating that the distributional boundary between these two species requires targeted field investigation. Hippocampus histrix sensu stricto is redescribed and its distribution restricted to the Pacific Ocean, including Japan, Indonesia, and the Philippines, based on direct examination of type material. Hippocampus jayakari, described from the Gulf of Oman, is confirmed as a distinct species of the northwestern Indian Ocean, readily distinguished by four cleithral spines with the ventral-most bifurcate, a shorter and deeper snout, and spines confined to alternating tail rings. Together, these three species represent geographically coherent lineages whose delineation resolves over a century of misidentification in museum collections and online databases, stabilises the application of long-used names, and provides a practical framework for regional conservation assessment and future systematic research on spiny seahorses across the Indo-Pacific.